From a recent Wireshark capture of a RSTP BPDU on a switch, both proposal and agreement bits were set to '1'. In my understanding, initially both switches 'propose' themselves as root. The better root is elected, and the other switch replies with the agreement bit set.

Also, after the whole syncing process, the root's proposal bit is '0' but agreement bit is still '1'. Why is this so?

Proposal and agreement are '1'

Proposal is still '1' after sync

  • 1
    does this answer the question? community.cisco.com/t5/switching/…. According to this ref: the answer is "the flag is ignored, so it doesn't matter if it is set or not"
    – Effie
    Sep 27, 2021 at 11:10
  • @Effie, yeah this feels right, although I feel it is an incorrect design to do so. Sep 27, 2021 at 11:35
  • i think this is written in the link too
    – Effie
    Sep 27, 2021 at 12:17
  • Please, never use an image for text. Simply copy the text, paste it into the question, and use the Preformatted-text option ({}). You can obfuscate any text prior to posting the question.
    – Ron Maupin
    Sep 27, 2021 at 12:33


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.