C3850-48T stack Issue

[houstonyang]

When I have the master C3850-48T and the slave C3850-48T are ready(version: 03.03.03SE), the priority of master C3850-48T is 15 and slave C3850-48T is 14. We plug in the stack cable from slave C3850-48T to master C3850-48T, the two C3850-48T have no response at this time, and the front of panel is always green light(STAT and SYST) on two C3850-48T. It’s also no response to press the “MODE” button on the front of panel. We pull the stack cable and plug in it, the two C3850-48T reload immediately and made stack completely. In normal, only the low priority will reboot, the master will not. So what problem between this procedure or what is wrong on these step?

[Leo Laohoo]

We pull the stack cable and plug in it, the two C3850-48T reload immediately and made stack completely. In normal, only the low priority will reboot, the master will not. 

If your slave is POWERED UP and then you CONNECT the stacking cable, the entire stack will reboot so it can go into a stack election.  This behaviour is to be expected.  

IF you need to connect the slave, make sure the slave is POWERED OFF and then connect the stacking cable.

[houstonyang]

Thanks for your reply. You say that when slave is POWERED UP and then you CONNECT the stacking cable, the entire stack will reboot so it can go into a stack election, But we try to test by

another platform "3750X" by the same situation. Only the low priority will reboot, and they don't go into a stack election. So the different platform have different result? Thanks....

[Leo Laohoo · Accepted solution]

You say that when slave is POWERED UP and then you CONNECT the stacking cable, the entire stack will reboot so it can go into a stack election

Presume the following scenario: 

• You have an existing stack of, say, three switches in a stack.  They are all operating normally and powered up and cabled up. 
• You want to introduce a fourth member to the stack.  The fourth member is powered up, NOT CABLED, and has the correct IOS version (and feature set).

Ok, you've got above setup.  The very minute you attach the stacking cable from the existing stack to an already-power-up new switch, the entire stack will reboot.  This is to be expected.  

This is why it's stated in the recommendation to POWER DOWN the new stack member before attaching/connecting the stacking cable.  Once you've attached, a minimum of, ONE stacking cable to the new member, you can power up the new member switch.  This will cause the new member to join the stack un-interrupted.  

It doesn't matter if you are talking about 2960S/X/XR, 3750-series family of switches, 3650 or 3850, the behaviour is the same to all the platform involved.

[houstonyang]

Thanks~ I got it. Thanks for your suggestion and answer...