I have a STP diameter related question. The STP standard specifies the max diameter with 7 and the default max age with 20 seconds (with 1 second delay per switch).To make sure I understand the diameter parameter correctly, the diameter is the maximal amount of switches between the two farthest points in a LAN (not to the root bridge).
For example (max 7 hops): SW < -> SW <-> SW <-> ROOT <-> SW <-> SW <-> SW
The 7 hop limitation could be an issue with a wide spread network.
The default max age value is 20 seconds and is increased by every switch in the network by one (start at the root bridge with 0). Hence the max distance from the root bridge to the farthest point (switch) is 19 switches/hops, before the BPDU’s are dropped. With this 19 hops in mind, STP is more robust and tolerant in regards of the network size/diameter.
I know some STP implementations where the STP diameter is 12 hops and more (from end to end) and the BPDU’s reach the farthest point. The STP works fine during a failover to a redundant path and back.
I would appreciate your feedback in regard of my experience/question.