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Understanding Nonstop Active Routing on EX Series Switches

You can configure nonstop active routing (NSR) on an EX Series switch with redundant Routing Engines or on an EX Series Virtual Chassis to enable the transparent switchover of the Routing Engines in the event that one of the Routing Engines goes down.

Nonstop active routing provides high availability for Routing Engines by enabling transparent switchover of the Routing Engines without requiring restart of supported routing protocols. Both Routing Engines are fully active in processing protocol sessions, and so each can take over for the other. The switchover is transparent to neighbor routing devices, which do not detect that a change has occurred.

Enable nonstop active routing when neighbor routing devices are not configured to support graceful restart of protocols or when you want to ensure graceful restart of protocols for which graceful restart is not supported—such as PIM.

You do not need to start the two Routing Engines simultaneously to synchronize them for nonstop active routing. If both Routing Engines are not present or not up when you issue a commit synchronize statement, the candidate configuration is committed in the primary Routing Engine and when the backup Routing Engine is inserted or comes online, its configuration is automatically synchronized with that of the primary.

Nonstop active routing uses the same infrastructure as graceful Routing Engine switchover (GRES) to preserve interface and kernel information. However, nonstop active routing also saves routing protocol information by running the routing protocol process (rpd) on the backup Routing Engine. By saving this additional information, nonstop active routing does not rely on other routing devices to assist in restoring routing protocol information.


After a graceful Routing Engine switchover, we recommend that you issue the clear interface statistics (interface-name | all) command to reset the cumulative values for local statistics on the new primary Routing Engine.

If you suspect a problem with the synchronization of Routing Engines when nonstop active routing is enabled, you can gather troubleshooting information using trace options. For example, if certain protocols lose connectivity with neighbors after a graceful Routing Engine switchover with NSR enabled, you can use trace options to help isolate the problem. See Tracing Nonstop Active Routing Synchronization Events.


Graceful restart and nonstop active routing are mutually exclusive. You will receive an error message upon commit if both are configured.


Nonstop active routing provides a transparent switchover mechanism only for Layer 3 protocol sessions. Nonstop bridging (NSB) provides a similar mechanism for Layer 2 protocol sessions. See Understanding Nonstop Bridging on EX Series Switches.