Moving from PVST+ to MST

[howlingthunder]

Recently found some loops caused by running out of STP instances (89 in use in one VTP domain). Have been looking at moving to MST for a couple of months. Wondering if anyone has some experiance they can share. I have looked at the design and configuration docs on Cisco. Thanks for any real world guidance

[Mohamed Sobair]

Hello,

This is absolutely a good decision you have made. the reason is not because of the Loop that you have experienced RATHER than having rapid Convergence and Interoperability with Other Vendors as well. Running MSTP in your Network would Provide you Rapid Convergence & Scalability you are looking for. No More Instances Per VLAN, Now you Can have a group of Vlans per instance which recieves similar treatment and have identical Spanning-Tree Topology.

My Advice Would be always to start Migrating from the Edge To the Core as much as possibly Can. You Can check a Guide Lines on the Cisco Site for Migrating from PVST+ to MSTP.

Regards,

Mohamed

[chris.smailes]

Hi Mohamed, I'm confused a bit by your answer; Have you done a migration where you started from the edge ? I'd be grateful to hear your experiences. I've been reading around mstp in preparation for migrating from rpvst+ to mstp because we will soon exceed the maximum no. of vlans (per vtp domain) that pvst on an edge switch can safely handle - 128. From what I've read, I thought that we would have to start from the core and work out because it is necessary that, for correct mstp to pvst interaction during the migration, the root for all vlans must be in the mstp region - see discussion -  https://supportforums.cisco.com/thread/2107908. Thanks, Chris.

[Mohamed Sobair]

Hello Chris,

You are absolutely right! Its just a typo mistake from my side, what I meant is to migrate from the Core to the Edge. I hope the original poster recieves this important details.

The Reason is because, normally your Core Switches is your Root Bridges, and migration should be started from here.

The Recommended Approach when migrating is to keep the MSTP Bridge the root bridge for all Vlans, although you can make the PVST+ the root for all Vlans including Vlan (1) the IST but its not recommended.

Note:

Dont make the PVST+ a root for some Vlans and the MSTP bridge a root for another Vlans!!

Thanks for the correction. Good Luck with your migration. BTW: I didnt migrate from PVST+ to MSTP, however, I have migrated from PVST+ to an RSTP.

Regards,

Mohamed

[chris.smailes]

Hi Mohamed - Thanks for the reply. I've only just seen it as I've been away.