The Nonstop Routing (NSR) feature on 7210 SAS devices ensures that routing neighbors are unaware of a routing process fault. If a fault occurs, a reliable and deterministic activity switch to the inactive control complex occurs; the routing topology and reachability are not affected, even during routing updates. NSR achieves HA through parallelization by maintaining up-to-date routing state information, at all times, on the standby route processor. This is achieved independent of protocols or protocol extensions and provides a more robust solution than graceful restart protocols between network routers.
The NSR implementation on the 7210 SAS routers supports all routing protocols. It allows existing sessions (BGP, LDP, OSPF, and others) to be retained during a CFM or CPM switchover, including the support for MPLS signaling protocols. No change is visible to the peers.
Protocol extensions are not required. There are no interoperability issues and defining protocol extensions for each protocol is not required. Unlike nonstop forwarding and graceful restart, the forwarding information in NSR is always up to date, which eliminates possible black holes or forwarding loops.
Traditionally, addressing HA issues has been patched through nonstop forwarding solutions. The NSR implementation overcomes these limitations by delivering an intelligent, hitless failover solution. This enables a carrier-class foundation for transparent networks that is required to support business IP services backed by stringent SLAs. This level of HA support poses a major issue for conventional routers whose architectural design limits or prevents them from implementing NSR.