Cisco Route: fast recovery and stable restart switching (1)

As we all know, to obtain a high network duration, you need to use a master router and a backup router with a hot fault recovery function and different network paths. But this is not enough. Routers themselves, especially those on insecure WAN edges, should be equipped with internal redundant hardware components, such as switching matrices, line cards, power supplies, and Route Processor RP ). High-availability routers must also support fast software recovery technology.

Vrouters that can isolate control and forwarding panels and use a stable restart mechanism-also known as Cisco NSF)-can greatly extend the normal running time of networks and applications. This software recovery technology can maintain the normal transmission of groups when the RP Process is interrupted, thus controlling the impact of interruption on the network.

Dual RP and continuous group forwarding

The RP contains the "brain" of the router ". It is responsible for storing the database of the optimal route information, storing the adjacent relationship with the peer-to-peer router, and processing specific management functions. Redundant hardware improves the availability of network components in the event of a fault. Cisco dual RP devices include 12000, 10000, and 7600 series high-end routers, as well as Cisco 7500 and 7300 series routers.

The degree of synchronization between the two RP statuses depends on the speed at which the router can restart or recover from a fault. This requires a balance between two extreme backup forms. An extreme form is RP's "cold" backup, that is, it does not contain any status information about layer-2 connections, joining relationships, and the optimal route table. In this case, all this information needs to be re-built, which may lead to a very long recovery time. Another extreme form is the uninterrupted synchronization of all information between two RP, which may occupy too much processing resources and affect the network scalability and performance.

The common approach is to maintain an appropriate balance between the two extreme RP Synchronization Methods, that is, to load most but not all of the recovery information into the backup RP. This synchronization can continue layer-3 packet forwarding when the RP and the centralized route table are switched.

What is Cisco IOS installed on the above router platform? Software 12.0 (22) S or later can support Cisco NSF. It can shorten the router downtime when the primary RP is scheduled for maintenance or when the RP encounters an unexpected fault. In most cases, to implement Cisco NSF, the restart router and its peer vro must save the forwarding information for all networks that can be reached by restarting the router. On the router restart, when switching from the primary RP to the standby RP, the control panel and the forwarding panel must be isolated from each other so that the forwarding panel can continue to forward data traffic.

Route Protocol Extension　

To achieve NSF, Some Cisco routers can use the common routing protocols-including Border Gateway Protocol BGP), IS-IS, and Open Shortest Path-first OSPF) to implement new stable restart expansion. These extensions can continue forwarding groups and maintain network connection stability while determining whether the primary RP can be quickly restored.

To enable most Cisco NSF/stable restart deployment, the peer router that restarts the router must also support these extensions. This is mainly because of the following two reasons. First, RP switching does not represent topology changes, but only indicates RP recovery. A peer-to-peer router can use the smooth restart and expansion to avoid disabling external broadcast and enabling and restarting the router. This prevents unnecessary broadcast information and route changes. Second, it enables peer-to-peer routers to continue forwarding groups to the restarted vrouters during recovery to provide NSF. It must also know which messages and information should be exchanged to help the primary router recover quickly.

Figure 1

Figure 1: Peer routers supporting Cisco NSF can help each other quickly recover from emergencies, minimizing downtime, forwarding groups, and maintaining the stability of the entire network.

Figure 2

Figure 2: No matter what protocol is used, user data groups are continuously transmitted between peer routers throughout the recovery process.