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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.
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 for MPLS LDP Session Protection" section.
Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
•Prerequisites for MPLS LDP Session Protection
•Restrictions for MPLS LDP Session Protection
•Information About MPLS LDP Session Protection
•How to Configure MPLS LDP Session Protection
•Configuration Examples for MPLS LDP Session Protection
•Feature Information for MPLS LDP Session Protection
Label switch routers (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.
This feature is not supported under the following circumstances:
•With extended access lists
•With LC-ATM routers
Before you configure the MPLS LDP Session Protection feature, you should understand the following:
•How MPLS LDP Session Protection Works
•MPLS LDP Session Protection Customization
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 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 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 specific 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. For example, two directly connected routers 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 keywords in the mpls ldp session protection command. The following sections explain how to customize the feature:
•How Long an LDP Targeted Hello Adjacency Should Be Retained
•Which Routers Should Have MPLS LDP Session Protection
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 vrf or for keyword to limit the number of neighbor sessions that are protected:
•You can use the vrf keyword to select which VRF is to be protected, if the router is configured with at least one VPN routing and forwarding (VRF) instance, 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.
This section explains how to configure and verify MPLS LDP Session Protection:
•Enabling MPLS LDP Session Protection (required)
•Verifying MPLS LDP Session Protection (optional)
To enable MPLS LDP session protection, perform the following task.
1. enable
2. configure terminal
3. ip cef distributed
4. interface loop back number
5. ip address prefix mask
6. exit
7. interface type slot/subslot/port[.subinterface-number]
8. mpls ip
9. mpls label protocol ldp
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 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.
To verify that LDP Session Protection has been correctly configured, perform the following steps.
1. enable
2. show mpls ldp discovery
3. show mpls ldp neighbor
4. show mpls ldp neighbor detail
5. exit
Step 1 enable
Use this command to enable privileged EXEC mode. Enter your password, if prompted. For example:
Router> enable
Router#
Step 2 show mpls ldp discovery
Use this command to verify that the output contains the term xmit/recv for the peer router. For example:
Router# show mpls ldp discovery
Local LDP Identifier:
10.0.0.5:0
Discovery Sources:
Interfaces:
ATM50/1/0.5 (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 3 show mpls ldp neighbor
Use this command to verify that the targeted hellos are active. For 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
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 4 show mpls ldp neighbor detail
Use this command to verify 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. For 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
Step 5 exit
Use this command to exit to user EXEC. For example:
Router# exit
Router>
This section contains the following configuration example for MPLS LDP Session Protection:
•Configuring MPLS LDP Session Protection: Example
Figure 1 shows a sample configuration for MPLS LDP Session Protection.
Figure 1 MPLS LDP Session Protection Example
The following configuration examples for R1, R2, and R3 are based on Figure 1.
R1
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
R2
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
R3
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
The following sections provide references related to the MPLS LDP Session Protection feature.
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MPLS LDP |
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MPLS LDP-IGP synchronization |
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LDP autoconfiguration |
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MPLS LDP commands |
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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 MIB |
To locate and download MIBs for selected platforms, Cisco IOS XE software releases, and feature sets, use Cisco MIB Locator found at the following URL: |
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RFC 3036 |
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RFC 3037 |
Table 1 lists the features in this module and provides links to specific configuration information.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note Table 1 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.
|
|
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MPLS LDP Session Protection |
Cisco IOS XE Release 2.1 |
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. In Cisco IOS XE Release 2.1, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers. The following sections provide information about this feature: •How MPLS LDP Session Protection Works •MPLS LDP Session Protection Customization •Enabling MPLS LDP Session Protection •Verifying MPLS LDP Session Protection The following commands were introduced or modified: debug mpls ldp session protection, mpls ldp session protection, show mpls ldp neighbor. |