Layer 3 Routing Commands 1745nsf helper strict-lsa-checkingUse the nsf-helper strict-lsa-checking command to require that an OSPFhelpful neighbor exit helper mode whenever a topology change occurs. Usethe “no” form of this command to allow OSPF to continue as a helpfulneighbor in spite of topology changes.Syntaxnsf [ietf] helper strict-lsa-checkingno nsf [ietf] helper strict-lsa-checking• ietf —This keyword is used to distinguish the IETF standardimplementation of graceful restart from other implementations. Since theIETF implementation is the only one supported, this keyword is optional.Default ConfigurationA helpful neighbor exits helper mode when a topology change occurs.Command ModeRouter OSPFv3 Configuration modeUser GuidelinesThe restarting router is unable to react to topology changes. In particular, therestarting router will not immediately update its forwarding table; therefore, atopology change may introduce forwarding loops or black holes that persistuntil the graceful restart completes. By exiting the graceful restart on atopology change, a router tries to eliminate the loops or black holes as quicklyas possible by routing around the restarting router.A helpful neighbor considers a link down with the restarting router to be atopology change, regardless of the strict LSA checking configuration.nsf restart-intervalUse the nsf restart-interval command to configure the length of the graceperiod on the restarting router. Use the “no” form of this command to revertthe grace period to its default.
