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The MPLS LDP Session Protection feature provides faster Label Distribution Protocol (LDP) convergence when a link recovers following an outage. MPLS LDP Session Protection protects an LDP session between directly connected neighbors or an LDP session established for a traffic engineering (TE) tunnel.
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and 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 module.
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Label switch routers (LSRs) must be able to respond to Label Distribution Protocol (LDP) targeted hellos. Otherwise, the LSRs cannot establish a targeted adjacency. All devices that participate in MPLS LDP Session Protection must be enabled to respond to targeted hellos. Both neighbor devices must be configured for session protection or one device must be configured for session protection and the other device must be configured to respond to targeted hellos.
The MPLS LDP Session Protection feature is not supported under the following circumstances:
MPLS LDP Session Protection maintains Label Distribution Protocol (LDP) bindings when a link fails. MPLS LDP sessions are protected through the use of LDP hello messages. When you enable Multiprotocol Label Switching (MPLS) LDP, the label switch routers (LSRs) send messages to find other LSRs with which they can create LDP sessions.
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 devices on the subnet. The hello message is called an LDP Link Hello. A neighboring LSR responds to the hello message, and the two devices 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 specific LSR. The hello message is called an LDP Targeted Hello. The nondirectly connected LSR responds to the Hello message and the two devices 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. For example, two directly connected devices have LDP enabled and can reach each other through alternate IP routes in the network. An LDP session that exists between two devices 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 devices 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 devices. 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.
You can modify MPLS LDP Session Protection by using keywords in the mpls ldp session protection command. The following sections explain how to customize the feature:
The default behavior of the mpls ldp session protection command allows a Label Distribution Protocol (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 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.
The default behavior of the mpls ldp session protection command allows MPLS LDP Session Protection for all neighbor sessions. You can issue either the vrf or for keyword to limit the number of neighbor sessions that are protected:
1. enable
2. configure terminal
3. ip cef [distributed]
4. interface loopback number
5. ip address prefix mask
6. exit
7. interface type number
8. mpls ip
9. mpls label protocol [ldp | tdp | both]
10. exit
11. mpls ldp session protection [vrf vpn-name] [for acl] [duration {infinite | seconds}]
12. exit
Use the clear mpls ldp neighbor command if you need to terminate a Label Distribution Protocol (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 protection command.
1. enable
2. show mpls ldp discovery
3. show mpls ldp neighbor
4. show mpls ldp neighbor detail
5. exit
The figure below shows a sample configuration for MPLS LDP Session Protection.
The following configuration examples for R1, R2, and R3 are based on the figure above.
redundancy no keepalive-enable 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 mpls ldp 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 FastEthernet1/0/0 ip address 10.3.123.1 255.255.0.0 no ip directed-broadcast ! interface FastEthernet2/0/0 no ip address no ip directed-broadcast shutdown ! interface FastEthernet2/0/1 description -- ip address 10.0.0.2 255.255.255.0 no ip address no ip directed-broadcast shutdown ! interface FastEthernet2/0/2 ip address 10.0.0.1 255.0.0.0 no ip directed-broadcast mpls label protocol ldp mpls ip ! interface FastEthernet2/1/2 ip address 10.0.0.1 255.0.0.0 no ip directed-broadcast mpls label protocol ldp mpls ip ! interface FastEthernet2/2/2 ip address 10.0.0.1 255.0.0.0 no ip directed-broadcast mpls label protocol ldp mpls 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
redundancy no keepalive-enable mode hsa ! ip subnet-zero ip cef distributed mpls label protocol ldp mpls ldp session protection no mpls traffic-eng auto-bw timers frequency 0 mpls ldp router-id Loopback0 force ! interface Loopback0 ip address 10.0.0.3 255.255.255.255 no ip directed-broadcast ! interface FastEthernet0/1/0 no ip address no ip directed-broadcast shutdown full-duplex ! interface FastEthernet0/1/2 ip address 10.0.0.1 255.0.0.0 no ip directed-broadcast full-duplex mpls label protocol ldp mpls ip ! interface FastEthernet0/1/1 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 mpls ip ! interface FastEthernet0/2/0 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
ip cef distributed 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 mpls ldp router-id Loopback0 force ! interface Loopback0 ip address 10.0.0.5 255.255.255.255 no ip directed-broadcast ! interface FastEthernet1/0/0 no ip address no ip directed-broadcast shutdown half-duplex ! interface FastEthernet1/2/0 ip address 10.0.0.2 255.0.0.0 no ip directed-broadcast full-duplex mpls label protocol ldp mpls ip ! interface FastEthernet1/3/0 ip address 10.0.0.2 255.0.0.0 no ip directed-broadcast full-duplex mpls label protocol ldp mpls 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
Related Topic |
Document Title |
---|---|
Cisco IOS commands |
|
MPLS commands |
|
MPLS LDP |
“MPLS Label Distribution Protocol” module in the MPLS Label Distribution Protocol Configuration Guide |
MPLS LDP IGP synchronization |
“MPLS LDP IGP Synchronization” module in the MPLS Label Distribution Protocol Configuration Guide |
MPLS LDP Autoconfiguration |
“MPLS LDP Autoconfiguration” module in the MPLS Label Distribution Protocol Configuration Guide |
MIBs |
MIBs Link |
---|---|
MPLS LDP MIB |
To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFCs |
Title |
---|---|
RFC 3036 |
|
RFC 3037 |
Description |
Link |
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The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
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.
Feature Name |
Releases |
Feature Information |
---|---|---|
MPLS LDP Session Protection |
12.0(30)S 12.2(27)SBA 12.2(33)SRA 12.2(33)SXH 12.3(14)T Cisco IOS XE Release 2.1 |
The MPLS LDP Session Protection feature provides faster Label Distribution Protocol (LDP) convergence when a link recovers following an outage. MPLS LDP Session Protection protects an LDP session between directly connected neighbors or an LDP session established for a traffic engineering (TE) tunnel. In Cisco IOS Release 12.0(30)S, this feature was introduced on the Cisco 7200 series routers. In Cisco IOS Release 12.2(27)SBA, this feature was implemented on the Cisco 10000 and 7500 series routers. In Cisco IOS Release 12.2(33)SRA, this feature was implemented on the Cisco 7600 series routers. In Cisco IOS Release 12.2(33)SXH, this feature was implemented on the Cisco 6500 series routers. In Cisco IOS Release 12.3(14)T, this feature was integrated. In Cisco IOS XE Release 2.1, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers. The following commands were introduced or modified: debug mpls ldp session protection, mpls ldp session protection, show mpls ldp neighbor. |