Hello Sathish
In RSTP, if a designated port sends a proposal but does not receive a BPDU with the agreement bit set, the following actions can occur:
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The designated port starts a proposal timer. This timer is intended to give the downstream switch (the one that should send the agreement) time to process the proposal and respond with an agreement BPDU.
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Until the agreement is received, the port that sent the proposal will not transition to the forwarding state, ensuring that no loops are created during the topology change.
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The designated port may periodically resend the proposal BPDU if it doesn’t receive an agreement within the expected timeframe.
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While waiting for the agreement, the port remains in the listening and learning states, during which it continues to receive and process BPDUs.
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If the agreement is not received within a certain period, the switch may fall back to traditional STP behavior. This of course involves a longer convergence time as the port transitions through the usual STP states (blocking, listening, learning, and finally forwarding).
The key point here is that RSTP’s proposal and agreement mechanism is designed to rapidly transition ports to the forwarding state while maintaining loop-free topologies. The absence of an agreement BPDU means that the transition to forwarding is halted to prevent potential network loops, or the operation falls back to STP.
I hope this has been helpful!
Laz