Can anyone tell me what this command does. The default for our switches is for it to be disabled, ie. "no spanning-tree optimise bpdu transmission". I have checked the documentation for the relevant switch models and can't find it in the command references or configuration guides.
That's really a subtle IOS architectural optimization so I don't want to enter into the details, but basically:
-Without optimized transmission, BPDUs are sent independently one by one from the STP process.
-When optimized BPDU transmission is used, the BPDUs for a given vlan are prepared first (they all look the same in fact) and then sent in a row at interrupt level (with no further CPU interruption). The main advantage is that the same packet buffer is allocated once and recycled for all the BPDUs, instead of being allocated and freed for each and every BPDU.