Cisco Cisco IOS Software Release 12.4(6)T
OSPF RFC 3623 Graceful Restart Helper Mode
Prerequisites for OSPF RFC 3623 Graceful Restart Helper Mode
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Cisco IOS Release 12.4(6)T
Prerequisites for OSPF RFC 3623 Graceful Restart Helper Mode
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OSPF must be configured on the router.
Restrictions for OSPF RFC 3623 Graceful Restart Helper Mode
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IETF Graceful Restart is not supported over sham-links.
Information About OSPF RFC 3623 Graceful Restart Helper Mode
Before configuring the OSPF RFC 3623 Graceful Restart Helper Mode feature, you should understand
the following concepts:
the following concepts:
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Cisco NSF Routing and Forwarding Operation
Prior to RFC 3623 Cisco implemented the Cisco proprietary NSF referred to as Cisco NSF. Users can
configure either Cisco or RFC 3623 IETF NSF, depending on which versions are supported by the
Cisco IOS software version running on the network. If the software version supports both types of NSF,
you need to configure all routers with the same type of NSF.
configure either Cisco or RFC 3623 IETF NSF, depending on which versions are supported by the
Cisco IOS software version running on the network. If the software version supports both types of NSF,
you need to configure all routers with the same type of NSF.
Cisco NSF is supported by the BGP, EIGRP, OSPF, and IS-IS protocols for routing and by Cisco Express
Forwarding (CEF) for forwarding. The BGP, EIGRP, OSPF, and IS-IS routing protocols have been
enhanced with NSF capability and awareness, which means that routers that run these protocols can
detect a switchover and take the necessary actions to continue forwarding network traffic and to recover
route information from the neighbor routers.
Forwarding (CEF) for forwarding. The BGP, EIGRP, OSPF, and IS-IS routing protocols have been
enhanced with NSF capability and awareness, which means that routers that run these protocols can
detect a switchover and take the necessary actions to continue forwarding network traffic and to recover
route information from the neighbor routers.
In this document, a networking device is said to be NSF-aware if it is running NSF-compatible software.
A device is said to be NSF-capable if it has been configured to support NSF; therefore, it would rebuild
routing information from NSF-aware or NSF-capable neighbors. The NSF router mode of operation
common to the Cisco and IETF NSF implementations is as follows:
A device is said to be NSF-capable if it has been configured to support NSF; therefore, it would rebuild
routing information from NSF-aware or NSF-capable neighbors. The NSF router mode of operation
common to the Cisco and IETF NSF implementations is as follows:
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Restarting Mode—Also known as IETF NSF-restarting mode or graceful-restarting mode. In this
mode, the OSPF router process is performing non-stop forwarding recovery because of an RP
switchover; this may result from an RP crash or a software upgrade on the active RP.
mode, the OSPF router process is performing non-stop forwarding recovery because of an RP
switchover; this may result from an RP crash or a software upgrade on the active RP.
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Helper Mode—Also known as IETF NSF-awareness. In this mode, the neighboring router is
restarting, and this router is helping in the non-stop forwarding recovery.
restarting, and this router is helping in the non-stop forwarding recovery.
For more information on Cisco NSF see the following information:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122s/122snwft/release/122s20/
fsnsf20s.htm
For more information on OSPF RFC 3623 Graceful Restart, see the following information:
http://www.ietf.org/rfc/rfc3623.txt