Brocade Multi-Service IronWare Routing Configuration Guide (Supporting R05.6.00) - Manual (Page 308)

280 Multi-Service IronWare Routing Configuration Guide
53-1003033-02
IS-IS Non-Stop Routing
IS-IS Non-Stop Routing (NSR) enables the IS-IS router to maintain topology and data flow to avoid
re-convergence in the network during a processor switchover or hitless-reload event. The IS-IS
Bidirectional Forwarding Detection (BFD) sessions survive the switchover and hitless-reload
conditions. In general, a router restart causes its peer to remove the routes originated from the
router and reinstalls them. This IS-IS NSR feature enables the router to maintain neighbors and LSA
database with its peer on the event of a router restart.
In IS-IS NSR, the processor switchovers and the hitless-reloads are treated the same as they are
during startup and the overload bit is set in the same way as it is after a reboot. For more
information on overload bit setup, refer to
“Setting the overload bit” on page 256.
NOTE
IS-IS NSR is independent of Graceful Restart (GR) and GR help role mechanisms.
Limitations
• The IS-IS over GRE tunnel feature does not support IS-IS NSR. The GRE tunnel interface types
are not supported.
• The IS-IS shortcuts are not supported because they depend on the MPLS tunnel.
• If the IS-IS hellos are forwarded at Layer 2 and the device executes a hitless-reload, hellos will
not be forwarded for a brief time. The IS-IS adjacencies are lost for 12 seconds and there will
be data traffic loss.
• The configuration events that occur close to switchover or hitless-reload may get lost due to CLI
synchronization issues.
• The neighbor or interface state changes close to switchover or hitless-reload cannot be
handled.
• The IS-IS neighbor hold timer is restarted upon IS-IS NSR switchover or hitless-reload.
• The traffic counters are not synchronized because the neighbor and LSP database counters
are recalculated on the standby module during synchronization.
• With IS-IS NSR enabled, after switchover or hitless-reload to standby MP, IS-IS routes, LSP
database and neighbor adjacencies are maintained so that there will be no loss of existing
traffic to the IS-IS destinations.
• The IS-IS NSR hitless failover event may not be completely invisible to the network because,
after switchover, additional flooding of CSNP packets will occur in the directly connected
neighbors.
Enabling and disabling IS-IS NSR
To globally enable IS-IS NSR, enter the following commands.
Brocade(config)# router isis
Brocade(config-isis-router)# nonstop-routing
To globally disable IS-IS NSR, enter the following commands.
Brocade(config)# router isis
Brocade(config-isis-router)# no nonstop-routing
Syntax: [no] nonstop-routing