MST - 2950, in multivendor environment

[TimLaffan]

Hi,

Hopefully a quick one,

We have a multi-vendor environment, consisting of HP, Cisco and Linksys switches. We have set all to use MST for interoperability reasons but on our Cisco 2950's i am unable to find away to show the digest code? Can anyone help?

The IOS on the 2950's is: c2950-i6k2l2q4-mz.121-22.EA13

Thanks

Tim

[Peter Paluch · Accepted solution]

Hi Tim,

It seems that there is a hidden command show spanning-tree mst configuration digest supported on 2950. Try that one for instance and please let me know if it worked for you. Thanks!

With 2950, there may be additional issues running the MST - the 2950 support a pre-standard MSTP version only that differs in some aspects from the current 802.1Q MSTP. Cisco devices can talk to each other nicely - if a Cisco device supports both newer and older (pre-standard) MSTP then it will adapt on a per-port basis to the neighbor's version. Therefore, if possible, I recommend connecting your 2950 directly to another Cisco device. Since IOS version 12.2(25)SEC, Cisco Catalyst switches support both standard and pre-standard MSTP version.

I am not sure which version is used by HPs and Linksys-es but I tend to believe they are running the current 802.1Q MSTP version.

Best regards,

Peter

[TimLaffan]

Hi Peter,

Thanks very much,

You were correct there was a hidden command, serves me right for relying on the "?"

Luckily, we are using a Cisco 3750 for the distribution\core with all switches aggregated to it - so this will will solve the issue of using the two different standard together.

Thanks

Tim

[Peter Paluch]

Hello Tim,

Thank you for your response and the generous rating.

Luckily, we are using a Cisco 3750 for the distribution\core with all 
switches aggregated to it - so this will will solve the issue of using 
the two different standard together.

Awesome. Yes, that will solve the issue, presuming you are running a recent IOS. One more hint: on the 3750, it is recommended to configure the switchports towards pre-standard MST switches using the spanning-tree mst pre-standard interface command to force the port to emit and process MSTP BPDUs in the pre-standard format. While the autodetection should be running fine (and you will see information about pre-standard neighbors using the ordinary show spanning-tree command), I have stumbled across a couple of cases where the detection actually did not work (or did not work soon enough) and a loop was formed. Relying on static configuration instead of using automagic procedures seems to be better in this case

Best regards,

Peter

[TimLaffan]

Hi Peter,

Sorry i didnt realise you replied again to this post but thanks again i will give that ago