pre-version of MSTP

[lcaruso]

Hi,

In reading about interoperability between cisco and hp switches, I've come across the following statement regarding MSTP:

cisco supports a pre-version of MSTP which appears the same as MSTP. The difference is not apparent in the command set. However, this pre-version does not interoperate with standards MSTP. Ensure the cisco device has the right version of IOS and the real MSTP not the pre-version of MSTP.

Can anyone tell me which IOS version I would have to obtain the real version of MSTP. This would be on an array of older switches shown below as well as some new 2960S switches. Thanks for any help.

WS-C2950T-48-SI

WS-C2960-24TT-L

WS-C2960G-24TC-L

WS-C2960S-24TS-S

WS-C2960S-48TS-S

WS-C3508G-XL

WS-C3524-PWR-XL

WS-C3548-XL

WS-C3550-12G

WS-C3550-24

WS-C3550-48

WS-C3560-24PS-S

WS-C3560G-24TS

WS-C3750G-24T

cisco 2611

OS-CIGESM-18TT-EBU

OS-CIGESM-18TT-EBU

[Peter Paluch · Accepted solution]

Hello,

For the 2960, 3550, 3560 and 3750 series switches, there is an interface-level spanning-tree mst pre-standard command. It is used to allow for interoperation between standard and pre-standard MST between Cisco switches. Presence of this command suggests that the switch supports both standard and pre-standard MST. The command first appeared in the following IOS versions:

C2960: 12.2(25)SED

C3550: 12.2(25)SEC

C3560: 12.2(25)SEC

C3750: 12.2(25)SEC

The following platforms do not appear to support the standard MST:

C2950, C3500-XL, Router 2611

Regarding the OS-CIGESM-18TT-EBU, I am not familiar with it. It seems to be a switch blade module. The spanning-tree mst pre-standard command is supported in IBM switch blade modules 3012 and 3110 since IOS version 12.2(40)EX2.

All these information were discovered using command references for particular platforms.

Best regards,

Peter

[lcaruso]

Peter, you are awesome. Thank you!

[Peter Paluch · Accepted solution]

Hello,

You are welcome!

Oh, and another trick to find out if the switch supports standard MST.

There is a (sometimes hidden) command show spanning-tree mst configuration digest - it will show you the computed MD5 digest of the VLAN-to-instance mapping table. If it shows you only a single MD5 sum then the switch supports pre-standard MST only. If it shows you two different MD5 sums, the switch supports both pre-standard and standard MST, as the MD5 hash is computed differently between the versions.

Example from a pre-standard MST only switch:

Switch# show spanning-tree mst configuration digest
% Switch is not in mst mode
Name      []
Revision  0
Instance  Vlans mapped
--------  ---------------------------------------------------------------------
0         1-4094
-------------------------------------------------------------------------------
Digest    BB3B6C15EF8D089BB55ED10D24DF44DE

Example from a standard MST switch:

Switch# show spanning-tree mst configuration digest 
% Switch is not in mst mode
Name      []
Revision  0     Instances configured 1
Digest          0xAC36177F50283CD4B83821D8AB26DE62
Pre-std Digest  0xBB3B6C15EF8D089BB55ED10D24DF44DE

Note that the Pre-std Digest matches on the MST-capable switch matches the Digest value on the pre-standard-only switch.

HP switches are capable of displaying this MD5 hash using the show spanning-tree mst-config command.

Best regards,

Peter

[lcaruso]

Peter,

Another great tip. Thanks kindly!!

Where do I send the the check?

[Peter Paluch]

Hi,

Seeing you satisfied is rewarding enough for me

Best regards,

Peter