Bgp Local Label Retention - Cisco ASR 9000 Series Configuration Manual

BGP Local Label Retention

During route processor switchover and In-Service System Upgrade (ISSU), NSR is achieved by stateful
switchover (SSO) of both TCP and BGP.
NSR does not force any software upgrades on other routers in the network, and peer routers are not required
to support NSR.
When a route processor switchover occurs due to a fault, the TCP connections and the BGP sessions are
migrated transparently to the standby route processor, and the standby route processor becomes active. The
existing protocol state is maintained on the standby route processor when it becomes active, and the protocol
state does not need to be refreshed by peers.
Events such as soft reconfiguration and policy modifications can trigger the BGP internal state to change. To
ensure state consistency between active and standby BGP processes during such events, the concept of post-it
is introduced that act as synchronization points.
BGP NSR provides the following features:
• NSR-related alarms and notifications
• Configured and operational NSR states are tracked separately
• NSR statistics collection
• NSR statistics display using show commands
• XML schema support
• Auditing mechanisms to verify state synchronization between active and standby instances
• CLI commands to enable and disable NSR
• Support for 5000 NSR sessions
BGP Local Label Retention
When a primary PE-CE link fails, BGP withdraws the route corresponding to the primary path along with its
local label and programs the backup path in the Routing Information Base (RIB) and the Forwarding Information
Base (FIB), by default.
However, until all the internal peers of the primary PE reconverge to use the backup path as the new bestpath,
the traffic continues to be forwarded to the primary PE with the local label that was allocated for the primary
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.1.x
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In case of process crash or process failure, NSR will be maintained only if nsr
Note
process-failures switchover command is configured. In the event of process failures
of active instances, the nsr process-failures switchover configures failover as a recovery
action and switches over to a standby route processor (RP) or a standby distributed route
processor (DRP) thereby maintaining NSR. An example of the configuration command
is RP/0/RSP0/CPU0:router(config) # nsr process-failures switchover
The nsr process-failures switchover command maintains both the NSR and BGP
sessions in the event of a BGP or TCP process crash. Without this configuration, BGP
neighbor sessions flap in case of a BGP or TCP process crash. This configuration does
not help if the BGP or TCP process is restarted in which case the BGP neighbors are
expected to flap.
Implementing BGP
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