When upgrading a Juniper Virtual Chassis switch from MIST, you may see the alert shown below:|
If you are planning to perform a system software rollback, the option "Revert to Previous Running Version" will be gray out so; you won't be able to.
This scenario is expected if 2 switches with different "Previous set" junos version are stacked in a Virtual Chassis, which is then added / claimed into MIST. You can check the actual "Previous set" version with the command "show system software sets all-members". For example:
user@switchname> show system software sets all-members | no-more
fpc0:
--------------------------------------------------------------------------
Previous set : 24.4R2.25
Active set : 24.4R2.25
Software rollback reverts to previous set
fpc1:
Previous set : 24.4R1-S2.15
The solution to this scenario is to perform a junos upgrade through MIST. That will have the VC to have the same "Previous set" (which would be the running junos version prior to upgrade/reboot).