How to configure MST priority in Cisco 4500 and 2960 switches stack

[Arpita]

Below is the stack of 4500 as the top switch and 2960 switches. I have configured MST on all the switches. Backbonefast is too enabled. I have tried a number of combination of priorities on all the switches yet the convergence time of whole network takes about 15-20 minutes.

Process of testing:

1) Run continuous ping command to all the switches from the command prompt of the laptop which is        connected to 4500 switch.

2) Disconnect the link L1 and test the ping results in the command prompt (will get Response Time Out      for all the switches).

3) Once I get the reply for ping command from all the switches then I connect Link 1 again and check        the ping results.

4) Then the same is repeated by disconnecting and connecting Link 2.

  Can someone please help me out with the configuration of MST priority.

  Thanks in advance!

[Reza Sharifi]

Here is a document on MST and how to configure priorities. 

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/31sga/configuration/guide/config/spantree.html#wp1021069

HTH

[Arpita]

Thanks Reza.

But is there any document on how to decide the pattern of priorities in a cisco stack?

[Reza Sharifi]

Hi,

If you are referring to stacking priorities, that is different. The highest priority for stacking is 15 and lowest is 1 (default).  So, you would need to pick one of the switches and make it the master by giving it priority 15, then the second switch could be 12, the 3rd switch could be 10 and so on...

have a look at this link for more info:

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/3se/ha_stack_manager/configuration_guide/b_hastck_3se_3850_cg/b_hastck_3se_3850_cg_chapter_010.html#con_1153255

HTH

[Arpita · Accepted solution]

Thanks Reza.

Finally I got the system working!

I notice that there were some pre-configured vlans on 4500 switch which were causing delay in the convergence of the network. I deleted all the unwanted vlans and re-configured the switch. Also configured the MST on the switch keeping the priorities of all the switches as default(32768). But made the 4500 (top switch) as the root primary switch. 

And then I got the MST working as I wanted.

[Reza Sharifi]

Glad to help and thanks for the feedback!