Layer 3 Routing Commands 1671executes a graceful restart, it informs its neighbors that the OSPF controlplane is restarting, but that it will be back shortly. Helpful neighbors continueto advertise to the rest of the network that they have full adjacencies with therestarting router, avoiding announcement of a topology change andeverything that goes with that (i.e., flooding of LSAs, SPF runs). Helpfulneighbors continue to forward packets through the restarting router. Therestarting router relearns the network topology from its helpful neighbors.This implementation of graceful restart restarting router behavior is onlyuseful with a router stack. Graceful restart does not work on a standalone,single-unit router.nsf helperUse the nsf-helper to allow OSPF to act as a helpful neighbor for a restartingrouter. Use the “no” form of this command to prevent OSPF from acting as ahelpful neighbor.Syntaxnsf [ietf] helper[planned-only]no nsf [ietf] helper• planned-only — This keyword indicates that OSPF should only help arestarting router performing a planned restart.Default ConfigurationOSPF may act as a helpful neighbor for both planned and unplanned restartsCommand ModeRouter OSPF Configuration modeUser GuidelinesThe grace LSA announcing the graceful restart includes a restart reason.Reasons 1 (software restart) and 2 (software reload/upgrade) are consideredplanned restarts. Reasons 0 (unknown) and 3 (switch to redundant controlprocessor) are considered unplanned restarts.nsf ietf helper disable is functionally equivalent to no nsf helper and issupported solely for IS CLI compatibility.
