How ISSU Works When Upgrading Stack Units
The following section describes the checks and the upgrade sequence for the typical 8-unit stack shown in the . For a step-by-step procedure on performing an ISSU, refer to Upgrading a Stack with ISSU.
After you have downloaded release software as described in
Initial steps and
The upgrade process, you can check the sequence in which stack units will be upgraded using the
show issu sequence command. The following example displays the ISSU upgrade sequence for the stack shown
in
.
device# show issu sequence Stack units will be upgraded in the following order ID Type Role 4 ICX7450-32ZP standby 3 ICX7450-32ZP member 2 ICX7450-32ZP member 5 ICX7450-32ZP member 6 ICX7450-32ZP member 7 ICX7450-32ZP member 8 ICX7450-32ZP member 1 ICX7450-32ZP active
All stack ISSU processes follow the same pattern. As reflected in the sample output,
the stack in our example responds to the
issu command in the following ways:
- Unit 4, the standby controller, is reloaded with the new image.
- Once the standby controller joins the stack, all member units from the standby controller to the active controller units (3 and 2 in the following example) reload the new image.
- All members from the standby controller to the active controller in the other direction (5,6,7, and 8 in the following example) reload the new image.
- Once all member units and the standby controller are reloaded with the new image, the active controller unit triggers a switchover, in which the old standby controller (4) becomes the new active controller unit, and the old active controller (unit 1) becomes the new standby controller.
- The new active controller (unit 4) reloads the old active controller (unit 1) with the new image.
- Once the old active controller (unit 1) comes up as a member unit and rejoins the stack, standby controller election occurs, and the stack becomes fully functional with the upgraded image.