Allied Telesis Network Router AR400 User Manual

AlliedWare™ OS  
Configure IGMP for Multicasting on Routers and  
Managed Layer 3 Switches  
How To |  
Introduction  
Allied Telesis routers and managed layer 3 switches use IGMP—Internet Group Management  
Protocol—to track which multicast groups their clients belong to. This enables them to send  
the correct multimedia streams to the correct destination.  
This How To Note describes basic and advanced IGMP configuration, in the following major  
sections:  
z
an overview of IGMP and definitions of some of the IGMP terminology  
z
examples and discussion of the most common IGMP functionality—IGMP snooping, IGMP  
Querier behaviour and selection, and IGMP proxy  
z
examples and discussion of the advanced functionality available through AlliedWare’s  
feature-rich IGMP implementation  
z
z
information for debugging  
information about the STP state of the simple three-switch ring used in most examples  
Contents  
www.alliedtelesis.com  
C613-16087-00 REV C  
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Introduction > Products and software versions this note applies to  
Switch 1 ........................................................................................................................ 108  
Products and software versions this note applies to  
IGMP is available on all the following Allied Telesis routers and managed layer 3 switches:  
z
z
z
z
z
z
z
z
z
z
z
z
AR400 series routers  
AR700 series routers  
AT-8600 series switches  
AT-8700XL series switches  
Rapier and Rapier i series switches  
AT-8800 series switches  
AT-9800 series switches  
SwitchBlade 4000 series switches  
AT-8948 switches  
AT-9900 series switches  
AT-9900s series switches  
x900 series switches  
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Introduction > Products and software versions this note applies to  
The following table shows the software versions and products each feature is available on.  
IGMP feature  
Software versions  
Products  
Snooping  
All  
All except AR4  
AR745  
10, AR410S, AR725 and  
Multiple potential queriers  
Proxy  
All  
All  
AT-8948, x900-48: 2.8.1 and later All except AT-9800 and SwitchBlade  
Other products: all versions  
Filtering  
2.7.5 and later  
2.8.1 and later  
2.7.5 and later  
All  
All that support this version  
All that support this version  
All that support this version  
All switches  
Filtering different message types  
Throttling  
Static IGMP  
Configurable counters and timers  
Snooping sub-features:  
Query Solicitation  
Fast Leave  
All  
All  
281-03 and 2.9.1 and later  
All switches that support this version  
All that support this version and snooping  
All that support snooping  
2.7.5 and later  
All  
Controlling which addresses create  
All Groups entries  
Preventing All Groups entries  
Statically specifying router ports  
2.7.1 and later  
All that support this version and snooping  
All that support this version and snooping  
281-04 and 291-04 and later  
For most examples in this How To Note, we used:  
z
z
z
z
one AT-8948 switch, with Software Version 2.7.6  
two Rapier 24i switches, with Software Version 2.7.6  
one PC running VLC media player as the multicast server (see www.videolan.org)  
client PCs  
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IGMP overview > Queriers and Snoopers  
IGMP overview  
IGMP terms:  
Clients in an IP subnetwork use IGMP to indicate  
that they are interested in receiving a multicast.  
IGMP then ensures that routers and switches  
forward multicast packets out the appropriate  
ports to the interested clients.  
Multicast or Multicast stream  
A flow of information—usually video or  
audio—that can go from one source to  
many destination clients.  
Group  
IGMP is very flexible, as the examples in this  
How To Note show, but the basic operation is  
simple. When a client wants to start receiving a  
multicast—which is also called joining a multicast  
group—the client sends an IGMP Membership  
Report message. When a router or switch is  
running IGMP and receives a Report message, it  
starts forwarding traffic for the relevant multicast  
group to the client.  
A multicast stream that clients can join.  
Groups have IP addresses in the  
224.0.0.0/4 network.  
Group member  
A client that belongs to a particular  
multicast group.  
IGMP Querier or Designated Router  
A device in a subnetwork that is the  
coordinator for all multicast streams  
and IGMP membership information.  
Each subnetwork has only one Querier  
IGMP periodically polls clients by sending  
General Query messages, to check that the  
clients still belong to their multicast groups.  
queriers" on page 15). The Querier  
generates Membership Query messages  
to check which clients are group  
members, and processes Membership  
Reports and Leave messages.  
To leave a group, a client sends an IGMP Leave  
message to indicate that it no longer needs to  
receive the group traffic.  
Note that IGMP does not exchange multicast  
routing information between subnets. The  
multicast routing protocols PIM and DVMRP do  
this.  
IGMP Snooper  
A device that spies on IGMP messages  
to create flow efficiencies by ensuring  
that multicast data streams are only sent  
to interested ports. A Snooper can  
decide on the best path to send  
multicast packets at Layer 2 but it  
cannot alter those packets or generate  
its own IGMP messages.  
Queriers and Snoopers  
It is neither necessary nor desirable for every  
router or switch in an IP subnetwork to  
coordinate multicast traffic flows. Instead, a single  
router or switch does this and is called the  
Querier or the Designated Router. The Querier  
generates Query messages to check group  
membership, and processes Membership Reports  
and Leave messages.  
IGMP Proxy  
A device that passes membership  
reports upstream and multicast streams  
and queries downstream. The proxy  
acts on behalf of clients and servers by  
altering packets.  
However, other routers and switches in the  
network need to know whether to send  
multicasts out each of their ports. They find out  
this information by becoming Snoopers. Each  
Snooper checks IGMP messages before  
forwarding them to and from the Querier, and  
uses the information in the messages to  
determine which ports to send multicasts out of.  
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IGMP overview > Messages  
The key differences between a network’s Querier and its Snoopers are:  
z
z
z
The Querier generates Query messages to find out which ports need to transmit each  
multicast stream. The Snoopers also use Query messages to find this out, but they use the  
Querier’s messages—Snoopers cannot create Query messages themselves.  
The Querier has IGMP enabled as part of its IP configuration. Snoopers do not require any  
configuration because snooping is enabled by default on Allied Telesis routers and managed  
layer 3 switches.  
Querying is a layer 3 feature—the Querier looks into the IP headers of packets to  
determine whether to forward them. IGMP snooping is a layer 2 feature. It does not  
require an IP configuration.  
Messages  
The following table describes the different IGMP messages in more detail.  
IGMP message types:  
Membership Report  
A client sends this when it wants to receive a multicast group. The Membership Report is  
essentially a message that declares an interest in listening to a specified group.  
Leave  
A client sends this when it wants to leave a group.  
General Query  
The Querier sends this to all clients—whether or not the Querier is currently sending multicasts  
to the client—to find out which groups they are listening to. Responses to General Queries ensure  
that the Querier’s group membership information stays up to date.  
The group address field for General Queries is set to 0.0.0.0. They are sent to a destination  
address of 224.0.0.1, and by default Allied Telesis routers and switches send them every 125  
seconds.  
Specific Query  
The Querier sends this to a group address, to check whether clients are still listening to that group.  
The Querier sends a Specific Query after a client sends a Leave message for that group. Specific  
Queries enable the Querier to confirm when all downstream clients have left a group, so that the  
Querier can stop sending the multicast stream.  
Membership Query  
This is a general term for both Specific and General Queries.  
Query Solicit  
Switches send this when STP or EPSR detects a topology change. The Querier responds by sending  
a General Query immediately instead of waiting until groups time out. This remaps IGMP to the  
new topology as quickly as possible.  
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IGMP overview > Choosing group addresses  
Choosing group addresses  
This section describes things you need to be aware of when choosing addresses for your  
multicast groups.  
Reserved IP IP addresses in the range 224.0.0.0-239.255.255.255 are multicast addresses, but many  
addresses addresses in this range are reserved. Therefore, before choosing a multicast address, you  
should check its status in the “Internet Multicast Addresses” document at the IANA website  
IPs using the Another complication is that multicasting is designed to use each packet’s group IP address to  
same MAC determine a multicast MAC address to send the packet to. However, multicasting does not  
have a  
1:1  
mapping of IP address to MAC address—instead each multicast MAC address  
corresponds to 32 multicast IP addresses. This means that different multicast IP addresses  
use the same MAC address.  
The MAC address only uses the last 23 bits of the IP address; it ignores the IP’s first octet and  
the first bit of the second octet. Note that all IP multicast MAC addresses start with  
0
1-00-5E.  
You need to avoid using multiple IP addresses that have the same MAC address. In practice,  
this means that if you use x.0.y.z, then do not use x. 28.y.z (or vice versa), where x is  
anything from 224-239, and y and z are the same in each IP address. For example, if y=6 and  
z=200 then these IP addresses use the same MAC: 224.0.6.200, 224. 28.6.200, 225.0.6.200,  
225. 28.6.200, etc.  
1
1
1
To see this in detail, consider 224.0.6.200. This has a multicast MAC of 01-00-5E-00-06-C8,  
like this:  
224.  
0.  
6.  
200  
IP address, decimal:  
IP address, binary:  
MAC address, binary:  
MAC address, hex:  
11100000 00000000 00000110 11001000  
0000000 00000110 11001000  
01-00-5E -00  
-06  
-C8  
Therefore, the following multicast IP addresses will all have the same MAC address as  
224.0.6.200, because their last 23 bits are all the same:  
IP address, decimal:  
224.0.6.200  
224.128.6.200  
225.0.6.200  
225.128.6.200  
226.0.6.200  
226.128.6.200  
227.0.6.200  
227.128.6.200  
...  
IP address, binary:  
11100000 0 0000000 00000110 11001000  
11100000 1 0000000 00000110 11001000  
11100001 0 0000000 00000110 11001000  
11100001 1 0000000 00000110 11001000  
11100010 0 0000000 00000110 11001000  
11100010 1 0000000 00000110 11001000  
11100011 0 0000000 00000110 11001000  
11100011 1 0000000 00000110 11001000  
...  
...  
239.0.6.200  
239.128.6.200  
11101111 0 0000000 00000110 11001000  
11101111 1 0000000 00000110 11001000  
Different IPs The same MAC  
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IGMP overview > Choosing group addresses  
Avoid x.0.0.y, x.0.1.y, x.128.0.y, and x.128.1.y  
It is particularly important to avoid using any address in the ranges x.0.0.y, x.  
or x. 28. .y (where x is 224-239 and y is -254).  
128.0.y, x.0.1.y,  
1
1
1
This is because x.0.0.y and x.  
Similarly, x.0. .y and x. 28. .y will map to the same multicast MAC address as 224.0.  
addresses in the ranges 224.0.0.y and 224.0. .y are reserved for contacting all routers, or for  
routing protocol messages, so they are always flooded out all ports in the relevant VLAN.  
1
28.0.y will map to the same multicast MAC address as 224.0.0.y.  
1
1
1
1.y. Most  
1
Therefore, all addresses in the ranges x.0.0.y, x.128.0.y, x.0.1.y, or x.128.1.y are flooded out  
every port in the relevant VLAN. Using these addresses can significantly increase multicast  
traffic in your network.  
If you are debugging a situation where it seems that certain multicast groups are forwarded  
when you think they shouldn’t be, check whether the choice of group addresses has violated  
any of the recommendations above.  
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IGMP snooping > Example  
IGMP snooping  
In this example, we discuss IGMP snooping, the key to efficient multicast traffic flow in a  
layer 2 network. IGMP snooping is enabled by default on switch ports in Allied Telesis  
managed layer 3 switches and routers—it does not require any configuration.  
In a single-switch network, IGMP snooping makes multicasting happen with no configuration  
at all. All you need to do is connect your server and clients to the switch.  
In a multi-switch network, at least one switch must also have an IGMP configuration. This  
switch is called the IGMP Querier and coordinates the flow of multicast information through  
the network. The following example describes a multi-switch configuration, so as well as  
discussing the effect of IGMP snooping, it outlines the actions that the Querier takes.  
"Multiple potential IGMP queriers" on page 15 discusses the role of the Querier in greater  
detail.  
Example  
This example has a 3-switch loop, as shown in the following figure. One of the switches is  
running IGMP and the other two switches are running IGMP snooping.  
Multicast Server  
port 1  
AT-8948  
Switch 1:  
Querier  
port 50  
port 49  
(blocked by STP)  
port 26  
port 25  
port 26  
port 25  
Rapier 24i  
Rapier 24i  
Switch 2:  
Snooper  
Switch 3:  
Snooper  
port 2  
port 3  
Client 1  
Client 2  
igmp-snooper.eps  
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IGMP snooping > Example  
X Configure switch 1  
Switch is configured with IGMP, which makes it the IGMP Querier in this network. It is best  
1
practice to make the Querier the closest switch to the multicast source, and in this example  
switch is closest. For more information about queriers see "Multiple potential IGMP  
1
set system name="Switch 1"  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-52  
# IP configuration  
enable ip  
add ip int=vlan100 ip=172.31.0.254 mask=255.255.255.0  
enable ip igmp  
enable ip igmp int=vlan100  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp=default port=1 edgeport=yes  
X Configure switch 2  
Switch 2 is an IGMP Snooper. It forwards multicast packets and IGMP messages as required.  
IGMP snooping is enabled by default and does not need any configuration.  
set system name="Switch 2"  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=2 edgeport=yes  
X Configure switch 3  
Switch 3 is also an IGMP Snooper. It forwards multicast packets and IGMP messages as  
required. IGMP snooping is enabled by default and does not need any configuration.  
set system name="Switch 3"  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=3 edgeport=yes  
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IGMP snooping > Explanation of IGMP snooping  
Explanation of IGMP snooping  
This section steps through the events that occur in a typical use of multicasting in this  
network: to stream multicast packets for a group.  
IGMP The following figure shows the process by which IGMP tracks multicast clients and ensures  
learning that the correct clients receive the stream.  
process  
What happens before a multicast client exists:  
49  
26  
1. Querier starts receiving multicast stream  
from server. Querier has no interested  
clients so doesn’t forward multicast.  
Multicast  
3
Blocked  
by STP  
Querier  
Snooper 2  
Snooper 1  
Pontential  
client  
Multicast  
server  
GQ  
2. Querier sends General Query (GQ)  
to find out if any would-be clients exist.  
Snooper 1 receives Query on port 26,  
snoops Query, and creates All Groups  
entry for port 26.  
49  
26  
Multicast  
3
Querier  
Snooper 1  
49  
26  
3. Snooper 1 forwards Query out all ports.  
No clients exist, so no clients reply to  
Query.  
Multicast  
GQ  
GQ  
3
Querier  
Snooper 1  
What happens when a client joins a multicast group:  
49  
Multicast  
26  
Report  
3
4. Client joins group by sending Membership  
Report to the group address.  
Querier  
Snooper 1  
Client  
Report  
5. Snooper 1 receives Report on port 3,  
snoops Report, and adds a group entry  
for port 3. Snooper 1 forwards Report  
out its All Groups port.  
49  
26  
Multicast  
3
Querier  
Snooper 1  
Multicast  
6. Querier receives Report on port 49  
and adds a group entry for port 49.  
Querier starts forwarding multicast  
stream out port 49.  
49  
26  
Multicast  
3
Querier  
Snooper 1  
Multicast  
49  
26  
Multicast  
Multicast  
3
7. Snooper 1 receives multicast stream  
and forwards it out port 3.  
Querier  
Snooper 1  
GQ  
Multicast  
8. Querier continues to send  
General Queries periodically.  
These keep All Groups entries  
alive on Snoopers.  
49  
26  
Multicast  
Multicast  
3
Querier  
Snooper 1  
igmp-join.eps  
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IGMP snooping > Explanation of IGMP snooping  
Using Show command output to investigate IGMP state  
No group In the first stage of the figure above, the multicast server is turned on and is streaming group  
members 224.12.13.14 to the Querier, switch . Switch knows about the group, but has nobody  
interested in receiving it. You can see this by using the command show igmpsnooping on  
switch . The output of this command shows that switch 1 has an entry for the group, but no  
1
1
1
associated ports.  
Manager Switch 1> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports None  
Entry timeout 136 secs  
------------------------------------------------------------------------  
Client joins When a client joins the group, the Group List changes for the Snooper that the client is  
the group attached to, and for the Querier. First, look at the output of the command show  
igmpsnooping on the Snooper.  
Manager Switch 3> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports 3  
Entry timeout 257 secs  
Entry timeout 235 secs  
All Groups  
Ports 26  
------------------------------------------------------------------------  
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IGMP snooping > Explanation of IGMP snooping  
This output now shows two entries, one for each of the following:  
z
group 224.12.13.14 and port 3, which shows that the client is attached to the Snooper  
through port 3 and is listening to group 224.12.13.14. The Snooper created this entry at  
stage 5 in the process ("IGMP learning process" on page 11). This entry means that the  
Snooper forwards packets from 224.12.13.14 out port 3.  
z
All Groups and port 26, which shows that the Snooper is connected to the Querier  
through port 26. The Snooper created this entry at stage 2 in the process. This entry  
means that the Snooper forwards all IGMP Reports and Leave messages out port 26.  
The All Groups entry means that the Snooper forwards the Report from the client out port  
26 to the Querier, switch . The Querier receives the Report on port 49.  
1
Next, look at the output of the command show ip igmp on the Querier.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
Group List ..............  
(DR)  
Group. 224.12.13.14  
Ports 49  
Last Adv. 172.31.0.223  
Refresh time 256 secs  
------------------------------------------------------------------------  
The output above shows an entry for group 224.12.13.14 and port 49. This entry shows that  
the Querier knows about a client for 224.12.13.14 which it reaches by forwarding the  
multicast out port 49. The Querier created this entry at stage 6 in the process.  
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IGMP snooping > Explanation of IGMP snooping  
Finally, look at the output of the command show igmpsnooping on the Querier. Even  
though switch 1 is the Querier for this network instead of a Snooper, this command shows  
that a client for group 224.12.13.14 is reached out port 49.  
Manager Switch 1> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports 49  
Entry timeout 247 secs  
------------------------------------------------------------------------  
When a client leaves a group  
When a client wants to stop receiving a group’s multicast stream, it sends an IGMP Leave  
message with a destination address of the group. The Snooper forwards the Leave message  
out its All Groups port, so the message arrives at the IGMP Querier. At this point, the IGMP  
Querier sends a series of Specific Queries (2 by default) to see if anybody else is still listening  
to this group.  
If the Snooper receives a response to the Specific Queries, it forwards the response to the  
Querier and continues to forward the multicast stream to the ports that want to receive it. If  
the Snooper does not receive a response to the Specific Queries, it stops forwarding the  
stream.  
For a detailed description of how the leave process works, see "How clients leave groups:  
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Multiple potential IGMP queriers > Example  
Multiple potential IGMP queriers  
To find out more about IGMP, we next investigate what happens when more than one router  
or switch has an IGMP configuration.  
should have only one IGMP Querier. You may configure IGMP on more than router or  
switch, perhaps for redundancy, but the routers and switches have a pseudo election and the  
device with the lower IP becomes the operating IGMP Querier. This example describes a  
network with two potential Queriers.  
Example  
The network for this example uses the same loop as for "IGMP snooping" on page 9 and is  
shown in the following figure.  
Multicast Server  
port 1  
AT-8948  
Switch 1:  
Potential Querier  
port 50  
port 49  
(blocked by STP)  
port 26  
port 25  
port 26  
port 25  
Rapier 24i  
Rapier 24i  
Switch 2:  
Elected Querier  
Switch 3:  
Snooper  
port 2  
port 3  
Client 1  
Client 2  
igmp-querier.eps  
Both switch  
1
and switch 2 are configured with IGMP, making both of them potential  
Queriers. Switch 3, by default configuration, is an IGMP Snooper.  
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Multiple potential IGMP queriers > Example  
X Configure switch 1  
Switch 1 is a potential IGMP Querier. It acts as a Snooper if it is not elected as the Querier.  
set system name="Switch 1"  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-52  
# IP configuration  
enable ip  
add ip int=vlan100 ip=172.31.0.254 mask=255.255.255.0  
enable ip igmp  
enable ip igmp int=vlan100  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp=default port=1 edgeport=yes  
X Configure switch 2  
Switch 2 is also a potential IGMP Querier. It acts as a Snooper if not elected as the Querier.  
set system name="Switch 2"  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
# IP configuration  
enable ip  
add ip int=vlan100 ip=172.31.0.253 mask=255.255.255.0  
enable ip igmp  
enable ip igmp int=vlan100  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=2 edgeport=yes  
X Configure switch 3  
Switch 3 is an IGMP Snooper. It forwards multicast packets and IGMP messages as required.  
IGMP snooping is enabled by default and does not need any configuration.  
set system name="Switch 3"  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=3 edgeport=yes  
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Multiple potential IGMP queriers > Explanation of Multiple potential IGMP queriers  
When there are no group members  
Switch 1 and switch 2 are both possible Queriers, and an election determines which switch  
becomes the actual Querier. We can see the results of the election by using the command  
show ip igmp on each switch.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
Other Querier timeout ... 209 secs  
Group List ..............  
------------------------------------------------------------------------  
Manager Switch 2> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
IGMP Proxy .............. Off  
Group List ..............  
(DR)  
------------------------------------------------------------------------  
In the output from switch 2 above, switch 2 reports that it has become the Querier by  
displaying (DR)—which stands for Designated Router—next to the interface name.  
In the output from switch 1 above, switch 1 has an entry for Other Querier timeout, which  
indicates that it is aware that another device is the IGMP Querier. If the timer expires,  
switch 1 will decide that the other Querier no longer exists, and will become the Querier  
itself. The timer is refreshed by a Membership Query or an IGMP Querier election.  
Note: Switch 2 shows an IGMP Proxy entry, which is set to Off (see "IGMP proxy" on  
page 21). Switch 1 does not show a Proxy entry because the AT-8948 did not  
support IGMP Proxy on Software Version 2.7.6 which this example used.  
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Multiple potential IGMP queriers > Explanation of Multiple potential IGMP queriers  
When a client joins a group  
Now imagine that Client 1 sends a Membership Report to switch 2 for the group  
224.12.13.14. If we check the group membership for switch 2 by using the command show  
igmpsnooping, we see a group entry for 224.12.13.14.  
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports 2  
Entry timeout 225 secs  
------------------------------------------------------------------------  
If we check the group membership for switches 1 and 3, we see no entries for 224.12.13.14,  
but see an All Groups entry on each switch. The All Groups entry points to the Querier,  
switch 2. The output for switch 1, for example, shows port 49 as the All Groups port,  
indicating that switch 1 reaches the Querier via port 49.  
Manager Switch 1> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports None  
Entry timeout 25 secs  
All Groups  
Ports 49  
Entry timeout 177 secs  
------------------------------------------------------------------------  
Note: An All Groups port does not necessarily indicate that an IGMP Querier can be found  
via that port—it could be a router instead. See "Controlling which addresses create  
All Groups entries" on page 95 for more information.  
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Multiple potential IGMP queriers > Explanation of Multiple potential IGMP queriers  
To see the difference between a switch acting as a Snooper and a switch acting as a Querier,  
compare the IGMP snooping table for switch 1 (above) with its IGMP table (below). They  
seem to contradict each other. The IGMP snooping table tells us that switch 1 is aware that it  
is receiving the group 224.12.13.14 and will send all groups (including this one) out port 49  
towards the IGMP Querier, switch 2. However, the IGMP table shows that IGMP has not  
registered any interested clients—the group list is empty.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
Other Querier timeout ... 214 secs  
Group List ..............  
------------------------------------------------------------------------  
This disparity between the IGMP snooping table and the IGMP table simply shows that  
switch 1 is acting as a Snooper because it did not become the Querier. The IGMP table on  
switch 1 has no entries because no Report message has been seen on switch 1. The disparity  
does not appear in the output for switch 2, because switch 2 is the Querier. The IGMP and  
IGMP snooping tables show the same group entries on switch 2.  
Manager Switch 2> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
IGMP Proxy .............. Off  
Group List ..............  
(DR)  
Group. 224.12.13.14  
Ports 2  
Last Adv. 172.31.0.222  
Refresh time 228 secs  
------------------------------------------------------------------------  
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Multiple potential IGMP queriers > Explanation of Multiple potential IGMP queriers  
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports 2  
Entry timeout 225 secs  
------------------------------------------------------------------------  
Also, note that (DR) appears in the output of show ip igmp on switch 2. This tells you that  
switch 2 is the Designated Router (the IGMP Querier) for vlan100.  
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IGMP proxy > Example  
IGMP proxy  
In very simple tree-design networks, IGMP Proxy is a useful simple alternative to a multicast  
routing protocol for multicasting between VLANs.  
An IGMP Proxy sends IGMP Membership Report and Leave group messages to an upstream  
subnetwork on behalf of downstream devices, and sends Queries downstream. In other  
words, an IGMP Proxy effectively ferries IGMP messages from one VLAN to another. The  
IGMP Proxy looks like an IGMP Querier to the downstream VLAN, and like a client to the  
upstream VLAN. Note that the Proxy can only have one configured upstream VLAN.  
IGMP Proxy is available on all Allied Telesis routers and managed layer 3 switches except  
AT-9800 and SwitchBlade series. For AT-8948, AT-9900 and x900-48 series switches, it  
requires software version 2.8. or later.  
1
If you use IGMP Proxy on a switch, multicast data packets are processed by the CPU so are  
not forwarded at wirespeed.  
Example  
IGMP Proxy only works in tree networks, so for this example we convert the network from  
a loop into a tree by disabling port 50 on the AT-8948 switch.  
Switch 3 is the IGMP Proxy. Switch  
1
is upstream of the Proxy. Switch 2 is downstream of the  
are now in different VLANs  
Proxy on vlan 00. Therefore, the multicast server and client  
1
1
and switch 3 sits on the boundary between the two VLANs. This network is shown in the  
following figure.  
AT-8948  
Multicast Server  
Switch 1:  
Querier  
port 1  
vlan200  
port 49  
upstream  
vlan200  
port 26  
Rapier 24i  
Rapier 24i  
Switch 2:  
Snooper  
Switch 3:  
Proxy  
downstream  
vlan100  
port 25  
port 25  
port 2  
Client 1  
igmp-proxy.eps  
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IGMP proxy > Example  
X Configure switch 1  
Switch 1—the closest switch to the multicast source—is an IGMP Querier.  
set system name="Switch 1"  
# Switching configuration  
disable switch port=50 link=disable  
# VLAN general configuration  
create vlan=vlan200 vid=200  
add vlan=200 port=1-49  
# IP configuration  
enable ip  
add ip int=vlan200 ip=172.31.1.254 mask=255.255.255.0  
enable ip igmp  
enable ip igmp int=vlan200  
X Configure switch 2  
Switch 2 is an IGMP Snooper. IGMP snooping is enabled by default and does not need any  
configuration.  
set system name="Switch 2"  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
# IP configuration  
enable ip  
add ip int=vlan100 ip=172.31.0.252 mask=255.255.255.0  
X Configure switch 3  
Switch 3 is an IGMP Proxy.  
set system name="Switch 3"  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-25  
create vlan=vlan200 vid=200  
add vlan=200 port=26  
# IP configuration  
enable ip  
add ip int=vlan100 ip=172.31.0.253 mask=255.255.255.0  
igmpproxy=downstream  
add ip int=vlan200 ip=172.31.1.253 mask=255.255.255.0 igmpproxy=upstream  
enable ip igmp  
enable ip igmp int=vlan100  
enable ip igmp int=vlan200  
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IGMP proxy > Explanation of IGMP proxy  
Explanation of IGMP proxy  
When there are no group members  
The multicast server streams group 224.12.  
detects the stream, as you can see by using the command show igmpsnooping on switch  
1
3.  
1
4 to switch  
1
through port 1. IGMP snooping  
1.  
Manager Switch 1> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan200 (200)  
Group List ..............  
Group. 224.12.13.14  
Ports None  
Entry timeout 122 secs  
------------------------------------------------------------------------  
When a client joins a group  
Client  
group 224.  
1
(attached to switch 2, the Snooper) sends an IGMP Membership Report for the  
2. 3. 4. Switch 2 forwards that report message in an unmodified state out its All  
1
1
1
Groups ports—in this case port 25.  
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports 2  
Entry timeout 256 secs  
All Groups  
Ports 25  
Entry timeout 145 secs  
------------------------------------------------------------------------  
Switch 3—the Proxy—receives the report on its downstream interface, vlan  
100. Switch 3  
then creates a new report with itself as the sender. It sends this report upstream to switch  
1
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IGMP proxy > Explanation of IGMP proxy  
through vlan200. Output of the commands show ip igmp and show igmpsnooping show  
that switch 3 knows of a client interested in the group 224.12.13.14 through port 25.  
Manager Switch 3> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
IGMP Proxy .............. Downstream  
Group List ..............  
(DR)  
Group. 224.12.13.14  
Ports 25  
Last Adv. 172.31.0.222  
Refresh time 243 secs  
Interface Name .......... vlan200  
Other Querier timeout ... 0 secs  
IGMP Proxy .............. Upstream  
Group List ..............  
No group memberships.  
------------------------------------------------------------------------  
Manager Switch 3> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports 25  
Entry timeout 239 secs  
Vlan Name (vlan id) ..... vlan200 (200)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports None  
Entry timeout 260 secs  
------------------------------------------------------------------------  
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IGMP proxy > Explanation of IGMP proxy  
Switch  
1
receives the proxied report from switch 3. Switch  
1
notes that switch 3 is interested  
in the group 224.  
1
2. 3. 4 and sends the group multicast to switch 3 on port 49. Output of  
1
1
the command show igmpsnooping shows the membership that switch  
1
is aware of.  
Manager Switch 1> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan200 (200)  
Group List ..............  
Group. 224.12.13.14  
Ports 49  
Entry timeout 182 secs  
------------------------------------------------------------------------  
When a client leaves a group  
When the client on switch 2 wants to stop receiving the group’s multicast stream, it sends an  
IGMP Leave message. The switches use the above process to transfer the message to  
switch 1.  
Note the following points about how IGMP Proxy deals with Leave messages:  
z
z
z
The Proxy sends an IGMP Leave Group message via its upstream interface only when the  
last interface on the Proxy leaves the group.  
The Proxy does not respond to IGMP Join or Leave Group messages received via its  
upstream interface, but only to those received via downstream interfaces.  
The Proxy does respond to IGMP query messages received via its upstream interface.  
When the Proxy—switch 3 in this example—sends a Leave Group message upstream, the  
upstream IGMP Querier—switch  
query and proxies it to the downstream interface, vlan  
72.3 .0.253). This means any other interested clients on switch 2 can declare their  
interest in continuing to receive the multicast stream.  
1
—sends a membership query. Switch 3 takes that  
100, with its own IP as the source  
(
1
1
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Query solicitation (rapid recovery from topology changes) > How query solicitation works  
Query solicitation (rapid recovery from topology  
changes)  
Query Solicitation minimises loss of multicast data after a topology change. It is a built-in  
feature of Allied Telesis managed layer 3 switches since software versions 281-03 and 2.9.1  
when running EPSR or spanning tree (STP, RSTP, or MSTP) for loop protection.  
Without Query Solicitation, when the underlying link layer topology changes, multicast data  
flow can stop for up to several minutes, depending on which port goes down and how much  
of the timeout period was left (see "Why convergence takes so long without query  
solicitation" on page 28). Query Solicitation greatly reduces this disruption.  
Query Solicitation operates without configuration in networks of Allied Telesis managed  
layer 3 switches running STP, RSTP, MSTP or EPSR. You may find it helpful to manually enable  
it in the following other situations:  
z
loop-free networks running IGMP (see page 33)  
z
networks in which not all switches support Query Solicitation (see page 33)  
How query solicitation works  
Query Solicitation monitors STP, RSTP, MSTP and EPSR messages for topology changes.  
When it detects a change, it generates a special IGMP Leave message called a Query Solicit.  
The switch floods the Query Solicit message to all ports in every VLAN that Query  
Solicitation is enabled on. When the Querier receives the Query Solicit message, it sends out  
a General Query and waits for clients to respond with Membership Reports. These Reports  
update the snooping information throughout the network.  
Query Solicit messages have a group address of 0.0.0.0.  
Query Solicitation works by default (without you enabling it) on all VLANs on the root  
bridge in an STP instance and on all data VLANs on the master node in an EPSR instance. By  
default, the root bridge or master node always sends a Query Solicit message when any of  
the following events occur:  
z
z
z
an STP BPDU packet with the Topology Change (TC) flag arrives at the root bridge  
an STP port on a switch goes from a Discarding to Forwarding state  
the FDB gets flushed by EPSR  
If necessary, you can make clients respond more quickly to the General Query by tuning the  
IGMP timers, especially the Query Response Interval—see page 77.  
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Query solicitation (rapid recovery from topology changes) > How query solicitation works  
The following figure shows how Query Solicitation works when a port goes down.  
Multicast  
Initial state:  
Port on Switch 3  
is blocking.  
Multicasts flow  
from server to  
client via Switches  
1 and 4  
Switch 1: Querier  
Switch 2: STP root  
Switch 3  
Switch 4  
Multicast  
Multicast  
1. Link to Switch 4  
goes down.  
Switch 2: STP root  
Switch 3  
Switch 3 stops  
blocking and  
sends topology  
change (TC)  
TC  
2. Switch 2 receives  
TC and sends  
Switch 2: STP root  
Query Solicit (QS)  
QS  
QS  
QS  
3. Switch 1 receives  
QS and sends  
Switch 1: Querier  
General Query (GQ)  
GQ  
GQ  
GQ  
GQ  
4. Host receives GQ  
and responds with  
Membership Report  
Report  
Report  
Report  
Report  
Final state:  
Switch 1: Querier  
Switch 2: STP root  
Switch 3  
Switch 4  
Multicasts flow  
from server to  
client via Switches  
1, 2, 3, and 4  
Multicast  
Multicast  
Multicast  
Multicast  
Multicast  
igmp-qs.eps  
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Query solicitation (rapid recovery from topology changes) > Why convergence takes so long without query solicitation  
Why convergence takes so long without query  
solicitation  
This section illustrates IGMP convergence in a simple network that does not need STP  
because it has no switch loops. Query Solicitation is disabled by default in networks like this,  
because no switch is an STP root bridge or an EPSR master node.  
In this network, it takes up to 125 seconds for multicasting to recover after a port comes  
back up. This section explains the reason for the slow convergence. "Speeding up IGMP  
Example  
The following figure shows the network for the example in this section.  
Multicast Server  
Client 1  
port 24  
port 9  
Switch 1:  
Querier  
Switch 2:  
Snooper  
port 1  
port 1  
Rapier 24i  
Rapier 24i  
igmp-no-qs.eps  
The example considers what happens when a port comes up. When the port was down, the  
client stopped receiving multicasts, because there was no backup route available. The  
example shows how the network recovers. The multicast group is 224.12.13.14.  
X Configure switch 1  
Switch  
1
is configured with IGMP, which makes it the IGMP Querier in this network.  
set system name="Switch 1"  
# IP configuration  
enable ip  
add ip int=vlan1 ip=10.13.2.191 mask=255.255.255.0  
enable ip igmp  
enable ip igmp int=vlan1  
X Configure switch 2  
Switch 2 is an IGMP Snooper. It forwards multicast packets and IGMP messages as required.  
IGMP snooping is enabled by default and does not need any configuration.  
set system name="Switch 2"  
# IP configuration  
enable ip  
add ip int=vlan1 ip=10.13.2.193 mask=255.255.255.0  
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Query solicitation (rapid recovery from topology changes) > Why convergence takes so long without query solicitation  
Explanation from the perspective of switch 2, the snooper  
When link When the link is connected (all ports are up), the Snooper has entries for two ports:  
is up  
z
port 9, which is the Snooper’s connection to the client. The Snooper sends the multicast  
stream out this port, as well as sending Queries (the Snooper floods Queries out all its  
ports)  
z
port  
1, which is the Snooper’s connection to the Querier. This is an All Groups entry, so  
the Snooper forwards Reports out this port.  
The output of the command show igmpsnooping shows both entries.  
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Query Solicitation ...... Off  
Static Router Ports ..... None  
Group List ..............  
Group. 224.12.13.14  
Ports 9  
Entry timeout 228 secs  
Entry timeout 232 secs  
All Groups  
Ports 1  
------------------------------------------------------------------------  
When link When we disconnect port 1 on the Snooper, the All Groups entry disappears.  
goes down  
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Query Solicitation ...... Off  
Static Router Ports ..... None  
Group List ..............  
Group. 224.12.13.14  
Ports 9  
Entry timeout 196 secs  
------------------------------------------------------------------------  
The Snooper still knows to send Queries and the multicast stream out port 9. However, it  
does not know where to send any IGMP Report messages.  
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Query solicitation (rapid recovery from topology changes) > Why convergence takes so long without query solicitation  
When link When we reconnect port 1 on the Snooper, the All Groups entry does not reappear.  
comes up  
Manager Switch 2> show igmpsnooping  
again  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Query Solicitation ...... Off  
Static Router Ports ..... None  
Group List ..............  
Group. 224.12.13.14  
Ports 9  
Entry timeout 140 secs  
------------------------------------------------------------------------  
Eventually, the Querier sends an IGMP Query, which the Snooper receives on port 1. This  
restores the All Groups port on the Snooper. By default the Querier sends General Queries  
every 125 seconds, so the IGMP convergence delay will be up to 125 seconds with the  
default settings. For more information about this timeout, see "Configurable IGMP timers  
and counters" on page 69—but do not change the timeout without very carefully considering  
the effect on your network.  
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Query Solicitation ...... Off  
Static Router Ports ..... None  
Group List ..............  
Group. 224.12.13.14  
Ports 9  
Entry timeout 107 secs  
All Groups  
Ports 1  
Entry timeout 236 secs  
------------------------------------------------------------------------  
When the Snooper receives the General Query, it forwards it out all its ports. The client  
responds with a Report. The Snooper forwards the Report out its All Groups port towards  
the Querier. The Querier responds by sending the multicast stream to the Snooper, which  
forwards the multicast stream out port 9 to the client.  
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Query solicitation (rapid recovery from topology changes) > Why convergence takes so long without query solicitation  
Explanation from the perspective of switch 1, the querier  
When link When the link is connected (all ports are up), the Querier has an entry for port 1, so it sends  
is up the group 224.12.13.14 out port 1. The output of the command show igmpsnooping  
shows this entry.  
Manager Switch 1> show igmpsnooping  
Manager A> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Query Solicitation ...... Off  
Static Router Ports ..... None  
Group List ..............  
Group. 224.12.13.14  
Ports 1  
Entry timeout 18 secs  
------------------------------------------------------------------------  
When link When we disconnect port 1 on the Snooper, the port disappears. The Querier is still  
goes down receiving the multicast stream from the server, so the group entry remains.  
Manager Switch 1> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Query Solicitation ...... Off  
Static Router Ports ..... None  
Group List ..............  
Group. 224.12.13.14  
Entry timeout 255 secs  
Ports None  
------------------------------------------------------------------------  
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Query solicitation (rapid recovery from topology changes) > Why convergence takes so long without query solicitation  
When link When we reconnect port 1 on the Snooper, the port does not reappear because the  
comes up Querier has not yet received a Report over it. Therefore, the Querier does not start  
again forwarding the multicast stream out the port.  
Eventually, the Querier sends an IGMP Query out all its ports. In response it receives a  
Report from the client (via the Snooper). This restores the port entry and the Querier starts  
sending the multicast stream again.  
The output of the commands show igmpsnooping and show ip igmp both show this  
restored entry.  
Manager Switch 1> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Query Solicitation ...... Off  
Static Router Ports ..... None  
Group List ..............  
Group. 224.12.13.14  
Ports 1  
Entry timeout 115 secs  
------------------------------------------------------------------------  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name ..................... vlan1  
IGMP Status ........................ Enabled  
IGMP Proxy ......................... Off  
General Query Reception Timeout .... None  
Group List .........................  
(DR)  
Group. 224.12.13.14  
Ports 1  
Last Adv. 10.13.2.11  
Refresh time 110 secs  
------------------------------------------------------------------------  
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Query solicitation (rapid recovery from topology changes) > Speeding up IGMP convergence in a non-looped topology  
Speeding up IGMP convergence in a non-looped  
topology  
The previous section described how it can take up to 125 seconds for multicasting to recover  
in a non-looped topology after a port comes back up. You can speed up convergence simply  
by enabling RSTP. This enables the network to use Query Solicitation and means that  
multicasting resumes within 3 seconds of the link coming up.  
Even though there is no loop in the network, one of the switches becomes the STP root  
bridge—it does not matter which switch does this. When the link comes up, the root bridge  
detects the topology change and sends a Query Solicitation.  
So you just need to enter the following commands on all switches:  
enable stp=default  
set stp=default mode=rapid  
Enabling query solicitation on multiple switches in a  
looped topology  
On networks that use spanning tree or EPSR, Query Solicitation is not normally required on  
switches other than the STP root bridge or EPSR master node. Therefore, it is only enabled  
by default on the root bridge and the master node.  
However, in some networks you may need to turn on Query Solicitation on all switches—for  
example, if the network includes other switches that do not support Query Solicitation and  
therefore the STP root bridge may be a switch that does not send Query Solicit messages. To  
enable Query Solicitation, use the command:  
set igmpsnooping vlan={vlan-name|1..4094|all} querysolicit={on|  
yes|true}  
Every switch that has Query Solicitation enabled sends a Query Solicit message when it  
detects a topology change. Enabling it on multiple switches means you get multiple messages,  
but has no other disadvantage.  
The following figure shows a the packet flow for a four-switch network with Query  
Solicitation enabled on all the switches.  
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Query solicitation (rapid recovery from topology changes) > Enabling query solicitation on multiple switches in a looped topology  
Multicast  
Initial state:  
Port on switch 3  
is blocking.  
Multicasts flow  
from server to  
client via switches  
1 and 4  
Switch 1: Querier  
Switch 2: STP root  
Switch 3  
Multicast  
Multicast  
1. Link to switch 4  
goes down.  
Switch 1: Querier  
Switch 2: STP root  
Switch 3  
Switch 4  
Switch 3 stops  
blocking and  
QS from 3  
QS from 3  
GQ from 1  
TC from 3  
sends Topology  
Change (TC) and  
Query Solicit (QS).  
Switch 2 forwards  
QS to switch 1.  
Switch 1 sends  
General Query (GQ)  
GQ from 1  
GQ from 1  
TC from 3  
GQ from 1  
2. Switch 2 receives TC  
from switch 3.  
Switch 1: Querier  
Switch 2: STP root  
Switch 3  
Switch 4  
Switch 2 sends QS.  
to switch 1.  
Switch 1 sends GQ  
QS from 2  
GQ from 1  
GQ from 1  
GQ from 1  
GQ from 1  
3. Switch 4 receives TC  
from switch 3.  
Switch 1: Querier  
Switch 2: STP root  
Switch 3  
Switch 4  
Switch 4 sends QS.  
towards switch 1.  
Switch 1 sends GQ  
QS from 4  
GQ from 1  
QS from 4  
GQ from 1  
QS from 4  
GQ from 1  
GQ from 1  
4. Client replies to each  
GQ by sending  
Switch 1: Querier  
Switch 2: STP root  
Switch 3  
Switch 4  
Membership Reports  
Report  
Report  
Report  
Report  
Report  
Report  
Report  
Report  
Report  
Report  
Report  
Report  
Final state:  
Switch 1: Querier  
Switch 2: STP root  
Multicast  
Switch 3  
Switch 4  
Multicasts flow  
from server to  
client via Switches  
1, 2, 3, and 4  
Multicast  
Multicast  
Multicast  
Multicast  
igmp-qs.eps  
So one topology change caused three Query Solicits, three General Queries, and three  
Reports.  
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IGMP filtering (controlling multicast distribution) > Example  
IGMP filtering (controlling multicast distribution)  
IGMP filtering lets you control the distribution of multicast services on each switch port.  
Filtering is useful for subscription services when clients must be explicitly authorised to view  
a multicast stream.  
IGMP Filtering is available in Software Version 2.7.5 or later.  
Example  
This example uses the same network configuration as "IGMP snooping" on page 9. For  
convenience, the diagram is reproduced below.  
Multicast Server  
port 1  
AT-8948  
Switch 1:  
Querier  
port 50  
port 49  
(blocked by STP)  
port 26  
port 25  
port 26  
port 25  
Rapier 24i  
Rapier 24i  
Switch 2:  
Snooper  
Switch 3:  
Snooper  
port 2  
port 3  
Client 1  
Client 2  
igmp-snooper.eps  
The network contains a Windows 2000 workstation that regularly sends SVRLOC messages  
(an IGMP Membership Report for 224.0. .22). This group gets added to the list of groups in  
vlan 00 on switch , as shown in the following output of the show ip igmp command.  
1
1
1
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
...  
Interface Name .......... vlan100  
Group List ..............  
(DR)  
Group. 224.0.1.22  
Ports 1  
Last Adv. 172.31.0.99  
Refresh time 251 secs  
------------------------------------------------------------------------  
We do not need to receive this multicast, so we will filter it out.  
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IGMP filtering (controlling multicast distribution) > Example  
X Configure switch 1  
Switch —the closest switch to the multicast source—is an IGMP Querier. The filter is  
1
configured on it, as shown in bold in the script below.  
Note that the order of entries in a filter is important. When IGMP tries to match a message  
to a filter, it performs a linear search of the filter to find a matching entry, starting with the  
lowest-numbered entry. It stops processing the filter at the first match it finds. Therefore,  
this filter has an entry with one multicast group and an action of exclude, followed by an  
entry with all multicast groups and an (implicit) action of include.  
Different Also note that in software versions 2.8.1 and later, each entry filters only one type of IGMP  
message message. To control the type of message, use the msgtype parameter in the following  
types command:  
add igmp filter=filter-id groupaddress={ipadd|ipadd-ipadd}  
[entry=1..65535] [action={include|exclude}] [msgtype={query|  
report|leave}]  
In software version 2.8.1, this parameter is mandatory. Since software versions 281-01 and  
2.9. , the parameter is optional with a default of report. In this example we are filtering  
1
Reports, so we do not need to specify the message type.  
set system name="Switch 1"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp=default port=1 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-52  
# Switching configuration  
set switch port=1 igmpfilter=1  
# IP configuration  
enable ip  
add ip int=vlan100 ip=172.31.0.254 mask=255.255.255.0  
enable ip igmp  
enable ip igmp int=vlan100  
create igmp filter=1  
add igmp filter=1 entry=1 group=224.0.1.22 action=exclude  
add igmp filter=1 entry=2 group=224.0.0.0-239.255.255.255  
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IGMP filtering (controlling multicast distribution) > Example  
X Configure switch 2  
Switch 2 is an IGMP Snooper. IGMP snooping is enabled by default and does not need any  
configuration.  
set system name="Switch 2"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=2 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
X Configure switch 3  
Switch 3 is also an IGMP Snooper.  
set system name="Switch 3"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=3 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
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IGMP filtering (controlling multicast distribution) > Explanation of IGMP filtering (controlling multicast distribution)  
Immediately after applying the filter, we check the group entries on switch  
1
by using the  
command show ip igmp, and see that the switch still has an entry for the group we are  
filtering out.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
Group List ..............  
(DR)  
Group. 224.0.1.22  
Ports 1  
Last Adv. 172.31.0.99  
Refresh time 192 secs  
------------------------------------------------------------------------  
This entry is still there because the switch had previously received a report for the group.  
Since applying the filter, there have not been any messages for the group, so the switch has  
not yet filtered the group out. We can see this by using the command show igmp filter to  
check the number of processed messages.  
Manager Switch 1> show igmp filter=1  
IGMP Filters  
------------------------------------------------------------------  
No. Entry Group Address  
Action  
Matches  
------------------------------------------------------------------  
1
1
2
224.0.1.22  
224.0.0.0  
224.0.1.22  
224.255.255.255 Include  
Exclude  
0
0
Received: 0  
Passed: 0  
Dropped: 0  
------------------------------------------------------------------------  
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IGMP filtering (controlling multicast distribution) > Explanation of IGMP filtering (controlling multicast distribution)  
If we enter these commands again a few minutes later, we see that the filter has dropped  
packets and the group entry has expired and disappeared.  
Manager Switch 1> show igmp filter=1  
IGMP Filters  
------------------------------------------------------------------  
No. Entry Group Address  
Action  
Matches  
------------------------------------------------------------------  
1
1
2
224.0.1.22  
224.0.0.0  
224.0.1.22  
224.255.255.255 Include  
Exclude  
2
0
Received: 2  
Passed: 0  
Dropped: 2  
------------------------------------------------------------------  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
Group List ..............  
(DR)  
No group memberships.  
------------------------------------------------------------------------  
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IGMP throttling (limiting the number of streams for each subscriber) > Example  
IGMP throttling (limiting the number of streams  
for each subscriber)  
IGMP throttling allows you to limit the number of streams that subscribers may access at a  
given time, for example, to protect from bandwidth oversubscription. When the number of  
multicast group memberships associated with a switch port reaches the configured limit, the  
port can either deny further Membership Reports, or replace an existing membership with  
the new group.  
IGMP filtering and throttling can be applied separately or together. The switch applies the  
filters first, then subjects any multicast group memberships passed by the filter to the limits  
imposed by throttling.  
IGMP Throttling is available in Software Version 2.7.5 or later.  
Example  
uses the same network configuration as "IGMP snooping" on page 9. For convenience, the  
diagram is reproduced below.  
Multicast Server  
port 1  
AT-8948  
Switch 1:  
Querier  
port 50  
port 49  
(blocked by STP)  
port 26  
port 25  
port 26  
port 25  
Rapier 24i  
Rapier 24i  
Switch 2:  
Snooper  
Switch 3:  
Snooper  
port 2  
port 3  
Client 1  
Client 2  
igmp-snooper.eps  
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IGMP throttling (limiting the number of streams for each subscriber) > Example  
X Configure switch 1  
Switch is an IGMP Querier. Note that it has a filter configured on it, which is from the  
1
previous example.  
set system name="Switch 1"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp=default port=1 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-52  
# Switching configuration  
set switch port=1 igmpfilter=1  
# IP configuration  
enable ip  
add ip int=vlan100 ip=172.31.0.254 mask=255.255.255.0  
enable ip igmp  
enable ip igmp int=vlan100  
create igmp filter=1  
add igmp filter=1 entry=1 group=224.0.1.22 action=exclude  
add igmp filter=1 entry=2 group=224.0.0.0-224.255.255.255  
X Configure switch 2  
Switch 2 is an IGMP Snooper. IGMP snooping is enabled by default and does not need any  
configuration. Switch 2 is limited to six multicast groups on port 2.  
set system name="Switch 2"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=2 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
# Switching configuration  
set switch port=2 igmpmaxgroup=6 igmpaction=replace  
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IGMP throttling (limiting the number of streams for each subscriber) > Example  
X Configure switch 3  
Switch 3 is also an IGMP Snooper.  
set system name="Switch 3"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=3 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
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IGMP throttling (limiting the number of streams for each subscriber) > Explanation of IGMP throttling (limiting the number of streams  
In this example, switch 2’s configuration limits port 2 to six concurrent multicast groups. The  
port has a throttling action of replace, meaning that any additional group replaces the oldest  
group.  
Consider switch 2 after a client on port 2 has joined six groups from 224.  
12.13.11-  
224. 2. 3. 6. Output from the command show igmpsnooping shows the six memberships.  
1
1
1
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.11  
Ports 2  
Entry timeout 251 secs  
Entry timeout 251 secs  
Entry timeout 251 secs  
Entry timeout 251 secs  
Entry timeout 251 secs  
Entry timeout 251 secs  
Entry timeout 257 secs  
Group. 224.12.13.12  
Ports 2  
Group. 224.12.13.13  
Ports 2  
Group. 224.12.13.14  
Ports 2  
Group. 224.12.13.15  
Ports 2  
Group. 224.12.13.16  
Ports 2  
All Groups  
Ports 25  
------------------------------------------------------------------------  
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IGMP throttling (limiting the number of streams for each subscriber) > Explanation of IGMP throttling (limiting the number of streams  
Next, the client joins three more groups (224.12.13.17-224.12.13.19). Output from the  
command show igmpsnooping still shows six memberships, but the oldest three groups  
have been dropped.  
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports 2  
Entry timeout 254 secs  
Entry timeout 254 secs  
Entry timeout 254 secs  
Entry timeout 256 secs  
Entry timeout 256 secs  
Entry timeout 256 secs  
Entry timeout 243 secs  
Group. 224.12.13.15  
Ports 2  
Group. 224.12.13.16  
Ports 2  
Group. 224.12.13.17  
Ports 2  
Group. 224.12.13.18  
Ports 2  
Group. 224.12.13.19  
Ports 2  
All Groups  
Ports 25  
------------------------------------------------------------------------  
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IGMP throttling (limiting the number of streams for each subscriber) > Explanation of IGMP throttling (limiting the number of streams  
When switch 2 drops groups by throttling, it does not send a Leave message, because IGMP  
snooping cannot generate IGMP packets. Therefore, the Querier (switch  
switch 2 is interested in the throttled groups, as output from the command show ip igmp  
on switch shows.  
1) still believes that  
1
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
Group List ..............  
(DR)  
Group. 224.12.13.13  
Ports 49  
Last Adv. 172.31.0.222  
Refresh time 215 secs  
Refresh time 215 secs  
Refresh time 215 secs  
Refresh time 215 secs  
Refresh time 217 secs  
Refresh time 217 secs  
Refresh time 217 secs  
Refresh time 238 secs  
Refresh time 238 secs  
Group. 224.12.13.14  
Ports 49  
Last Adv. 172.31.0.222  
Group. 224.12.13.15  
Ports 49  
Last Adv. 172.31.0.222  
Last Adv. 172.31.0.222  
Last Adv. 172.31.0.222  
Last Adv. 172.31.0.222  
Last Adv. 172.31.0.222  
Last Adv. 172.31.0.222  
Last Adv. 172.31.0.222  
Group. 224.12.13.16  
Ports 49  
Group. 224.12.13.17  
Ports 49  
Group. 224.12.13.18  
Ports 49  
Group. 224.12.13.19  
Ports 49  
Group. 224.12.13.11  
Ports 49  
Group. 224.12.13.12  
Ports 49  
------------------------------------------------------------------------  
This can cause the Querier to temporarily send more groups than necessary to a switch. The  
older groups will eventually time out.  
Note that the group list is sorted by refresh time, not group address.  
The output above also shows that the IGMP Querier only records the IP address of the last  
interested client—the Last Adv field shows the IP of the client who last sent an IGMP  
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IGMP throttling (limiting the number of streams for each subscriber) > Explanation of IGMP throttling (limiting the number of streams  
Membership Report for that group. IGMP throttling cannot distinguish between different  
clients on the same port. For this reason, the limit is tied to the port, not to the client.  
When we deny groups instead of replacing them  
Finally, we will consider the effect of changing the IGMP throttle action to deny, by using the  
command below.  
X Modify switch 2 Configuration  
set switch port=2 igmpmaxgroup=6 igmpaction=deny  
Once the six slots are filled, additional attempts to join other groups fail. Neither switch 2’s  
IGMP snooping table nor switch 1’s IGMP table register the new groups, because switch 2  
drops the client’s Membership Report without taking any further action.  
However, if the client attempts to join a group that already occupies one of the six slots, this  
renews the IGMP Querier’s refresh time and the IGMP Snooper’s entry timeout for the  
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IGMP throttling (limiting the number of streams for each subscriber) > Explanation of IGMP throttling (limiting the number of streams  
group. The following output for the command show igmpsnooping demonstrates this.  
Note that the timeout for the groups 224.12.13.11 and 224.12.13.12 has been reset.  
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.13  
Ports 2  
Entry timeout 228 secs  
Entry timeout 228 secs  
Entry timeout 228 secs  
Entry timeout 228 secs  
Entry timeout 255 secs  
Entry timeout 255 secs  
Entry timeout 168 secs  
Group. 224.12.13.14  
Ports 2  
Group. 224.12.13.15  
Ports 2  
Group. 224.12.13.16  
Ports 2  
Group. 224.12.13.11  
Ports 2  
Group. 224.12.13.12  
Ports 2  
All Groups  
Ports 25  
------------------------------------------------------------------------  
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Static IGMP > Example  
Static IGMP  
Static IGMP enables you to configure a switch with specified group-to-interface or group-to-  
port mappings, which you may want to do if:  
z
your network includes hosts that cannot send IGMP Membership Reports  
z
you need to guarantee that a specific multicast stream is instantly available on a port,  
without any delay from the joining process  
A common usage of Static IGMP is for protocols like Service Location Protocol (SLP). This  
protocol sends out multicast packets that need to be forwarded to designated ports. You may  
want SLP packets to be forwarded to ports that have servers who need to respond to these  
packets. Static IGMP allows you to specify that traffic for this group should go to hosts who  
will respond to, or are interested in, these messages. For detailed information about using  
Static IGMP and SLP, see How to configure IGMP snooping with unregistered multicast addresses  
such as Service Location Protocol (SLP) in the Allied Telesis website’s Technical Library.  
Static IGMP is available on all the Allied Telesis managed layer 3 switches listed on page 3.  
Example  
In this example, we will start by setting an IGMP static entry for the group 224.  
to port 5 on switch (part of vlan 00). On that port we have attached a host which has no  
multicast client software running. After examining the effect of static IGMP on switch , we  
12.13.14 to go  
1
1
1
will add a static IGMP entry to switch 3 and consider the effect this has on multicasting  
through the network.  
The network for this example has three switches in a loop and is shown in the following  
figure.  
Static client  
port 5  
AT-8948  
Multicast Server  
Switch 1:  
Querier  
port 1  
port 50  
port 49  
(blocked by STP)  
port 26  
port 26  
port 25  
Rapier 24i  
Rapier 24i  
Switch 2:  
Snooper  
port 25  
Switch 3  
port 5  
Static client  
(added later in example)  
igmp-static.eps  
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Static IGMP > Example  
X Configure switch 1  
Switch is an IGMP Querier and has the static IGMP entry. Static IGMP also requires you to:  
1
z
z
z
add an IP address to the interface to which you will attach the static entry  
enable IGMP  
enable the interface as an IGMP interface  
set system name="Switch 1"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp=default port=1 edgeport=yes  
set stp=default port=5 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-52  
# IP configuration  
enable ip  
add ip int=vlan100 ip=172.31.0.254 mask=255.255.255.0  
enable ip igmp  
enable ip igmp int=vlan100  
create ip igmp destination=224.12.13.14 int=vlan100 port=5  
X Configure switch 2  
Switch 2 is an IGMP Snooper.  
set system name="Switch 2"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=2 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
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Static IGMP > Example  
X Configure switch 3  
Switch 3 is also an IGMP Snooper. Later in this example, we will add a static IGMP entry on  
this switch. "Modify switch 3 Configuration" on page 52 shows the extra commands for this.  
set system name="Switch 3"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=3 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
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Static IGMP > Explanation of Static IGMP  
Explanation of Static IGMP  
When the IGMP static entry is created on switch  
snooping table and the IGMP table.  
1, entries immediately appear in the IGMP  
Manager Switch 1> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports 5  
Entry timeout Infinity  
------------------------------------------------------------------------  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
Group List ..............  
(DR)  
Group. 224.12.13.14  
Ports 5  
Static association  
Refresh time Infinity  
Static Ports 5  
------------------------------------------------------------------------  
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Static IGMP > Explanation of Static IGMP  
When the group 224.  
12.1  
3.1  
4 starts streaming into switch 1, we can use the command show  
switch port=5 counter to watch the number of multicast packets sent on port 5 increase.  
This means that the link is up and the static IGMP entry is working.  
Manager Switch 1> show switch port=5 counter  
Switch Port Counters  
--------------------------------------------------------------------------  
Port 5. Ethernet MAC counters:  
Combined receive/transmit packets by size (octets) counters:  
64  
5502 512 - 1023  
153355 1024 - MaxPktSz  
110102  
160356  
109314  
65 - 127  
128 - 255  
256 - 511  
137200  
General Counters:  
Receive  
Transmit  
Octets  
Pkts  
0 Octets  
0 Pkts  
341385876  
675829  
CRCErrors  
0
MulticastPkts  
BroadcastPkts  
FlowCtrlFrms  
OversizePkts  
Fragments  
0 MulticastPkts  
0 BroadcastPkts  
0 FlowCtrlFrms  
0
675826  
3
0
0
Jabbers  
0
UpsupportOpcode  
UndersizePkts  
0
0
Collisions  
LateCollisions  
ExcessivCollsns  
0
0
0
Miscellaneous Counters:  
MAC TxErr  
MAC RxErr  
0
0
0
Drop Events  
--------------------------------------------------------------------------  
When we add a static entry on another switch  
Now we add a static IGMP entry on port 5 of switch 3, by adding the commands below.  
X Modify switch 3 Configuration  
set stp port=5 edgeport=yes  
# IP configuration  
enable ip  
add ip int=vlan100 ip=172.31.0.253 mask=255.255.255.0  
enable ip igmp  
enable ip igmp int=vlan100  
create ip igmp destination=224.12.13.14 int=vlan100 po=5  
Both switches are potential IGMP Queriers and switch 3 becomes the Querier. This is  
because we gave switch 3 a lower IP address (  
172.3  
1
.0.253) than switch  
1
(173.31.0.254).  
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Static IGMP > Explanation of Static IGMP  
To see the effect that the new configuration has on switch  
1, we can check the IGMP  
snooping and IGMP tables. The IGMP snooping table shows that switch  
1
now has an All  
Groups entry because it is no longer the Querier. The IGMP table also shows that switch  
1
is  
not the Querier.  
Manager Switch 1> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports 5  
Entry timeout Infinity  
All Groups  
Ports 49  
Entry timeout 247 secs  
------------------------------------------------------------------------  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
Other Querier timeout ... 239 secs  
Group List ..............  
Group. 224.12.13.14  
Ports 5  
Static association  
Refresh time Infinity  
Static Ports 5  
------------------------------------------------------------------------  
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Static IGMP > Explanation of Static IGMP  
We can see the static entry on switch 3 by checking the IGMP snooping and IGMP tables.  
Manager Switch 3> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports 5  
Entry timeout Infinity  
------------------------------------------------------------------------  
Manager Switch 3> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
IGMP Proxy .............. Off  
Group List ..............  
(DR)  
Group. 224.12.13.14  
Ports 5  
Static association  
Refresh time Infinity  
Static Ports 5  
------------------------------------------------------------------------  
Note that switch 3—the Querier—has no entry for port 26 and therefore does not send the  
multicast to switch  
1. This is because the static entry joined switch  
1
to the stream without  
any client sending a Membership Report.  
If the multicast server was attached to switch 3 instead of switch 1, we would have to change  
switch 3’s configuration. We would need to add a static entry for the port that switch 3 uses  
to connect to switch (port 26). Although this is unnecessary in this scenario, we will do it  
to demonstrate the effect, by using the following commands.  
1
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Static IGMP > Explanation of Static IGMP  
X Modify switch 3 Configuration  
destroy ip igmp destination=224.12.13.14 int=vlan100  
create ip igmp destination=224.12.13.14 int=vlan100 port=5,26  
To see the new static entry, we use the commands show igmpsnooping and show ip  
igmp, and to see multicast packets streaming, we use the command show switch  
port=5,26 counter.  
Manager Switch 3> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports 5,26  
Entry timeout Infinity  
------------------------------------------------------------------------  
Manager Switch 3> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
IGMP Proxy .............. Off  
Group List ..............  
(DR)  
Group. 224.12.13.14  
Ports 5,26  
Static association  
Refresh time Infinity  
Static Ports 5,26  
------------------------------------------------------------------------  
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Static IGMP > Explanation of Static IGMP  
Manager Switch 3> show switch port=5,26 counter  
Switch Port Counters  
--------------------------------------------------------------------------  
Port 5. Fast Ethernet MAC counters:  
Combined receive/transmit packets by size (octets) counters:  
64  
3027 512 - 1023  
0 1024 - MaxPktSz  
0 1519 - 1522  
0
0
33365  
0
65 - 127  
128 - 255  
256 - 511  
General Counters:  
Receive  
Transmit  
Octets  
Pkts  
FCSErrors  
MulticastPkts  
BroadcastPkts  
0 Octets  
0 Pkts  
0 FCSErrors  
0 MulticastPkts  
0 BroadcastPkts  
45636858  
36392  
0
36350  
42  
.
.
.
Port 26. Gigabit Ethernet MAC counters:  
Combined receive/transmit packets by size (octets) counters:  
64  
3099 512 - 1023  
6 1024 - MaxPktSz  
0 1519 - 1522  
0
0
18598  
0
65 - 127  
128 - 255  
256 - 511  
General Counters:  
Receive  
Octets  
Transmit  
9342286 Octets  
6945 Pkts  
16186973  
Pkts  
14758  
FCSErrors  
0 FCSErrors  
0
MulticastPkts  
BroadcastPkts  
PauseMACCtlFrms  
OversizePkts  
6905 MulticastPkts  
40 BroadcastPkts  
0 PauseMACCtrlFrm  
0 OversizePkts  
14756  
2
0
0
.
.
.
--------------------------------------------------------------------------  
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Static IGMP > Explanation of Static IGMP  
When a static entry’s port goes down  
Finally, note that when the port attached to a static entry goes down, the static entry remains  
but no ports are attached to it. You can see this from the output of the commands show  
igmpsnooping and show ip igmp for switch  
1
when port 5 has been disconnected.  
Manager Switch 1> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports None  
Entry timeout Infinity  
All Groups  
Ports 49  
Entry timeout 152 secs  
------------------------------------------------------------------------  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
Other Querier timeout ... 140 secs  
Group List ..............  
Group. 224.12.13.14  
Ports None  
Static association  
Refresh time Infinity  
Static Ports None  
------------------------------------------------------------------------  
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How clients leave groups: queries and timers > Overview of leave process  
How clients leave groups: queries and timers  
When a client leaves a group, the Snoopers and the Querier check which ports now have  
clients that belong to that group. They will stop forwarding the group’s traffic out any ports  
that are now unnecessary. In this section, we describe the process in detail.  
Overview of leave process  
The basic process when a client leaves a group is as follows:  
1. The client sends a Leave message to indicate that it no longer needs to receive that  
multicast group.  
2. The Snooper receives the Leave message and forwards it towards the Querier.  
3. For all ports that belong to the group, the Querier changes its internal group membership  
timer to a short value (2 seconds by default—see Querier timer values below).  
4. The Querier sends a Specific Query to ask which other clients still belong to that group.  
5. The aforementioned Snooper receives the Specific Query. For all ports that belong to the  
group, the Snooper changes its internal group membership timer to a short value  
(2 seconds by default—see Snooper timer values below) unless the timer is already short.  
It forwards the Query out all its ports.  
6. The Querier waits for the Last Member Query Interval time, 1 second by default, and then  
sends a second Specific Query.  
7. The aforementioned Snooper snoops this second Specific Query and uses it to set the  
internal group membership timer for each port, unless the timer is already short (which it  
will be if the Snooper received the first Query). It forwards the Query out all its ports.  
8. If the Snooper or Querier receives a Membership Report on a port, it sets the port timer  
to the Default Timeout Interval value and continues to forward the multicast stream out  
that port. Otherwise, the timers for that port expire and the Snooper and/or Querier  
stops forwarding the multicast stream out that port.  
Querier timer values  
As described in Step 3 above, when the Querier sends a Specific Query for a group in  
response to a Leave message, the Querier updates a timer for ports that forward that group.  
The timer is the following two values multiplied together:  
z
Last Member Query Count (LMQC)—the number of Specific Queries the Querier sends,  
2 by default, and  
z
Last Member Query Interval (LMQI)—the time between the Specific Queries,  
by default  
1
second  
The default LMQC and LMQI give a timeout of 2 seconds. Therefore, by default the Querier  
must see the client response within 2 seconds of sending the first Specific Query.  
Because of this process, sensible values for LMQC and LMQI are essential. In most networks,  
the defaults are appropriate and you should not change them. If you need to change them,  
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How clients leave groups: queries and timers > Snooper timer values  
The command show ip igmp displays the timer for the most recently updated port as  
the group’s Refresh Time. From Software Version 291-08, the command show  
igmpsnooping vlan={<vid>|all} detail displays the timers for each individual port.  
Snooper timer values  
As described in Step 5 above, when the Snooper receives a Specific Query from the Querier,  
it may update a timer for ports that forward that group. The following flow chart describes  
the decision-making process for updating the timer.  
Start:  
Switch receives  
Query for which  
it has a group  
entry.  
Has the switch  
previously seen a  
Leave message?  
no  
yes  
For this  
Do not alter port-specific  
group membership timer.  
Flood Query out all ports.  
port, is the group  
entry dynamic  
(not static)?  
no  
yes  
Is the ports  
current timer  
LMQI from Querier  
LMQC from  
Snooper?  
no  
yes  
Set port-specific group  
membership timer to:  
LMQI from Querier  
LMQC from Snooper.  
Note that:  
The command show igmpsnooping displays the timer for the most recently updated  
port as the group’s Timeout in ... value. From Software Version 29 -08, the command  
z
1
show igmpsnooping vlan={<vid>|all} detail displays the timers for each individual  
port.  
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How clients leave groups: queries and timers > Comparing the Querier and Snooper timers  
z
z
To calculate the timer, the Snooper takes the LMQI value that it receives from the  
Querier and multiplies it by the Snooper’s own LMQC.  
The Snooper only reduces the timer if it receives a Leave message followed by a Specific  
Query—one of the messages is not enough.  
Changes with In software versions earlier than 281-03, the Snooper reset the group timer for all its ports  
281-03 and when it received a Specific Query. Since versions 28 -03 and 2.9. , each port has a separate  
1
1
2.9.1 timer and the Snooper only changes those which exceed the threshold. The flow chart above  
describes the new behaviour.  
Comparing the Querier and Snooper timers  
By default, the Querier and Snooper port-specific group timers have the same value  
(2 seconds). This is because the LMQC is the same for the Querier and the Snoopers.  
Consequences for high-loss and high-lag networks  
If packet loss or lag time is an issue in your network, we recommend increasing the  
Robustness Variable on the Snoopers and the Querier.  
On Allied Telesis Snoopers and Queriers, LMQC = Robustness Variable. For Snoopers, not  
all vendors make these counters the same. RFC 2236 requires that LMQC and Robustness  
Variable have the same value on Queriers, but the IGMP timer rules for IGMP Snoopers are  
less well-defined.  
Increasing the Querier LMQC (or Robustness Variable) increases the number of Specific  
Queries that the Querier sends. This increases the probability that an interested client will  
receive a Query.  
Increasing the Snooper LMQC (or Robustness Variable) increases the length of time that the  
Snooper waits before aging out the port. This gives the client more time to reply to the  
Queries.  
For example, if you increase the LMQC to 5 (the maximum) on the Querier and the  
Snooper, then the Querier sends 5 Queries and the Snooper waits for 5 * LMQI, which is  
5 seconds with the default LMQI.  
Make sure that the values on the Querier and the Snoopers match, so that the Snooper has  
time to forward all the Queries. For example, if you changed the Querier’s Robustness  
Variable to 5 but left the Snooper unchanged, the Querier would send out 5 Queries  
1 second apart but the Snooper would age out the group entry after only the first 2 Queries.  
For more information about setting the Robustness Variable, and the consequences of this,  
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IGMP fast leave > Example  
IGMP fast leave  
IGMP Fast Leave enhances your control over router or switch bandwidth. Enabling Fast Leave  
tells IGMP snooping to stop the transmission of a group multicast stream to a port as soon as  
it receives a Leave message on that port. No timeouts are observed.  
Ordinarily, when IGMP snooping sees a Leave message, it waits for a Membership Query  
message before setting the entry timeout to 2 seconds. Fast Leave tells IGMP to drop the  
entry from the port as soon as the Leave message is seen. For this reason, Fast Leave should  
only be configured on interfaces that have one clien t per port.  
Availability IGMP Fast Leave is available in Software Version 2.7.5 or later. In Software Versions  
earlier than 281-03 and 2.9.1, configure it by using the command:  
set igmpsnooping fastleave={on|off} interface=vlanx  
In Software Versions 281-03 and 2.9.1, the syntax changed to make it consistent with  
Query Solicitation. Therefore, the above syntax is still valid but the recommended syntax is  
now:  
set igmpsnooping vlan=vlanx fastleave={on|off}  
Software Version 291-08 introduced multiple mode for Fast Leave. See "Multiple host  
Example  
This example uses the same network configuration as "IGMP snooping" on page 9. For  
convenience, the diagram is reproduced below.  
Multicast Server  
port 1  
AT-8948  
Switch 1:  
Querier  
port 50  
port 49  
(blocked by STP)  
port 26  
port 25  
port 26  
port 25  
Rapier 24i  
Rapier 24i  
Switch 2:  
Snooper  
Switch 3:  
Snooper  
port 2  
port 3  
Client 1  
Client 2  
igmp-snooper.eps  
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IGMP fast leave > Example  
X Configure switch 1  
Switch is an IGMP Querier.  
1
set system name="Switch 1"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp=default port=1 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-52  
# IP configuration  
enable ip  
add ip int=vlan100 ip=172.31.0.254 mask=255.255.255.0  
enable ip igmp  
enable ip igmp int=vlan100  
X Configure switch 2  
Switch 2 is an IGMP Snooper. IGMP snooping is enabled by default and does not need any  
configuration.  
set system name="Switch 2"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=2 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
X Configure switch 3  
Switch 3 is also an IGMP Snooper. Fast leave is enabled on this switch.  
set system name="Switch 3"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=3 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
# IP configuration  
set igmpsnooping vlan=vlan100 fastleave=on  
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IGMP fast leave > Explanation of IGMP fast leave  
Explanation of IGMP fast leave  
Imagine that client 2 on switch 3 sends a Membership Report to join the group 224.12.13.14.  
The Snooper, switch 3, adds this to its the IGMP snooping table. When the same client then  
sends a Leave message, the IGMP Querier responds with a Membership Query and waits for  
a configured time for a response.  
The next sections describe in detail the differences between having Fast Leave disabled and  
enabled, but in summary:  
z
Without Fast Leave, the IGMP Snooper waits the same length of time as the Querier, then  
expires the entry if there was no response.  
z
With Fast Leave, the IGMP Snooper expires the entry as soon as it sees the Leave message  
from the client. By the time the Querier sends the Membership Query, the Snooper will  
have already expired the entry and therefore stopped sending the stream to the client.  
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IGMP fast leave > Explanation of IGMP fast leave  
When fast leave is disabled  
The IGMP Snooper sees the Membership Query from the Querier and accordingly sets its  
expiry time to match the Querier. Output of the command show igmpsnooping on  
switch 3 shows that the timeout for the group 224.  
that port 3 is still attached to the group. Likewise, output of the command show ip igmp on  
switch shows a timeout of 2 seconds.  
12.13.14 has dropped to 2 seconds and  
1
Manager Switch 3> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports 3  
Entry timeout 2 secs  
All Groups  
Ports 26  
Entry timeout 258 secs  
------------------------------------------------------------------------  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
Group List ..............  
(DR)  
Group. 224.12.13.14  
Ports 49  
Last Adv. 172.31.0.222  
Refresh time 2 secs  
------------------------------------------------------------------------  
If no Membership Report is received by the time the counters go to zero, then the client’s  
entry is dropped from both the IGMP Querier and Snooper.  
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IGMP fast leave > Explanation of IGMP fast leave  
When you enable fast leave on switch 3  
When Fast Leave is enabled on switch 3, but not on switch 1, an interesting chain of events  
occurs when the client sends a Leave message, as shown in the following diagram.  
Client 2  
Switch 3  
1
1
2
3
Client sends Leave message  
Switch 3  
Switch 3  
Switch 1  
Switch 1  
2
3
Switch 3 forwards Leave message  
and deletes snooping entry  
Switch 1 sends Membership Query  
with 2 second timeout period  
igmp-fast-leave.eps  
The result of this is that switch 3 adds the group back into its snooping table (with the same  
timeout as the IGMP Querier) but has no ports interested in receiving the group. Because  
Fast Leave is enabled on port 3, that port was removed from the group as soon as switch 3  
received the Leave message.  
Manager Switch 3> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. On  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. On  
Group List ..............  
Group. 224.12.13.14  
Ports None  
Entry timeout 2 secs  
All Groups  
Ports 26  
Entry timeout 258 secs  
------------------------------------------------------------------------  
Adding Fast Leave to switch  
other ports on switch 3. If you enabled Fast Leave on switch  
1
would not be sensible, since there may be clients attached to  
, one Leave message from  
1
switch 3 would drop the multicast stream for everyone on that switch.  
It is safe to ignore the group entry on switch 3.  
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IGMP fast leave > Explanation of IGMP fast leave  
When you set fast leave on all interfaces  
Fast leave is enabled on a per-interface basis, but if you do not specify an interface, it is  
enabled on all interfaces. In this example, that means that if no VLAN is specified when  
enabling Fast Leave, it is enabled on all VLANs (vlan and vlan100). The configuration  
1
resulting from the create config and show config dynamic commands always reflects the  
per-interface nature of Fast Leave, as the following output shows.  
Manager Switch 3> set igmpsnooping fastleave=on  
Info (1005420): IGMPSnooping 'Fast Leave' was successfully set on for all  
vlans.  
Manager Switch 3> show conf dyn=ip  
# IP configuration  
set igmpsnooping fastleave=on interface=vlan1  
set igmpsnooping fastleave=on interface=vlan100  
Similarly, we can easily disable Fast Leave on all interfaces.  
Manager Switch 3> set igmpsnooping fastleave=off  
Info (1005420): IGMPSnooping 'Fast Leave' was successfully set off for all  
vlans.  
Manager Switch 3> show conf dyn=ip  
# IP configuration  
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IGMP fast leave > Explanation of IGMP fast leave  
Multiple host mode for fast leave  
The previous discussion assumes that only one client is attached to the port on the Snooper.  
Imagine instead a situation where multiple clients are attached to a single port on the  
snooping switch, as the following figure shows.  
Multicast Server:  
TV source for  
channels 1-3  
port 1  
AT-8948  
Switch 1:  
Querier  
port 49  
port 26  
Rapier 24i  
Switch 3:  
Snooper  
port 3  
TV A  
1
TV B  
2
TV C  
3
TV D  
3
Channel:  
igmp-snooper.eps  
In this situation, you need to use fast leave in multiple host mode. In multiple host mode,  
the Snooper tracks which clients are joined to a given IP multicast group on a given port. The  
Snooper shuts off the multicast group to that port as soon as the last client leaves the group  
on the port.  
Multiple host mode is available in Software Version 291-08 and later.  
The alternative mode is called single host mode. In single host mode, as soon as the  
Snooper receives a leave message for a group on a port, it shuts off the multicast. This mode  
assumes that there are no other clients on the port that are still interested in receiving the  
multicast, so is suitable only when clients are directly attached to the Snooper.  
To specify multiple mode, use the command:  
set igmpsnooping vlan={name|1..4094|all} fastleave=multiple  
To specify single mode, use either of the commands:  
set igmpsnooping vlan={name|1..4094|all} fastleave=single  
set igmpsnooping vlan={name|1..4094|all} fastleave=on  
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IGMP fast leave > Explanation of IGMP fast leave  
You can see the list of hosts for each port by entering the command show igmpsnooping  
and specifying the detail parameter:  
show igmpsnooping vlan={name|1..4094|all}  
[group={multicast-ip-address|allgroups}] detail  
The group parameter lets you display information for only one group or for only the All  
Groups port (the allgroups option).  
The following example shows output when the detail parameter has been specified.  
IGMP Snooping  
--------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Multiple Host Topology  
Query Solicitation ...... Off  
Static Router Ports ..... None  
Group List .............. 3 groups  
Group 224.12.13.14  
Port 3  
Timeout in 256 secs  
Timeout in 257 secs  
Hosts: 1  
00-00-cd-12-34-56 (172.20.176.200)  
Timeout in 257 secs  
Group 224.12.13.15  
Port 3  
Timeout in 204 secs  
Timeout in 205 secs  
Hosts: 1  
00-00-ab-ab-cd-ef (172.20.176.201)  
Timeout in 205 secs  
Group 224.12.13.16  
Port 3  
Timeout in 192 secs  
Timeout in 193 secs  
Hosts: 2  
00-00-ab-27-be-f5 (172.20.176.202)  
00-00-cd-12-34-ab (172.20.176.203)  
Timeout in 193 secs  
Timeout in 100 secs  
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Configurable IGMP timers and counters > Timer and counter relationships  
Configurable IGMP timers and counters  
This section looks at some of the timers and counters that control how often IGMP sends  
queries and how quickly entries time out. First, it gives background information in the  
following subsections:  
z
z
z
z
Then it looks at each of the configurable timers and counters, in the following subsections:  
z
z
z
z
z
"Default Timeout Interval" on page 78 (the Group Membership Interval of RFC 2236)  
RFC 2236 also describes other counters and timers that this section does not describe,  
because this section only describes the counters and timers that you can directly set. The  
router or switch derives other counters and timers from the above subset.  
Timer and counter relationships  
The above timers and counters are related to each other and to others in RFC 2236 by the  
following formulae:  
z
Last Member Query Count = Robustness Variable  
z
Default Timeout Interval = (Robustness Variable * Default Query Interval) +  
one Query Response Interval in seconds  
z
z
Startup Query Count = Robustness Variable  
The Startup Query Count is the number of General Queries that the Querier sends when  
it starts up.  
Other Querier Timeout = (Robustness Variable * Default Query Interval) +  
(Query Response Interval in seconds/2)  
The Other Querier Timeout is the length of time that a potential Querier waits after  
receiving a Query before it assumes that it should become the Querier.  
These relationships mean you need to take care if you change timers or counters. "Example  
of bad choices for timer values" on page 83 describes the consequences of a bad combination  
of values.  
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Configurable IGMP timers and counters > Software versions  
Software versions  
Since software versions 28  
1-03 and 2.9.  
1, IGMP automatically sets the Default Timeout  
Interval to the value from the formula in the section above. Therefore, if you change any of  
the Robustness Variable, the LMQC, the Default Query Interval, or the Query Response  
Interval, IGMP changes the Default Timeout Interval to match. You can override the Default  
Timeout Interval if necessary, but we do not recommend doing so.  
The examples in this section come from version 2.9.  
automatically changes.  
1, so the Default Query Interval  
Initial configuration  
These examples use the same network configuration as "IGMP snooping" on page 9. For  
convenience, the diagram is reproduced below.  
Multicast Server  
port 1  
AT-8948  
Switch 1:  
Querier  
port 50  
port 49  
(blocked by STP)  
port 26  
port 25  
port 26  
port 25  
Rapier 24i  
Rapier 24i  
Switch 2:  
Snooper  
Switch 3:  
Snooper  
port 2  
port 3  
Client 1  
Client 2  
igmp-snooper.eps  
Each example modifies the following base configuration.  
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Configurable IGMP timers and counters > Initial configuration  
X Configure switch 1  
Switch 1 is an IGMP Querier.  
set system name="Switch 1"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp=default port=1 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-52  
# IP configuration  
enable ip  
add ip int=vlan100 ip=172.31.0.254 mask=255.255.255.0  
enable ip igmp  
enable ip igmp int=vlan100  
X Configure switch 2  
Switch 2 is an IGMP Snooper.  
set system name="Switch 2"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=2 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
X Configure switch 3  
Switch 3 is also an IGMP Snooper.  
set system name="Switch 3"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=3 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
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Configurable IGMP timers and counters > Default values  
Default values  
Output of the command show ip igmp shows the values of the configurable IGMP settings.  
The following output shows the default values.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
.
.
.
Note that units for Last Member Query Interval (LMQI) and Query Response Interval are  
0.1 seconds. Therefore, the default LMQI is  
Interval is 0 seconds.  
1
second and the default Query Response  
1
Last Member Query Count and Last Member  
Query Interval  
The Last Member Query Count (LMQC) is the number of Specific Queries the Querier  
sends after receiving a Leave message— to 5 messages.  
1
The Last Member Query Interval (LMQI) is the time between the Specific Queries—  
1
to 255  
in units of 0. seconds.  
1
These counters determine how quickly a group times out when the last client leaves the  
group. You should read this section in conjunction with "How clients leave groups: queries  
and timers" on page 58, which has an outline of the leave process and a detailed discussion of  
the timers.  
What these counters do  
On the Querier and all Snoopers, IGMP keeps group membership timeout values on each  
port. During general multicasting, these timeouts are (by default) 260 seconds. When a client  
leaves a group, these timeouts are reduced to make multicasting stop quickly after the last  
client leaves. The LMQC and LMQI determine the value of the timeout during this leave  
process (2 seconds with the default LMQC and LMQI).  
On the Querier, the timeout during the leave process = LMQC * LMQI  
On Snoopers, the timeout during the leave process =  
LMQI from Querier * LMQC from Snooper  
From Software Version 29  
1-08, the command show igmpsnooping vlan={<vid>|all}  
detail displays the timers for each individual port.  
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Configurable IGMP timers and counters > Last Member Query Count and Last Member Query Interval  
Potential problems with changing these counters  
For most networks, the default LMQI and LMQC values work. You should only change them  
if you are aware of the likely effect on the network. In particular, note that:  
z
Changing the LMQC automatically changes the Robustness Variable. Therefore, we do not  
recommend setting the LMQC to , because it removes the system’s allowance for packet  
1
loss. See page 75 for more information about the consequences of changing the  
Robustness Variable.  
z
If you set the LMQI (or LMQC, or both) too low, clients will not be able to reply to Specific  
Queries quickly enough and the Querier and Snoopers may delete group entries for ports  
that still need to receive multicasts. If this happens, some or all clients briefly lose the  
multicast stream.  
The default values of LMQI (10) and LMQC (2) mean that the Querier must receive client  
Membership Reports within 2 seconds of the first Query. This is already quite a short time  
and we do not recommend reducing it even more. For example, reducing the LMQI to 5  
would allow only  
1
second for responses, which may be too little.  
How to change these counters  
The following example increases LMQI a lot, and then shows the resulting changed refresh  
time.  
Manager Switch 1> set ip igmp lmqi=255  
Info (1005003): Operation successful.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 255 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
Group List ..............  
(DR)  
Group. 224.12.13.14  
Ports 49  
Last Adv. 172.31.0.222  
Refresh time 49 secs  
------------------------------------------------------------------------  
The refresh time in seconds is (LMQI/10) * LMQC = 255/10 * 2 = 51 seconds  
So with the new LMQI setting of 255 and the default LMQC setting of 2, the IGMP Querier  
waits 5 seconds for a Membership Report to arrive before it ages out the IGMP entry. Note  
1
that the output above displays 49 seconds, because it took us 2 seconds to enter the  
command show ip igmp.  
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Configurable IGMP timers and counters > Last Member Query Count and Last Member Query Interval  
Similarly, if we change the LMQC from 2 to 3, the refresh time also changes.  
Manager Switch 1> set ip igmp lmqc=3  
Info (1005003): Operation successful.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 385 secs  
Last Member Query Interval ....... 255 (1/10secs)  
Last Member Query Count .......... 3  
Robustness Variable .............. 3  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
Group List ..............  
(DR)  
Group. 224.12.13.14  
Ports 49  
Last Adv. 172.31.0.222  
Refresh time 74 secs  
------------------------------------------------------------------------  
The refresh time in seconds is (LMQI/10) * LMQC = 255/10 * 3 = 76.5 seconds  
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Configurable IGMP timers and counters > Robustness Variable  
Robustness Variable  
What this counter does  
The Robustness Variable (RV) allows you to tune for the expected packet loss on a subnet. If  
you expect a subnet to be lossy, you can increase the RV. IGMP is robust to packet loss of  
one packet less than the RV. The RV is an integer from  
1
to 5 and should not be set to  
1.  
If packet loss or lag time is an issue in your network, we recommend increasing the  
Robustness Variable on the Snoopers and the Querier. This increases the following:  
z
the number of Queries that the Querier sends out (by increasing the LMQC)  
the amount of time that the Querier and the Snoopers wait for clients to reply  
z
Potential problems with changing this counter  
The RV is the counter you are most likely to need to change. However, you need to  
appreciate the effect this has on your network, as described in RFC 2236. Changing the RV  
changes other values from the RFC, as follows:  
z
Last Member Query Count = Robustness Variable  
z
Default Timeout Interval = (Robustness Variable * Default Query Interval) +  
one Query Response Interval in seconds  
Since software versions 281-03 and 2.9.1, the Default Timeout Interval automatically  
changes to match the above formula. For earlier versions, you must change it yourself, as  
described on page 82.  
z
z
Startup Query Count = Robustness Variable  
Other Querier Timeout = (Robustness Variable * Default Query Interval) +  
(Query Response Interval in seconds/2)  
How to change this counter  
The following example changes RV to 5, which is suitable for an extremely lossy network.  
Note that the Last Member Query Count and Default Timeout Interval also change.  
Manager Switch 1> set ip igmp robustness=5  
Info (1005003): Operation successful.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 635 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 5  
Robustness Variable .............. 5  
Query Response Interval .......... 100 (1/10secs)  
.
.
.
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Configurable IGMP timers and counters > Default Query Interval  
Default Query Interval  
What this timer does  
To maintain an accurate picture of group membership, the Querier periodically sends  
General Queries to all its IGMP interfaces. The Default Query Interval is the gap between  
General Queries.  
Note that General Queries are quite different from Specific Queries, which the Querier  
sends to a group address when it receives a Leave message for that group.  
The router or switch only sends General or Specific Queries if it is the Querier. If another  
router or switch is elected as the Querier, the non-elected router or switch ignores the  
Default Query Interval and other such settings.  
Potential problems with changing this timer  
If you change the Default Query Interval, the Default Timeout Interval also needs to change  
so that clients have an appropriate amount of time to reply to the Query. Since software  
versions 281-03 and 2.9.1, this happens automatically. For earlier versions, you need to  
change it yourself as described on page 82.  
How to change this timer  
The Default Query Interval is an integer from  
1
to 65535 seconds, specified using the  
queryinterval parameter. The default is 125 seconds. The following example tweaks the  
interval. Note that the Default Timeout Interval also changes.  
Manager Switch 1> set ip igmp queryinterval=120  
Info (1005003): Operation successful.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 120 secs  
Default Timeout Interval ......... 250 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
.
.
.
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Configurable IGMP timers and counters > Query Response Interval  
Query Response Interval  
What this timer does  
The Query Response Interval determines the longest time clients can take to reply to a  
General Query. The Querier inserts the Query Response Interval into General Query  
messages. Clients randomly choose a time between 0 and the Query Response Interval at  
which to respond to a General Query. Increasing the Query Response Interval spreads IGMP  
messages over a longer time period, which reduces the burstiness of traffic on the network.  
The Query Response Interval is also referred to as the Max Response Time in RFC 2236.  
It may be useful to decrease the Query Response Interval if you are running EPSR or RSTP.  
Decreasing the Query Response Interval reduces the recovery time after a topology change.  
Potential problems with changing this timer  
If your network has many multicast clients and you make the Query Response Interval too  
short, you may congest the Snoopers and Querier with too many Report messages in a short  
time.  
If you change the Query Response Interval, the Default Timeout Interval also needs to  
change, so that clients have an appropriate amount of time to reply to the Query. Since  
software versions 281-03 and 2.9.1, this happens automatically. For earlier versions, you need  
to change it yourself as described on page 82.  
How to change this timer  
The Query Response Interval is an integer from  
1
to 255 in units of 0.  
1
seconds, specified  
using the queryresponseinterval parameter. The default is  
1
00 ( 0 seconds). The  
1
following example would return a modified Query Response Interval to its default value.  
Manager Switch 1> set ip igmp queryresponseinterval=100  
Info (1005003): Operation successful.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
.
.
.
In this example, the Querier sends a General Query every  
125 seconds. The General Query  
contains the Query Response Interval of  
reply to this General Query message.  
1
00, which tells clients that they have 0 seconds to  
1
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Configurable IGMP timers and counters > Default Timeout Interval  
Default Timeout Interval  
The Default Timeout Interval is referred to as the Group Membership Interval in RFC 2236.  
What this timer does  
The Default Timeout Interval specifies the length of time before the router or switch deletes  
a group from its multicast group database after the router or switch last receives a  
Membership Report for that group. All IGMP routers and switches in a network use this  
interval to maintain their group membership databases, not just the Querier.  
The Querier also uses this interval to close down multicasting if it receives no replies to all  
General Queries for a group. If the Querier sends a General Query and does not receive any  
Membership Reports in response, it continues to send any existing multicast streams. In the  
meanwhile, the Default Timeout Interval counts down until it hits zero, at which point the  
Querier stops propagating the multicast streams through the LAN.  
Potential problems with changing this timer  
Make the Default Timeout Interval too short has serious consequences. You remove the  
network’s ability to cope with losing a General Query and you may not give enough time for  
client responses to reach the Querier. These problems would cause multicasting to stop for  
some or all clients. For more information, see "Example of bad choices for timer values" on  
Synchronisation of timers  
The Default Timeout Interval is a function of several other timers, according to the following  
formula from RFC 2236:  
Default Timeout Interval = (Robustness Variable * Default Query  
Interval) +  
one Query Response Interval in seconds  
Since software versions 281-03 and 2.9.1, the Default Timeout Interval changes automatically  
if you change any of the Robustness Variable, the LMQC, the Default Query Interval, or the  
Query Response Interval. You can override the Default Timeout Interval value, but the  
router or switch displays a warning message if you do so.  
For earlier versions, you need to calculate and change the interval yourself.  
The following examples show how changing the timers changes the Default Timeout Interval.  
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Configurable IGMP timers and counters > Default Timeout Interval  
Defaults First, the following output shows the default settings.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
.
.
.
The Default Timeout Interval = (2*  
1
25) + (  
1
00/10) = 260 seconds.  
Increase Next, change the Default Query Interval to  
130 seconds.  
Default  
Query  
Interval  
Manager Switch 1> set ip igmp queryinterval=130  
Info (1005003): Operation successful.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 130 secs  
Default Timeout Interval ......... 270 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
.
.
.
The Default Timeout Interval = (2*130) + (100/10) = 270 seconds.  
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Configurable IGMP timers and counters > Default Timeout Interval  
Increase Next, change the Query Response Interval to 200 tenths of a second.  
Query  
Response  
Interval  
Manager Switch 1> set ip igmp queryresponseinterval=200  
Info (1005003): Operation successful.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 130 secs  
Default Timeout Interval ......... 280 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 200 (1/10secs)  
.
.
.
The Default Timeout Interval = (2*  
130) + (200/  
10) = 280 seconds.  
Reduce Next, reduce the Default Query Interval to  
Intervals 00 tenths of a second again.  
125 seconds and the Query Response Interval to  
1
Manager Switch 1> set ip igmp queryinterval=125  
Info (1005003): Operation successful.  
Manager Switch 1> set ip igmp queryresponseinterval=100  
Info (1005003): Operation successful.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
.
.
.
The Default Timeout Interval = (2*125) + (100/10) = 260 seconds.  
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Configurable IGMP timers and counters > Default Timeout Interval  
Override To support existing configurations and for maximum flexibility, you can manually override the  
Default Default Timeout Interval. We do not recommend this.  
Timeout  
Manager Switch 1> set ip igmp timeout=180  
Interval  
Warning (2005430): The Default Timeout Interval is below the default safe value of  
(Default Query Interval * Robustness ) + (Query Response Interval / 10).  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 180 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
.
.
.
The warning message also displays when the router or switch starts up and in the log file, as  
the following output shows.  
Manager Switch 1> show log tail  
Date/Time S Mod Type SType Message  
-------------------------------------------------------------------------------  
02 01:22:17 4 ENCO ENCO STAC STAC SW Initialised  
02 01:22:17 7 SYS REST NORM Router startup, ver 2.9.2-00, 30-Mar-2003, Clock  
Log: 01:22:03 on 02-Dec-2006  
02 01:22:19 6 SWIT PINT UP  
02 01:22:19 6 SWIT PINT UP  
Port1: interface is UP  
Port16: interface is UP  
02 01:22:19 3 USER USER LON manager login on port0  
02 01:36:59 3 CH MSG WARN The Default Timeout Interval is below the  
default safe value of (Default Query Interval *  
Robustness ) + (Query Response Interval / 10)  
-------------------------------------------------------------------------------  
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Configurable IGMP timers and counters > Default Timeout Interval  
Earlier With software versions earlier than 281-03 and 2.9.1, you need to manually calculate and  
software change the Default Timeout Interval if you change any of the Robustness Variable, the  
versions LMQC, the Default Query Interval, or the Query Response Interval. Simply use the formula  
Default Timeout Interval =  
(Robustness Variable * Default Query Interval)  
+ one Query Response Interval in seconds  
Note that the Query Response Interval is in seconds in this formula, instead of tenths of  
seconds as displayed in the output of the command show ip igmp.  
For example, if you set a Default Query Interval of 200 seconds (and otherwise have default  
settings), you also need to set the Default Timeout Interval to:  
Default Timeout Interval = 2 * 200 + 10 = 410 seconds  
Manager Switch 1> set ip igmp queryinterval=200  
Info (1005003): Operation successful.  
Manager Switch 1> set ip igmp timeout=410  
Info (1005003): Operation successful.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 200 secs  
Default Timeout Interval ......... 410 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
.
.
.
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Example of bad choices for timer values > Example  
Example of bad choices for timer values  
It is generally unwise to change any of the default IGMP settings unless you have advanced  
knowledge of how IGMP works. As "Timer and counter relationships" on page 69 describes,  
most of the timers and counters are related. This means setting timers can cause problems  
unless you understand the potential impact on the IGMP process.  
This example sets three timers to excessively short values and discusses the potential  
consequences.  
Example  
Imagine the following changes to the configuration:  
Timer  
New value  
Last Member Query Interval  
Query Response Interval  
Default Timeout Interval  
5
5
126  
The commands to configure these settings are:  
set ip igmp lmqi=5  
set ip igmp queryresponseinterval=5  
set ip igmp timeout=126  
The resulting values are displayed in the following output.  
Manager Switch 1> show ip igmp  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 126 secs  
Last Member Query Interval ....... 5 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 5 (1/10secs)  
.
.
.
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Example of bad choices for timer values > Problem 1: Last Member Query Interval too short  
Problem 1: Last Member Query Interval too short  
The Last Member Query Interval was set to 5, using the command:  
set ip igmp lmqi=5  
This value is incredibly low—actually 5 tenths of a second (half a second). A Last Member  
Query Count of 2 (the default), gives your clients 1 second to get their Report back to the  
Querier before the Snooper and Querier stop sending the data stream. Using too low a Last  
Member Query Interval may mean that some or all clients briefly lose the multicast stream.  
Problem 2: Query Response Interval short  
The Query Response Interval was also set to 5, using the command:  
set ip igmp queryresponseinterval=5  
This value is also half a second. This value means that clients randomly pick a time between 0  
and 0.5 seconds to respond (send a Report) to a Query. Using a short time here congests the  
Snoopers and Querier with Reports in a short space of time. This is not necessarily a  
problem if you only have a few clients, but 0.5 seconds is definitely a short window of time.  
Problem 3: Default Timeout Interval too short  
The Default Timeout Interval was set to 126, using the command:  
set ip igmp timeout=126  
There are two issues with having the Default Timeout Interval so short:  
z
There is no longer any allowance for packet loss in the network.  
The Querier sends a General Query every Default Query Interval seconds and waits for  
the Default Interval Timeout seconds for replies. Then it deletes any existing group entries  
that did not get refreshed. Therefore, if the Default Interval Timeout is less than twice the  
Default Query Interval, the Querier deletes entries if they do not reply to one General  
Query. A single dropped General Query causes multicasting to stop for the whole Layer 2  
network.  
z
Clients may not have time to reply.  
In this example, the Default Timeout Interval (  
the Default Query Interval ( 25). There is only  
1
26 seconds) is only  
1
second longer than  
1
1 second for clients to receive the General  
Query and generate a Report and all Snoopers and the Querier to receive the Report.  
Depending on the network, this may not be long enough. If a client Report does not get  
back to the Querier in time, the Querier deletes that port’s entry and multicasting stops  
briefly for the client.  
RFC 2236 says that the Default Timeout Interval (the Group Membership Interval) must be:  
(Robustness Variable * Default Query Interval) + one Query  
Response Interval  
For the settings in this example, that means (2*125) + 0.5 = 250.5 seconds.  
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Example of bad choices for timer values > Problem 3: Default Timeout Interval too short  
Note that the Query Response Interval is specified in  
1/10 second units on the command line  
and in output of show ip igmp, but in units of seconds in the above formula. In this example,  
the Query Response Interval was set with queryresponseinterval=5, so is 0.5 seconds.  
Automatic Since software versions 281-03 and 2.9.1, IGMP automatically changes the Default Timeout  
changes Interval if you change any of the Robustness Variable, the LMQC, the Default Query Interval,  
or the Query Response Interval. You can override the setting, as in this example, but we do  
not recommend this.  
Before these releases, if you changed any of these other timers or counters, you had to  
manually calculate and change the Default Timeout Interval yourself.  
For more information, see "Synchronisation of timers" on page 78.  
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Stopping snoopers from snooping non-IGMP messages > Example  
Stopping snoopers from snooping non-IGMP  
messages  
Some networks include routers that have no interest in IGMP, but still generate multicast  
messages by running protocols like OSPF. When a Snooper receives multicast messages from  
such a router, the Snooper adds the router’s port to its All Groups port list. This means the  
router is unnecessarily sent IGMP and multicast traffic. Using IGMP features to prevent the  
excess traffic is particularly helpful when you cannot or do not want to control the traffic at  
the router.  
This example describes how to use AlliedWare’s advanced IGMP features to prevent this  
behaviour, by limiting the ports that the Snooper adds to the All Groups list, or by stopping  
particular types of traffic from adding ports to the All Groups list.  
Example  
The example is based around a network that has a router running OSPF. The router is  
connected to a LAN through a switch. The LAN is a single subnet with no OSPF routers  
inside it. The network for this example uses the same loop as for "IGMP snooping" on page 9,  
with a router attached to switch 2. The network is shown in the following figure.  
Multicast Server  
port 1  
AT-8948  
Switch 1:  
Querier  
port 50  
port 49  
(blocked by STP)  
port 26  
port 25  
port 26  
port 25  
OSPF  
Rapier 24i  
Rapier 24i  
Switch 2:  
Snooper  
Switch 3:  
Snooper  
port 3  
port 24 port 2  
Client 2  
Client 1  
Router  
igmp-all-groups.eps  
We used an AR410 router, but the router configuration works on any AR400 or AR700  
series router.  
Each example in this section modifies the following base configuration.  
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Stopping snoopers from snooping non-IGMP messages > Example  
X Configure switch 1  
Switch 1 is an IGMP Querier.  
set system name="Switch 1"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp=default port=1 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-52  
# IP configuration  
enable ip  
add ip int=vlan100 ip=172.31.0.254 mask=255.255.255.0  
enable ip igmp  
enable ip igmp int=vlan100  
X Configure switch 2  
Switch 2 is an IGMP Snooper.  
set system name="Switch 2"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=2 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
X Configure switch 3  
Switch 3 is also an IGMP Snooper.  
set system name="Switch 3"  
# STP general configuration  
enable stp=default  
set stp=default mode=rapid  
set stp port=3 edgeport=yes  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-26  
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Stopping snoopers from snooping non-IGMP messages > Example  
X Configure the router  
The router uses OSPF.  
set system name=Router  
# VLAN general configuration  
create vlan=vlan100 vid=100  
add vlan=100 port=1-4  
# IP configuration  
enable ip  
set ip autonomous=65000  
add ip int=vlan100 ip=172.31.0.1 mask=255.255.255.0  
add ip int=eth0 ip=10.0.0.1  
# OSPF configuration  
set ospf routerid=172.31.0.1  
add ospf area=0.0.0.1  
add ospf range=172.31.0.0 area=0.0.0.1 mask=255.255.255.0  
add ospf interface=vlan100 area=0.0.0.1  
enable ospf  
With the above configuration, the router sends OSPF messages to switch 2. As the following  
outputs show, this means that:  
z
switch 2 designates port 24 an All Groups port  
z
switch 2 forwards the OSPF packets to uplink port 25 on switch 3, so switch 3 designates  
port 25 an All Groups port  
z
switch 3 forwards the OSPF packets to uplink port 49 on switch 1, so switch designates  
1
port 49 an All Groups port  
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
All Groups  
Entry timeout 256 secs  
Ports 24-25  
------------------------------------------------------------------------  
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Stopping snoopers from snooping non-IGMP messages > Example  
Manager Switch 3> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
All Groups  
Entry timeout 257 secs  
Ports 25-26  
------------------------------------------------------------------------  
Manager Switch 1> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
All Groups  
Entry timeout 260 secs  
Ports 49  
------------------------------------------------------------------------  
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Stopping snoopers from snooping non-IGMP messages > Preventing an All Groups entry for a port  
Preventing an All Groups entry for a port  
This section stops port 24 from being in switch 2’s All Groups entry, then adds it back again.  
Disabling All Groups entry for a port  
You can avoid the All Groups entries shown above by simply disabling the All Groups entry  
for the port that switch 2 uses to connect to the router.  
Manager Switch 2> disable ip igmp allgroups=24  
Info (1005003): Operation successful.  
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ 24  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports None  
Entry timeout 164 secs  
Entry timeout 251 secs  
All Groups  
Ports 24#,25  
------------------------------------------------------------------------  
Port 24 is now accompanied by a hash. This is because All Groups was disabled for the port  
while the port was part of All Groups. The switch will keep sending port 24 traffic for the  
group 224.  
12.13.14 until either port 24’s internal timer or the timer for the group  
224. 2. 3.  
1
1
14 hits zero.  
Note: The switch keeps an internal timer for each port in its All Groups list, which is  
separate from the All Groups entry timeout displayed in output of the command  
show igmpsnooping. There are no commands to view the internal timer, but every  
time the switch receives a new IGMP (or in this case OSPF) message the timer  
resets. This timer means that if the router stopped sending OSPF messages to the  
port, the switches would eventually drop the relevant entries from their All Groups  
lists.  
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Stopping snoopers from snooping non-IGMP messages > Preventing an All Groups entry for a port  
Enabling All Groups entry again  
To further explore the system we will next reverse the process and follow switch 2 while  
group entries time out and the switch starts transmitting traffic for the group 224.12.13.14 to  
the router again. This sequence illustrates the time delay between when you change a port’s  
All Groups configuration and when multicast traffic flow changes.  
1. Permit port 24 to be an All Groups port again.  
Manager Switch 2> enable ip igmp allgroups=24  
Info (1005003): Operation successful.  
2. Check the group entry timeout values.  
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports None  
Entry timeout 216 secs  
All Groups  
Entry timeout 254 secs  
Ports 24-25  
------------------------------------------------------------------------  
Port 24 is now an All Groups port. However, this not mean that it immediately starts  
receiving multicast packets for the group 224.12.13.14, as the next few steps show.  
3. Reset port 24’s packet counters.  
Manager Switch 2> reset switch port=24 counter  
Info (1087003): Operation successful.  
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Stopping snoopers from snooping non-IGMP messages > Preventing an All Groups entry for a port  
4. Display port 24’s packet counters, which show that only a few multicast packets  
have been transmitted on the port.  
Manager Switch 2> show switch port=24 counter  
Switch Port Counters  
------------------------------------------------------------------------  
Port 24. Fast Ethernet MAC counters:  
Combined receive/transmit packets by size (octets) counters:  
64  
2 512 - 1023  
0 1024 - MaxPktSz  
0 1519 - 1522  
0
0
0
0
65 - 127  
128 - 255  
256 - 511  
General Counters:  
Receive  
Transmit  
Octets  
Pkts  
0 Octets  
0 Pkts  
128  
2
FCSErrors  
0 FCSErrors  
0 MulticastPkts  
0 BroadcastPkts  
0 PauseMACCtrlFrm  
0 OversizePkts  
0 Fragments  
0 Jabbers  
0
2
0
0
0
0
0
MulticastPkts  
BroadcastPkts  
PauseMACCtlFrms  
OversizePkts  
Fragments  
Jabbers  
.
.
.
------------------------------------------------------------------------  
5. Check the group entry timeout values again.  
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports None  
Entry timeout 3 secs  
All Groups  
Entry timeout 255 secs  
Ports 24-25  
------------------------------------------------------------------------  
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Stopping snoopers from snooping non-IGMP messages > Preventing an All Groups entry for a port  
6. Enable IGMP debugging.  
Manager Switch 2> enable ip igmp debug  
Info (1005003): Operation successful.  
7. Observe the debugging output, which shows that the group 224.12.13.14 was  
deleted when its timer expired, then was immediately added in again.  
Manager Switch 2> IGMP Snoop Timeout: group=224.12.13.14 (0) is deleted  
Deleting all ports for group 224.12.13.14 on vlan100  
IGMP Snoop Unregistered Multicast: Source 172.31.0.99, Group 224.12.13.14  
-> snd group 224.0.0.2 added  
Adding port 24 for group 224.0.0.2 on vlan100  
IGMP Snoop: added all router membership  
8. Check the group entry timeout values again.  
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports None  
Entry timeout 259 secs  
All Groups  
Entry timeout 259 secs  
Ports 24-25  
------------------------------------------------------------------------  
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Stopping snoopers from snooping non-IGMP messages > Preventing an All Groups entry for a port  
9. Display port 24’s packet counters, which show that many multicast packets have  
been transmitted on the port.  
Manager Switch 2> show switch port=24 counter  
Switch Port Counters  
------------------------------------------------------------------------  
Port 24. Fast Ethernet MAC counters:  
Combined receive/transmit packets by size (octets) counters:  
64  
84 512 - 1023  
16 1024 - MaxPktSz  
0 1519 - 1522  
0
0
830  
0
65 - 127  
128 - 255  
256 - 511  
General Counters:  
Receive  
Octets  
Transmit  
1312 Octets  
1135836  
Pkts  
FCSErrors  
16 Pkts  
0 FCSErrors  
914  
0
MulticastPkts  
BroadcastPkts  
PauseMACCtlFrms  
OversizePkts  
Fragments  
16 MulticastPkts  
0 BroadcastPkts  
0 PauseMACCtrlFrm  
0 OversizePkts  
0 Fragments  
914  
0
0
0
0
Jabbers  
0 Jabbers  
0
.
.
.
------------------------------------------------------------------------  
In summary, when a port receives the All Groups designation, a stream is sent to that port  
when either:  
z
the stream's group entry times out and is refreshed, or  
the port's internal timer hits zero and is refreshed  
z
It is most likely that the group entry will time out first.  
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Stopping snoopers from snooping non-IGMP messages > Controlling which addresses create All Groups entries  
Controlling which addresses create All Groups entries  
The router or switch adds a port to its All Groups list when it determines that the port has a  
router attached to it. This example shows how to influence the router or switch’s process in  
determining who is a router, and therefore when to add a port to the All Groups list.  
You can control the criteria for deciding which packets actually indicate the presence of a  
router on a particular port, by using the command:  
set igmpsnooping routermode={all|default|ip|multicastrouter|  
none}  
With this command, you specify (in effect) a list of IP addresses. When the router or switch  
receives a multicast packet on a port, it compares the packet’s destination IP address with the  
list. If they match, the router or switch considers the packet to be from a “router”, and adds  
the port to the All Groups list.  
The following table shows the address lists that each command option gives.  
This option...  
means that the port is treated as a multicast router port if it receives  
packets from...  
all  
any reserved multicast addresses (224.0.0.1 to 224.0.0.255)  
default  
224.0.0.1 (IGMP Queries)  
224.0.0.2 (all routers on this subnet)  
224.0.0.4 (DVMRP routers)  
224.0.0.5 (all OSPFIGP routers)  
224.0.0.6 (OSPFIGP designated routers)  
224.0.0.9 (RIP2 routers)  
224.0.0.13 (all PIM routers)  
224.0.0.15 (all CBT routers)  
multicastrouter  
ip  
224.0.0.4 (DVMRP routers)  
224.0.0.13 (all PIM routers)  
the current list of addresses,  
plus addresses specified using the command add igmpsnooping  
routeraddress,  
minus addresses specified using the command delete igmpsnooping  
routeraddress.  
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Stopping snoopers from snooping non-IGMP messages > Controlling which addresses create All Groups entries  
Configuring switch 2  
The example below shows how to tailor the list of router addresses on switch 2. In summary,  
you do this by using the commands:  
set igmpsnooping routermode=ip  
delete igmpsnooping routeraddress=224.0.0.5  
The example removes 224.0.0.5 because it is the address for OSPF messages, as the table  
above shows.  
Manager Switch 2> set igmpsnooping routermode=ip  
Info (1005282): IGMPSnooping Routermode successfully updated.  
Manager Switch 2> show igmpsnooping routeraddress  
IGMP Snooping Router Address  
----------------------------------------------------------------------  
IGMP Snooping Router Mode ......... ip  
Router Address List  
--------------------------------------------------------  
224.0.0.1  
224.0.0.2  
224.0.0.4  
224.0.0.5  
224.0.0.6  
224.0.0.9  
224.0.0.13  
224.0.0.15  
----------------------------------------------------------------------  
Manager Switch 2> enable ip igmp debug  
Info (1005003): Operation successful.  
Manager Switch 2> delete igmpsnooping routeraddress=224.0.0.5  
Info (1005272): Multicast addresses successfully deleted.  
Manager Switch 2> show igmpsnooping routeraddress  
IGMP Snooping Router Address  
----------------------------------------------------------------------  
IGMP Snooping Router Mode ......... ip  
Router Address List  
--------------------------------------------------------  
224.0.0.1  
224.0.0.2  
224.0.0.4  
224.0.0.6  
224.0.0.9  
224.0.0.13  
224.0.0.15  
----------------------------------------------------------------------  
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Stopping snoopers from snooping non-IGMP messages > Controlling which addresses create All Groups entries  
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
All Groups  
Entry timeout 214 secs  
Ports 24-25  
------------------------------------------------------------------------  
Manager Switch 2> Timing out port 24 from group 224.0.0.2 on vlan100  
Deleting port 24 from group 224.0.0.2 on vlan100  
Reconstructing snooping entries: 24,  
Manager Switch 2> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
Group. 224.12.13.14  
Ports None  
Entry timeout 224 secs  
Entry timeout 242 secs  
All Groups  
Ports 25  
------------------------------------------------------------------------  
Looking at the above outputs, note that debugging did not print out any messages about the  
OSPF router after we removed the address, but it did tell us when the port had been  
removed from the All Groups list. Also, remember that port 24 only times out of the All  
Groups list when its internal IGMP message timer counts down to zero.  
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Stopping snoopers from snooping non-IGMP messages > Controlling which addresses create All Groups entries  
Configuring switches 1 and 3  
The output of the command show igmpsnooping, above, shows that switch 2 is still  
receiving the multicast group 224.12.13.14 even though it has no ports interested in receiving  
it. This is because switch 2 still switches the OSPF Hello packet, which it received on port 24,  
to switch 3. Switch 3 receives this Hello packet on port 25, adds port 25 to its All Groups list  
and forwards the packet on to switch  
1.  
The best solution to this is to remove 224.0.0.5 from switch 3 and switch  
the following commands on each switch:  
1
as well, by using  
set igmpsnooping routermode=ip  
delete igmpsnooping routeraddress=224.0.0.5  
Adding other router addresses  
If you want to specify that other addresses belong to routers, you can use the commands:  
set igmpsnooping routermode=ip  
add igmpsnooping routeraddress=ipadd  
The ipadd must be of the form 224.0.0.x, and can be a comma-separated list of addresses.  
The example below starts again with the default configuration, and first removes the OSPF  
router address, then adds another address—224.0.0.254—to illustrate use of the command.  
Manager Switch 2> set igmpsnooping routerm=ip  
Info (1005282): IGMPSnooping Routermode successfully updated.  
Manager Switch 2> show igmpsnooping routeraddress  
IGMP Snooping Router Address  
----------------------------------------------------------------------  
IGMP Snooping Router Mode ......... ip  
Router Address List  
--------------------------------------------------------  
224.0.0.1  
224.0.0.2  
224.0.0.4  
224.0.0.5  
224.0.0.6  
224.0.0.9  
224.0.0.13  
224.0.0.15  
----------------------------------------------------------------------  
Manager Switch 2> del igmpsnooping routeraddress=224.0.0.5  
Info (1005272): Multicast addresses successfully deleted.  
Manager Switch 2> add igmpsnooping routeraddress=224.0.0.254  
Info (1005275): Multicast addresses successfully added.  
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Stopping snoopers from snooping non-IGMP messages > Controlling which addresses create All Groups entries  
Manager Switch 2> show igmpsnooping routeraddress  
IGMP Snooping Router Address  
----------------------------------------------------------------------  
IGMP Snooping Router Mode ......... ip  
Router Address List  
--------------------------------------------------------  
224.0.0.1  
224.0.0.2  
224.0.0.4  
224.0.0.6  
224.0.0.9  
224.0.0.13  
224.0.0.15  
224.0.0.254  
----------------------------------------------------------------------  
Returning to the default list  
To return to the default list, change the router mode to default.  
Manager Switch 2> set igmpsnooping routermode=default  
Info (1005282): IGMPSnooping Routermode successfully updated.  
Manager Switch 2> show igmpsnooping routeraddress  
IGMP Snooping Router Address  
----------------------------------------------------------------------  
IGMP Snooping Router Mode ......... default  
Router Address List  
--------------------------------------------------------  
224.0.0.1  
224.0.0.2  
224.0.0.4  
224.0.0.5  
224.0.0.6  
224.0.0.9  
224.0.0.13  
224.0.0.15  
----------------------------------------------------------------------  
If we then go back to routermode=ip, we are still left with the default set of IPs—changing  
the router mode to ip does not make the switch change the list of router addresses. Instead,  
it puts the switch into a mode in which we can add or delete addresses in the list, which lets  
us customise the list afresh.  
Manager Switch 2> set igmpsnooping routermode=ip  
Info (1005282): IGMPSnooping Routermode successfully updated.  
Manager Switch 2> show igmpsnooping routeraddress  
IGMP Snooping Router Address  
----------------------------------------------------------------------  
IGMP Snooping Router Mode ......... ip  
Router Address List  
--------------------------------------------------------  
224.0.0.1  
224.0.0.2  
224.0.0.4  
224.0.0.5  
224.0.0.6  
224.0.0.9  
224.0.0.13  
224.0.0.15  
----------------------------------------------------------------------  
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Stopping snoopers from snooping non-IGMP messages > Controlling which addresses create All Groups entries  
Using the other routermode options  
As described earlier, routermode=multicastrouter is just a shortcut for the two IP  
addresses for DVMRP and PIM.  
Manager Switch 2> set igmpsnooping routermode=multicastrouter  
Info (1005282): IGMPSnooping Routermode successfully updated.  
Manager Switch 2> show igmpsnooping routeraddress  
IGMP Snooping Router Address  
----------------------------------------------------------------------  
IGMP Snooping Router Mode ......... multicastrouter  
Router Address List  
--------------------------------------------------------  
224.0.0.4  
224.0.0.13  
----------------------------------------------------------------------  
The mode routermode=none stops any reserved multicast addresses from being identified  
as coming from routers.  
Manager Switch 2> set igmpsnooping routerm=none  
Info (1005282): IGMPSnooping Routermode successfully updated.  
Manager Switch 2> show igmpsnooping routeraddress  
IGMP Snooping Router Address  
----------------------------------------------------------------------  
IGMP Snooping Router Mode ......... none  
Router Address List  
--------------------------------------------------------  
No reserved multicast addresses configured  
----------------------------------------------------------------------  
Conversely, the mode routermode=all means that all reserved multicast addresses  
(224.0.0. to 224.0.0.255) are identified as coming from routers.  
1
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Statically specifying that a port is a router port > Example  
Statically specifying that a port is a router port  
Since software versions 281-04 and 291-04, you can statically configure particular ports as  
multicast router ports. This feature is useful in some unusual network configurations in which  
the learning process cannot identify all router ports. You could also use it creatively in special  
circumstances, when a Querier is unnecessary.  
To specify router ports, use the command:  
add igmpsnooping vlan={vlan-name|1..4094}  
routerport={port-list|all}  
This command causes the switch to immediately forward all IGMP and multicast data packets  
to the designated router port.  
Note that this is an IGMP snooping command, designed to give administrators greater  
control of layer 2 multicasting. It does not provide static multicast routing.  
Example  
The following sequence explores the effect of adding a static router port on a Rapier 48i  
switch.  
1. Enable IGMP debugging so you can see some of the mechanics behind the  
commands.  
Manager Rapier 48i> enable ip igmp debug  
Info (1005003): Operation successful.  
2. Check the current IGMP snooping entries.  
Note that there is one All Groups entry for port 50.  
Manager Rapier 48i> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Query Solicitation ...... On  
Static Router Ports ..... None  
Group List ..............  
Group. 239.255.255.250  
Ports 7  
Entry timeout 190 secs  
Entry timeout 255 secs  
All Groups  
Ports 50  
------------------------------------------------------------------------  
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Statically specifying that a port is a router port > Example  
3. Statically add port 6 as a router port attached to VLAN 1.  
Manager Rapier 48i> add igmpsnooping vlan=1 routerport=6  
snooped group 224.0.0.2 added  
Adding port 6 for group 224.0.0.2 on default  
Info (1005003): Operation successful.  
Manager Rapier 48i> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Query Solicitation ...... On  
Static Router Ports ..... 6  
Group List ..............  
Group. 239.255.255.250  
Ports 7  
Entry timeout 184 secs  
All Groups  
Entry timeout Infinity  
Ports 6,50  
------------------------------------------------------------------------  
The above output shows that port 6 has joined port 50 as an All Groups port. Also note that  
the Entry timeout is infinity. This timeout of infinity only applies to the static entry—port 50  
will time out as normal if Queries stop arriving on that port.  
4. Stop port 6 from being a static router port.  
To remove the static configuration, simply delete it.  
Manager Rapier 48i> delete igmpsnooping vlan=1 routerport=6  
Deleting port 6 from group 224.0.0.2 on default  
Reconstructing snooping entries(224.0.0.2/vlan1): 49,  
Info (1005003): Operation successful.  
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IGMP debugging > Example  
IGMP debugging  
In this section, we shall examine the debugging messages that the router or switch outputs  
when certain events occur while debugging is enabled. To enable debugging, use the  
command:  
enable ip igmp debug  
Example  
This example uses the same network configuration as "IGMP snooping" on page 9. For  
convenience, the diagram is reproduced below.  
Multicast Server  
port 1  
AT-8948  
Switch 1:  
Querier  
port 50  
port 49  
(blocked by STP)  
port 26  
port 25  
port 26  
port 25  
Rapier 24i  
Rapier 24i  
Switch 2:  
Snooper  
Switch 3:  
Snooper  
port 2  
port 3  
Client 1  
Client 2  
igmp-snooper.eps  
X A client joins a group  
Client 2 sends a Membership Report for group 224.  
12.  
13.1  
4. Switch  
1
sees the report on  
vlan100 (port 49), and adds the port to its IGMP and IGMP snooping tables.  
Manager Switch 1> IGMP Snoop(48): Report -> snooped group 224.12.13.14 added  
Adding port 49 for group 224.12.13.14 on vlan100  
IGMP Rx(48): Report -> group 224.12.13.14 added  
Note that the debugging output does not identify which client sent the Membership Report.  
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IGMP debugging > Example  
X A client leaves a group  
Client 2 sends a Leave message for group 224.  
12.  
13.1  
4. Switch  
1
sees the Leave message on  
vlan100 (port 49). The port is in a state of “deferred deletion” because of the Last Member  
page 72).  
Switch  
1
is an IGMP Querier, so it sends out two Membership Queries and waits 2 seconds  
deletes the entry.  
for a response. None arrives, so switch  
1
Manager Switch 1> IGMP Snoop(48) on vlan100: Leave -> IGMP Snoop(48): Leave g.  
group 224.12.13.14 - Port 49 in deferred deletion.  
IGMP Rx(48) on vlan100: Leave -> IGMP Rx(48): Leave group=224.12.13.14 -> group .  
Several minutes later the group entry times out.  
Manager Switch 1> IGMP Snoop Timeout: group=224.12.13.14 (0) is deleted  
Deleting all ports for group 224.12.13.14 on vlan100  
IGMP Timeout: group=224.12.13.14 (0) is deleted  
Meanwhile, switch 3, which has the client attached to it, sees the same sequence but debugs  
it differently. Like switch 1, switch 3 logs the Leave message, but its output also includes the  
port on which it received the Leave message. This enables you to identify the client. Switch 3  
also logs the two Specific Queries and notes the 2 second timeout. After 2 seconds it also  
deletes the entry from its IGMP snooping table.  
Manager Switch 3> IGMP Snoop: resending pkt to vlan  
utPorts: 1-4,6-26 fwdPorts: 26  
IGMP Snoop(2) on vlan100: Leave -> IGMP Snoop(2): Leave group=224.12.13.14-> gr.  
group 224.12.13.14 - Port 3 in deferred deletion.  
IGMP MVR Snoop: discard - no MVR snooper for code 23  
IGMP Snoop: resending pkt to vlan  
utPorts: 1-4,6-26 fwdPorts: 3,26  
IGMP Snoop(25) on vlan100: Query -> code 10  
igmpSnoopMembershipQuery >> setting timer at 2 secs for group 224.12.13.14  
snooped group 224.0.0.2 added  
Adding port 26 for group 224.0.0.2 on vlan100  
IGMP MVR Snoop: discard - no MVR snooper for code 17  
Manager Switch 3> IGMP Snoop: resending pkt to vlan  
utPorts: 1-4,6-26 fwdPorts: 3,26  
IGMP Snoop(25) on vlan100: Query -> code 10  
igmpSnoopMembershipQuery >> setting timer at 2 secs for group 224.12.13.14  
snooped group 224.0.0.2 added  
Adding port 26 for group 224.0.0.2 on vlan100  
IGMP MVR Snoop: discard - no MVR snooper for code 17  
Manager Switch 3> IGMP Snoop Timeout: group=224.12.13.14 (0) is deleted  
Deleting all ports for group 224.12.13.14 on vlan100  
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IGMP debugging > Example  
X A port entry times out  
Client 2 sends a Membership Report for group 224.  
12.  
13.1  
4. Switch  
1
sees the report on  
vlan100 (port 49) and adds an entry. The entry eventually expires.  
Manager Switch 1> IGMP Snoop(48): Report -> snooped group 224.12.13.14 added  
Adding port 49 for group 224.12.13.14 on vlan100  
IGMP Rx(48): Report -> group 224.12.13.14 added  
Manager Switch 1> IGMP Snoop Timeout: group=224.12.13.14 (0) is deleted  
Deleting all ports for group 224.12.13.14 on vlan100  
IGMP Timeout: group=224.12.13.14 (0) is deleted  
X Snooped ports change  
Switch 3—a Snooper—sees a Version 2 Membership Query message on vlan100 from the  
Querier and forwards it to all ports in the same VLAN. In the debugging output, the list of  
ports is the fwdports list. If we take a port out of the VLAN, the fwdports list changes.  
Manager Switch 3> IGMP Snoop: resending pkt to vlan  
utPorts: 1-26 fwdPorts: 1-26  
IGMP Snoop(25) on vlan100: Query -> code 100  
snooped group 224.0.0.2 added  
Adding port 26 for group 224.0.0.2 on vlan100  
IGMP MVR Snoop: discard - no MVR snooper for code 17  
Manager Switch 3> del vlan=100 port=5  
Info (1089003): Operation successful.  
Manager Switch 3> IGMP Snoop: resending pkt to vlan  
utPorts: 1-4,6-26 fwdPorts: 1-4,6-26  
IGMP Snoop(25) on vlan100: Query -> code 100  
snooped group 224.0.0.2 added  
Adding port 26 for group 224.0.0.2 on vlan100  
IGMP MVR Snoop: discard - no MVR snooper for code 17  
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IGMP debugging > Example  
This example also shows what debugging output looks like when the Snooper receives a  
General Query. The Querier sends the General Query to the destination address 224.0.0.  
1
(the IGMP Query address) and the Snooper tells us that it has added the “router” port to its  
All Groups list. In the IGMP standards, “All routers on this subnet” are identified with the  
group address of 224.0.0.2, so the debugging output refers to that address.  
Manager Switch 3> show igmpsnooping  
IGMP Snooping  
------------------------------------------------------------------------  
Status ........................... Enabled  
Disabled All-groups ports ........ None  
Vlan Name (vlan id) ..... default (1)  
Fast Leave .............. Off  
Group List ..............  
No group memberships.  
Vlan Name (vlan id) ..... vlan100 (100)  
Fast Leave .............. Off  
Group List ..............  
All Groups  
Ports 26  
Entry timeout 144 secs  
------------------------------------------------------------------------  
For more information about router addresses, see "Controlling which addresses create All  
X A report is filtered out  
The switch drops a Membership Report because of an IGMP filter. See "Explanation of IGMP  
Manager Switch 1>  
IGMP filter: discarded report for group 224.0.1.22 on port 1  
X A port in the All Groups list is unplugged  
The switch deletes a port from the All Groups list after the port is disconnected.  
Manager Switch 3> Deleting port 24 from group 224.0.0.2 on vlan100  
Reconstructing snooping entries: 25,  
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IGMP debugging > Example  
X Output for show ip igmp changes  
When IGMP debugging is enabled, the command show ip igmp gives more information  
about static IGMP associations, as shown in bold in the following output. See "Explanation of  
Static IGMP" on page 51 for more information about static associations.  
IGMP Protocol  
------------------------------------------------------------------------  
Status ........................... Enabled  
Default Query Interval ........... 125 secs  
Default Timeout Interval ......... 260 secs  
Last Member Query Interval ....... 10 (1/10secs)  
Last Member Query Count .......... 2  
Robustness Variable .............. 2  
Query Response Interval .......... 100 (1/10secs)  
Disabled All-groups ports ........ None  
Interface Name .......... vlan100  
Group List ..............  
(DR)  
Group. 224.12.13.14  
Ports 5  
Static association  
Refresh time Infinity  
Static Ports 5  
User-created static IGMP associations:  
--------------------------------------  
Group. 224.12.13.14  
Static Ports 5  
Static association  
Refresh time Infinity  
------------------------------------------------------------------------  
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Appendix: STP state > Switch  
1
Appendix: STP state  
In most of the examples in this document, the switches are configured in a loop and are all in  
the same VLAN. To prevent packets from looping the network, STP is configured. The STP  
state on each switch is given in the following output screens.  
Switch 1  
Note that port 50 on switch  
1
is in a discarding state.  
Manager Switch 1> show stp=default port=49-50  
STP Port Information  
------------------------------------------------------------------------  
STP ..................... default  
STP Status ............ ON  
Port .................. 49  
RSTP Port Role ...... Root  
State ............... Forwarding  
Point To Point ...... Yes (Auto)  
Port Priority ....... 128  
Port Identifier ..... 8031  
Pathcost ............ 20000 (auto configured)  
Designated Root ..... 32768 : 00-00-cd-01-4b-10  
Designated Cost ..... 0  
Designated Bridge ... 32768 : 00-00-cd-01-4b-10  
Designated Port ..... 801a  
EdgePort ............ No  
VLAN membership ..... 1  
Counters:  
Loopback Disabled  
0
Port .................. 50  
RSTP Port Role ...... Alternate  
State ............... Discarding  
Point To Point ...... Yes (Auto)  
Port Priority ....... 128  
Port Identifier ..... 8032  
Pathcost ............ 20000 (auto configured)  
Designated Root ..... 32768 : 00-00-cd-01-4b-10  
Designated Cost ..... 20000  
Designated Bridge ... 32768 : 00-00-cd-02-e5-40  
Designated Port ..... 801a  
EdgePort ............ No  
VLAN membership ..... 1  
Counters:  
Loopback Disabled  
0
------------------------------------------------------------------------  
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Appendix: STP state > Switch 2  
Switch 2  
Manager Switch 2> show stp=default port=25-26  
STP Port Information  
------------------------------------------------------------------------  
STP ..................... default  
STP Status ............ ON  
Port .................. 25  
RSTP Port Role ...... Root  
State ............... Forwarding  
Point To Point ...... Yes (Auto)  
Port Priority ....... 128  
Port Identifier ..... 8019  
Pathcost ............ 20000 (auto configured)  
Designated Root ..... 32768 : 00-00-cd-01-4b-10  
Designated Cost ..... 0  
Designated Bridge ... 32768 : 00-00-cd-01-4b-10  
Designated Port ..... 8019  
EdgePort ............ No  
Counters:  
Loopback Disabled  
0
Port .................. 26  
RSTP Port Role ...... Designated  
State ............... Forwarding  
Point To Point ...... Yes (Auto)  
Port Priority ....... 128  
Port Identifier ..... 801a  
Pathcost ............ 20000 (auto configured)  
Designated Root ..... 32768 : 00-00-cd-01-4b-10  
Designated Cost ..... 20000  
Designated Bridge ... 32768 : 00-00-cd-02-e5-40  
Designated Port ..... 801a  
EdgePort ............ No  
Counters:  
Loopback Disabled  
0
------------------------------------------------------------------------  
Page 109 | AlliedWare™ OS How To Note: IGMP  
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Switch 3  
Manager Switch 3> show stp port=25-26  
STP Port Information  
------------------------------------------------------------------------  
STP ..................... default  
STP Status ............ ON  
Port .................. 25  
RSTP Port Role ...... Designated  
State ............... Forwarding  
Point To Point ...... Yes (Auto)  
Port Priority ....... 128  
Port Identifier ..... 8019  
Pathcost ............ 20000 (auto configured)  
Designated Root ..... 32768 : 00-00-cd-01-4b-10  
Designated Cost ..... 0  
Designated Bridge ... 32768 : 00-00-cd-01-4b-10  
Designated Port ..... 8019  
EdgePort ............ No  
Counters:  
Loopback Disabled  
0
Port .................. 26  
RSTP Port Role ...... Designated  
State ............... Forwarding  
Point To Point ...... Yes (Auto)  
Port Priority ....... 128  
Port Identifier ..... 801a  
Pathcost ............ 20000 (auto configured)  
Designated Root ..... 32768 : 00-00-cd-01-4b-10  
Designated Cost ..... 0  
Designated Bridge ... 32768 : 00-00-cd-01-4b-10  
Designated Port ..... 801a  
EdgePort ............ No  
Counters:  
Loopback Disabled  
0
------------------------------------------------------------------------  
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