In-Service Software Upgrade (ISSU) Feature Overview and Configuration Guide

In-Service Software Upgrade (ISSU) is a feature that allows you to upgrade the software version of the release on a chassis device with no network downtime.

AlliedWare Plus

ISSU works because it allows the chassis to run two different software versions at the same time. This is important, because the chassis must continue to correctly forward traffic while it performs the software version upgrade. This necessarily involves a period in which two different software versions are in operation simultaneously.

With ISSU, you can upgrade the chassis to a future maintenance release - which may contain new functionality, or resolve a software issue - without disrupting network operation.