Dell N1100-ON, Reference Manual

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Layer 3 Routing Commands
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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 [ ietf ] helper [ planned-only ]
no nsf [ietf] 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
Command Mode
Router OSPF Configuration mode
User Guidelines
The grace LSA announcing the graceful restart includes a restart reason.
Reasons 1 (software restart) and 2 (software reload/upgrade) are considered
planned restarts. Reasons 0 (unknown) and 3 (switch to redundant control
processor) are considered unplanned restarts.
nsf ietf helper disable is functionally equivalent to no nsf helper and is
supported solely for IS CLI compatibility.