Understanding Nonstop Active Routing On Ex Series Switches - Juniper JUNOS OS 10.4 - FOR EX REV 1 Manual

Understanding Nonstop Active Routing on EX Series Switches

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Copyright © 2010, Juniper Networks, Inc.
You can configure nonstop active routing (NSR) on an EX Series switch with redundant
Routing Engines 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
master Routing Engine and when the backup Routing Engine is inserted or comes online,
its configuration is automatically synchronized with that of the master.
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 (
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.
NOTE: After a graceful Routing Engine switchover, we recommend that you
issue the clear interface statistics (interface-name | all)
cumulative values for local statistics on the new master 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" on page 1191.
NOTE: Graceful restart and nonstop active routing are mutually exclusive.
You will receive an error message upon commit if both are configured.
Configuring Nonstop Active Routing on EX Series Switches (CLI Procedure) on page 1190
Example: Configuring Nonstop Active Routing on EX Series Switches on page 1183
statement, the candidate configuration is committed in the
Chapter 50: High Availability—Overview
command to reset the
rpd ) on
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