MST to PVST migration.

[Hosam Badreldin]

Hello All,

I would like to know is it possible to migrate from MST to PVST+ (rapid-pvst) without services interruption? Are they some how backward compatible? The old network admin had some switch set to pvst and others to mst and i'm not sure what to do?

I appreciate your input.

[IAN WHITMORE]

Well MST is just the IEEE way of doing PVST+ once they actually realised that doing multiple instances of SPT was a good idea. Maybe not one per VLAN like Cisco, but multiple nonetheless.

They are all compatible, backwards compatible, but when you change the version, you will cause the switches to recalculate and therefore there will be some network interference. You should coun't on that...listening + learning, at least 30secs (if it's rapid-pvst)...

Regards,

Ian

[Hosam Badreldin]

I have tried to move from MST to PVST and I got network outage where switchs could see each other in cdp but they can't communicate. Now I would like to try MST with PVST+ which I'm not sure what is going to happen.

I'm still not sure.

[IAN WHITMORE]

Well I had some HP blade switches and when I changed from STP to RSTP it deleted all my VLANs Never did that again (on the HP switches I mean).

As for Cisco, as far as I'm aware, changing versions shouldn't remove any of the VLANs. Are you using VTP?

Also, please read the other comments in this post. They may help you.

Regards,

Ian

[Richard Michael · Accepted solution]

Hello Hosam,

The sequence I suggest you to take while implementing this migration is Start the configuration on the access switches, and then when finished would  do the aggregation switches, where the root and secondary

root are normally  located. This way the disruption to the MST region is reduced upon a change of STP protocol in one switch. At the last step, you'd have a MST switch alone (the root), talking to everyone else on PVST.

The reason for this is, MST is backwards compatible with PVST but not the other way around. So if you start at the core, your MST switches will lose its root.The STP instance will be recalculated per-vlan upon mode change per switch.

There will be a slight outage for convergence; approximately 30 seconds.I do not think there should be a problem doing this remotely.

In your case its PVST+ so there wont be 30 secs outage too...

Thanks,

Ricky Micky

*Pls rate if the posts are useful

[Hosam Badreldin]

Thanks Ricky. I agree with what you have said and I think this is the way to go .

- Hosam

[lgijssel]

Hi Hpsam,

Probably you should consider migrating to rapid-pvst instead because it converges faster and is widely supported on cisco switches. PVST and MST are compatible but in general, having a mix of stp protocols is not advisable.

Your choice to leave MST is probably the best choice when the network is small enough.

It will be almost impossible to predict how you could migrate your stp setup to another protocol WITHOUT outages.

This may simply not be feasible and/or require a lot of step-by-step posts.

I found a link to guide a migration in the opposite direction:

http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a00807b075f.shtml

It may help to identify pitfalls etc. Best idea is to educate yourself on the task ahead. If you are confident, and your businees allows for it, prepare the configs, plan a late night with pizza or whatever and make sure everything is running fine te next day.

regards,

Leo

.

[Hosam Badreldin]

Thanks Leo. I found that link 2 days a go actually and it is was some what helpful. I'll just keep reading about it and see what I could do.

- Hosam