I need some information about RSTP

If the port state is blocking, discarding alternate .

Should BPDU be sent to external ports? I cant see any BPDU in wireshark if the port states Alternate,Discarding mode.

  • Unfortunately, for a device to be on-topic here, the manufacturer must offer optional, paid support. Your custom-built network switch is off-topic. We have not idea about it.
    – Ron Maupin
    Aug 12, 2020 at 13:41
  • not about custom switch it is a RSTP network protocole rule !
    – mathco
    Aug 12, 2020 at 14:07
  • 3
    BPDUs are sent out all ports except edge ports.
    – Ron Trunk
    Aug 12, 2020 at 14:28
  • If my port state discarding , is that port send BPDU out of port ? Should I see on wireshark that BPDU ?
    – mathco
    Aug 12, 2020 at 14:32
  • 1
    Yes. To repeat, BPDUs are sent out all ports except edge ports.
    – Ron Trunk
    Aug 12, 2020 at 14:56

1 Answer 1


All the switches in network intially sends and receives BPDU messages when connected in network and election process starts . Switch Ports enters blocking state during the time of election process, when a switch receives a BPDU on a port that indicates a better path to the Root Switch Root Bridge and if a port is not a Root Port or a Designated Port.

The port in the blocking state does not participate in sending any BPDU message it's only in listene for BPDU messages nor it does not sends frame forwarding and also discards frames received from the attached network segment. During blocking state, the port is only listening to and processing BPDUs on its interfaces. After 20 seconds, the switch port will changes its state from blocking state to listening state.

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