Can I change the STP mode on VSS without reload?

Answered Question
Dec 17th, 2009

Hello all,

I have two Catalyst 6506 in VSS mode with STP running PVST mode.

The question is...

When I change the STP mode on the VSS, I found the following message.
-------------------------------------
VSS(config)#spanning-tree mode mst
%Changing the STP mode will reset the standby VSS.


Do you want to proceed? ? [yes/no]:
-------------------------------------
Is this the feature of the VSS???

If so,are there any reference to it in any of the docs?

Best Regards,

Tomoyuki

I have this problem too.
0 votes
Correct Answer by vvasisth about 6 years 11 months ago
this warning is valid. In some corner cases while changing STP 
mode, the active STP has switched to the new mode and has started
sending HA sync messages for the new protocol. The standby is still in
the old mode (the mode change has not kicked in yet or in progress) and
the incoming HA sync messages are incompatible. The exisiting code
processes these message and caused a memory corruption leading to the
crash.

Here is the exact match for your issue :-
CSCsy93171

Correct Answer by Giuseppe Larosa about 6 years 11 months ago

Hello Tomoyuki,

you are right for example best practices document for VSS does not mention this and actually there is no section for STP mode change.

http://www.cisco.com/en/US/products/ps9336/products_tech_note09186a0080a7c837.shtml

and there is no note in command reference:

http://www.cisco.com/en/US/docs/ios/lanswitch/command/reference/lsw_s2.html#wp1015453

We know that from outside the VSS presents itself as a single box, I wonder if STP mode has effects on the VSL link or the reload is caused by the need to be sure that standby supervisor config is taken from the active one. Or it can be a SW defect.

What IOS version are you running in your VSS?

Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Thu, 12/17/2009 - 02:22

Hello Tomoyuki,

you are right for example best practices document for VSS does not mention this and actually there is no section for STP mode change.

http://www.cisco.com/en/US/products/ps9336/products_tech_note09186a0080a7c837.shtml

and there is no note in command reference:

http://www.cisco.com/en/US/docs/ios/lanswitch/command/reference/lsw_s2.html#wp1015453

We know that from outside the VSS presents itself as a single box, I wonder if STP mode has effects on the VSL link or the reload is caused by the need to be sure that standby supervisor config is taken from the active one. Or it can be a SW defect.

What IOS version are you running in your VSS?

Hope to help

Giuseppe

Correct Answer
vvasisth Thu, 12/17/2009 - 02:23
this warning is valid. In some corner cases while changing STP 
mode, the active STP has switched to the new mode and has started
sending HA sync messages for the new protocol. The standby is still in
the old mode (the mode change has not kicked in yet or in progress) and
the incoming HA sync messages are incompatible. The exisiting code
processes these message and caused a memory corruption leading to the
crash.

Here is the exact match for your issue :-
CSCsy93171

t-yamashita Thu, 12/17/2009 - 03:14

At first, my VSS is running 12.2(33)SXH and I found the message.

But now, I upgraded to 12.2(33)SXI and didn't appear it.

Thank you for all of your help.

Best regards,

Tomoyuki

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