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MPLS LDP Configuration Guide, Cisco IOS  
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Contents  
MPLS LDP Configuration Guide, Cisco IOS Release 12.4  
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iv  
Contents  
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vi  
MPLS Label Distribution Protocol (LDP)  
Multiprotocol Label Switching (MPLS) Label Distribution Protocol (LDP) enables peer label switch  
routers (LSRs) in an MPLS network to exchange label binding information for supporting hop-by-hop  
forwarding in an MPLS network. This module explains the concepts related to MPLS LDP and describes  
how to configure MPLS LDP in a network.  
Finding Feature Information  
Your software release may not support all the features documented in this module. For the latest feature  
information and caveats, see the release notes for your platform and software release. To find information  
about the features documented in this module, and to see a list of the releases in which each feature is  
supported, see the Feature Information Table at the end of this document.  
Use Cisco Feature Navigator to find information about platform support and Cisco software image support.  
To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.  
Prerequisites for MPLS LDP  
Label switching on a router requires that Cisco Express Forwarding (CEF) be enabled on that router.  
Information About MPLS LDP  
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Introduction to MPLS LDP  
Information About MPLS LDP  
Introduction to MPLS LDP  
MPLS LDP provides the means for LSRs to request, distribute, and release label prefix binding information  
to peer routers in a network. LDP enables LSRs to discover potential peers and to establish LDP sessions  
with those peers for the purpose of exchanging label binding information.  
MPLS LDP enables one LSR to inform another LSR of the label bindings it has made. Once a pair of  
routers communicate the LDP parameters, they establish a label-switched path (LSP). MPLS LDP enables  
LSRs to distribute labels along normally routed paths to support MPLS forwarding. This method of label  
distribution is also called hop-by-hop forwarding. With IP forwarding, when a packet arrives at a router the  
router looks at the destination address in the IP header, performs a route lookup, and forwards the packet to  
the next hop. With MPLS forwarding, when a packet arrives at a router the router looks at the incoming  
label, looks up the label in a table, and then forwards the packet to the next hop. MPLS LDP is useful for  
applications that require hop-by-hop forwarding, such as MPLS VPNs.  
MPLS LDP Functional Overview  
Cisco MPLS LDP provides the building blocks for MPLS-enabled applications, such as MPS Virtual  
Private Networks (VPNs).  
LDP provides a standard methodology for hop-by-hop, or dynamic label, distribution in an MPLS network  
by assigning labels to routes that have been chosen by the underlying Interior Gateway Protocol (IGP)  
routing protocols. The resulting labeled paths, called label switch paths (LSPs), forward label traffic across  
an MPLS backbone to particular destinations. These capabilities enable service providers to implement  
MPLS-based IP VPNs and IP+ATM services across multivendor MPLS networks.  
LDP and TDP Support  
LDP supercedes Tag Distribution Protocol (TDP). See the table below for information about LDP and TDP  
support in Cisco IOS releases.  
Use caution when upgrading the image on a router that uses TDP. Ensure that the TDP sessions are  
established when the new image is loaded. You can accomplish this by issuing the global configuration  
command mpls label protocol tdp. Issue this command and save it to the startup configuration before  
loading the new image. Alternatively, you can enter the command and save the running configuration  
immediately after loading the new image.  
Table 1  
LDP and TDP Support  
Train and Release  
LDP/TDP Support  
12.0S Train  
TDP is enabled by default.  
Cisco IOS Release 12.0(29)S and earlier releases: TDP is  
supported for LDP features.  
Cisco IOS Release 12.0(30)S and later releases: TDP is  
not support for LDP features.  
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Introduction to LDP Sessions  
Directly Connected MPLS LDP Sessions  
Train and Release  
LDP/TDP Support  
12.2S, SB, and SR Trains  
LDP is enabled by default.  
Cisco IOS Release 12.2(25)S and earlier releases: TDP is  
supported for LDP features.  
Cisco IOS Releases 12.2(27)SBA, 12.2(27)SRA,  
12.2(27)SRB and later releases: TDP is not supported for  
LDP features.  
12.T/Mainline Trains  
Cisco IOS Release 12.3(14)T and earlier releases: TDP is  
enabled by default.  
Cisco IOS Releases 12.4 and 12.4T and later releases:  
LDP is enabled by default.  
Cisco IOS Release 12.3(11)T and earlier releases: TDP is  
supported for LDP features.  
Cisco IOS Release 12.3(14)T and later releases: TDP is  
not support ed for LDP features.  
Introduction to LDP Sessions  
When you enable MPLS LDP, the LSRs send out messages to try to find other LSRs with which they can  
create LDP sessions. The following sections explain the differences between directly connected LDP  
sessions and nondirectly connected LDP sessions.  
Directly Connected MPLS LDP Sessions  
If an LSR is one hop from its neighbor, it is directly connected to its neighbor. The LSR sends out LDP link  
Hello messages as User Datagram Protocol (UDP) packets to all the routers on the subnet (multicast). A  
neighboring LSR may respond to the link Hello message, allowing the two routers to establish an LDP  
session. This is called basic discovery.  
To initiate an LDP session between routers, the routers determine which router will take the active role and  
which router will take the passive role. The router that takes the active role establishes the LDP TCP  
connection session and initiates the negotiation of the LDP session parameters. To determine the roles, the  
two routers compare their transport addresses. The router with the higher IP address takes the active role  
and establishes the session.  
After the LDP TCP connection session is established, the LSRs negotiate the session parameters, including  
the method of label distribution to be used. Two methods are available:  
Downstream Unsolicited: An LSR advertises label mappings to peers without being asked to.  
Downstream on Demand: An LSR advertises label mappings to a peer only when the peer asks for  
them.  
For information about creating LDP sessions, see the Enabling Directly Connected LDP Sessions, page  
6.  
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Introduction to LDP Label Bindings Label Spaces and LDP Identifiers  
Nondirectly Connected MPLS LDP Sessions  
Nondirectly Connected MPLS LDP Sessions  
If the LSR is more than one hop from its neighbor, it is nondirectly connected to its neighbor. For these  
nondirectly connected neighbors, the LSR sends out a targeted Hello message as a UDP packet, but as a  
unicast message specifically addressed to that LSR. The nondirectly connected LSR responds to the Hello  
message and the two routers begin to establish an LDP session. This is called extended discovery.  
An MPLS LDP targeted session is a label distribution session between routers that are not directly  
connected. When you create an MPLS traffic engineering tunnel interface, you need to establish a label  
distribution session between the tunnel headend and the tailend routers. You establish nondirectly  
connected MPLS LDP sessions by enabling the transmission of targeted Hello messages.  
You can use the mpls ldp neighbor targetedcommand to set up a targeted session when other means of  
establishing targeted sessions do not apply, such as configuring mpls ipon a traffic engineering (TE) tunnel  
or configuring Any Transport over MPLS (AToM) virtual circuits (VCs). For example, you can use this  
command to create a targeted session between directly connected MPLS label switch routers (LSRs) when  
MPLS label forwarding convergence time is an issue.  
The mpls ldp neighbor targetedcommand can improve label convergence time for directly connected  
neighbor LSRs when the link(s) directly connecting them are down. When the links between the neighbor  
LSRs are up, both the link and targeted Hellos maintain the LDP session. If the links between the neighbor  
LSRs go down, the targeted Hellos maintain the session, allowing the LSRs to retain labels learned from  
each other. When a link directly connecting the LSRs comes back up, the LSRs can immediately reinstall  
labels for forwarding use without having to reestablish their LDP session and exchange labels.  
The exchange of targeted Hello messages between two nondirectly connected neighbors can occur in  
several ways, including the following:  
Router 1 sends targeted Hello messages carrying a response request to Router 2. Router 2 sends  
targeted Hello messages in response if its configuration permits. In this situation, Router 1 is  
considered to be active and Router 2 is considered to be passive.  
Router 1 and Router 2 both send targeted Hello messages to each other. Both routers are considered to  
be active. Both, one, or neither router can also be passive, if they have been configured to respond to  
requests for targeted Hello messages from each other.  
The default behavior of an LSR is to ignore requests from other LSRs that send targeted Hello messages.  
You can configure an LSR to respond to requests for targeted Hello messages by issuing the mpls ldp  
discovery targeted-hello accept command.  
The active LSR mandates the protocol that is used for a targeted session. The passive LSR uses the protocol  
of the received targeted Hello messages.  
For information about creating MPLS LDP targeted sessions, see the Establishing Nondirectly Connected  
Introduction to LDP Label Bindings Label Spaces and LDP Identifiers  
An LDP label binding is an association between a destination prefix and a label. The label used in a label  
binding is allocated from a set of possible labels called a label space.  
LDP supports two types of label spaces:  
Interface-specific--An interface-specific label space uses interface resources for labels. For example,  
label-controlled ATM (LC-ATM) interfaces use virtual path identifiers/virtual circuit identifiers (VPIs/  
VCIs) for labels. Depending on its configuration, an LDP platform may support zero, one, or more  
interface-specific label spaces.  
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MPLS Label Distribution Protocol (LDP)  
How to Configure MPLS LDP  
Platform-wide--An LDP platform supports a single platform-wide label space for use by interfaces that  
can share the same labels. For Cisco platforms, all interface types, except LC-ATM, use the platform-  
wide label space.  
LDP uses a 6-byte quantity called an LDP Identifier (or LDP ID) to name label spaces. The LDP ID is  
made up of the following components:  
The first four bytes, called the LPD router ID, identify the LSR that owns the label space.  
The last two bytes, called the local label space ID, identify the label space within the LSR. For the  
platform-wide label space, the last two bytes of the LDP ID are always both 0.  
The LDP ID takes the following form:  
<LDP router ID> : <local label space ID>  
The following are examples of LPD IDs:  
172.16.0.0:0  
192.168.0.0:3  
The router determines the LDP router ID as follows, if the mpls ldp router-id command is not executed,  
1
2
The router examines the IP addresses of all operational interfaces.  
If these IP addresses include loopback interface addresses, the router selects the largest loopback  
address as the LDP router ID.  
3
Otherwise, the router selects the largest IP address pertaining to an operational interface as the LDP  
router ID.  
The normal (default) method for determining the LDP router ID may result in a router ID that is not usable  
in certain situations. For example, the router might select an IP address as the LDP router ID that the  
routing protocol cannot advertise to a neighboring router. The mpls ldp router-id command allows you to  
specify the IP address of an interface as the LDP router ID. Make sure the specified interface is operational  
so that its IP address can be used as the LDP router ID.  
When you issue the mpls ldp router-id command without the force keyword, the router select selects the  
IP address of the specified interface (provided that the interface is operational) the next time it is necessary  
to select an LDP router ID, which is typically the next time the interface is shut down or the address is  
configured.  
When you issue the mpls ldp router-idcommand with the force keyword, the effect of the mpls ldp  
router-idcommand depends on the current state of the specified interface:  
If the interface is up (operational) and if its IP address is not currently the LDP router ID, the LDP  
router ID changes to the IP address of the interface. This forced change in the LDP router ID tears  
down any existing LDP sessions, releases label bindings learned via the LDP sessions, and interrupts  
MPLS forwarding activity associated with the bindings.  
If the interface is down (not operational) when the mpls ldp router-idinterface force command is  
issued, when the interface transitions to up, the LDP router ID changes to the IP address of the  
interface. This forced change in the LDP router ID tears down any existing LDP sessions, releases  
label bindings learned via the LDP sessions, and interrupts MPLS forwarding activity associated with  
the bindings.  
How to Configure MPLS LDP  
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Enabling Directly Connected LDP Sessions  
How to Configure MPLS LDP  
Enabling Directly Connected LDP Sessions  
This procedure explains how to configure MPLS LDP sessions between two directly connected routers.  
SUMMARY STEPS  
1.  
2.  
3.  
enable  
configure terminal  
mpls ip  
4. mpls label protocol {ldp | tdp | both}  
5.  
Router(config)# interface type number  
6.  
mpls ip  
7.  
exit  
8.  
exit  
9.  
show mpls interfaces [interface] [detail  
show mpls ldp discovery [all | vrf vpn-name] [detail  
show mpls ldp neighbor [[vrf vpn-name] [address | interface] [detail] | [all]]  
10.  
11.  
DETAILED STEPS  
Command or Action  
Purpose  
Step 1  
Step 2  
Step 3  
Enables privileged EXEC mode.  
enable  
Enter your password if prompted.  
Example:  
Router> enable  
configure terminal  
Enters global configuration mode.  
Example:  
Router# configure terminal  
Configures MPLS hop-by-hop forwarding globally.  
mpls ip  
The mpls ip command is enabled by default; you do not have  
to specify this command.  
Globally enabling MPLS forwarding does not enable it on the  
router interfaces. You must enable MPLS forwarding on the  
interfaces as well as for the router.  
Example:  
Router(config)# mpls ip  
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MPLS Label Distribution Protocol (LDP)  
How to Configure MPLS LDP  
Command or Action  
Purpose  
Configures the use of LDP on all interfaces. LDP is the default.  
Step 4 mpls label protocol {ldp | tdp | both}  
If you set all interfaces globally to LDP, you can override  
specific interfaces with either the tdp or both keyword by  
specifying the command in interface configuration mode.  
Example:  
Router(config)# mpls label protocol ldp  
Step 5  
Step 6  
Step 7  
Specifies the interface to be configured and enters interface  
configuration mode.  
Router(config)# interface type number  
Example:  
Router(config)# interface ethernet3/0  
Configures MPLS hop-by-hop forwarding on the interface.  
mpls ip  
You must enable MPLS forwarding on the interfaces as well  
as for the router.  
Example:  
Router(config-if)# mpls ip  
Exits interface configuration mode and enters global configuration  
mode.  
exit  
Example:  
Router(config-if)# exit  
Step 8  
Step 9  
Step 10  
Exits global configuration mode and enters privileged EXEC  
mode.  
exit  
Example:  
Router(config)# exit  
show mpls interfaces [interface] [detail  
Verifies that the interfaces have been configured to use LDP, TDP,  
or both.  
Example:  
Router# show mpls interfaces  
show mpls ldp discovery [all | vrf vpn-name] [detail  
Verifies that the interface is up and is sending Discovery Hello  
messages.  
Example:  
Router# show mpls ldp discovery  
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Establishing Nondirectly Connected MPLS LDP Sessions  
How to Configure MPLS LDP  
Command or Action  
Purpose  
Displays the status of LDP sessions.  
Step 11  
show mpls ldp neighbor [[vrf vpn-name] [address |  
interface] [detail] | [all]]  
Example:  
Router# show mpls ldp neighbor  
Examples  
The following show mpls interfaces command verifies that interfaces Ethernet 1/0 and 1/1 have been  
configured to use LDP:  
Router# show mpls interfaces  
Interface  
IP  
Tunnel  
No  
No  
BGP Static Operational  
Ethernet3/0  
Ethernet3/1  
Yes (ldp)  
Yes  
No No  
No No  
Yes  
Yes  
The following show mpls ldp discovery command verifies that the interface is up and is sending LDP  
Discovery Hello messages (as opposed to TDP Hello messages):  
Router# show mpls ldp discovery  
Local LDP Identifier:  
172.16.12.1:0  
Discovery Sources:  
Interfaces:  
Ethernet3/0 (ldp): xmit  
The following example shows that the LDP session between routers was successfully established:  
Router# show mpls ldp neighbor  
Peer LDP Ident: 10.1.1.2:0; Local LDP Ident 10.1.1.1:0  
TCP connection: 10.1.1.2.18 - 10.1.1.1.66  
State: Oper; Msgs sent/rcvd: 12/11; Downstream  
Up time: 00:00:10  
LDP discovery sources:  
FastEthernet1/0, Src IP addr: 10.20.10.2  
Addresses bound to peer LDP Ident:  
10.1.1.2  
10.20.20.1  
10.20.10.2  
For examples on configuring directly connected LDP sessions, see the Configuring Directly Connected  
Establishing Nondirectly Connected MPLS LDP Sessions  
This section explains how to configure nondirectly connected MPLS LDP sessions, which enable you to  
establish an LDP session between routers that are not directly connected.  
MPLS requires CEF.  
You must configure the routers at both ends of the tunnel to be active or enable one router to be  
passive with the mpls ldp discovery targeted-hello accept command.  
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MPLS Label Distribution Protocol (LDP)  
How to Configure MPLS LDP  
SUMMARY STEPS  
1.  
2.  
3.  
enable  
configure terminal  
mpls ip  
4. mpls label protocol {ldp | tdp | both}  
5. interface tunnelnumber  
6.  
tunnel destination ip-address  
7.  
mpls ip  
8.  
exit  
9.  
exit  
10.  
show mpls ldp discovery [all | vrf vpn-name] [detail  
DETAILED STEPS  
Command or Action  
Purpose  
Step 1  
Step 2  
Step 3  
Enables privileged EXEC mode.  
enable  
Enter your password if prompted.  
Example:  
Router> enable  
configure terminal  
Enters global configuration mode.  
Example:  
Router# configure terminal  
Configures MPLS hop-by-hop forwarding globally.  
mpls ip  
The mpls ip command is enabled by default; you do not have to  
specify this command.  
Globally enabling MPLS forwarding does not enable it on the  
router interfaces. You must enable MPLS forwarding on the  
interfaces as well as for the router.  
Example:  
Router(config)# mpls ip  
Step 4 mpls label protocol {ldp | tdp | both}  
Configures the use of LDP on all interfaces. LDP is the default.  
If you set all interfaces globally to LDP, you can override  
specific interfaces with either the tdp or both keyword by  
specifying the command in interface configuration mode.  
Example:  
Router(config)# mpls label protocol ldp  
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MPLS Label Distribution Protocol (LDP)  
How to Configure MPLS LDP  
Command or Action  
Purpose  
Step 5 interface tunnelnumber  
Configures a tunnel interface and enters interface configuration  
mode.  
Example:  
Router(config)# interface tunnel1  
Step 6  
Assigns an IP address to the tunnel interface.  
tunnel destination ip-address  
Example:  
Router(config-if)# tunnel destination  
172.16.1.1  
Step 7  
Step 8  
Configures MPLS hop-by-hop forwarding on the interface.  
mpls ip  
You must enable MPLS forwarding on the interfaces as well as  
for the router.  
Example:  
Router(config-if)# mpls ip  
Exits interface configuration mode and enters global configuration  
mode.  
exit  
Example:  
Router(config-if)# exit  
Step 9  
Exits global configuration mode and enters privileged EXEC mode.  
exit  
Example:  
Router(config)# exit  
Step 10  
Verifies that the interface is up and is sending Discovery Hello  
messages.  
show mpls ldp discovery [all | vrf vpn-name]  
[detail  
Example:  
Router# show mpls ldp discovery  
Example  
The following example shows the output of the show mpls ldp discovery command for a nondirectly  
connected LDP session.  
Router# show mpls ldp discovery  
Local LDP Identifier:  
172.16.0.0:0  
Discovery Sources:  
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Saving Configurations MPLS Tag Switching Commands  
How to Configure MPLS LDP  
Interfaces:  
POS2/0 (ldp): xmit/recv  
LDP Id: 172.31.255.255:0  
Tunnel1 (ldp): Targeted -> 192.168.255.255  
Targeted Hellos:  
172.16.0.0 -> 192.168.255.255 (ldp): active, xmit/recv  
LDP Id: 192.168.255.255:0  
172.16.0.0 -> 192.168.0.0 (tdp): passive, xmit/recv  
TDP Id: 192.168.0.0:0  
This command output indicates that:  
The local LSR (172.16.0.0) sent LDP link Hello messages on interface POS2/0 and discovered  
neighbor 172.31.255.255.  
The local LSR sent LDP targeted Hello messages associated with interface Tunnel1 to target  
192.168.255.255. The LSR was configured to use LDP.  
The local LSR is active for targeted discovery activity with 192.168.255.255; this means that the  
targeted Hello messages it sends to 192.168.255.255 carry a response request. The local LSR was  
configured to have an LDP session with the nondirectly connected LSR 192.168.255.255.  
The local LSR is not passive from the discovery activity with 192.168.255.255 for one of the  
following reasons:  
The targeted Hello messages it receives from 192.168.255.255 do not carry a response request.  
The local LSR has not been configured to respond to such requests.  
The local LSR sent TDP directed Hello messages to the target LSR 192.168.0.0. This LSR uses TDP  
because the Hello messages received from the target LSR 192.168.0.0 were TDP directed Hello  
messages.  
The local LSR is passive in discovery activity with LSR 192.168.0.0. This means that the directed  
Hello messages it receives from LSR 192.168.0.0 carry a response request and that the local LSR has  
been configured with the mpls ldp discovery targeted-hello accept command to respond to such  
requests from LSR 192.168.0.0.  
The local LSR is not active in discovery activity with LSR 192.168.0.0, because no application that  
requires an LDP session with LSR 192.168.0.0 has been configured on the local LSR.  
For examples of configuring LDP targeted sessions, see the Establishing Nondirectly Connected MPLS  
Saving Configurations MPLS Tag Switching Commands  
In releases of Cisco IOS software prior to 12.4(2)T, some MPLS commands had both a tag-switching  
version and an MPLS version. For example, the two commands tag-switching ip and mpls ip were the  
same. To support backward compatibility, the tag-switching form of the command was written to the saved  
configuration.  
Starting in Cisco IOS Release 12.4(2)T, the MPLS form of the command is written to the saved  
configuration.  
For example, if an ATM interface is configured using the following commands, which have both a tag-  
switching form and an MPLS form:  
Router(config)# interface ATM3/0  
Router(config-if)# ip unnumbered Loopback0  
router(config-if)# tag-switching ip  
Router(config-if)# mpls label protocol ldp  
After you enter these commands and save this configuration or display the running configuration with the  
show runningcommand, the commands saved or displayed appear as follows:  
interface ATM3/0  
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Specifying the LDP Router ID  
How to Configure MPLS LDP  
ip unnumbered Loopback0  
mpls ip  
mpls label protocol ldp  
Specifying the LDP Router ID  
The mpls ldp router-id command allows you to establish the IP address of an interface as the LDP router  
ID.  
The following steps describe the normal process for determining the LDP router ID:  
1
2
The router considers all the IP addresses of all operational interfaces.  
If these addresses include loopback interface addresses, the router selects the largest loopback address.  
Configuring a loopback address helps ensure a stable LDP ID for the router, because the state of  
loopback addresses does not change. However, configuring a loopback interface and IP address on each  
router is not required.  
The loopback IP address does not become the router ID of the local LDP ID under the following  
circumstances:  
If the loopback interface has been explicitly shut down.  
If the mpls ldp router-id command specifies that a different interface should be used as the LDP  
router ID.  
If you use a loopback interface, make sure that the IP address for the loopback interface is configured with  
a /32 network mask. In addition, make sure that the routing protocol in use is configured to advertise the  
corresponding /32 network.  
1
Otherwise, the router selects the largest interface address.  
The router might select a router ID that is not usable in certain situations. For example, the router might  
select an IP address that the routing protocol cannot advertise to a neighboring router.  
The router implements the router ID the next time it is necessary to select an LDP router ID. The effect of  
the command is delayed until the next time it is necessary to select an LDP router ID, which is typically the  
next time the interface is shut down or the address is deconfigured.  
If you use the force keyword with the mpls ldp router-id command, the router ID takes effect more  
quickly. However, implementing the router ID depends on the current state of the specified interface:  
If the interface is up (operational) and its IP address is not currently the LDP router ID, the LDP router  
ID is forcibly changed to the IP address of the interface. This forced change in the LDP router ID tears  
down any existing LDP sessions, releases label bindings learned via the LDP sessions, and interrupts  
MPLS forwarding activity associated with the bindings.  
If the interface is down, the LDP router ID is forcibly changed to the IP address of the interface when  
the interface transitions to up. This forced change in the LDP router ID tears down any existing LDP  
sessions, releases label bindings learned via the LDP sessions, and interrupts MPLS forwarding  
activity associated with the bindings.  
Make sure the specified interface is operational before assigning it as the LDP router ID.  
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MPLS Label Distribution Protocol (LDP)  
How to Configure MPLS LDP  
SUMMARY STEPS  
1.  
2.  
3.  
4.  
5.  
6.  
7.  
enable  
configure terminal  
mpls ip  
mpls label protocol {ldp | tdp | both}  
mpls ldp router-id interface [force]  
exit  
show mpls ldp discovery [all | detail |vrf vpn-name]  
DETAILED STEPS  
Command or Action  
Purpose  
Step 1  
Step 2  
Step 3  
Enables privileged EXEC mode.  
enable  
Enter your password if prompted.  
Example:  
Router> enable  
configure terminal  
Enters global configuration mode.  
Example:  
Router# configure terminal  
Configures MPLS hop-by-hop forwarding globally.  
mpls ip  
The mpls ip command is enabled by default; you do not have  
to specify this command.  
Globally enabling MPLS forwarding does not enable it on the  
router interfaces. You must enable MPLS forwarding on the  
interfaces as well as for the router.  
Example:  
Router(config)# mpls ip  
Step 4  
Step 5  
Configures the use of LDP on all interfaces. LDP is the default.  
mpls label protocol {ldp | tdp | both}  
If you set all interfaces globally to LDP, you can override  
specific interfaces with either the tdp or both keyword by  
specifying the command in interface configuration mode.  
Example:  
Router(config)# mpls label protocol ldp  
mpls ldp router-id interface [force]  
Specifies the preferred interface for determining the LDP router ID.  
Example:  
Router(config)# mpls ldp  
router-id pos2/0/0  
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Preserving QoS Settings with MPLS LDP Explicit Null  
How to Configure MPLS LDP  
Command or Action  
Purpose  
Exits global configuration mode and enters privileged EXEC mode.  
Step 6  
Step 7  
exit  
Example:  
Router(config)# exit  
Displays the LDP identifier for the local router.  
show mpls ldp discovery [all | detail |vrf vpn-  
name]  
Example:  
Router# show mpls ldp discovery  
Example  
The following example assigns interface pos2/0/0 as the LDP router ID:  
Router> enable  
Router# configure terminal  
Router(config)# mpls ip  
Router(config)# mpls label protocol ldp  
Router(config)#  
mpls ldp router-id pos2/0/0 force  
The following example displays the LDP router ID (10.15.15.15):  
Router# show mpls ldp discovery  
Local LDP Identifier:  
10.15.15.15:0  
Discovery Sources:  
Interfaces:  
Ethernet4 (ldp): xmit/recv  
LDP Id: 10.14.14.14:0  
Preserving QoS Settings with MPLS LDP Explicit Null  
Normally, LDP advertises an Implicit Null label for directly connected routes. The Implicit Null label  
causes the second last (penultimate) label switched router (LSR) to remove the MPLS header from the  
packet. In this case, the penultimate LSR and the last LSR do not have access to the quality of service  
(QoS) values that the packet carried before the MPLS header was removed. To preserve the QoS values,  
you can configure the LSR to advertise an explicit NULL label (a label value of zero). The LSR at the  
penultimate hop forwards MPLS packets with a NULL label instead of forwarding IP packets.  
An explicit NULL label is not needed when the penultimate hop receives MPLS packets with a label stack  
that contains at least two labels and penultimate hop popping is performed. In that case, the inner label can  
still carry the QoS value needed by the penultimate and edge LSR to implement their QoS policy.  
Note  
When you issue the mpls ldp explicit-null command, Explicit Null is advertised in place of Implicit Null  
for directly connected prefixes.  
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MPLS Label Distribution Protocol (LDP)  
How to Configure MPLS LDP  
SUMMARY STEPS  
1.  
2.  
3.  
4.  
5.  
6.  
7.  
8.  
9.  
10.  
enable  
configure terminal  
mpls ip  
mpls label protocol {ldp | tdp | both}  
interface type number  
mpls ip  
exit  
mpls ldp explicit-null [for prefix-acl | to peer-acl | for prefix-acl to peer-acl]  
exit  
show mpls forwarding-table [network {mask | length} | labels label [- label] | interface interface |  
next-hop address | lsp-tunnel[tunnel-id]] [vrf vpn-name] [detail]  
DETAILED STEPS  
Command or Action  
Purpose  
Step 1  
Step 2  
Step 3  
Enables privileged EXEC mode.  
enable  
Enter your password if prompted.  
Example:  
Router> enable  
configure terminal  
Enters global configuration mode.  
Example:  
Router# configure terminal  
Configures MPLS hop-by-hop forwarding globally.  
mpls ip  
The mpls ip command is enabled by default; you do not  
have to specify this command.  
Globally enabling MPLS forwarding does not enable it on  
the router interfaces. You must enable MPLS forwarding on  
the interfaces as well as for the router.  
Example:  
Router(config)# mpls ip  
Step 4  
Configures the use of LDP on all interfaces. LDP is the default.  
mpls label protocol {ldp | tdp | both}  
If you set all interfaces globally to LDP, you can override  
specific interfaces with either the tdp or both keyword by  
specifying the command in interface configuration mode.  
Example:  
Router(config)# mpls label protocol ldp  
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MPLS Label Distribution Protocol (LDP)  
How to Configure MPLS LDP  
Command or Action  
Purpose  
Step 5  
Step 6  
Step 7  
Specifies the interface to be configured and enters interface  
configuration mode.  
interface type number  
Example:  
Router(config)# interface atm2/0  
Configures MPLS hop-by-hop forwarding on the interface.  
mpls ip  
You must enable MPLS forwarding on the interfaces as well  
as for the router.  
Example:  
Router(config-if)# mpls ip  
Exits interface configuration mode and enters global  
configuration mode.  
exit  
Example:  
Router(config-if)# exit  
Step 8  
Step 9  
Advertises an Explicit Null label in situations where it would  
normally advertise an Implicit Null label.  
mpls ldp explicit-null [for prefix-acl | to peer-acl |  
for prefix-acl to peer-acl]  
Example:  
Router(config)# mpls ldp explicit-null  
Exits global configuration mode and enter privileged EXEC  
mode.  
exit  
Example:  
Router(config)# exit  
Step 10  
Verifies that MPLS packets are forwarded with an explicit-null  
label (value of 0).  
show mpls forwarding-table [network {mask |  
length} | labels label [- label] | interface interface |  
next-hop address | lsp-tunnel[tunnel-id]] [vrf vpn-  
name] [detail]  
Example:  
Router# show mpls forwarding-table  
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MPLS Label Distribution Protocol (LDP)  
How to Configure MPLS LDP  
Examples  
Enabling explicit-null on an egress LSR causes that LSR to advertise the explicit-null label to all adjacent  
MPLS routers.  
Router# configure terminal  
Router(config)# mpls ldp explicit-null  
If you issue the show mpls forwarding-table command on an adjacent router, the output shows that MPLS  
packets are forwarded with an explicit-null label (value of 0). In the following example, the second column  
shows that entries have outgoing labels of 0, where once they were marked “Pop label”.  
Router# show mpls forwarding-table  
Local Outgoing  
Prefix  
Bytes label Outgoing  
Next Hop  
label label or VC or Tunnel Id  
switched  
interface  
Fa2/1/0  
Fa2/0/0  
Fa2/0/0  
Fa2/0/0  
Fa2/0/0  
Fa2/0/0  
Fa2/0/0  
Fa2/0/0  
19  
22  
23  
24  
25  
26  
27  
28  
Pop tag  
10.12.12.12/32  
10.14.14.14/32  
172.24.24.24/32  
192.168.0.0/8  
10.15.15.15/32  
172.16.0.0/8  
0
0
0
0
0
0
0
0
172.16.0.1  
192.168.0.2  
192.168.0.2  
192.168.0.2  
192.168.0.2  
192.168.0.2  
192.168.0.22  
192.168.0.2  
0
0
0
0
0
25  
0
10.16.16.16/32  
10.34.34.34/32  
Enabling explicit-null and specifying the forkeyword with a standard access control list (ACL) changes all  
adjacent MPLS routers' tables to swap an explicit-null label for only those entries specified in the access-  
list. In the following example, an access-list is created that contains the 10.24.24.24/32 entry. Explicit null  
is configured and the access list is specified.  
Router# configure terminal  
Router(config)# mpls label protocol ldp  
Router(config)# access-list 24 permit host 10.24.24.24  
Router(config)# mpls ldp explicit-null for 24  
If you issue the show mpls forwarding-table command on an adjacent router, the output shows that the  
only the outgoing labels for the addresses specified (172.24.24.24/32) change from Pop label to 0. All other  
Pop label outgoing labels remain the same.  
Router# show mpls forwarding-table  
Local Outgoing  
Prefix  
Bytes label Outgoing  
Next Hop  
label label or VC or Tunnel Id  
switched  
interface  
Fa2/1/0  
Fa2/0/0  
Fa2/0/0  
Fa2/0/0  
Fa2/0/0  
Fa2/0/0  
Fa2/0/0  
Fa2/0/0  
19  
22  
23  
24  
25  
26  
27  
28  
Pop tag  
10.12.12.12/32  
10.14.14.14/32  
172.24.24.24/32  
192.168.0.0/8  
10.15.15.15/32  
172.16.0.0/8  
0
0
0
0
0
0
0
0
172.16.0.1  
192.168.0.2  
192.168.0.2  
192.168.0.2  
192.168.0.2  
192.168.0.2  
192.168.0.22  
192.168.0.2  
0
0
0
0
0
25  
0
10.16.16.16/32  
10.34.34.34/32  
Enabling explicit null and adding the to keyword and an access list enables you to advertise explicit-null  
labels to only those adjacent routers specified in the access-list.To advertise explicit-null to a particular  
router, you must specify the router's LDP ID in the access-list.  
In the following example, an access-list contains the 10.15.15.15/32 entry, which is the LDP ID of an  
adjacent MPLS router. The router that is configured with explicit null advertises explicit-null labels only to  
that adjacent router.  
Router# show mpls ldp discovery  
Local LDP Identifier:  
10.15.15.15:0  
Discovery Sources:  
Interfaces:  
Ethernet4 (ldp): xmit/recv  
TDP Id: 10.14.14.14:0  
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Protecting Data Between LDP Peers with MD5 Authentication  
How to Configure MPLS LDP  
Router# configure terminal  
Router(config)# mpls label protocol ldp  
Router(config)# access-list 15 permit host 10.15.15.15  
Router(config)# mpls ldp explicit-null to 15  
If you issue the show mpls forwarding-table command, the output shows that explicit null labels are  
going only to the router specified in the access list.  
Router# show mpls forwarding-table  
Local Outgoing  
Prefix  
Bytes label Outgoing  
Next Hop  
label label or VC or Tunnel Id  
switched  
interface  
Fa2/1/0  
Fa2/0/0  
Fa2/0/0  
Fa2/0/0  
Fa2/0/0  
Fa2/0/0  
Fa2/0/0  
Fa2/0/0  
19  
22  
23  
24  
25  
26  
27  
28  
Pop tag  
10.12.12.12/32  
10.14.14.14/32  
172.24.24.24/32  
192.168.0.0/8  
10.15.15.15/32  
172.16.0.0/8  
0
0
0
0
0
0
0
0
172.16.0.1  
192.168.0.2  
192.168.0.2  
192.168.0.2  
192.168.0.2  
192.168.0.2  
192.168.0.22  
192.168.0.2  
0
0
0
0
0
25  
0
10.16.16.16/32  
10.34.34.34/32  
Enabling explicit-null with both the forand tokeywords enables you to specify which routes to advertise  
with explicit-null labels and to which adjacent routers to advertise these explicit-null labels.  
Router# show access 15  
Standard IP access list 15  
permit 10.15.15.15 (7 matches)  
Router# show access 24  
Standard IP access list 24  
permit 10.24.24.24 (11 matches)  
Router# configure terminal  
Router(config)# mpls label protocol ldp  
Router(config)# mpls ldp explicit-null for 24 to 15  
If you issue the show mpls forwarding-table command on the router called 47K-60-4, the output shows  
that it receives explicit null labels for 10.24.24.24/32.  
Router# show mpls forwarding-table  
Local Outgoing  
Prefix  
Bytes label Outgoing  
Next Hop  
label label or VC or Tunnel Id  
switched  
interface  
Et4  
17  
20  
21  
22  
23  
25  
27  
28  
29  
0 <---  
Pop tag  
20  
10.24.24.24/32  
172.16.0.0/8  
10.12.12.12/32  
10.0.0.0/8  
10.13.13.13/32  
10.14.14.14/32  
192.168.0.0/8  
10.16.16.16/32  
192.168.34.34/32  
0
0
172.16.0.1  
172.16.0.1  
172.16.0.1  
172.16.0.1  
172.16.0.1  
172.16.0.1  
172.16.0.1  
172.16.0.1  
172.16.0.1  
Et4  
0
Et4  
16  
0
Et4  
21  
0
Et4  
Pop tag  
Pop tag  
25  
0
Et4  
0
Et4  
0
Et4  
Pop tag  
0
Et4  
Protecting Data Between LDP Peers with MD5 Authentication  
You can enable authentication between two LDP peers, which verifies each segment sent on the TCP  
connection between the peers. You must configure authentication on both LDP peers using the same  
password; otherwise, the peer session is not established.  
Authentication uses the Message Digest 5 (MD5) algorithm to verify the integrity of the communication  
and authenticate the origin of the message.  
To enable authentication, issue the mpls ldp neighborcommand with the passwordkeyword. This causes  
the router to generate an MD5 digest for every segment sent on the TCP connection and check the MD5  
digest for every segment received from the TCP connection.  
When you configure a password for an LDP neighbor, the router tears down existing LDP sessions and  
establishes new sessions with the neighbor.  
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MPLS Label Distribution Protocol (LDP)  
How to Configure MPLS LDP  
If a router has a password configured for a neighbor, but the neighboring router does not have a password  
configured, a message such as the following appears on the console who has a password configured while  
the two routers attempt to establish an LDP session. The LDP session is not established.  
%TCP-6-BADAUTH: No MD5 digest from [peer's IP address](11003) to [local router's IP address](646)  
Similarly, if the two routers have different passwords configured, a message such as the following appears  
on the console. The LDP session is not established.  
%TCP-6-BADAUTH: Invalid MD5 digest from [peer's IP address](11004) to [local router's IP address]  
(646)  
SUMMARY STEPS  
1.  
2.  
3.  
4.  
5.  
6.  
7.  
enable  
configure terminal  
mpls ip  
mpls label protocol {ldp | tdp | both}  
mpls ldp neighbor [vrf vpn-name] ip-address[password[0-7] password-string]  
exit  
show mpls ldp neighbor [[vrf vpn-name] [address | interface] [detail] | [all]]  
DETAILED STEPS  
Command or Action  
Purpose  
Step 1  
Step 2  
Step 3  
Enables privileged EXEC mode.  
enable  
Enter your password if prompted.  
Example:  
Router> enable  
configure terminal  
Enters global configuration mode.  
Example:  
Router# configure terminal  
Configures MPLS hop-by-hop forwarding globally.  
mpls ip  
The mpls ip command is enabled by default; you do not have  
to specify this command.  
Globally enabling MPLS forwarding does not enable it on the  
router interfaces. You must enable MPLS forwarding on the  
interfaces as well as for the router.  
Example:  
Router(config)# mpls ip  
Step 4  
Configures the use of LDP on all interfaces. LDP is the default.  
mpls label protocol {ldp | tdp | both}  
If you set all interfaces globally to LDP, you can override  
specific interfaces with either the tdp or both keyword by  
specifying the command in interface configuration mode.  
Example:  
Router(config)# mpls label protocol ldp  
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MPLS Label Distribution Protocol (LDP)  
How to Configure MPLS LDP  
Command or Action  
Purpose  
Step 5  
Specifies authentication between two LDP peers.  
mpls ldp neighbor [vrf vpn-name] ip-  
address[password[0-7] password-string]  
Example:  
Router(config)# mpls ldp  
neighbor 172.27.0.15 password onethirty9  
Step 6  
Step 7  
Exits global configuration mode and enters privileged EXEC  
mode.  
exit  
Example:  
Router(config)# exit  
Displays the status of LDP sessions.  
show mpls ldp neighbor [[vrf vpn-name] [address |  
interface] [detail] | [all]]  
If the passwords have been set on both LDP peers and the  
passwords match, the show mpls ldp neighbor command displays  
that the LDP session was successfully established.  
Example:  
Router# show mpls ldp neighbor detail  
Examples  
The following example configures a router with the password cisco:  
Router> enable  
Router# configure terminal  
Router(config)# mpls ip  
Router(config)# mpls label protocol ldp  
Router(config)# mpls ldp neighbor 10.1.1.1 password cisco  
Router(config)# exit  
The following example shows that the LDP session between routers was successfully established:  
Router# show mpls ldp neighbor  
Peer LDP Ident: 10.1.1.2:0; Local LDP Ident 10.1.1.1:0  
TCP connection: 10.1.1.2.11118 - 10.1.1.1.646  
State: Oper; Msgs sent/rcvd: 12/11; Downstream  
Up time: 00:00:10  
LDP discovery sources:  
FastEthernet1/0, Src IP addr: 10.20.10.2  
Addresses bound to peer LDP Ident:  
10.1.1.2  
10.20.20.1  
10.20.10.2  
The following show mpls ldp neighbor detail command shows that MD5 (shown in bold) is used for the  
LDP session.  
Router# show mpls ldp neighbor 10.0.0.21 detail  
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Configuring Directly Connected MPLS LDP Sessions Example  
MPLS LDP Configuration Examples  
Peer LDP Ident: 10.0.0.21:0; Local LDP Ident 10.0.0.22:0  
TCP connection: 10.0.0.21.646 - 10.0.0.22.14709; MD5 on  
State: Oper; Msgs sent/rcvd: 1020/1019; Downstream; Last TIB rev sent 2034  
Up time: 00:00:39; UID: 3; Peer Id 1;  
LDP discovery sources:  
FastEthernet1/1; Src IP addr: 172.16.1.1  
holdtime: 15000 ms, hello interval: 5000 ms  
Addresses bound to peer LDP Ident:  
10.0.0.21  
10.0.38.28  
10.88.88.2  
172.16.0.1  
172.16.1.1  
Peer holdtime: 180000 ms; KA interval: 60000 ms; Peer state: estab  
MPLS LDP Configuration Examples  
Configuring Directly Connected MPLS LDP Sessions Example  
The figure below shows a sample network for configuring directly connected LDP sessions.  
This example configures the following:  
MPLS hop-by-hop forwarding for the POS links between Router 1 and Router 2 and between Router 1  
and Router 3.  
LDP for label distribution between Router 1 and Router 2.  
TDP for label distribution between Router 1 and Router 3.  
A loopback interface and IP address for each LSR that can be used as the LDP router ID.  
Figure 1  
Configuration of MPLS LDP  
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MPLS Label Distribution Protocol (LDP)  
MPLS LDP Configuration Examples  
The configuration examples below show only the commands related to configuring LDP for Router 1,  
Router 2, and Router 3 in the sample network shown in the figure above.  
Note  
Router 1 Configuration  
ip cef distributed  
interface Loopback0  
ip address 172.16.0.11 255.255.255.255  
!
!Assumes R1 supports distributed CEF  
!Loopback interface for LDP ID.  
interface POS3/0/0  
ip address 10.0.0.44 255.0.0.0  
mpls ip  
mpls label protocol ldp  
!
!Enable hop-by-hop MPLS forwarding  
!Use LDP for this interface  
interface POS3/0/1  
ip address 192.168.0.44 255.0.0.0  
mpls ip  
!Enable hop-by-hop MPLS forwarding  
!Use TDP for this interface  
mpls label protocol tdp  
Router 2 Configuration  
ip cef distributed  
!Assumes R2 supports distributed CEF  
!Loopback interface for LDP ID.  
!
interface Loopback0  
ip address 172.16.0.22 255.255.255.255  
!
interface POS2/0/0  
ip address 10.0.0.33 255.0.0.0  
mpls ip  
!Enable hop-by-hop MPLS forwarding  
!Use LDP for this interface  
mpls label protocol ldp  
Router 3 Configuration  
ip cef  
!Assumes R3 does not support dCEF  
!Loopback interface for LDP ID.  
!
interface Loopback0  
ip address 172.16.0.33 255.255.255.255  
!
interface POS1/0  
ip address 192.168.0.55 255.0.0.0  
mpls ip  
mpls label protocol tdp  
!Enable hop-by-hop MPLS forwarding  
!Use tDP for this interface  
The LDP configuration for Router 1 uses the mpls label protocol ldpcommand in interface configuration  
mode, because some of its interfaces use LDP and some use TDP. Another way to configure Router 1 is to  
use the mpls label protocol ldpcommand in global configuration mode to configure LDP as the default  
protocol for interfaces and use the mpls label protocol tdpcommand in interface configuration mode to  
configure TDP for the POS3/0/1 link to Router 3. This alternative way to configure Router 1 is shown  
below:  
Router 1 Configuration  
ip cef distributed  
mpls label protocol ldp  
!
interface Loopback0  
ip address 172.16.0.11 255.255.255.255  
interface POS3/0/0  
ip address 10.0.0.44 255.0.0.0  
mpls ip  
!Assumes R1 supports dCEF  
!Use LDP for the default protocol  
!Loopback interface for LDP ID.  
!Enable hop-by-hop MPLS forwarding  
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Establishing Nondirectly Connected MPLS LDP Sessions Example  
MPLS LDP Configuration Examples  
!Use LDP (configured i/f default)  
interface POS3/0/1  
ip address 192.168.0.44 255.0.0.0  
mpls ip  
mpls label protocol tdp  
!Enable hop-by-hop MPLS forwarding  
!Use TDP for this interface  
The configuration of Router 2 also uses the mpls label protocol ldpcommand in interface configuration  
mode. To specify LDP for all interfaces, use the mpls label protocol ldpcommand in global configuration  
mode without any interface mpls label protocol commands.  
Configuring the mpls ip command on an interface triggers the transmission of discovery Hello messages  
for the interface.  
Establishing Nondirectly Connected MPLS LDP Sessions Example  
The following examples illustrate the configuration of platforms for MPLS LDP nondirectly connected  
sessions using the sample network shown in the figure below. Note that Routers 1, 4, 5, and 6 in this  
sample network are not directly connected to each other.  
Figure 2  
Sample Network for Configuring LDP for Targeted Sessions  
The configuration example shows the following:  
Targeted sessions between Routers 1 and 4 use LDP. Routers 1 and 4 are both active.  
Targeted sessions between Routers 1 and 6 use LDP. Router 1 is active and Router 6 is passive.  
Targeted sessions between Routers 1 and 5 use TDP. Router 5 is active.  
These examples assume that the active ends of the nondirectly connected sessions are associated with  
tunnel interfaces, such as MPLS traffic engineering tunnels. They show only the commands related to  
configuring LDP targeted sessions. The examples do not show configuration of the applications that initiate  
the targeted sessions.  
Router 1 Configuration  
Tunnel interfaces Tunnel14 and Tunnel16 specify LDP for targeted sessions associated with these  
interfaces. The targeted session for Router 5 requires TDP. The mpls label protocol ldp command in  
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MPLS Label Distribution Protocol (LDP)  
MPLS LDP Configuration Examples  
global configuration mode makes it unnecessary to explicitly specify LDP as part of the configuration from  
the Tunnel14 and Tunnel16.  
ip cef distributed  
mpls label protocol ldp  
interface Loopback0  
ip address 10.25.0.11 255.255.255.255  
interface Tunnel14  
!Router1 supports distributed CEF  
!Use LDP as default for all interfaces  
!Loopback interface for LDP ID.  
!Tunnel to Router 4 requiring label distribution  
tunnel destination 10.11.0.4 !Tunnel endpoint is Router 4  
mpls ip  
interface Tunnel15  
!Enable hop-by-hop forwarding on the interface  
!Tunnel to Router 5 requiring label distribution  
tunnel destination 10.11.0.5 !Tunnel endpoint is Router 5  
mpls label protocol tdp  
mpls ip  
interface Tunnel16  
!Use TDP for session with Router 5  
!Enable hop-by-hop forwarding on the interface  
!Tunnel to Router 6 requiring label distribution  
tunnel destination 10.11.0.6 !Tunnel endpoint is Router 6  
mpls ip  
!Enable hop-by-hop forwarding on the interface  
Router 4 Configuration  
The mpls label protocol ldp command in global configuration mode makes it unnecessary to explicitly  
specify LDP as part of the configuration for the Tunnel41 targeted session with Router 1.  
ip cef distributed  
mpls label protocol ldp  
interface Loopback0  
ip address 10.25.0.44 255.255.255.255  
interface Tunnel41  
tunnel destination 10.11.0.1 !Tunnel endpoint is Router 1  
mpls ip  
!Router 4 supports distributed CEF  
!Use LDP as default for all interfaces  
!Loopback interface for LDP ID.  
!Tunnel to Router 1 requiring label distribution  
!Enable hop-by-hop forwarding on the interface  
Router 5 Configuration  
Router 5 must use TDP for all targeted sessions. Therefore, its configuration includes the mpls label  
protocol tdpcommand.  
ip cef  
mpls label protocol tdp  
interface Loopback0  
ip address 10.25.0.55 255.255.255.255  
interface Tunnel51  
tunnel destination 10.11.0.1 !Tunnel endpoint is Router 1  
mpls ip  
!Router 5 supports CEF  
!Use TDP as default for all interfaces  
!Loopback interface for LDP ID.  
!Tunnel to Router 1 requiring label distribution  
!Enable hop-by-hop forwarding on the interface  
Router 6 Configuration  
By default, a router cannot be a passive neighbor in targeted sessions. Therefore, Router 1, Router 4, and  
Router 5 are active neighbors in any targeted sessions. The mpls ldp discovery targeted-hello accept  
command permits Router 6 to be a passive target in targeted sessions with Router 1. Router 6 can also be an  
active neighbor in targeted sessions, although the example does not include such a configuration.  
ip cef distributed  
!Router 6 supports distributed CEF  
!Loopback interface for LDP ID.  
interface Loopback0  
ip address 10.25.0.66 255.255.255.255  
mpls ldp discovery targeted-hellos accept from LDP_SOURCES  
!Respond to requests for targeted hellos  
!from sources permitted by acl LDP_SOURCES  
!Define acl for targeted hello sources.  
!Accept targeted hello request from Router 1.  
!Deny requests from other sources.  
ip access-list standard LDP_SOURCES  
permit 10.11.0.1  
deny any  
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MPLS Label Distribution Protocol (LDP)  
Additional References  
Additional References  
Related Documents  
Related Topic  
Document Title  
Configures LDP on every interface associated with MPLS LDP Autoconfiguration  
a specified IGP instance.  
Ensures that LDP is fully established before the  
IGP path is used for switching.  
MPLS LDP-IGP Synchronization  
Allows ACLs to control the label bindings that an  
LSR accepts from its peer LSRs.  
MPLS LDP Inbound Label Binding Filtering  
Enables standard, SNMP-based network  
management of the label switching features in  
Cisco IOS.  
MPLS Label Distribution Protocol MIB Version 8  
Upgrade  
Standards  
Standard  
None  
Title  
--  
MIBs  
MIB  
MIBs Link  
To locate and download MIBs for selected  
platforms, Cisco IOS releases, and feature sets, use  
Cisco MIB Locator found at the following URL:  
MPLS Label Distribution Protocol MIB (draft-  
ietf-mpls-ldp-mib-08.txt)  
SNMP-VACM-MIB The View-based Access  
Control Model (ACM) MIB for SNMP  
RFCs  
RFC  
Title  
RFC 3036  
LDP Specification  
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MPLS Label Distribution Protocol (LDP)  
Feature Information for MPLS Label Distribution Protocol  
Technical Assistance  
Description  
Link  
The Cisco Technical Support website contains  
thousands of pages of searchable technical content,  
including links to products, technologies, solutions,  
technical tips, and tools. Registered Cisco.com  
users can log in from this page to access even more  
content.  
Feature Information for MPLS Label Distribution Protocol  
The following table provides release information about the feature or features described in this module.  
This table lists only the software release that introduced support for a given feature in a given software  
release train. Unless noted otherwise, subsequent releases of that software release train also support that  
feature.  
Use Cisco Feature Navigator to find information about platform support and Cisco software image support.  
To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.  
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MPLS Label Distribution Protocol (LDP)  
Feature Information for MPLS Label Distribution Protocol  
Table 2  
Feature Information for MPLS Label Distribution Protocol Overview  
Feature Name  
Releases  
Feature Information  
MPLS Label Distribution  
Protocol  
12.0(10)ST 12.0(14)ST 12.1(2)T This feature was introduced in  
12.1(8a)E 12.2(2)T 12.2(4)T  
12.2(8)T 12.0(21)ST 12.0(22)S  
12.0(23)S 12.2(13)T 12.4(3)  
12.4(5)  
Cisco IOS Release 12.0(10)ST,  
incorporating a new set of  
Multiprotocol Label Switching  
(MPLS) CLI commands  
implemented for use with Cisco  
routers and switches. The CLI  
commands in this release  
reflected MPLS command syntax  
and terminology, thus facilitating  
the orderly transition from a  
network using the Tag  
Distribution Protocol (TDP) to  
one using the Label Distribution  
Protocol (LDP).  
In Cisco IOS Release 12.0(14)ST,  
several new MPLS CLI  
commands were introduced,  
support for MPLS VPNs was  
added by means of a new vrf vpn-  
nameparameter in certain existing  
commands, and other commands  
were modified to ensure  
consistent interpretation of  
associated prefix-access-list  
arguments by Cisco IOS  
software.  
In Cisco IOS 12.1(2)T, this  
feature was integrated into this  
release. Also, the debug mpls  
atm-ldp api, debug mpls atm-  
ldp routes,and debug mpls atm-  
ldp statescommandswere  
modified.  
This feature was integrated into  
Cisco IOS Release 12.1(8a)E.  
This feature was integrated into  
Cisco IOS Release 12.2(2)T.  
The following commands were  
introduced or modified by this  
feature: mpls label protocol  
(global configuration), mpls ldp  
router-id.  
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MPLS Label Distribution Protocol (LDP)  
Feature Information for MPLS Label Distribution Protocol  
Feature Name  
Releases  
Feature Information  
In Cisco IOS Release 12.2(4)T,  
support was added for Cisco  
MGX 8850 and MGX 8950  
switches equipped with a Cisco  
MGX RPM-PR card, and the VPI  
range in the show mpls atm-ldp  
bindings and show mpls ip  
binding commands was changed  
to 4095.  
In Cisco IOS Release 12.2(8)T,  
the debug mpls atm-ldp  
failurecommand was introduced.  
In Cisco IOS Release 12.0(21)ST,  
the mpls ldp neighbor implicit-  
withdrawcommand was  
introduced.  
This feature was integrated into  
Cisco IOS Release 12.0(22)S.  
The mpls ldp neighbor  
targeted-sessioncommand and  
the interface keyword for the  
mpls ldp advertise-  
labelscommand were added.  
This feature was integrated into  
Cisco IOS Release 12.0(23)S.  
Default values for the mpls ldp  
discoverycommand holdtime  
and interval keywords were  
changed.  
This feature was integrated into  
Cisco IOS Release 12.2(13)T.  
In Cisco IOS Release 12.4(3), the  
default MPLS label distribution  
protocol changed from TDP to  
information. If no protocol is  
explicitly configured by the mpls  
label protocol command, LDP is  
the default label distribution  
protocol. See the mpls label  
protocol (global configuration)  
command for more information.  
Also in Cisco IOS Release  
12.4(3), LDP configuration  
commands are saved by using the  
MPLS form of the command  
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MPLS Label Distribution Protocol (LDP)  
Feature Name  
Releases  
Feature Information  
rather than the tag-switching  
form. Previously, commands  
were saved by using the tag-  
switching form of the command,  
for backward compatibility. See  
11 for more information.  
In Cisco IOS Release 12.4(5), the  
vrf vrf-name keyword/argument  
pair was added for the mpls ldp  
router-id command to allow you  
to associate the LDP router ID  
with a nondefault VRF.  
Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S.  
and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks.  
Third-party trademarks mentioned are the property of their respective owners. The use of the word partner  
does not imply a partnership relationship between Cisco and any other company. (1110R)  
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be  
actual addresses and phone numbers. Any examples, command display output, network topology diagrams,  
and other figures included in the document are shown for illustrative purposes only. Any use of actual IP  
addresses or phone numbers in illustrative content is unintentional and coincidental.  
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Establishing Nondirectly Connected MPLS LDP Sessions Example  
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MPLS LDP Session Protection  
The MPLS LDP Session Protection feature provides faster label distribution protocol convergence when a  
link recovers following an outage. MPLS LDP Session Protection protects a label distribution protocol  
(LDP) session between directly connected neighbors or an LDP session established for a traffic  
engineering (TE) tunnel.  
Finding Feature Information  
Your software release may not support all the features documented in this module. For the latest feature  
information and caveats, see the release notes for your platform and software release. To find information  
about the features documented in this module, and to see a list of the releases in which each feature is  
supported, see the Feature Information Table at the end of this document.  
Use Cisco Feature Navigator to find information about platform support and Cisco software image support.  
To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.  
Restrictions for MPLS LDP Session Protection  
This feature is not supported under the following circumstances:  
With TDP sessions  
With extended access lists  
With LC-ATM routers  
Information About MPLS LDP Session Protection  
MPLS LDP Session Protection maintains LDP bindings when a link fails. MPLS LDP sessions are  
protected through the use of LDP Hello messages. When you enable MPLS LDP, the label switched routers  
(LSRs) send messages to find other LSRs with which they can create LDP sessions.  
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MPLS LDP Session Protection Customizations  
Information About MPLS LDP Session Protection  
If the LSR is one hop from its neighbor, it is directly connected to its neighbor. The LSR sends out  
LDP Hello messages as User Datagram Protocol (UDP) packets to all the routers on the subnet. The  
hello message is called an LDP Link Hello. A neighboring LSR responds to the hello message and the  
two routers begin to establish an LDP session.  
If the LSR is more than one hop from its neighbor, it is not directly connected to its neighbor. The  
LSR sends out a directed hello message as a UDP packet, but as a unicast message specifically  
addressed to that LSR. The hello message is called an LDP Targeted Hello. The nondirectly connected  
LSR responds to the Hello message and the two routers establish an LDP session. (If the path between  
two LSRs has been traffic engineered and has LDP enabled, the LDP session between them is called a  
targeted session.)  
MPLS LDP Session Protection uses LDP Targeted Hellos to protect LDP sessions. Take, for example, two  
directly connected routers that have LDP enabled and can reach each other through alternate IP routes in  
the network. An LDP session that exists between two routers is called an LDP Link Hello Adjacency.  
When MPLS LDP Session Protection is enabled, an LDP Targeted Hello Adjacency is also established for  
the LDP session. If the link between the two routers fails, the LDP Link Adjacency also fails. However, if  
the LDP peer is still reachable through IP, the LDP session stays up, because the LDP Targeted Hello  
Adjacency still exists between the routers. When the directly connected link recovers, the session does not  
need to be reestablished, and LDP bindings for prefixes do not need to be relearned.  
MPLS LDP Session Protection Customizations  
You can modify MPLS LDP Session Protection by using the keywords in the mpls ldp session protection  
command.  
Specifying How Long an LDP Targeted Hello Adjacency Should Be Retained  
The default behavior of the mpls ldp session protection command allows an LDP Targeted Hello  
Adjacency to exist indefinitely following the loss of an LDP Link Hello Adjacency. You can issue the  
duration keyword to specify the number of seconds (from 30 to 2,147,483) that the LDP Targeted Hello  
Adjacency is retained after the loss of the LDP Link Hello Adjacency. When the link is lost, a timer starts.  
If the timer expires, the LDP Targeted Hello Adjacency is removed.  
Specifying Which Routers Should Have MPLS LDP Session Protection  
The default behavior of the mpls ldp session protection command allows MPLS LDP Session Protection for  
all neighbor sessions. You can issue either the vrfor for keyword to limit the number of neighbor sessions  
that are protected.  
Enabling MPLS LDP Session Protection on Specified VPN Routing and Forwarding Instances  
If the router is configured with at least one VPN routing and forwarding (VRF) instance, you can use the  
vrf keyword to select which VRF is to be protected. You cannot specify more than one VRF with the mpls  
ldp session protection command. To specify multiple VRFs, issue the command multiple times.  
Enabling MPLS LDP Session Protection on Specified Peer Routers  
You can create an access list that includes several peer routers. You can specify that access list with the for  
keyword to enable LDP Session Protection for the peer routers in the access control list.  
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Enabling MPLS LDP Session Protection  
How to Configure MPLS LDP Session Protection  
How to Configure MPLS LDP Session Protection  
Enabling MPLS LDP Session Protection  
You use the mpls ldp session protection command to enable MPLS LDP Session Protection. This command  
enables LDP sessions to be protected during a link failure. By default, the command protects all LDP  
sessions. The command has several options that enable you to specify which LDP sessions to protect. The  
vrfkeyword lets you protect LDP sessions for a specified VRF. The for keyword lets you specify a  
standard IP access control list (ACL) of prefixes that should be protected. The duration keyword enables  
you to specify how long the router should retain the LDP Targeted Hello Adjacency following the loss of  
the LDP Link Hello Adjacency.  
LSRs must be able to respond to LDP targeted hellos. Otherwise, the LSRs cannot establish a targeted  
adjacency. All routers that participate in MPLS LDP Session Protection must be enabled to respond to  
targeted hellos. Both neighbor routers must be configured for session protection or one router must be  
configured for session protection and the other router must be configured to respond to targeted hellos.  
SUMMARY STEPS  
1.  
2.  
3.  
4.  
5.  
6.  
7.  
8.  
9.  
10.  
enable  
configure terminal  
ip cef [distributed]  
interface loopback number  
ip address {prefix mask}  
interface interface  
mpls ip  
mpls label protocol {ldp | tdp | both}  
exit  
mpls ldp session protection [vrf vpn-name] [for acl] [duration seconds]  
DETAILED STEPS  
Command or Action  
Purpose  
Step 1  
Enables privileged EXEC mode.  
enable  
Enter your password if prompted.  
Example:  
Router> enable  
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MPLS LDP Session Protection  
How to Configure MPLS LDP Session Protection  
Command or Action  
Purpose  
Step 2  
Step 3  
Enters global configuration mode.  
configure terminal  
Example:  
Router# configure terminal  
ip cef [distributed]  
Configures Cisco Express Forwarding.  
Example:  
Router(config)# ip cef  
Step 4  
Step 5  
Configures a loopback interface and enters interface  
configuration mode.  
interface loopback number  
Example:  
Router(config)# interface Loopback0  
ip address {prefix mask}  
Assigns an IP address to the loopback interface.  
Example:  
Router(config-if)# ip address 10.25.0.11  
255.255.255.255  
Step 6  
Step 7  
Specifies the interface to configure.  
interface interface  
Example:  
Router(config-if)# interface POS3/0  
Configures MPLS hop-by-hop forwarding for a specified  
interface.  
mpls ip  
Example:  
Router(config-if)# mpls ip  
Step 8  
Configures the use of LDP on a specific interface or on all  
interfaces.  
mpls label protocol {ldp | tdp | both}  
In interface configuration mode, the command sets the  
default label distribution protocol for the interface to be  
LDP, overriding any default set by the global mpls label  
protocolcommand.  
Example:  
Router(config-if)# mpls label protocol ldp  
In global configuration mode, the command sets all the  
interfaces to LDP.  
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Verifying MPLS LDP Session Protection  
How to Configure MPLS LDP Session Protection  
Command or Action  
Purpose  
Step 9  
Exits from interface configuration mode.  
exit  
Example:  
Router(config-if)# exit  
Step 10  
Enables MPLS LDP Session Protection.  
mpls ldp session protection [vrf vpn-name] [for acl]  
[duration seconds]  
Example:  
Router(config)# mpls ldp session protection  
Verifying MPLS LDP Session Protection  
SUMMARY STEPS  
1.  
2.  
3.  
show mpls ldp discovery  
show mpls ldp neighbor  
show mpls ldp neighbor detail  
DETAILED STEPS  
Step 1  
show mpls ldp discovery  
Issue this command and check that the output contains xmit/recv to the peer router.  
Example:  
Router# show mpls ldp discovery  
Local LDP Identifier:  
10.0.0.5:0  
Discovery Sources:  
Interfaces:  
ATM5/1/0.5 (ldp): xmit/recv  
LDP Id: 10.0.0.1:0  
Targeted Hellos:  
10.0.0.5 -> 10.0.0.3 (ldp): active, xmit/recv  
LDP Id: 10.0.0.3:0  
Step 2  
show mpls ldp neighbor  
Issue this command to check that the targeted hellos are active.  
Example:  
Router# show mpls ldp neighbor  
Peer LDP Ident: 10.0.0.3:0; Local LDP Ident 10.0.0.5:0  
TCP connection: 10.0.0.3.646 - 10.0.0.5.11005  
State: Oper; Msgs sent/rcvd: 1453/1464; Downstream  
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Troubleshooting Tips  
Configuration Examples for MPLS LDP Session Protection  
Up time: 21:09:56  
LDP discovery sources:  
Targeted Hello 10.0.0.5 -> 10.0.0.3, active  
Addresses bound to peer LDP Ident:  
10.3.104.3  
10.0.0.2  
10.0.0.3  
Step 3  
show mpls ldp neighbor detail  
Issue this command to check that the MPLS LDP Session Protection state is Ready or Protecting. If the second last  
line of the output shows Incomplete, the Targeted Hello Adjacency is not up yet.  
Example:  
Router# show mpls ldp neighbor detail  
Peer LDP Ident: 10.16.16.16:0; Local LDP Ident 10.15.15.15:0  
TCP connection: 10.16.16.16.11013 - 10.15.15.15.646  
State: Oper; Msgs sent/rcvd: 53/51; Downstream; Last TIB rev sent 74  
Up time: 00:11:32; UID: 1; Peer Id 0;  
LDP discovery sources:  
Targeted Hello 10.15.15.15 -> 10.16.16.16, active, passive;  
holdtime: infinite, hello interval: 10000 ms  
Addresses bound to peer LDP Ident:  
10.0.0.2  
10.16.16.16  
10.101.101.101 11.0.0.1  
Peer holdtime: 180000 ms; KA interval: 60000 ms; Peer state: estab  
Clients: Dir Adj Client  
LDP Session Protection enabled, state: Protecting  
duration: infinite  
Troubleshooting Tips  
Use the clear mpls ldp neighbor command if you need to terminate an LDP session after a link goes  
down. This is useful for situations where the link needs to be taken out of service or needs to be connected  
to a different neighbor.  
To enable the display of events related to MPLS LDP Session Protection, use the debug mpls ldp session  
protectioncommand.  
Configuration Examples for MPLS LDP Session Protection  
The figure below shows a sample configuration for MPLS LDP Session Protection.  
Figure 3  
MPLS LDP Session Protection Example  
R1  
redundancy  
no keepalive-enable  
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MPLS LDP Session Protection  
Configuration Examples for MPLS LDP Session Protection  
mode hsa  
!
ip cef distributed  
no ip domain-lookup  
multilink bundle-name both  
mpls label protocol ldp  
mpls ldp session protection  
no mpls traffic-eng auto-bw timers frequency 0  
tag-switching tdp router-id Loopback0 force  
!
interface Loopback0  
ip address 10.0.0.1 255.255.255.255  
no ip directed-broadcast  
no ip mroute-cache  
!
interface Multilink4  
no ip address  
no ip directed-broadcast  
no ip mroute-cache  
load-interval 30  
ppp multilink  
multilink-group 4  
!
interface Ethernet1/0/0  
ip address 10.3.123.1 255.255.0.0  
no ip directed-broadcast  
!
interface Ethernet4/0/0  
no ip address  
no ip directed-broadcast  
shutdown  
!
interface Ethernet4/0/1  
description -- ip address 10.0.0.2 255.255.255.0  
no ip address  
no ip directed-broadcast  
shutdown  
!
interface Ethernet4/0/4  
ip address 10.0.0.1 255.0.0.0  
no ip directed-broadcast  
mpls label protocol ldp  
tag-switching ip  
!
interface Ethernet4/0/6  
ip address 10.0.0.1 255.0.0.0  
no ip directed-broadcast  
mpls label protocol ldp  
tag-switching ip  
!
interface Ethernet4/0/7  
ip address 10.0.0.1 255.0.0.0  
no ip directed-broadcast  
mpls label protocol ldp  
tag-switching ip  
!
router ospf 100  
log-adjacency-changes  
redistribute connected  
network 10.0.0.1 0.0.0.0 area 100  
network 10.0.0.0 0.255.255.255 area 100  
network 10.0.0.0 0.255.255.255 area 100  
network 10.0.0.0 0.255.255.255 area 100  
network 10.0.0.0 0.255.255.255 area 100  
!
ip classless  
R2  
redundancy  
no keepalive-enable  
mode hsa  
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MPLS LDP Session Protection  
Configuration Examples for MPLS LDP Session Protection  
!
ip subnet-zero  
ip cef distributed  
mpls label protocol ldp  
mpls ldp session protection  
no mpls traffic-eng auto-bw timers frequency 0  
tag-switching tdp router-id Loopback0 force  
!
interface Loopback0  
ip address 10.0.0.3 255.255.255.255  
no ip directed-broadcast  
!
interface Ethernet5/0/0  
no ip address  
no ip directed-broadcast  
shutdown  
full-duplex  
!
interface Ethernet5/0/2  
ip address 10.0.0.1 255.0.0.0  
no ip directed-broadcast  
full-duplex  
mpls label protocol ldp  
tag-switching ip  
!
interface Ethernet5/0/6  
ip address 10.0.0.2 255.0.0.0  
no ip directed-broadcast  
ip load-sharing per-packet  
full-duplex  
mpls label protocol ldp  
tag-switching ip  
!
interface FastEthernet5/1/0  
ip address 10.3.123.112 255.255.0.0  
no ip directed-broadcast  
!
router ospf 100  
log-adjacency-changes  
redistribute connected  
network 10.0.0.3 0.0.0.0 area 100  
network 10.0.0.0 0.255.255.255 area 100  
network 10.0.0.0 0.255.255.255 area 100  
!
ip classless  
R3  
ip cef  
no ip domain-lookup  
mpls label range 200 100000 static 16 199  
mpls label protocol ldp  
no mpls traffic-eng auto-bw timers frequency 0  
tag-switching tdp router-id Loopback0 force  
!
interface Loopback0  
ip address 10.0.0.5 255.255.255.255  
no ip directed-broadcast  
!
interface Ethernet1/0  
no ip address  
no ip directed-broadcast  
shutdown  
half-duplex  
!
interface Ethernet1/2  
ip address 10.0.0.2 255.0.0.0  
no ip directed-broadcast  
full-duplex  
mpls label protocol ldp  
tag-switching ip  
!
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MPLS LDP Session Protection  
Additional References  
interface Ethernet1/4  
ip address 10.0.0.2 255.0.0.0  
no ip directed-broadcast  
full-duplex  
mpls label protocol ldp  
tag-switching ip  
!
router ospf 100  
log-adjacency-changes  
redistribute connected  
network 10.0.0.5 0.0.0.0 area 100  
network 10.0.0.0 0.255.255.255 area 100  
network 10.0.0.0 0.255.255.255 area 100  
!
ip classless  
Additional References  
Related Documents  
Related Topic  
MPLS LDP  
Document Title  
MPLS Label Distribution Protocol  
MPLS LDP-IGP Synchronization  
LDP Autoconfiguration  
MPLS LDP-IGP synchronization  
LDP autoconfiguration  
Standards  
Standards  
None  
Title  
--  
MIBs  
MIBs  
MIBs Link  
MPLS LDP MIB  
To locate and download MIBs for selected  
platforms, Cisco IOS releases, and feature sets, use  
Cisco MIB Locator found at the following URL:  
RFCs  
RFCs  
Title  
RFC 3036  
RFC 3037  
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MPLS LDP Session Protection  
Command Reference  
Technical Assistance  
Description  
Link  
The Cisco Support website provides extensive  
online resources, including documentation and tools  
for troubleshooting and resolving technical issues  
with Cisco products and technologies. Access to  
most tools on the Cisco Support website requires a  
Cisco.com user ID and password. If you have a  
valid service contract but do not have a user ID or  
password, you can register on Cisco.com.  
Command Reference  
The following commands are introduced or modified in the feature or features documented in this module.  
For information about these commands, see the Cisco IOS Multiprotocol Label Switching Command  
information about all Cisco IOS commands, go to the Command Lookup Tool at http://tools.cisco.com/  
Support/CLILookup or to the Cisco IOS Master Commands List.  
debug mpls ldp session protection  
mpls ldp session protection  
show mpls ldp neighbor  
Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S.  
and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks.  
Third-party trademarks mentioned are the property of their respective owners. The use of the word partner  
does not imply a partnership relationship between Cisco and any other company. (1110R)  
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be  
actual addresses and phone numbers. Any examples, command display output, network topology diagrams,  
and other figures included in the document are shown for illustrative purposes only. Any use of actual IP  
addresses or phone numbers in illustrative content is unintentional and coincidental.  
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MPLS LDP Inbound Label Binding Filtering  
Multiprotocol Label Switching (MPLS) Label Distribution Protocol (LDP) supports inbound label binding  
filtering. You can use the MPLS LDP Inbound Label Binding Filtering feature to configure access control  
lists (ACLs) for controlling the label bindings a label switch router (LSR) accepts from its peer LSRs.  
Finding Feature Information  
Your software release may not support all the features documented in this module. For the latest feature  
information and caveats, see the release notes for your platform and software release. To find information  
about the features documented in this module, and to see a list of the releases in which each feature is  
supported, see the Feature Information Table at the end of this document.  
Use Cisco Feature Navigator to find information about platform support and Cisco software image support.  
To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.  
Restrictions  
Inbound label binding filtering does not support extended ACLs; it only supports standard ACLs.  
Information about MPLS LDP Inbound Label Binding Filtering  
The MPLS LDP Inbound Label Binding Filtering feature may be used to control the amount of memory  
used to store LDP label bindings advertised by other routers. For example, in a simple MPLS Virtual  
Private Network (VPN) environment, the VPN provider edge (PE) routers may require LSPs only to their  
peer PE routers (that is, they do not need LSPs to core routers). Inbound label binding filtering enables a PE  
router to accept labels only from other PE routers.  
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Configuring MPLS LDP Inbound Label Binding Filtering  
How to Configure MPLS LDP Inbound Label Binding Filtering  
How to Configure MPLS LDP Inbound Label Binding Filtering  
Configuring MPLS LDP Inbound Label Binding Filtering  
Perform this task to configure a router for inbound label filtering. The following configuration allows the  
router to accept only the label for prefix 25.0.0.2 from LDP neighbor router 10.12.12.12.  
SUMMARY STEPS  
1.  
2.  
3.  
4.  
5.  
6.  
7.  
enable  
configure terminal  
ip access-list standard access-list-number  
permit {source [source-wildcard] | any} [log]  
exit  
mpls ldp neighbor [vrf vpn-name] nbr-address labels accept acl  
end  
DETAILED STEPS  
Command or Action  
Purpose  
Step 1  
Enables privileged EXEC mode.  
enable  
Enter your password if prompted.  
Example:  
Router> enable  
configure terminal  
Step 2  
Enters global configuration mode.  
Example:  
Example:  
Router# configure terminal  
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MPLS LDP Inbound Label Binding Filtering  
How to Configure MPLS LDP Inbound Label Binding Filtering  
Command or Action  
Purpose  
Step 3  
Defines a standard IP access list with a number.  
ip access-list standard access-list-number  
Example:  
Example:  
Router(config)# ip access-list standard 1  
permit {source [source-wildcard] | any} [log]  
Step 4  
Specifies one or more prefixes permitted by the  
access list.  
Example:  
Example:  
Router(config-std-nacl)# permit 10.0.0.0  
Step 5  
Exits the current mode and goes to the next higher  
level.  
exit  
Example:  
Example:  
Router(config-std-nacl)# exit  
mpls ldp neighbor [vrf vpn-name] nbr-address labels accept acl  
Step 6  
Step 7  
Specifies the ACL to be used to filter label  
bindings for the specified LDP neighbor.  
Example:  
Router(config)# mpls ldp neighbor 10.12.12.12 labels  
accept 1  
Exits the current mode and enters privileged Exec  
mode.  
end  
Example:  
Example:  
Router(config)# end  
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Verifying that MPLS LDP Inbound Label Bindings are Filtered  
How to Configure MPLS LDP Inbound Label Binding Filtering  
Verifying that MPLS LDP Inbound Label Bindings are Filtered  
If inbound filtering is enabled, perform the following steps to verify that inbound label bindings are  
filtered:  
SUMMARY STEPS  
1.  
2.  
3.  
Enter the show mpls ldp neighbor command to show the status of the LDP session, including the name  
or number of the ACL configured for inbound filtering.  
Enter the show ip access-list command to display the contents of all current IP access lists or of a  
specified access list.  
Enter the show mpls ldp bindingscommand to verify that the LSR has remote bindings only from a  
specified peer for prefixes permitted by the access list.  
DETAILED STEPS  
Step 1  
Enter the show mpls ldp neighbor command to show the status of the LDP session, including the name or number of  
the ACL configured for inbound filtering.  
Example:  
show mpls ldp neighbor  
[vrf  
vpn-name  
][  
address  
|
interface  
] [detail  
Note To display information about inbound label binding filtering, you must enter the detail keyword.  
Following is sample output from the show mpls ldp neighbor command.  
Example:  
Router# show mpls ldp neighbor 10.12.12.12 detail  
Peer LDP Ident: 10.12.12.12:0; Local LDP Ident 10.13.13.13:0  
TCP connection: 10.12.12.12.646 - 10.13.13.13.12592  
State: Oper; Msgs sent/rcvd: 49/45; Downstream; Last TIB rev sent 1257  
Up time: 00:32:41; UID: 1015; Peer Id 0;  
LDP discovery sources:  
Serial1/0; Src IP addr: 25.0.0.2  
holdtime: 15000 ms, hello interval: 5000 ms  
Addresses bound to peer LDP Ident:  
10.0.0.129  
10.12.12.12  
10.0.0.2  
Peer holdtime: 180000 ms; KA interval: 60000 ms; Peer state: estab  
LDP inbound filtering accept acl: 1  
Step 2  
Enter the show ip access-list command to display the contents of all current IP access lists or of a specified access list.  
Example:  
show ip access-list  
[
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MPLS LDP Inbound Label Binding Filtering  
Configuration Examples for MPLS LDP Inbound Label Binding Filtering  
access-list-number  
|
access-list-name  
]
It is important that you enter this command to see how the access list is defined; otherwise, you cannot verify  
inbound label binding filtering.  
Note  
The following command output shows the contents of IP access list 1:  
Example:  
Router# show ip access 1  
Standard IP access list 1  
permit 10.0.0.0, wildcard bits 0.0.0.255 (1 match)  
Step 3  
Enter the show mpls ldp bindingscommand to verify that the LSR has remote bindings only from a specified peer for  
prefixes permitted by the access list.  
Example:  
Router# show mpls ldp bindings  
tib entry: 10.0.0.0/8, rev 4  
local binding: tag: imp-null  
tib entry: 10.2.0.0/16, rev 1137  
local binding: tag: 16  
tib entry: 10.2.0.0/16, rev 1139  
local binding: tag: 17  
tib entry: 10.12.12.12/32, rev 1257  
local binding: tag: 18  
tib entry: 10.13.13.13/32, rev 14  
local binding: tag: imp-null  
tib entry: 10.10.0.0/16, rev 711  
local binding: tag: imp-null  
tib entry: 10.0.0.0/8, rev 1135  
local binding: tag: imp-null  
remote binding: tsr: 12.12.12.12:0, tag: imp-null  
tib entry: 10.0.0.0/8, rev 8  
local binding: tag: imp-null  
Router#  
Configuration Examples for MPLS LDP Inbound Label Binding  
Filtering  
In the following example, the mpls ldp neighbor labels accept command is configured with an access  
control list to filter label bindings received on sessions with the neighbor 10.110.0.10.  
Label bindings for prefixes that match 10.b.c.d are accepted, where b is less than or equal to 63, and c and d  
can be any integer between 0 and 128. Other label bindings received from 10.110.0.10 are rejected.  
Router# configure terminal  
Router(config)# access-list 1 permit 10.63.0.0 0.63.255.255  
Router(config)# mpls ldp neighbor 10.110.0.10 labels accept 1  
Router(config)# end  
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MPLS LDP Inbound Label Binding Filtering  
Additional References  
In the following example, the show mpls ldp bindings neighborcommand displays label bindings that  
were learned from 10.110.0.10. This example verifies that the LIB does not contain label bindings for  
prefixes that have been excluded.  
Router# show mpls ldp bindings neighbor 10.110.0.10  
tib entry: 10.2.0.0/16, rev 4  
remote binding: tsr: 10.110.0.10:0, tag: imp-null  
tib entry: 10.43.0.0/16, rev 6  
remote binding: tsr: 10.110.0.10:0, tag: 16  
tib entry: 10.52.0.0/16, rev 8  
remote binding: tsr: 10.110.0.10:0, tag: imp-null  
Additional References  
Related Documents  
Related Topic  
Document Title  
MPLS Label Distribution Protocol (LDP)  
MPLS Label Distribution Protocol  
Standards  
Standard  
None  
Title  
--  
MIBs  
MIB  
MIBs Link  
LDP Specification, draft-ietf-mpls-ldp-08.txt  
To locate and download MIBs for selected  
platforms, Cisco IOS releases, and feature sets, use  
Cisco MIB Locator found at the following URL:  
RFCs  
RFC  
Title  
RFC 3036  
RFC 3037  
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MPLS LDP Inbound Label Binding Filtering  
Feature Information for MPLS LDP Inbound Label Binding Filtering Feature  
Technical Assistance  
Description  
Link  
The Cisco Technical Support website contains  
thousands of pages of searchable technical content,  
including links to products, technologies, solutions,  
technical tips, and tools. Registered Cisco.com  
users can log in from this page to access even more  
content.  
Feature Information for MPLS LDP Inbound Label Binding  
Filtering Feature  
The following table provides release information about the feature or features described in this module.  
This table lists only the software release that introduced support for a given feature in a given software  
release train. Unless noted otherwise, subsequent releases of that software release train also support that  
feature.  
Use Cisco Feature Navigator to find information about platform support and Cisco software image support.  
To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.  
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MPLS LDP Inbound Label Binding Filtering  
Glossary  
Table 3  
Feature Information for MPLS LDP Inbound Label Binding Filtering Feature  
Feature Name  
Releases  
Feature Information  
MPLS LDP Inbound Label  
Binding Filtering Feature  
12.0(26)S  
12.2(25)S  
12.3(14)T  
12.2(18)SXE  
You can use the MPLS LDP  
Inbound Label Binding Filtering  
feature to configure access  
control lists (ACLs) for  
controlling the label bindings a  
label switch router (LSR) accepts  
from its peer LSRs.  
In Cisco IOS Release 12.0(26)S,  
this feature was introduced on the  
Cisco 7200.  
This feature was integrated into  
Cisco IOS Release 12.2(25)S for  
the Cisco 7500 series router.  
This feature was integrated into  
Cisco IOS Release 12.3(14)T.  
This feature was integrated into  
Cisco IOS Release 12.2(18)SXE  
for the Cisco 7600 series router.  
The following commands were  
introduced or modified:  
clear mpls ldp neighbor  
mpls ldp neighbor labels  
accept  
show mpls ldp neighbor  
Glossary  
carrier supporting carrier --A situation where one service provider allows another service provider to use  
a segment of its backbone network. The service provider that provides the segment of the backbone  
network to the other provider is called the backbone carrier. The service provider that uses the segment of  
the backbone network is called the customer carrier.  
CE router --customer edge router. A router that is part of a customer network and that interfaces to a  
provider edge (PE) router.  
inbound label binding filtering --Allows LSRs to control which label bindings it will accept from its  
neighboring LSRs. Consequently, an LSR does not accept or store some label bindings that its neighbors  
advertise.  
label --A short fixed-length identifier that tells switching nodes how to forward data (packets or cells).  
label binding --An association between a destination prefix and a label.  
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MPLS LDP Inbound Label Binding Filtering  
Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S.  
and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks.  
Third-party trademarks mentioned are the property of their respective owners. The use of the word partner  
does not imply a partnership relationship between Cisco and any other company. (1110R)  
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be  
actual addresses and phone numbers. Any examples, command display output, network topology diagrams,  
and other figures included in the document are shown for illustrative purposes only. Any use of actual IP  
addresses or phone numbers in illustrative content is unintentional and coincidental.  
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Verifying that MPLS LDP Inbound Label Bindings are Filtered  
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50  
MPLS LDP Autoconfiguration  
The MPLS LDP Autoconfiguration feature enables you to globally configure Label Distribution Protocol  
(LDP) on every interface associated with a specified Interior Gateway Protocol (IGP) instance.  
Finding Feature Information  
Your software release may not support all the features documented in this module. For the latest feature  
information and caveats, see the release notes for your platform and software release. To find information  
about the features documented in this module, and to see a list of the releases in which each feature is  
supported, see the Feature Information Table at the end of this document.  
Use Cisco Feature Navigator to find information about platform support and Cisco software image support.  
To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.  
Restrictions for MPLS LDP Autoconfiguration  
In Cisco IOS Release 12.0(32)SY, the mpls ldp autoconfig command is supported only with OSPF.  
Other IGPs are not supported.  
If LDP is disabled globally, the mpls ldp autoconfigcommand fails and generates a console message  
explaining that LDP must first be enabled globally by means of the global mpls ip command.  
If the mpls ldp autoconfig command is configured for an IGP instance, you cannot issue the global no  
mpls ip command. To disable LDP, you must first issue the no mpls ldp autoconfig command.  
For interfaces running IS-IS processes, you can enable Multiprotocol Label Switching (MPLS) for  
each interface, using the router mode command mpls ldp autoconfig or mpls ldp igp autoconfig at  
the interface level.  
You specify that the default label distribution protocol is LDP for a router or for an interface. Tag  
Distribution Protocol (TDP) is not supported.  
The MPLS LDP Autoconfiguration feature is not supported on traffic engineering tunnel interfaces.  
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MPLS LDP Autoconfiguration on OSPF and IS-IS Interfaces  
Information About MPLS LDP Autoconfiguration  
Information About MPLS LDP Autoconfiguration  
To enable LDP, you should configure it globally and on each interface where it is needed. Configuring  
LDP on many interfaces can be time-consuming. The following section provides information about  
autoconfiguration feature on OSPF and IS-IS interfaces:  
MPLS LDP Autoconfiguration on OSPF and IS-IS Interfaces  
The MPLS LDP Autoconfiguration feature enables you to globally enable LDP on every interface  
associated with an IGP instance. This feature is supported on OSPF and IS-IS IGPs. It provides a means to  
block LDP from being enabled on interfaces that you do not want enabled. The goal of the MPLS LDP  
Autoconfiguration feature is to make configuration easier, faster, and error free.  
You issue the mpls ldp autoconfigcommand to enable LDP on each interface that is running an OSPF or  
IS-IS process. If you do not want some of the interfaces to have LDP enabled, you can issue the no form of  
the mpls ldp igp autoconfig command on those interfaces.  
How to Configure MPLS LDP Autoconfiguration  
Configuring MPLS LDP Autoconfiguration with OSPF Interfaces  
The following steps explain how to configure LDP for interfaces running OSPF processes.  
SUMMARY STEPS  
1.  
enable  
2.  
configure terminal  
mpls ip  
3.  
4.  
mpls label protocol ldp  
interface type number  
ip address prefix mask  
exit  
5.  
6.  
7.  
8.  
router ospf process-id  
network ip-address wildcard-mask area area-id  
mpls ldp autoconfig [area area-id]  
end  
9.  
10.  
11.  
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MPLS LDP Autoconfiguration  
How to Configure MPLS LDP Autoconfiguration  
DETAILED STEPS  
Command or Action  
Purpose  
Enables privileged EXEC mode.  
Enter your password if prompted.  
Step 1  
Step 2  
Step 3  
Step 4  
Step 5  
Step 6  
enable  
Example:  
Router> enable  
configure terminal  
Enters global configuration mode.  
Example:  
Router# configure terminal  
Globally enables hop-by-hop forwarding.  
Specifies LDP as the default label distribution protocol.  
mpls ip  
Example:  
Router(config)# mpls ip  
mpls label protocol ldp  
Example:  
Router(config)# mpls label protocol ldp  
interface type number  
Specifies the interface to configure and enters interface  
configuration mode.  
Example:  
Router(config)# interface POS 3/0  
ip address prefix mask  
Assigns an IP address to the interface.  
Exits interface configuration mode.  
Example:  
Router(config-if)# ip address 10.0.0.11  
255.255.255.255  
Step 7  
exit  
Example:  
Router(config-if)# exit  
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Disabling MPLS LDP Autoconfiguration from Selected OSPF Interfaces  
How to Configure MPLS LDP Autoconfiguration  
Command or Action  
Purpose  
Step 8  
Step 9  
Enables OSPF routing and enters router configuration mode.  
router ospf process-id  
Example:  
Router(config)# router ospf 1  
network ip-address wildcard-mask area area-id  
Specifies the interface on which OSPF runs and defines the  
area ID for that interface.  
Example:  
Router(config-router)# network 10.0.0.0  
0.0.255.255 area 3  
Step 10  
Step 11  
Enables the MPLS LDP Autoconfiguration feature to enable  
LDP on interfaces belonging to an OSPF process.  
mpls ldp autoconfig [area area-id]  
If no area is specified, the command applies to all  
interfaces associated with the OSPF process. If an area  
ID is specified, then only interfaces associated with that  
OSPF area are enabled with LDP.  
Example:  
Router(config-router)# mpls ldp autoconfig  
area 3  
Exits router configuration mode and returns to privileged  
EXEC mode.  
end  
Example:  
Router(config-router)# end  
Disabling MPLS LDP Autoconfiguration from Selected OSPF Interfaces  
When you issue the mpls ldp autoconfig command, all the interfaces that belong to an OSPF area are  
enabled for LDP. To remove LDP from some interfaces, use the no mpls ldp igp autoconfigcommand on  
those interfaces. The following configuration steps show how to disable LDP from some of the interfaces  
after they were configured with the MPLS LDP Autoconfiguration feature with the mpls ldp autoconfig  
command.  
SUMMARY STEPS  
1.  
2.  
3.  
4.  
5.  
enable  
configure terminal  
interface type number  
no mpls ldp igp autoconfig  
end  
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Verifying MPLS LDP Autoconfiguration with OSPF  
How to Configure MPLS LDP Autoconfiguration  
DETAILED STEPS  
Command or Action  
Purpose  
Enables privileged EXEC mode.  
Enter your password if prompted.  
Step 1  
Step 2  
Step 3  
Step 4  
Step 5  
enable  
Example:  
Router> enable  
configure terminal  
Enters global configuration mode.  
Example:  
Router# configure terminal  
interface type number  
Specifies the interface to configure and enters interface  
configuration mode.  
Example:  
Router(config)# interface POS 3/0  
no mpls ldp igp autoconfig  
Disables LDP for that interface.  
Example:  
Router(config-if)# no mpls ldp igp autoconfig  
Exits interface configuration mode and returns to privileged EXEC  
mode.  
end  
Example:  
Router(config-if)# end  
Verifying MPLS LDP Autoconfiguration with OSPF  
The following steps explain how to verify the MPLS LDP Autoconfiguration feature.  
SUMMARY STEPS  
1.  
2.  
3.  
enable  
show mpls interfaces [type number | vrf vpn-name][all] [detail] [internal]  
show mpls ldp discovery [vrf vpn-name | all] [detail]  
DETAILED STEPS  
Step 1  
enable  
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MPLS LDP Autoconfiguration  
How to Configure MPLS LDP Autoconfiguration  
Enables privileged EXEC mode. Enter your password if prompted.  
Step 2  
show mpls interfaces [type number | vrf vpn-name][all] [detail] [internal]  
The show mpls interfaces command displays the method used to enable LDP on an interface:  
If LDP is enabled by the mpls ldp autoconfigcommand, the output displays:  
Example:  
IP labeling enabled (ldp):  
IGP config  
If LDP is enabled by the mpls ip command, the output displays:  
Example:  
IP labeling enabled (ldp):  
Interface config  
If LDP is enabled by the mpls ip command and the mpls ldp autoconfig command, the output displays:  
Example:  
IP labeling enabled (ldp):  
Interface config  
IGP config  
The following example shows that LDP was enabled on the interface by both the mpls ip and mpls ldp autoconfig  
commands:  
Example:  
Router# show mpls interfaces Serial 2/0 detail  
Interface Serial2/0:  
IP labeling enabled (ldp):  
Interface config  
IGP config  
LSP Tunnel labeling enabled  
BGP labeling not enabled  
MPLS operational  
Fast Switching Vectors:  
IP to MPLS Fast Switching Vector  
MPLS Turbo Vector  
MTU = 1500  
Step 3  
show mpls ldp discovery [vrf vpn-name | all] [detail]  
The show mpls ldp discovery detailcommand alsoshows how LDP was enabled on the interface. In the following  
example, LDP was enabled by both the mpls ip and mpls ldp autoconfig commands:  
Example:  
Router# show mpls ldp discovery detail  
Local LDP Identifier:  
10.11.11.11:0  
Discovery Sources:  
Interfaces:  
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Configuring MPLS LDP Autoconfiguration with IS-IS Interfaces  
How to Configure MPLS LDP Autoconfiguration  
Serial2/0 (ldp): xmit/recv  
Enabled: Interface config, IGP config;  
Hello interval: 5000 ms; Transport IP addr: 10.11.11.11  
LDP Id: 10.10.10.10:0  
Src IP addr: 10.0.0.1; Transport IP addr: 10.10.10.10  
Hold time: 15 sec; Proposed local/peer: 15/15 sec  
Configuring MPLS LDP Autoconfiguration with IS-IS Interfaces  
The following steps explain how to configure the MPLS LDP Autoconfiguration feature for interfaces that  
are running IS-IS processes.  
SUMMARY STEPS  
1.  
enable  
2.  
configure terminal  
interface type number  
ip address prefix mask  
ip router isis  
3.  
4.  
5.  
6.  
exit  
7.  
mpls ip  
8.  
mpls label protocol ldp  
router isis  
9.  
10.  
11.  
mpls ldp autoconfig [level-1 | level-2]  
end  
DETAILED STEPS  
Command or Action  
Purpose  
Step 1  
Enables privileged EXEC mode.  
enable  
Enter your password if prompted.  
Example:  
Router> enable  
configure terminal  
Step 2  
Enters global configuration mode.  
Example:  
Router# configure terminal  
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MPLS LDP Autoconfiguration  
How to Configure MPLS LDP Autoconfiguration  
Command or Action  
Purpose  
Step 3  
Step 4  
Step 5  
Step 6  
Step 7  
Step 8  
Step 9  
Specifies the interface to configure and enters interface  
configuration mode.  
interface type number  
Example:  
Router(config)# interface POS 0/2  
ip address prefix mask  
Assigns an IP address to the interface.  
Enables IS-IS for IP on the interface.  
Example:  
Router(config-if)# ip address 10.50.72.4 255.0.0.0  
ip router isis  
Example:  
Router(config-if)# ip router isis  
Exits interface configuration mode.  
exit  
Example:  
Router(config-if)# exit  
mpls ip  
Globally enables hop-by-hop forwarding.  
Specifies LDP as the default label distribution protocol.  
Example:  
Router(config)# mpls ip  
mpls label protocol ldp  
Example:  
Router(config)# mpls label protocol ldp  
Enables an IS-IS process on the router and enters router  
configuration mode.  
router isis  
Example:  
Router(config)# router isis  
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Disabling MPLS LDP Autoconfiguration from Selected IS-IS Interfaces  
How to Configure MPLS LDP Autoconfiguration  
Command or Action  
Purpose  
Step 10  
Enables the LDP for interfaces that belong to an IS-IS  
process.  
mpls ldp autoconfig [level-1 | level-2]  
Example:  
Router(config-router)# mpls ldp autoconfig  
Step 11  
Exits router configuration mode and returns to privileged  
EXEC mode.  
end  
Example:  
Router(config-router)# end  
Disabling MPLS LDP Autoconfiguration from Selected IS-IS Interfaces  
When you issue the mpls ldp autoconfig command, all the interfaces that belong to an IS-IS process are  
enabled for LDP. To remove LDP from some interfaces, use the no mpls ldp igp autoconfig command on  
those interfaces. The following configuration steps show how to disable LDP from some of the interfaces  
after they were configured with the MPLS LDP Autoconfiguration feature with the mpls ldp autoconfig  
command.  
SUMMARY STEPS  
1.  
2.  
3.  
4.  
5.  
enable  
configure terminal  
interface type number  
no mpls ldp igp autoconfig  
end  
DETAILED STEPS  
Command or Action  
Purpose  
Step 1  
Enables privileged EXEC mode.  
enable  
Enter your password if prompted.  
Example:  
Router> enable  
configure terminal  
Step 2  
Enters global configuration mode.  
Example:  
Router# configure terminal  
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Verifying MPLS LDP Autoconfiguration with IS-IS  
How to Configure MPLS LDP Autoconfiguration  
Command or Action  
Purpose  
Step 3  
Step 4  
Step 5  
Specifies the interface to configure and enters interface  
configuration mode.  
interface type number  
Example:  
Router(config)# interface POS 3/0  
no mpls ldp igp autoconfig  
Disables LDP for that interface.  
Example:  
Router(config-if)# no mpls ldp igp autoconfig  
Exits interface configuration mode and returns to privileged EXEC  
mode.  
end  
Example:  
Router(config-if)# end  
Verifying MPLS LDP Autoconfiguration with IS-IS  
You can verify that the MPLS LDP Autoconfiguration feature is working correctly with the show isis mpls  
ldp command.  
SUMMARY STEPS  
1.  
2.  
enable  
show isis mpls ldp  
DETAILED STEPS  
Step 1  
Step 2  
enable  
Enables privileged EXEC mode.  
show isis mpls ldp  
The output of the following show isis mpls ldp command shows that IS-IS is configured on the interface and that  
LDP is enabled:  
Example:  
Router# show isis mpls ldp  
Interface: POS0/2; ISIS tag null enabled  
ISIS is UP on interface  
AUTOCONFIG Information :  
LDP enabled: YES  
SYNC Information :  
Required: NO  
The output shows :  
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MPLS LDP Autoconfiguration with OSPF Example  
Troubleshooting Tips  
IS-IS is up.  
LDP is enabled.  
If the MPLS LDP Autoconfiguration feature is not enabled on an interface, the output looks like the following:  
Example:  
Interface: Ethernet0; ISIS tag null enabled  
ISIS is UP on interface  
AUTOCONFIG Information :  
LDP enabled: NO  
SYNC Information :  
Required: NO  
Troubleshooting Tips  
You can use the debug mpls ldp autoconfigcommand to display events that are related to the MPLS LDP  
Autoconfiguration feature.  
Configuration Examples for MPLS LDP Autoconfiguration  
The following sections show examples for the MPLS LDP Autoconfiguration feature with OSPF and IS-IS  
processes.  
MPLS LDP Autoconfiguration with OSPF Example  
The following configuration commands enable LDP for OSPF process 1 area 3. The mpls ldp autoconfig  
area 3 command and the OSPF network commands enable LDP on POS interfaces 0/0, 0/1, and 1/1. The  
no mpls ldp igp autoconfig command on POS interface 1/0 prevents LDP from being enabled on POS  
interface 1/0, even though OSPF is enabled for that interface.  
configure terminal  
interface POS 0/0  
ip address 10.0.0.1 255.0.0.0  
!
interface POS 0/1  
ip address 10.0.1.1 255.0.0.1  
!
interface POS 1/1  
ip address 10.1.1.1 255.255.0.0  
!
interface POS 1/0  
ip address 10.1.0.1 0.1.0.255  
exit  
!
router ospf 1  
network 10.0.0.0 0.0.255.255 area 3  
network 10.1.0.0 0.0.255.255 area 3  
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MPLS LDP Autoconfiguration with IS-IS Examples  
Additional References  
mpls ldp autoconfig area 3  
end  
interface POS 1/0  
no mpls ldp igp autoconfig  
MPLS LDP Autoconfiguration with IS-IS Examples  
The following example shows the configuration of the MPLS LDP Autoconfiguration feature on POS0/2  
and 0/3 interfaces, which are running IS-IS processes:  
configure terminal  
interface POS 0/2  
ip address 10.0.0.1 255.0.0.1  
ip router isis  
!
interface POS 0/3  
ip address 10.1.1.1 255.0.1.0  
ip router isis  
exit  
mpls ip  
mpls label protocol ldp  
router isis  
mpls ldp autoconfig  
Additional References  
The following sections provide references related to the MPLS LDP Autoconfiguration feature.  
Related Documents  
Related Topic  
Document Title  
MPLS commands  
Cisco IOS Multiprotocol Label Switching  
Command Reference  
MPLS LDP  
MPLS Label Distribution Protocol  
MPLS LDP-IGP Synchronization  
MPLS LDP Session Protection  
The MPLS LDP-IGP Synchronization feature  
The MPLS LDP Session Protection feature  
Configuring integrated IS-IS  
Integrated IS-IS Routing Protocol Overview  
Standards  
Standard  
Title  
No new or modified standards are supported by this --  
feature, and support for existing standards has not  
been modified by this feature  
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MPLS LDP Autoconfiguration  
Feature Information for MPLS LDP Autoconfiguration  
MIBs  
MIB  
MIBs Link  
MPLS LDP MIB  
To locate and download MIBs for selected  
platforms, Cisco IOS releases, and feature sets, use  
Cisco MIB Locator found at the following URL:  
RFCs  
RFC  
Title  
RFC 3036  
RFC 3037  
Technical Assistance  
Description  
Link  
The Cisco Support website provides extensive  
online resources, including documentation and tools  
for troubleshooting and resolving technical issues  
with Cisco products and technologies.  
To receive security and technical information about  
your products, you can subscribe to various  
services, such as the Product Alert Tool (accessed  
from Field Notices), the Cisco Technical Services  
Newsletter, and Really Simple Syndication (RSS)  
Feeds.  
Access to most tools on the Cisco Support website  
requires a Cisco.com user ID and password.  
Feature Information for MPLS LDP Autoconfiguration  
The following table provides release information about the feature or features described in this module.  
This table lists only the software release that introduced support for a given feature in a given software  
release train. Unless noted otherwise, subsequent releases of that software release train also support that  
feature.  
Use Cisco Feature Navigator to find information about platform support and Cisco software image support.  
To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.  
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MPLS LDP Autoconfiguration  
Table 4  
Feature Information for MPLS LDP Autoconfiguration  
Feature Name  
Releases  
Feature Information  
MPLS LDP Autoconfiguration  
12.0(30)S 12.0(32)SY  
12.2(28)SB 12.2(33)SRB  
12.3(14)T 15.0(1)M  
12.2(33)XNE  
This feature enables you to  
globally configure LDP on every  
interface associated with a  
specified Interior Gateway  
Protocol (IGP) instance.  
In Cisco IOS Release 12.0(30)S,  
this feature was introduced with  
support for OSPF.  
In Cisco IOS Release  
12.0(32)SY, support for IS-IS  
was added.  
This feature was integrated into  
Cisco IOS Release 12.2(28)SB  
with support for OSPF.  
This feature was integrated into  
Cisco IOS Release 12.2(33)SRB.  
This feature was integrated into  
Cisco IOS Release 12.3(14)T  
with support for OSPF.  
In Release 15.0(1)M, support for  
IS-IS was added.  
This feature was integrated into  
Cisco IOS Release 12.2(33)XNE  
with support for IS-IS on the  
Cisco 10000 series router.  
The following commands were  
modified: mpls ldp autoconfig,  
mpls ldp igp autoconfig, show  
isis mpls ldp, and show mpls ldp  
discovery.  
Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S.  
and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks.  
Third-party trademarks mentioned are the property of their respective owners. The use of the word partner  
does not imply a partnership relationship between Cisco and any other company. (1110R)  
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be  
actual addresses and phone numbers. Any examples, command display output, network topology diagrams,  
and other figures included in the document are shown for illustrative purposes only. Any use of actual IP  
addresses or phone numbers in illustrative content is unintentional and coincidental.  
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MPLS LDP Graceful Restart  
When a router is configured with Multiprotocol Label Switching (MPLS) Label Distribution Protocol  
(LDP) Graceful Restart (GR), it assists a neighboring router that has MPLS LDP Stateful Switchover/  
Nonstop Forwarding (SSO/NSF) Support and Graceful Restart to recover gracefully from an interruption  
in service. In this Cisco IOS release, MPLS LDP GR functions strictly in helper mode, which means it can  
only help other routers that are enabled with MPLS SSO/NSF and GR to recover. If the router with LDP  
GR fails, its peer routers cannot help it recover.  
Notes:  
MPLS LDP SSO/NSF Support and Graceful Restart is supported in Cisco IOS Release 12.2(25)S.  
For brevity, this feature is called LDP SSO/NSF in this document.  
The MPLS LDP GR feature described in this document refers to helper mode.  
When you enable MPLS LDP GR on a router that peers with an MPLS LDP SSO/NSF-enabled router, the  
SSO/NSF-enabled router can maintain its forwarding state when the LDP session between them is  
interrupted. While the SSO/NSF-enabled router recovers, the peer router forwards packets using stale  
information. This enables the SSO/NSF-enabled router to become operational more quickly.  
Finding Feature Information  
Your software release may not support all the features documented in this module. For the latest feature  
information and caveats, see the release notes for your platform and software release. To find information  
about the features documented in this module, and to see a list of the releases in which each feature is  
supported, see the Feature Information Table at the end of this document.  
Use Cisco Feature Navigator to find information about platform support and Cisco software image support.  
To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.  
Restrictions  
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How MPLS LDP Graceful Restart Works  
Information About MPLS LDP Graceful Restart  
MPLS LDP GR is supported in strict helper mode.  
Tag Distribution Protocol (TDP) sessions are not supported. Only LDP sessions are supported.  
MPLS LDP GR cannot be configured on label-controlled ATM (LC-ATM) interfaces.  
MPLS LDP SSO/NSF is supported in IOS Release 12.2(25)S. It is not supported in this release.  
Information About MPLS LDP Graceful Restart  
How MPLS LDP Graceful Restart Works  
MPLS LDP GR works in strict helper mode, which means it helps a neighboring route processor that has  
MPLS LDP SSO/NSF to recover from disruption in service without losing its MPLS forwarding state. The  
disruption in service could be the result of a TCP or UDP event or the stateful switchover of a route  
processor. When the neighboring router establishes a new session, the LDP bindings and MPLS forwarding  
states are recovered.  
In the topology shown in the figure below, the following elements have been configured:  
LDP sessions are established between Router 1 and Router 2, as well as between Router 2 and Router  
3.  
Router 2 has been configured with MPLS LDP SSO/NSF. Routers 1 and 3 have been configured with  
MPLS LDP GR.  
A label switched path (LSP) has been established between Router 1 and Router 3.  
Figure 4  
Example of a Network Using LDP Graceful Restart  
The following process shows how Routers 1 and 3, which have been configured with LDP GR help Router  
2, which has been configured with LDP SSO/NSF recover from a disruption in service:  
1
2
Router 1 notices an interruption in service with Router 2. (Router 3 also performs the same actions in  
this process.)  
Router 1 marks all the label bindings from Router 2 as stale, but it continues to use the bindings for  
MPLS forwarding.  
Router 1 reestablishes an LDP session with Router 2, but keeps its stale label bindings. If you issue a show  
mpls ldp neighbor command with the graceful-restart keyword, the command output displays the  
recovering LDP sessions.  
1
Both routers readvertise their label binding information. If Router 1 relearns a label from Router 2 after  
the session has been established, the stale flags are removed. The show mpls forwarding-  
tablecommand displays the information in the MPLS forwarding table, including the local label,  
outgoing label or VC, prefix, label-switched bytes, outgoing interface, and next hop.  
You can set various graceful restart timers. See the following commands for more information:  
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How a Route Processor Advertises That It Supports MPLS LDP Graceful Restart  
How to Configure MPLS LDP Graceful Restart  
mpls ldp graceful-restart timers neighbor-liveness  
mpls ldp graceful-restart timers max-recovery  
How a Route Processor Advertises That It Supports MPLS LDP Graceful  
Restart  
A route processor that is configured to perform MPLS LDP GR includes the Fault Tolerant (FT) Type  
Length Value (TLV) in the LDP initialization message. The route processor sends the LDP initialization  
message to a neighbor to establish an LDP session.  
The FT session TLV includes the following information:  
The Learn from Network (L) flag is set to 1, which indicates that the route processor is configured to  
perform MPLS LDP GR.  
The Reconnect Timeout field shows the time (in milliseconds) that the neighbor should wait for a  
reconnection if the LDP session is lost. In this release, the timer is set to 0, which indicates that if the  
local router fails, its peers should not wait for it to recover. The timer setting indicates that the local  
router is working in helper mode.  
The Recovery Time field shows the time (in milliseconds) that the neighbor should retain the MPLS  
forwarding state during a recovery. If a neighbor did not preserve the MPLS forwarding state before  
the restart of the control plane, the neighbor sets the recovery time to 0.  
What Happens If a Route Processor Does Not Have LDP Graceful Restart  
If two route processors establish an LDP session and one route processor is not configured for MPLS LDP  
GR, the two route processors create a normal LDP session but do not have the ability to perform MPLS  
LDP GR. Both route processors must be configured for MPLS LDP GR.  
How to Configure MPLS LDP Graceful Restart  
Configuring MPLS LDP Graceful Restart  
You must enable MPLS LDP GR on all route processors for an LDP session to be preserved during an  
interruption in service.  
MPLS LDP GR is enabled globally. When you enable MPLS LDP GR, it has no effect on existing LDP  
sessions. New LDP sessions that are established can perform MPLS LDP GR.  
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MPLS LDP Graceful Restart  
How to Configure MPLS LDP Graceful Restart  
SUMMARY STEPS  
1.  
2.  
3.  
4.  
5.  
6.  
7.  
enable  
configure terminal  
ip cef [distributed]  
mpls ldp graceful-restart  
interface type slot/port  
mpls ip  
mpls label protocol {ldp| tdp| both}  
DETAILED STEPS  
Command or Action  
Purpose  
Step 1  
Step 2  
Step 3  
Step 4  
Step 5  
Enables privileged EXEC mode.  
enable  
Enter your password if prompted.  
Example:  
Router> enable  
configure terminal  
Enters global configuration mode.  
Example:  
Router# configure terminal  
ip cef [distributed]  
Enables Cisco Express Forwarding (CEF).  
Example:  
Router(config)# ip cef distributed  
mpls ldp graceful-restart  
Enables the router to protect the LDP bindings and MPLS  
forwarding state during a disruption in service.  
Example:  
Router(config)# mpls ldp graceful-restart  
interface type slot/port  
Specifies an interface and enters interface configuration mode.  
Example:  
Router(config)# interface pos 3/0  
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Verifying the Configuration  
Configuration Example for MPLS LDP Graceful Restart  
Command or Action  
Purpose  
Step 6  
Configures MPLS hop-by-hop forwarding for an interface.  
mpls ip  
Example:  
Router(config-if)# mpls ip  
mpls label protocol {ldp| tdp| both}  
Step 7  
Configures the use of LDP for an interface. You must use LDP.  
Example:  
Router(config-if)# mpls label protocol ldp  
Note  
You can also issue the mpls label protocol ldp command in global configuration mode, which enables  
LDP on all interfaces configured for MPLS.  
Verifying the Configuration  
The following commands help verify that MPLS LDP GR has been configured correctly:  
Displays the Graceful Restart information for LDP  
show mpls ldp neighbor with the graceful-restart  
sessions.  
keyword  
Displays Graceful Restart sessions and session  
parameters.  
show mpls ldp graceful-restart  
Configuration Example for MPLS LDP Graceful Restart  
The figure below shows a configuration where MPLS LDP GR is enabled on Router 1 and MPLS LDP  
SSO/NSF is enabled on Routers 2 and 3. In this configuration example, Router 1 creates an LDP session  
with Router 2. Router 1 also creates a targeted session with Router 3 through a traffic engineering tunnel  
using Router 2.  
MPLS LDP SSO/NSF is supported in Cisco IOS Release 12.2(25)S. It is not supported in this release.  
Note  
Figure 5  
MPLS LDP Graceful Restart Configuration Example  
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MPLS LDP Graceful Restart  
Configuration Example for MPLS LDP Graceful Restart  
Router 1 configured with LDP GR:  
boot system slot0:rsp-pv-mz  
hw-module slot 2 image slot0:rsp-pv-mz  
hw-module slot 3 image slot0:rsp-pv-mz  
!
ip subnet-zero  
ip cef  
mpls label range 16 10000 static 10001 1048575  
mpls label protocol ldp  
mpls ldp logging neighbor-changes  
mpls ldp graceful-restart  
mpls traffic-eng tunnels  
no mpls traffic-eng auto-bw timers frequency 0  
mpls ldp router-id Loopback0 force  
!
interface Loopback0  
ip address 20.20.20.20 255.255.255.255  
no ip directed-broadcast  
no ip mroute-cache  
!
interface Tunnel1  
ip unnumbered Loopback0  
no ip directed-broadcast  
mpls label protocol ldp  
mpls ip  
tunnel destination 19.19.19.19  
tunnel mode mpls traffic-eng  
tunnel mpls traffic-eng autoroute announce  
tunnel mpls traffic-eng priority 7 7  
tunnel mpls traffic-eng bandwidth 500  
tunnel mpls traffic-eng path-option 1 dynamic  
!
interface ATM5/1/0  
no ip address  
no ip directed-broadcast  
atm clock INTERNAL  
no atm enable-ilmi-trap  
no atm ilmi-keepalive  
!
interface ATM5/1/0.5 point-to-point  
ip address 12.0.0.2 255.0.0.0  
no ip directed-broadcast  
no atm enable-ilmi-trap  
pvc 6/100  
encapsulation aal5snap  
mpls label protocol ldp  
mpls traffic-eng tunnels  
mpls ip  
ip rsvp bandwidth 1000  
!
router ospf 100  
log-adjacency-changes  
redistribute connected  
network 12.0.0.0 0.255.255.255 area 100  
network 20.20.20.20 0.0.0.0 area 100  
mpls traffic-eng router-id Loopback0  
mpls traffic-eng area 100  
Router 2 configured with LDP SSO/NSF:  
boot system slot0:rsp-pv-mz  
hw-module slot 2 image slot0:rsp-pv-mz  
hw-module slot 3 image slot0:rsp-pv-mz  
redundancy  
mode sso  
!
ip cef  
no ip domain-lookup  
mpls label range 17 10000 static 10001 1048575  
mpls label protocol ldp  
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MPLS LDP Graceful Restart  
Configuration Example for MPLS LDP Graceful Restart  
mpls ldp logging neighbor-changes  
mpls ldp graceful-restart  
mpls traffic-eng tunnels  
no mpls traffic-eng auto-bw timers frequency 0  
no mpls advertise-labels  
mpls ldp router-id Loopback0 force  
!
interface Loopback0  
ip address 17.17.17.17 255.255.255.255  
no ip directed-broadcast  
!
interface ATM4/0/0  
no ip address  
no ip directed-broadcast  
no ip mroute-cache  
atm clock INTERNAL  
atm sonet stm-1  
no atm enable-ilmi-trap  
no atm ilmi-keepalive  
!
interface ATM4/0/0.5 point-to-point  
ip address 12.0.0.1 255.0.0.0  
no ip directed-broadcast  
no atm enable-ilmi-trap  
pvc 6/100  
encapsulation aal5snap  
mpls label protocol ldp  
mpls traffic-eng tunnels  
mpls ip  
ip rsvp bandwidth 1000  
!
interface POS5/1/0  
ip address 11.0.0.1 255.0.0.0  
no ip directed-broadcast  
encapsulation ppp  
mpls label protocol ldp  
mpls traffic-eng tunnels  
mpls ip  
no peer neighbor-route  
clock source internal  
ip rsvp bandwidth 1000  
!
router ospf 100  
log-adjacency-changes  
redistribute connected  
nsf enforce global  
network 11.0.0.0 0.255.255.255 area 100  
network 12.0.0.0 0.255.255.255 area 100  
network 17.17.17.17 0.0.0.0 area 100  
mpls traffic-eng router-id Loopback0  
mpls traffic-eng area 100  
!
ip classless  
Router 3 configured with LDP SSO/NSF:  
boot system slot0:rsp-pv-mz  
hw-module slot 2 image slot0:rsp-pv-mz  
hw-module slot 3 image slot0:rsp-pv-mz  
redundancy  
mode sso  
!
ip subnet-zero  
ip cef  
!
no ip finger  
no ip domain-lookup  
mpls label protocol ldp  
mpls ldp neighbor 11.11.11.11 targeted ldp  
mpls ldp logging neighbor-changes  
mpls ldp graceful-restart  
mpls traffic-eng tunnels  
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MPLS LDP Graceful Restart  
Additional References  
no mpls traffic-eng auto-bw timers frequency 0  
mpls ldp discovery directed-hello interval 12  
mpls ldp discovery directed-hello holdtime 130  
mpls ldp discovery directed-hello accept  
mpls ldp router-id Loopback0 force  
!
interface Loopback0  
ip address 19.19.19.19 255.255.255.255  
no ip directed-broadcast  
!
interface POS1/0  
ip address 11.0.0.2 255.0.0.0  
no ip directed-broadcast  
encapsulation ppp  
mpls label protocol ldp  
mpls traffic-eng tunnels  
mpls ip  
no peer neighbor-route  
clock source internal  
ip rsvp bandwidth 1000  
!
router ospf 100  
log-adjacency-changes  
redistribute connected  
nsf enforce global  
network 11.0.0.0 0.255.255.255 area 100  
network 19.19.19.19 0.0.0.0 area 100  
mpls traffic-eng router-id Loopback0  
mpls traffic-eng area 100  
!
ip classless  
Additional References  
Related Documents  
Related Topic  
Document Title  
MPLS Label Distribution Protocol  
Standards  
Standards  
None  
Title  
MIBs  
MIBs1  
MIBs Link  
To locate and download MIBs for selected  
platforms, Cisco IOS releases, and feature sets, use  
Cisco MIB Locator found at the following URL:  
MPLS Label Distribution Protocol MIB  
Version 8 Upgrade  
1
Not all supported MIBs are listed.  
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MPLS LDP Graceful Restart  
Feature Information for MPLS LDP Graceful Restart  
RFCs  
RFCs2  
Title  
RFC 3036  
LDP Specification  
RFC 3478  
Graceful Restart Mechanism for Label Distribution  
Technical Assistance  
Description  
Link  
The Cisco Technical Support & Documentation  
website contains thousands of pages of searchable  
technical content, including links to products,  
technologies, solutions, technical tips, and tools.  
Registered Cisco.com users can log in from this  
page to access even more content.  
Feature Information for MPLS LDP Graceful Restart  
The following table provides release information about the feature or features described in this module.  
This table lists only the software release that introduced support for a given feature in a given software  
release train. Unless noted otherwise, subsequent releases of that software release train also support that  
feature.  
Use Cisco Feature Navigator to find information about platform support and Cisco software image support.  
To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.  
2
Not all supported RFCs are listed.  
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MPLS LDP Graceful Restart  
Table 5  
Feature Information for MPLS LDP Graceful Restart  
Feature Name  
Releases  
Feature Information  
MPLS LDP Graceful Restart  
12.0(29)S 12.3(14)T  
12.2(33)SRA  
MPLS LDP Graceful Restart  
assists a neighboring router that  
has MPLS LDP Stateful  
Switchover/Nonstop Forwarding  
(SSO/NSF) Support and Graceful  
Restart to recover gracefully from  
an interruption in service.  
In Cisco IOS Release 12.0(29)S,  
this feature was introduced.  
This feature was integrated into  
Cisco IOS Release 12.3(14)T.  
This feature was integrated into  
Cisco IOS Release 12.2(33)SRA.  
The following sections provide  
information about this feature:  
The following commands were  
introduced or modified:  
debug mpls ldp graceful-  
restart  
mpls ldp graceful-restart  
mpls ldp graceful-restart  
timers max-recovery  
mpls ldp graceful-restart  
timers neighbor-liveness  
show mpls ip binding  
show mpls ldp bindings  
show mpls ldp graceful-  
restart  
show mpls ldp neighbor  
Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S.  
and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks.  
Third-party trademarks mentioned are the property of their respective owners. The use of the word partner  
does not imply a partnership relationship between Cisco and any other company. (1110R)  
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be  
actual addresses and phone numbers. Any examples, command display output, network topology diagrams,  
and other figures included in the document are shown for illustrative purposes only. Any use of actual IP  
addresses or phone numbers in illustrative content is unintentional and coincidental.  
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