Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

Adding instances to mst

Hi everyone,

My question is very basic - if I add another instance to my mst configuration, will that trigger a reconvergence of mst?

The new instances will now consist of any VLANs already in production or part of another instance.

1 REPLY
Silver

Adding instances to mst

MST works by sending a MD5 digest which is used to compare the MST configuration. Name, revision and instance to VLAN mapping makes up this digest whic his compared between all switches.

Adding another instance or moving a VLAN between instances will trigger Topology Change. When the change is done for a while there will be different MST regions because they don't agree on the mapping. The switch with lowest priority for MST0 will be the CIST root. Switches in different regions will have a single port elected as root towards that region, it will be the switch with lowest external cost towards the CIST root. Other ports will be blocked.

I would suggest to only do these kind of changes outside of production hours. Also see this thread which contains a lot of useful information:

https://supportforums.cisco.com/thread/2118116

Daniel Dib

CCIE #37149

Please rate helpful posts.

Daniel Dib CCIE #37149 Please rate helpful posts.
118
Views
0
Helpful
1
Replies
CreatePlease to create content