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Routing Engine Redundancy

With redundant Routing Engines, one functions as the master, while the other stands by as a backup should the master Routing Engine fail. When a Routing Engine is configured as master, it has full functionality. It receives and transmits routing information, builds and maintains routing tables, communicates with interfaces and Packet Forwarding Engine components, and has full control over the chassis. When a Routing Engine is configured to be the backup, it does not communicate with the Packet Forwarding Engine or chassis components.

Note: With the introduction of JUNOS Release 8.4, both Routing Engines cannot be configured to be master at the same time. This configuration causes the commit check to fail.

A failover from the master Routing Engine to the backup Routing Engine occurs automatically when the master Routing Engine experiences a hardware failure or when you have configured the software to support a change in mastership based on specific conditions. You can also manually switch Routing Engine mastership by issuing one of the request chassis routing-engine commands. In this chapter, the term failover refers to an automatic event, whereas switchover refers to either an automatic or a manual event.

When a failover or a switchover occurs, the backup Routing Engine takes control of the system as the new master Routing Engine:

If graceful Routing Engine switchover is not configured, when the backup Routing Engine becomes master, it resets the switch plane and downloads its own version of the microkernel to the Packet Forwarding Engine components. Traffic is interrupted while the Packet Forwarding Engine is reinitialized. All kernel and forwarding processes are restarted.
If graceful Routing Engine switchover is configured, interface and kernel information is preserved. The switchover is faster because the Packet Forwarding Engines are not restarted. The new master Routing Engine restarts the routing protocol process (rpd). All hardware and interfaces are acquired by a process that is similar to a warm restart. For more information about graceful Routing Engine switchover, see Graceful Routing Engine Switchover Overview.
If graceful Routing Engine switchover and nonstop active routing (NSR) are configured, traffic is not interrupted during the switchover. Interface, kernel, and routing protocol information is preserved. For more information about nonstop active routing, see Nonstop Active Routing Overview.
If graceful Routing Engine switchover and graceful restart are configured, traffic is not interrupted during the switchover. Interface and kernel information is preserved. Graceful restart protocol extensions quickly collect and restore routing information from the neighboring routers. For more information about graceful restart, see Graceful Restart Overview.

For more information about Routing Engine redundancy, see the following sections:

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