Graceful restart

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12.4T Configuration Guides -> IP Routing -> IP Routing: OSPF Configuration Guide, Cisco IOS Release 12.4T -> OSPF RFC 3623 Graceful Restart Helper Mode


Graceful restart is a feature that enables a router to keep forwarding packets in the events that the routing process is restarted. This is useful when you need to change the router ID which requires a restart of OSPF process.

There are two versions of graceful restart, the Cisco implementation which proceeded the IETF implementation (RFC 3623.

Graceful restart is enabled by default and can be disabled on a per routing process basis.


NSF ... helper disable

The nsf <<helper>> helper disable command specifies which graceful restart helper to disable.

R6(config-router)#nsf cisco helper disable


Show ip ospf interface

The show ip ospf interface command provides detailed information about hello and dead timers, as well as the graceful restart or NSF helper status currently active on the interface.

R6#sh ip ospf interface fa0/0
FastEthernet0/0 is up, line protocol is up
  Internet Address, Area 0
  Process ID 1, Router ID, Network Type BROADCAST, Cost: 1
  Transmit Delay is 1 sec, State BDR, Priority 1
  Designated Router (ID), Interface address
  Backup Designated router (ID), Interface address
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:00
  Supports Link-local Signaling (LLS)
  Cisco NSF helper support enabled
  IETF NSF helper support enabled
  Index 1/1, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor  (Designated Router)
  Suppress hello for 0 neighbor(s)

See Also

  1. Cisco on OSPF
  2. Wikipedia on OSPF
  3. RFC 3623
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