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Beginner

RSTP - Proposal/Agreement SYNC Process

Hi.

In the SYNC process, does switchports pass across for learning state?

Thanks!

6 REPLIES 6
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Hall of Fame Cisco Employee

Juan,

The "SYNC" means that all non-edge Designated ports have been put into Discarding state. These ports by definition send Proposals (each Designated Discarding or Designated Learning port sends Proposals). If their Proposal is not replied to (and no superior BPDU is received in these ports), they will gradually proceed from Discarding to Listening to Forwarding. After reaching the Forwarding state, the Proposal bit will cease to be set.

I am not sure if this answers your question so please feel welcome to ask further.

Best regards,

Peter

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Hi Peter, thanks again! RSTP is a chapter very interesting.

Then, the learning state, is only utilized when the SYNC process can´t be realize? (e.x if the switch has connected a STP 802.1d switch.)

Thanks!

Juan

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Hi,

If agreement message is not received after proposal was sent port slowly transitions into forwarding state. And falls back into traditional 802.1d listening, learning sequences.

Sent from Cisco Technical Support iPhone App

Best regards,
Abzal
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Hi Abzal, thanks! but, then, when does RSTP utilize ONLY the learning state?

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As you might know RSTP converge very quick on almost BPDU transmission speed and timers are involved as with 802.1D protocol. Port bypasses learning state. Because suppose you have root bridge and you connect second switch to it. Their connected port come up with Designated blocking state. Then Root port sends BPDU with proposal bit set once second switch receives it switch puts non-edge DP ports into designated discarding state. Then it responds with copy of received from root BPDU but with agreement bit set . Once it sends message second puts it's port into FW state. And when root bridge receives BPDU agreement it puts it's port into FW as well. This process very quickly. May be less than second.

Hope it will help.

Sent from Cisco Technical Support iPhone App

Best regards,
Abzal
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Thanks Abzal, but then native RSTP, never use Learning State?

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