STP Messages (BPDU)

STP messages are called BPDU (Bridge Protocol Data Unit). BPDU contains BID (Bridge Priority + MAC Address)

  • BID is 8 Byte in size. MAC Address is 6 byte, hence the remaining 2 bytes are Priority.

Hello BPDU contains the following fields:

  1. RB ID

    • Bridge ID of the Root Bridge

  2. Sender's BID

    • BID of the switch sending this BPDU

  3. Sender's Root Cost

    • STP cost between this Switch & the current Root

  4. Timer Values on the RB

    • Hello Timer, Max Age Timer, Forward Delay Timer

Reference:

  • CCNA 200-301 OCG, Volume 1, Pg. 218- Wendell Odom.

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