Strange case of Spanning-tree (MSTP)

Unanswered Question
Aug 8th, 2010
User Badges:

Hi all,

I have a strage spanning-tree case seeking your help, the background is as follow:

Currently we have 3 physical sites, site A (production data centre), site B (DR data centre) and site C (BCP office), those 3 sites has Cisco 6506E, a pair of stacked 3750 and a 3560 switch respectively. The service provider using QinQ tunnel to provide the WAN services to us like the following simple picture:

site A (switch A) -------trunk in my switch and SP using VLAN ID 701-------site B (switch B)-------trunk in my switch and SP using VLAN ID 709 --------site C (switch C)

all these 3 switches are running the same MSTP region and the configuration are the same, same region name, same revision number, and instance (instance 0 for VLAN 1 and VLAN 2-4094 in instance 1), and we have manually configure the switch A being the root bridge for all of the instance.

However, recently, the switch B say it is the root bridge of instance 1, so there are 2 root bridge in the network for instance 1 and switch C also said switch B is the root of instance 1. Switch B is successful to receive BPDU from switch A, and it say switch A is root for instance 0. But from the debug spanning-tree all message, it said the trunk port connecting to switch A (sanity: mrecord missing).

I have searched in Internet but have no luck. Now we don't have spanning-tree issue because the connection is not a loop in our network. But I will feel more comfortable if switch B can get BPDU normally. Would you please help in this case and how can I solve the problem of mrecord missing?

Thank you

Best Regards,

Terry Chow

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Tharak Abraham Sun, 08/08/2010 - 18:45
User Badges:
  • Bronze, 100 points or more


How did you assign Switch A as root ?

Could you do a "spanning-tree mst 0 priority 0" and "spanning-tree mst 1 priority 0" on Switch A?

Reset the revision number to a +1 higher than whats in Switch B

Check the Status on both

Please carry out these changes in non-production hours or weekends..

MST can be a real PITA if not handled properly..-:)

chowterry Sun, 08/08/2010 - 19:26
User Badges:

Hi Tharak,

I am using the command "spanning-tree mst 0-1 priority 24576" to set switch A as the root, and other switches using the default 32768.

Should I also change the revision number in switch B and C also?

Thank you.

Tharak Abraham Mon, 08/09/2010 - 04:38
User Badges:
  • Bronze, 100 points or more

Yes, you need to set the revision number as same in all the switches in the same region...say 10.

This parameter wont get incremented on changes.

chowterry Mon, 08/09/2010 - 18:06
User Badges:

Thank you Tharak,

I will schedule a maintenance window to test it.

Thank you.

Best Regards,

Terry Chow


This Discussion