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1108 OSPF Commands
Default Configuration
Graceful restart is disabled by default
Command Mode
Router OSPF Configuration mode
User Guidelines
Graceful restart works in concert with nonstop forwarding to enable the
hardware to continue forwarding IPv4 packets using OSPFv2 routes while a
backup unit takes over management unit responsibility. When OSPF
executes a graceful restart, it informs its neighbors that the OSPF control
plane is restarting, but that it will be back shortly. Helpful neighbors continue
to advertise to the rest of the network that they have full adjacencies with the
restarting router, avoiding announcement of a topology change and
everything that goes with that (i.e., flooding of LSAs, SPF runs). Helpful
neighbors continue to forward packets through the restarting router. The
restarting router relearns the network topology from its helpful neighbors.
This implementation of graceful restart restarting router behavior is only
useful with a router stack. Graceful restart does not work on a standalone,
single-unit router.
nsf helper
Use the nsf-helper to allow OSPF to act as a helpful neighbor for a restarting
router. Use the “no” form of this command to prevent OSPF from acting as a
helpful neighbor.
Syntax
nsf helper[ planned-only ]
no nsf helper
•
planned-only
— This keyword indicates that OSPF should only help a
restarting router performing a planned restart.
Default Configuration
OSPF may act as a helpful neighbor for both planned and unplanned restarts
2CSPC4.XModular-SWUM200.book Page 1108 Thursday, March 10, 2011 11:18 AM