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Router Behavior During a Unified In-Service Software Upgrade
The following behaviors are characteristic of a
unified in-service software upgrade.
- Connections that were established before you begin the
in-service software upgrade are maintained across the upgrade. Any
such connection that was forwarding data continues to do so during
and after the upgrade.
- New connections are denied until the upgrade is completed.
- Packet loss during the upgrade is limited. Bandwidth through
the modules is reduced, but the impact is minimal.
- Graceful restart protocols do not time out during the
in-service software upgrade.
- The unified in-service software upgrade has a minimal
effect on the control and data planes. During the SRP module upgrade
phase, forwarding through the fabric is interrupted for about 1 second
on the E120 and E320 routers and about 4 seconds on the ERX-1440 router.
During the line module upgrade phase, forwarding through the chassis
is interrupted for about 15 seconds on the E120 and E320 routers and
for about 50 seconds on the ERX-1440 router.
- Diagnostic software is not run on any modules during a
unified in-service software upgrade.
- The router will undergo a cold restart if you attempt
to upgrade the software to a lower-numbered version with unified ISSU.
The in-service software upgrade must be to a higher-numbered release
than the running release.
- Additional memory is consumed during a unified in-service
software upgrade. Available memory on a line module might not be sufficient
due to the module’s configuration. Unified ISSU can detect this
limitation during the upgrade procedure and exit the process.
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