As near as I can tell, way too many networking vendors handle autonegotation incorrectly for 100M ethernet.
I mean, it could be worse -- things could fall back to 10M.
If a fastethernet port is set to autonegotiate, when it sees link, it tries to - as you might guess - negotiate the speed and duplex. If the device at the far side doesn't negotiate in a compatible fashion or at all, a port set to autonegotiate will fall back to half duplex.
If this happens, then at best you end up with both sides at half duplex (annoying but not catastophic) or with a duplex mismatch. A duplex mismatch can totally hose your performance.
Honestly, when dealing with 100M, I'd just as soon hard-set everything to full duplex and be done with it.
- ▼ April (6)