Nonstop Routing (Nsr) - Alcatel-Lucent 7210 SAS M Configuration Manual

System Basics Introduction
Nonstop forwarding is used to notify peer routers to continue forwarding and receiving packets,
even if the route processor (control plane) is not working or is in a switch-over state. Nonstop
forwarding requires clean control plane and data plane separation and usually the forwarding
information is distributed to the line cards. This method of availability has both advantages and
disadvantages. Nonstop forwarding continues to forward packets using the existing stale
forwarding information during a failure. This may cause routing loops and black holes, and also
requires that surrounding routers adhere to separate extension standards for each protocol. Every
router vendor must support protocol extensions for interoperability.

Nonstop Routing (NSR)

With NSR on the 7210 SAS routers devices, 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 such that routing topology and the reach ability are not affected, even in the presence of
routing updates. NSR achieves high availability through parallelization by maintaining up to date
routing state information, at all times, on the standby route processor. This capability is achieved
independently of protocols or protocol extensions, providing a more robust solution than graceful
restart protocols between network routers.
The NSR implementation on the 7210 SAS routers supports all routing protocols. NSR makes it
possible to keep the existing sessions (BGP, LDP, OSPF, etc.) during a CFM/CPM switchover,
including support for MPLS signaling protocols. Peers will not see any change.
Protocol extensions are not required. There are no interoperability issues and there is no need to
define protocol extensions for every protocol. Unlike nonstop forwarding and graceful restart, the
forwarding information in NSR is always up to date, which eliminates possible blackholes or
forwarding loops.
Traditionally, addressing high availability issues have been patched through non-stop forwarding
solutions. With the implementation of NSR, these limitations are overcome by delivering an
intelligent hitless fail over solution. This enables a carrier-class foundation for transparent
networks, required to support business IP services backed by stringent SLAs. This level of high
availability poses a major issue for conventional routers whose architectural design limits or
prevents them from implementing NSR.
Page 208 7210 SAS M, T, X, R6 Basic System Configuration Guide