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Multiple spanning-tree

Abdul salaam
Level 1
Level 1

Hello guys

what is Revision number and its impact in MSTP ? 

Thank you 

2 Accepted Solutions

Accepted Solutions

Hello,

 

The MST process uses the Revision number, name, and Vlan-to- instance mapping to create a hash. The neighbors exchange their hash and if any of those 3 values are different the hash will not match up and therefore will not exchange information. If they match then the neighbors exchange their VLAN information.

 

Hope that helps

-David

View solution in original post

The configuration revision number gives you a means of tracking changes to the MST region configuration. Each time you make changes to the configuration, you should increase the number by one.

View solution in original post

5 Replies 5

Hello,

 

The MST process uses the Revision number, name, and Vlan-to- instance mapping to create a hash. The neighbors exchange their hash and if any of those 3 values are different the hash will not match up and therefore will not exchange information. If they match then the neighbors exchange their VLAN information.

 

Hope that helps

-David

The configuration revision number gives you a means of tracking changes to the MST region configuration. Each time you make changes to the configuration, you should increase the number by one.

You might be thinking of VTP as when you make a change on the root switch the revision number increases and propagates the new revision number down. With MST its a manual configuration and it is NOT propagated through the network. If you change it when you make a change you have to do so on all devices manually. When you change it you will lose your spanning tree information and take down the network until the revision matches on all devices. I would NOT recommend doing this in production.

if I do config and then I need to add some VLAN to instance and add other instance how can do that ?

You would most likely do it in a maintenance window. All VLANs are mapped to Instance 0, so creating a new VLAN would not require any change to be made. If you wanted to add a new VLAN to another instance then unfortunately it needs to be done during off hours. I was mainly referring to do it during the business day and you don't HAVE to change the revision number. Its not required but you can for tracking purposes. You would just have to make 2 changes - the revision number and adding the VLAN to a specific instance. But I see your point of trying to add a new VLAN. 

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