Existing 3850 stack member removed when new stack member added

[graham robinson]

We have a production stack of 3x 3850's but have run out of ports and need to add a 4th member; I followed the recommended procedure for adding a new member [Configure “software auto-upgrade enable” on the existing stack, rack the new switch but dont power it up, connect the stacking cables to the new member, then power up the new member].

For the first few minutes everything seemed normal [the existing stack members continued passing traffic whilst the new switch booted up], but then stack member 2 [the "standby" stack member] stopped passing traffic and showed as "removed" when the "show switch detail" command was issued. After a few minutes it then showed as "initializing" and I was hopeful it would rejoin the stack, however after approx 10mins it still showed as "initializing" and I felt I could not wait any longer, so I removed the stacking cables from the new switch and put them back to normal, and then rebooted switch 2. After a few minutes it rejoined the stack and started functioning normally again.

During the whole process the new switch 4 was never shown when the "show switch detail" command was issued.

Any idea what might have caused this to occur and how I can avoid this again?

[Seb Rupik]

Hi there,

What mode is your stack running in? The auto-upgrade feature doesn't work in BUNDLE mode.

Personally I would always take the extra step of putting the correct software version and installing it in the same mode as the stack I was attempting to join it to.

cheers,

Seb.

[graham robinson]

Hi Seb

The stack and the new member are both running in install mode, however the stack is running version 3.06.04.E and the new member is running version 16.3.6

[Seb Rupik]

I wager that the 3.x.x and 16.x are not able to communicate correctly to facilitate an auto-upgrade.

Looking through the 16.x.x release notes, the 'auto-upgrade' command is not available so methods called by that command are probably not present.

Put your new switch on a 3.6.x release and the auto-upgrade will work. Or just put the stack version on the new switch and save yourself ore heartache.

Cheers,

Seb.

[graham robinson]

Thanks Seb

[Varun Jacob]

Hi Graham, 

I am assuming that the new member in the stack was configured/re-numbered as switch 4 before plugging it to the existing stack.

[graham robinson]

No it had a default config straight out of the box - my understanding from the documentation is that when a new switch joins a stack it will have a default member number of 1, but during the process of joining the stack it will be assigned the lowest member number that is currently available [e.g. if a stack already has member numbers 1,2 and 3 in use the new switch will be assigned member number 4]. I have done this with other stacks and it worked fine, but I think they were running the same major software version [e.g. the stack and the new switch were both running 3.x.x]