Unified ISSU Upgrade Phase Overview

During the upgrade phase, the CLI supports only a reduced set of administrative commands. You cannot interrupt the upgrade phase. The upgrade phase cannot commence if any CLI commands outside of this set are executing when you issue the issu start command.

Note: Although you can use any CLI session to issue the issu start command, we recommend that you issue the command from a session to the management console port. When the standby SRP module switchover takes place, all management network connections through the Ethernet management port are dropped, and you can access the router only through a console port until the service restoration phase is completed.

When you issue the issu start command, unified ISSU performs the following operations:

1. Verifies that the unified ISSU requirements on the router are still met.
2. Verifies that the active and standby SRP modules are synchronized. If they are not synchronized, forces a synchronization to ensure that all configuration and file system changes are propagated to the standby SRP module before proceeding with the upgrade.
3. Copies the NVS configuration from a backup memory area to the flash card on the standby SRP module. During the initialization phase, this configuration data was mirrored from NVS on the active SRP module and upgraded as required by the armed release.
4. Upgrades the control plane on each line module at the same time.
5. Switches control from the primary SRP module (running the current release) to the standby SRP module (running the armed upgrade release).
6. Upgrades the forwarding plane on each line module at the same time. The fabric is switched and upgraded.

You can view the status of the router and the progress of the upgrade at any time by issuing the show issu command from another terminal session to the router.

Note: While a unified ISSU operation is in progress, do not remove the SRP modules or attempt to reset them. Removing the SRP modules anytime during unified ISSU has an adverse impact. After the unified ISSU operation is completed, issue the show version command. The output should indicate the following: The formerly active SRP module has rebooted and come up as the new standby SRP module. The newly active SRP module indicates that the formerly active SRP has rebooted and has come up as standby SRP module You can then remove an SRP module after issuing the halt command.

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