Adding 2960-X to existing 2960-S stack

[tdorsey123]

I am not having luck adding a newer 2960-X to and existing 2960-S stack

Only 3 switches here.

Existing stack:

WS-C2960S-48TS-L  - Switch priority 14 (c2960s-universalk9-mz.152-2.E4.bin)

WS-C2960S-48TS-L - Switch priority 12 (c2960s-universalk9-mz.152-2.E4.bin)

New Switch:

WS-C2960X-48TS-L - Switch priority 1 (c2960x-universalk9-mz.152-2.E4.bin)

All 3 switches have been upgraded to 152-2.E4

All 3 switches SDM template has been set to 'default'

Switch#sh sdm prefer
 The current template is "default" template

Stack wiring follows Cisco's diagram for 3 switches

Tried booting the existing switch, then powering the new switch: no luck

Tried booting all three switches together: no luck

What did I miss?

[Philip D'Ath]

Look for something interesting in "show log".  It will probably give the failure reason.

[tdorsey123]

Thanks for the input Philip, The buffered logs were too short to capture any of the stack election alarms but sitting on console during boot I didn't capture any errors.  Unfortunatey I am out of my outage window to expand the buffered logs and reboot.

[Philip D'Ath]

Being the new switch, I wouldn't be surprised if it needs to be the stack master - priority 15.

It would seem more reasonable that a newer switch could "step down" to an older switch, and less reasonable that an older switch could control a newer switch that didn't exist what it was created.

Backup your switch configs first though!  As if the 2960-X becomes the master you might end up with no config and might need to paste the config back in.

[adwang_bing · Accepted solution]

I believe in order to add a 2960X into a contiguous stack of 2960S switches you have to force the stack port speed on a 2960X to 10Gbps via the command switch stack port-speed 10 according to this guide you MUST set this manually, as the switch won't auto-detect this difference in stack port speeds.

[tdorsey123]

Thank you Adwang.  After talking with TAC the Stack port speed change was necessary and in that same document is the recommendation to use the LAN-Routing SDM templates on all switches.