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Spirent TestCenter: Why MSTP still sends BPDU messages after becoming a root port?

Environment/Versions
  • Spirent TestCenter
    • Spanning Tree
    • MSTP

 

Answer
  • 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