Need clarity on 3850 Stack member install

[vaughnconcepts615]

Scenario is a 2 member 3850 (IOS XE) stack.  Switch 1 died, Switch 2 is active waiting on 1 to be placed back in the stack.  I'm being asked to fully configure switch 1 before adding back to the stack?  As I understand it, Switch 2 has a full copy of the config, won't that just overwrite the configuration I put on Switch 1 when it's put back into the stack membership?  Any reason to configure switch 1 with what is already on switch 2 (active) as a preliminary step?  

Just trying to get some clarity on this, if I'm not approaching it correctly.

[Francesco Molino · Accepted solution]

Hi

Depending on your stack configuration, the only thing I would suggest is to clear the config on the new switch and insure that IOS version is same as on the actual stack. Insure that the new model is the same to avoid a new switch member

Except that, just plug it in and that's it. We will be seen as stack member number 1 and the configuration will be applied by the actual master.

[vaughnconcepts615]

That was my thoughts too, and even if it has a config on it, won't it still go through the process of overwriting that with what's on the Active switch?  I think there may some misunderstanding from the person I'm working with about how this works.  They are thinking the switch won't undergo an overwrite of the config, if it matches maybe?  I dunno, I just started a month ago and I'm trying to approach gingerly. 

[Francesco Molino]

As soon as you are connecting the new switch and it has been provisioned (just replacement) the configuration from the stack will be applied.

Just to avoid specific cases and to insure no disruption, I'm always managing it manually but doing upgrade/downgrade with the right IOS and doing wr erase that takes only few seconds.

But except that you don't need to do anything. More than that, if the stack is configured  to do automatic update on new stack member, you have zero action to do, just plug it in.

[vaughnconcepts615]

I don't see the auto-update enabled command in the running config... So does that mean it's just going to sit with a default config if I don't pre-configure?  It should still "inherit" the config that's on Switch 2 correct?

[Francesco Molino]

Yes it should get the config from the master corresponding to the stack member number. If it will be switch 3 it will get all ports configuration beginning by 3/x/x and all other stuff (dot1x, radius, snmp,...)