RSTP - Message Age

[Juan Urti]

Hi all!

Someone knows, in RSTP, when one switch receive a BPDU, how does the switches manipulate the message age timer in RSTP? Does it modify the message age?

Thanks

[Peter Paluch · Accepted solution]

Hello Juan,

In RSTP, each non-root switch receives a BPDU on its Root Port with the Message Age set to N, N>=0. As a result, the switch itself will send out its own BPDUs with the Message Age set to N+1. A root swich sends its BPDUs with the Message Age set to 0.

Best regards,

Peter

[Juan Urti]

Great Answer Peter, it was very useful.

Your answer, allows me to comprend how RSTP solve the Count to Infinity problem.

Thanks!!!!

[Juan Urti]

Peter, really your answer is correct. I have verified with 4 switches and the wireshark.

The topology was a chain with:

SW1 -> SW2 -> SW3 -> SW4  where SW 1 is the root, and i have inspected the bpdu in sense SW3 (DP) to SW4 (RP).

SW1 send his bpdu with Message Age = 0

SW2 send his bpdu with Message Age = 1

SW3 send his bpdu with Message Age = 2

Thanks Again!