To day came across something i’d not seen before. One of our interconnect providers had set the port to which we connect as follows and had assured us that it would auto negotiate to whatever speed it could but in the absence of that it would default to 10 MB
interface FastEthernet 0/X
speed auto 10
We found this not to be the case, and according to the test switch we used it will autonegotiate but will announce 10MB speed only. Not much of a negotiation! Interestingly our side was set to 100 full and showed no errors at all. The speed through the link was being limited to 10MB despite our switch claiming it was 100MB. I’ll need to set up some tests in our lab to check out whats really happening as strangely our suppliers are reluctant to allow me to log into their equipment. I’ll update when time permits.