Configuring LSQ Interface Redundancy Across Multiple Routers Using SONET APS

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Link services IQ (lsq-) interfaces that are paired with SONET PICs can use the Automatic Protection Switching (APS) configuration already available on SONET networks to provide failure recovery. SONET APS provides stateless failure recovery, if it is configured on SONET interfaces in separate chassis and each SONET PIC is paired with an AS or MultiServices PIC in the same chassis. If one of the following conditions for APS failure is met, the associated SONET PIC triggers recovery to the backup circuit and its associated AS or MultiServices PIC. The failure conditions are:

Failure of Link Services IQ PIC
Failure of FPC that hosts the Link Services IQ PIC
Failure of Packet Forwarding Engine
Failure of chassis

The guidelines for configuring SONET APS are described in the JUNOS Network Interfaces Configuration Guide.

The following sections describe how to configure failover properties:

Configuring the Association between LSQ and SONET Interfaces

To configure the association between AS or MultiServices PICs hosting link services IQ interfaces and the SONET interfaces, include the lsq-failure-options statement at the [edit interfaces] hierarchy level:


            
               lsq-fpc/pic/port {
               
               
                  
                     lsq-failure-options {
                     
                     no-termination-request;
                     
                     [ trigger-link-failure interface-name ];
                     
                     }
                  
               
               }

For example, consider the following network scenario:

Primary router includes interfaces oc3-0/2/0 and lsq-1/1/0.
Backup router includes interfaces oc3-2/2/0 and lsq-3/2/0.

Configure SONET APS, with oc3-0/2/0 as the working circuit and oc3-2/2/0 as the protect circuit. Include the trigger-link-failure statement to extend failure to the LSQ PICs:


            
               interfaces lsq-1/1/0 {
               
                  
                     lsq-failure-options {
                     trigger-link-failure oc3-0/2/0;
                     }
                  
               
               }

Note: You must configure the lsq-failure-options statement on the primary router only. The configuration is not supported on the backup router.

To inhibit the router from sending PPP termination-request messages to the remote host if the Link Services IQ PIC fails, include the no-termination-request statement at the [edit interfaces lsq-fpc/pic/port lsq-failure-options] hierarchy level:


            
               [edit interfaces lsq-fpc/pic/port lsq-failure-options]
               
               no-termination-request;

This functionality is supported on link PICs as well. To inhibit the router from sending PPP termination-request messages to the remote host if a link PIC fails, include the no-termination-request statement at the [edit interfaces interface-name ppp-options] hierarchy level.


            
               [edit interfaces interface-name ppp-options]
               
               no-termination-request;

The no-termination-request statement is supported only with MLPPP and SONET APS configurations and works with PPP, PPP over Frame Relay, and MLPPP interfaces only, on the following PICs:

Channelized OC3 IQ PICs
Channelized OC12 IQ PICs
Channelized STM1 IQ PICs
Channelized STM4 IQ PICs

Configuring SONET APS Interoperability with Cisco Systems FRF.16

Juniper Networks routers configured with APS might not interoperate correctly with Cisco FRF.16. To enable interoperation, include the cisco-interoperability statement at the [edit interfaces lsq-fpc/pic/port mlfr-uni-nni-bundle-options] hierarchy level:


            
               [edit interfaces lsq-fpc/pic/port mlfr-uni-nni-bundle-options]
               
               cisco-interoperability send-lip-remove-link-for-link-reject;

The send-lip-remove-link-for-link-reject option prompts the router to send a Link Integrity Protocol remove link when it receives an add-link rejection message.

Restrictions on APS Redundancy for LSQ Interfaces

The following restrictions apply to LSQ failure recovery:

It applies only to Link Services IQ PICs installed in M-series routing platforms, except for M320 routers.
You must configure the failure-options statement on physical LSQ interfaces, not on MLFR channelized units.
The Link Services IQ PICs must be associated with SONET link PICs. The paired PICs can be installed on different routers or in the same router; in other words, both interchassis and intrachassis recovery are supported
Failure recovery is stateless; as a result, route flapping and loss of link state is expected in interchassis recovery, requiring PPP renegotiation. In intrachassis recovery, no impact on traffic is anticipated with Routing Engine failover, but PIC failover results in PPP renegotiation.
The switchover is not revertive: when the original hardware is restored to service, traffic does not automatically revert back to it.

Normal APS switchover and PIC-triggered APS switchover can be distinguished only by checking the system log messages.

Note: When an AS PIC experiences persistent back pressure as a result of high traffic volume for 3 seconds, the condition triggers an automatic core dump and reboot of the PIC to help clear the blockage. A system log message at level LOG_ERR is generated. This mechanism applies to both Layer 2 and Layer 3 service packages.

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