In Service Software Upgrade is a feature to upgrade your IOS with minimum or no impact.
1. Both supervisory engines must be in SSO mode.
2. IOS version must be compatible i.e. SGA train cannot be upgraded to a SG train. An incompatibility issue during the upgrade will cause the redundancy mode in RPR mode. ISSU cannot work in RPR mode because the standby supervisory engine is in standby cold.
3. Manual force switch-over is not recommended, a system force switch-over will start after the Runversion command is executed.
4. Standby supervisory engine must be in Standby Hot.
Configuration step: If slot 3 is active and slot 4 is standby
1. copy tftp: <ios file name with .bin format> bootflash:
2. copy tftp: <ios file name with .bin format> slavebootflash:
These two commands transfer new IOS from your computer to the active sup engine flash (bootflash) and standby sup engine flash (slavebootflash) via tftp.
3. show bootflash: and show slavebootflash:
This is to verify the newly transferred IOS exist in both flashes.
4. In active supervisory engine: issu loadversion 3 bootflash: <new ios file name with .bin format> 4 slavebootflash: <new ios file name with .bin format>
This command turns on ISSU, during ISSU process redundancy mode cannot be changed. The command means turn on Load version for Active and Standby supervisory engine.
5. show issu state detail
This command makes sure active and standby slot are both in Load Version ISSU state.
6. Once ensured both slots are in Load Version ISSU state. Execute runversion command:
issu runversion 4 <new ios file name with .bin format>
This command will invoke a forced switch-over by the system, slot 3 will reboot and become standby, slot 4 will become active immediately.
7. In slot 4 active supervisory engine, execute this command:
issu runversion 3 <new ios file name with .bin format>
This command will invoke a forced switch-over by the system, slot 3 will become active immediately, slot 4 will reboot and become standby. Ensure slot 3 had finished initialization before executing this command.
8. Default rollback timer of 45minutes starts after both sup engines are running the new IOS version, once the rollback timer expires and user did not execute acceptversion command the whole ISSU upgrade process will be aborted i.e. new ios will not be loaded; old ios will be reverted.
9. issu acceptversion 3
This command confirm the IOS version for active sup engine, once this command is executed the rollback timer stops and you are advised to execute commitversion command for standby sup engine.
10. issu commitversion 4
This is the last step for the whole issu upgrade process. Once this command is executed the new IOS will be booted for both active and standby sup henceforth.