Cisco NCS 5500 Series Configuration Manual page 147

Implementing BGP
• Route processor switchover
• Process crash or process failure of BGP or TCP
Note
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
BGP NSR is enabled by default. Use the nsr disable command to turn off BGP NSR.
The no nsr disable command can also be used to turn BGP NSR back on if it has been
disabled.
In case of process crash or process failure, NSR will be maintained only if nsr
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.
BGP Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
Information about Implementing BGP
137