Virtual Chassis configurations can use sequential upgrade to install new software releases with minimal network downtime. Sequential upgrade is an alternative to unified ISSU that installs a new release and reboots each Virtual Chassis member router one at a time. While the upgrade installs on one member router, the other member router continues to operate and handle network operations.
To perform a sequential upgrade in an Virtual Chassis, you first issue the request virtual-chassis upgrade protocol-backup package-name command from the CLI for the Virtual Chassis primary router. This initiates the upgrade process on the Virtual Chassis backup router. After the upgrade finishes on the backup router, issue the request virtual-chassis upgrade protocol-primary package-name command from the backup router CLI to begin the same upgrade process for the Virtual Chassis primary router.
