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In trying to wrap my head around MSTP and RSTP I have read conflicting information about which ports a switch will send BPDUs through. It is clear to me that for MSTP the switch sends the BPDUs needed to maintain the CST and the information about other spanning tree instances go along for the ride. So I am guessing I need to look for the role/state of a port for the CST instance. If a port is in the following states for the CST instance will it be sending BPDUs:

  • Root/Forwarding?
  • Designated/Forwarding?
  • Alternate/Discarding?
  • Backup/Discarding?

Similarly on which port state/roles would a switch listen to a BPDU?

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