First thing first, for a switch stack you don't need to cable them in specific pattern or arrangement. As long as every switch is connected in a big uninterrupted loop it will work it out and you'll be fine. For a stack of four switches here are some options:
Which is best? Really it all depends on how they are deployed in a rack or across racks and what length stack-cables you have. The default is 50cm but longer cables can be ordered (I think 3m is the max).
For the 3750X/3850 don't forget you also have StackPower cables to worry about as well.
So back to the main topic, how does the switch renumbering work... I had a stack of 4 switches I built recently. After connecting and booting them all it turned out that...
Switch 1 thinks its stack member 2The switch renumber command swaps a single switch with the number of another switch. Logically this shouldn't work as I had multiple overlaps in the above. I gave it a go regardless. So in the above I tried to:
Switch 2 thinks its stack member 4
Switch 3 thinks its stack member 3
Switch 4 thinks its stack member 1
- Swap 1 & 2
- Swap 2 & 4
- Swap 4 & 1
It didn't work. :) I ended up with another mess altogether.
The best way I've found to do this is to do all the renumber commands you can without overlapping with the previously applied renumber commands. Then you need to reboot! Once that's done renumber out the remaining switch members and reboot... again. This chews up time since the reboot takes roughly 10mins for 3850 switches.
Lastly, you can figure out which switch is which switch member based on the lights on the front of the chassis. Highlight the "stack" LED by pressing the mode button and the switchports LEDs instead indicate the "stack" member number.
Thanks for reading. Hope it helps.
