To enable Cisco nonstop forwarding (NSF) operations on a router that is running Open Shortest Path First (OSPF), use the nsf cisco command in router configuration mode. To return to the default, use the no form of this command.
For Cisco IOS Release 12.0(32)S and later releases, this command replaces the nsf (OSPF) command.
This command enables Cisco NSF on an OSPF router. When NSF is enabled on a router, the router is NSF-capable and will operate in restarting mode.
If a router is expected to cooperate with a neighbor that is doing an NSF graceful restart only, the neighbor router must be running a Cisco software release that supports NSF but NSF need not be configured on the router. When a router is running a Cisco software release that supports NSF, the router is NSF-aware.
By default, neighboring NSF-aware routers will operate in NSF helper mode during a graceful restart. To disable Cisco NSF helper mode on an NSF-aware router, use this command with the disable keyword. To reenable helper mode after explicitly disabling helper mode on an NSF-aware router, use the no nsf cisco helper disable command.
If neighbors that are not NSF-aware are detected on a network interface during an NSF graceful restart, restart is aborted on that interface only and graceful restart will continue on other interfaces. To cancel restart for the entire OSPF process when neighbors that are not NSF-aware are detected during restart, configure this command with the enforce global keywords.
The NSF graceful restart will also be canceled for the entire process when a neighbor adjacency reset is detected on any interface or when an OSPF interface goes down.
The following example enables Cisco NSF restarting mode on a router and causes the NSF restart to be canceled for the entire OSPF process if neighbors that are not NSF-aware are detected on any network interface during the restart.
router ospf 24
nsf cisco enforce global