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Route Switch Processor (RSP8) Installation and Configuration Guide
OL-4920-02
Enabling High Availability Features
Configuring Nonstop Forwarding (NSF)
Cisco Nonstop Forwarding (NSF) always runs together with SSO. If you have not already configured
SSO, refer to the “Configuring aStateful Switchover (SSO)” section onpage 49. Cisco NSF is supported
by the BGP, OSPF, and IS-IS protocols for routing and by Cisco Express Forwarding (CEF) for
forwarding. Of the routing protocols, BGP, OSPF, and IS-IS have been enhanced with NSF-capability
and awareness, which means that routers running these protocols can detect a switchover and take the
necessary actions to continue forwarding network traffic and to recover route information from the peer
devices. The IS-IS protocol can be configured to use state information that has been synchronized
between the active and the standby RSP to recover route information following a switchover instead of
information received from peer devices.
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.
Each protocol depends on CEF to continue forwarding packets during switchover while the routing
protocols rebuild the RoutingInformation Base (RIB)tables. Once therouting protocols have converged,
CEF updates the FIB table and removes stale route entries. CEF, in turn, updates the line cards with the
new FIB information.
See the following sections for the NSF feature. Each task in the list is identified as either required or
optional.
• Configuring CEF NSF, page 52 (required)
• Configuring BGP NSF, page 52 (required)
• Configuring OSPF NSF, page 53 (required)
• Configuring IS-IS NSF, page 53 (required)
• Verifying CEF NSF, page 54 (optional)
• Verifying BGP NSF, page 55 (optional)
• Verifying OSPF NSF, page 56 (optional)
• Verifying IS-IS NSF, page 56 (optional)
• Troubleshooting NSF Features, page 58 (optional)
• BGP NSF Configuration Example, page 59 (optional)
• BGP NSF Neighbor Device Configuration Example, page 59 (optional)
• OSPF NSF Configuration Example, page 59 (optional)
• IS-IS NSF Configuration Example, page 59 (optional)
Configuring CEF NSF
The CEF NSF feature operates by default while the networking device is running in SSO mode. No
configuration is necessary.
Configuring BGP NSF
Note You must configure BGP graceful restart on all peer devices participating in BGP NSF.