How ISSU Works When Upgrading Stack Units
The checks and upgrade sequence for a typical 8-unit stack is shown in Stack Units to Be Upgraded. 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 Stack Units to Be Upgraded.
ICX7850-48F# show issu sequence Stack units will be upgraded in the following order ID Type Role 4 ICX7850-48F standby 3 ICX7850-48F member 2 ICX7850-48F member 5 ICX7850-48F member 6 ICX7850-48F member 7 ICX7850-48F member 8 ICX7850-48F member 1 ICX7850-48F active
All stack ISSU processes follow the same pattern.
As reflected in the sample output, the stack in the example responds to the
show issu sequence 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) reload the new image.
- All members from the standby controller to the active controller in the other direction (units 5, 6, 7, and 8) 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 (unit 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.