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Nonstop Forwarding
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 7710 SR-Series routers, 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 reachability 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 7710 SR-Series routers supports all routing protocols. NSR
makes it possible to keep the existing sessions (BGP, LDP, OSPF, etc.) during a CFM 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. This is also called the Alcatel-Lucent Carrier Environment Internet System
(ACEIS). NSR is a relatively new high availability technique. However, it is regarded the most
promising to ensure IP packets continue to forward once a route processor fails and allows for in-
service software upgrades.
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 failover 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.
The following NSR entities remain intact after a switchover:
•
7710 SR OS Basic System Configuration Guide
BGP sessions — BGP peers should not see any change after the switchover.
System Management
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