On Sat, 5 Jan 2002, Donald Becker wrote: > I write this many times a day: > Don't use forced-full-duplex! > > Anytime the speed or duplex is forced, autonegotation is disabled. Read > http://scyld.com/expert/NWay.html That is actually incorred. It should be "Anytime the speed AND duplex is forced". It is a very common problem and there are way too many people that miss this. The above is true for cisco for instance. Speed 10 and duplex auto will still autoneg but only at 10 megabit. With Extreme Networks you can either "auto on" (both speed/duplex) or "auto off" (and then you have to set both). As far as I know switches should be able to still auto but only announce certain capabilities (Sun boxen does this for instance, you can turn off capabilities (10/half, 10/full and 100/half) and still use auto, and the machine will only announce 100/full over NWAY and only use that, but any switch connected to it will auto to 100/full) Otherwise you are right of course. Rule of thumb: If you force a speed/duplex at one end, you have to force it at the other as well. Use auto at both ends and it works 99% of the time. Only time I force full duplex is over fiber links when I use media converters from copper to fiber and back again, and then I make damn sure I force it at both ends. If you really REALLY have to force it and you have problems, always force half duplex and see if it works with ok performance. If you force half duplex at one end, the other party will either autoneg to half duplex, or not autoneg at all and default to half duplex, in any case you'll be ok. The exception here again is the fiber links, especially over long distances. You do not want to use half duplex over 500 meters (or even shorter). Signs of duplex problems: Late collisions, CRC errors and other errors, and few megabits of thruput and packet loss. -- Mikael Abrahamsson email: swmike@swm.pp.se - : send the line "unsubscribe linux-net" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
