Multiple Spanning Tree (MST)

[lagapidis (Lazarus Agapidis)]

Hello Samir

@samirkhair

When you say outside the region is seen as one big switch, does that mean if you were to look at the IST BPDUs being sent outside of the region (from a boundry port) the Bridge ID would be the same no matter which switch it was sent from?

Yes that is correct.

@samirkhair

And if so, what bridge ID would it use from the region, the root?

The bridge ID of the root bridge in the IST.

Take a look at this lesson.

MST and PVST+ Interoperability

If you go through it step by step, you will see that the bridge ID for the “imaginary big MST switch” that is seen by switches outside of the MST is indeed the bridge ID of the root bridge of instance 0 or the IST.

I hope this has been helpful!

Laz