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Help MSTP

Hi Guys,

I want to ask for your help to have a look at one of our problems that we configured STP for Cisco switches.

STP Problem.jpg

In this scenario

All the switches have that stp mst mode configure.

Except that all the access switches don't have instance 3.

For instance 0-1, the access sw1 port 47 will be blocked and the distribution 2 will become root bridge (which is correct i suppose)

When come to instance 2-3, the access switch 1 will elect itself as root bridge

and will be block the same port (gi1/0/47) for all instances.

We have tried to enable debug and clear the stp protocols, configure name and revision number but the problem still the same.

Is there any config missing, or its the structure that is causing the problem? Please kindly advise. Thanks!

Everyone's tags (3)
1 REPLY
Silver

Help MSTP

You need to have the same instance to VLAN mapping on all switches. Otherwise you will create different MST regions. You don't have instance 3 on the access switches? You have the default priority for instance 0? That is the CIST root, mayebe access SW1 has the lowest MAC?

Daniel Dib
CCIE #37149

Daniel Dib CCIE #37149 Please rate helpful posts.
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