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Link PIC Redundancy

Link state replication, also called interface preservation, is an addition to the SONET Automatic Protection Switching (APS) functionality that helps promote redundancy of the link PICs used in LSQ configurations.

Link state replication provides the ability to add two sets of links, one from the active (working) SONET PIC and the other from the backup (protect) SONET PIC to the same bundle. If the active SONET PIC fails, links from the standby PIC are used without causing a link renegotiation. All the negotiated state is replicated from the active links to the standby links to prevent link renegotiation. For more information about SONET APS configurations, see the JUNOS Network Interfaces Configuration Guide.

To configure link state replication, include the preserve-interface statement at the [edit interfaces interface-name sonet-options aps] hierarchy level on both network interfaces:



edit interfaces interface-name sonet-options
aps]

preserve-interface;

The following constraints apply to link PIC redundancy:

APS functionality must be available on the SONET PICs and the interface configurations must be identical on both ends of the link. Any configuration mismatch causes the commit operation to fail.
This feature is supported only with LSQ and SONET APS-enabled link PICs, including Channelized OC3, Channelized OC12, and Channelized STM1 intelligent queuing (IQ) PICs.
Link state replication supports MLPPP and PPP over Frame Relay (frame-relay-ppp) encapsulation, and fully supports GRES.

Enabling the interface or protocol traceoptions with a large number of MLPPP links can trigger Link Control Protocol (LCP) renegotiation during the link switchover time.

Note: This renegotiation is more likely to take place for configurations with back-to-back Juniper Networks routers than in networks in which a Juniper Networks router is connected to an add/drop multiplexer (ADM).

In general, networks that connect a Juniper Networks router to an ADM allow faster MLPPP link switchover than those with back-to-back Juniper Networks routers. The MLPPP link switchover time difference may be significant, especially for networks with a large number of MLPPP links.
An aggressive LCP keepalive timeout configuration can lead to LCP renegotiation during the MLPPP link switchover. By default, the LCP keepalive timer interval is 10 seconds and the consecutive link down count is 3. The MLPPP links start LCP negotiation only after a timeout of 30 seconds. Lowering these configuration values may trigger one or more of the MLPPP links to renegotiate during the switchover time.

Note: LCP renegotiation is more likely to take place for configurations with back-to-back Juniper Networks routers than in networks in which a Juniper Networks router is connected to an ADM.

As an example, the following configuration shows the link state replication configuration between the ports coc3-1/0/0 and coc3-2/0/0.



interfaces {


coc3-1/0/0 {


sonet-options {


aps {
preserve-interface;
working-circuit aps-group-1;
}


}


}




coc3-2/0/0 {


sonet-options {


aps {
preserve-interface;
protect-circuit aps-group-1;
}


}


}


}

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