Cisco 7609-S Software Configuration Guide - Page 102

Understanding NSF with SSO Supervisor Engine Redundancy Chapter 7 Configuring NSF with SSO Supervisor Engine Redundancy If at least one of the peer routers is NSF-aware, the restarting router would then receive updates and rebuild its database. The restarting router must then find out if it had converged so that it can notify the routing information base (RIB). Each NSF-aware router is required to send an end of table (EOT) marker in the last update packet to indicate the end of the table content. The restarting router knows it has converged when it receives the EOT marker. The restarting router can then begin sending updates. An NSF-aware peer would know when the restarting router had converged when it receives an EOT indication from the restarting router. The peer then scans its topology table to search for the routes with the restarted neighbor as the source. The peer compares the route timestamp with the restart event timestamp to determine if the route is still available. The peer then goes active to find alternate paths for the routes that are no longer available through the restarted router. When the restarting router has received all EOT indications from its neighbors or when the NSF converge timer expires, EIGRP will notify the RIB of convergence. EIGRP waits for the RIB convergence signal and then floods its topology table to all awaiting NSF-aware peers. NSF Benefits and Restrictions Cisco NSF provides these benefits: • Improved network availability NSF continues forwarding network traffic and application state information so that user session information is maintained after a switchover. • Overall network stability Network stability may be improved with the reduction in the number of route flaps that had been created when routers in the network failed and lost their routing tables. • Neighboring routers do not detect a link flap Because the interfaces remain up throughout a switchover, neighboring routers do not detect a link flap (the link does not go down and come back up). • Prevents routing flaps Because SSO continues forwarding network traffic in the event of a switchover, routing flaps are avoided. • No loss of user sessions User sessions established before the switchover are maintained. Cisco NSF with SSO has these restrictions: • For NSF operation, you must have SSO configured on the device. • NSF with SSO supports IP Version 4 traffic and protocols only. • Enhanced Object Tracking is not SSO-aware and cannot be used with Hot Standby Routing Protocol (HSRP), Virtual Router Redundancy Protocol (VRRP), or Gateway Load Balancing Protocol (GLBP) in SSO mode. • The HSRP is not SSO-aware, meaning state information is not maintained between the active and standby supervisor engine during normal operation. HSRP and SSO can coexist but both features work independently. Traffic that relies on HSRP may switch to the HSRP standby in the event of a supervisor switchover. Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX 7-8 OL-4266-08