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Spirent KB Article
Doc ID: FAQ15540
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Spirent TestCenter: Why MSTP still sends BPDU messages after becoming a root port?
Spanning Tree Ports
• Blocked - Doesn't send BPDU's, but is receiving them.
• Designated - Send BPDU's and Receives BPDU's.
• Root - Doesn't send BPDU's, but is receiving them.
So after one port becomes Root, it no longer needs to send BPDU’s except maybe for a topology change.
For MSTP, there seem to be port rolls for CIST and for MSTI which both are conveyed in BPDU’s.
If a port becomes Root for both CIST and MSTI then you will not see any BPDU’s from the port unless there is a topology change.
It's possible to have on port to be root for CIST and another port to be root for MSTI
In this case you will still see BPDU’s from both ports.
Product : STP