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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.
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This feature is not supported under the following circumstances:
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.
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.
You can modify MPLS LDP Session Protection by using the keywords in the mpls ldp session protection command.
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.
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.
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.
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.
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 vrf keyword 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.
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 protection command.
The figure below shows a sample configuration for MPLS LDP Session Protection.
Figure 1 | MPLS LDP Session Protection Example |
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 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
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 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
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 ! 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
Related Topic |
Document Title |
---|---|
MPLS LDP |
MPLS Label Distribution Protocol |
MPLS LDP-IGP synchronization |
MPLS LDP-IGP Synchronization |
LDP autoconfiguration |
LDP Autoconfiguration |
Standards |
Title |
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None |
-- |
MIBs |
MIBs Link |
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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 |
Title |
---|---|
RFC 3036 |
|
RFC 3037 |
Description |
Link |
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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 Reference at http://www.cisco.com/en/US/docs/ios/mpls/command/reference/mp_book.html . For 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.
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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.