I've to provide support for STP/RSTP/MSTP, while going through the specification I see the Force Protocol Version majorly ensures compatibility between STP/RSTP bridges. Mostly, I see the transmission and topology state machines handles those parts. Although, I don't see the Listening phase being used in the RSTP state machine even when the Protocol Version says STP. Any thoughts on like can I implement MSTP and switching between protocols using the Force Protocol Version would be the right thing to do ? or need a separate implementation for each
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Has any answer solved your question? Then please accept it or your question will keep popping up here forever. Please also consider voting for useful answers.– Zac67 ♦Commented Jun 26 at 19:28
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MSTP is designed to interoperate with RSTP. RSTP bridges are always part of the Common Spanning Tree (CST) in MSTP - see IEEE 802.1Q Clause 13.5.2 for details.
Both are also designed to be backward compatible with obsolete STP (802.1D). You should adapt STP's interface cost calculation though to avoid poor root port selection. As initially defined in IEEE 802.1D, STP bases interface cost on a rate of just 1 Gbit/s by default, while RSTP and MSTP use 20 Tbit/s.
Usually, there's no need to force a protocol version, assuming that your central infrastructure uses the more modern versions and there's only some obsolete hardware at the edge.
You can download current IEEE 802 standards from http://ieeexplore.ieee.org/browse/standards/get-program/page/series?id=68 (free after registration).
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you're right the backward compatibility is ensured in MSTP for STP/RSTP, what I need to to provide implementation for each of these protocols STP/RSTP/MSTP for the user to use whichever they need, the question I had was if I implement MSTP and use the Force Protocol Version to enforce STP how close will it be to the original STP state machines– esdeathCommented Jan 28 at 15:55
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MSTP and RSTP are automatically downward compatible with STP. You only need to force a version when you e.g. want two RSTP bridges to talk STP between them.– Zac67 ♦Commented Jan 28 at 15:58
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sorry I asked the question as guest so am unable to add comment, thanks for your reply, one last thing, MSTP will adjust it's state machines based on the neighbouring bridge supporting STP, but how closely will it mimic STP (as I don't see Listening phase at all in the MSTP state machines), in short, an MSTP compatible STP and a full fledged STP implementation -> how different will these be wrt each other from users pov... thanks again !– esdeathCommented Jan 28 at 16:19
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MSTP and RSTP don't mimic STP exactly - interface states do differ. However, they implement as much of the original STP protocol as required for the distributed algorithm to work.– Zac67 ♦Commented Jan 28 at 16:26