Hi all, I think this is a simple question but I can´t find the answer, yet!
In a RSTP or MST enviroment, BPDUs are used as keepalives in point-to-point links. Correct ?? So if three consecutives BPDUs are lost, we can assume the path between the two switches is down. The question is: which is the time the switch receiving BPDUs waits before considering one BDPU lost ?? It is the hello interval ??
I´am looking for this answer to know which is the maximum latency supported between two switches running RSTP or MST.
You are welcome.
I am agree with you about the theory. I just want to add just as the previous link stated that unlike STP 802.1D, in 802.1w BPDU are sent out every switch port every hello-time (thus inside 802.1s region), and not simply relayed anymore (regardless of whether BPDUs are received from the root).
In this way, any switch anywhere in the network can play an active role in maintaining the topology.
Otherwise an intersting document of STP timers considerations (with aspects like "message-age" for the exact calculation of the max-age formula etc ..) is at the following link : http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a0080094954.shtml
BUT as this link states the document only discusses how to tune STP timers for regular 802.1D (not 802.1w/802.1s).
With that being said, after having checked the IEEE standard for RSTP (http://standards.ieee.org/getieee802/download/802.1D-2004.pdf)
I have seen there is likely an underlying timer "rcvdInfoWhile" which should track the BPDU reception and refresh the timer each time it receives a BPDU =>
17. Rapid Spanning Tree Protocol (RSTP) /*/ 17.17 State machine timers /*/ 17.17.6 rcvdInfoWhile
rcvdInfoWhile / The Received Info timer => The time remaining before the spanning tree information received by this Port [portPriority (17.19.21) and portTimes (17.19.22)] is aged out if not refreshed by the receipt of a further Configuration Message (check schema in attachments).
Hope it helps..