Thats a very good point John! Any thoughts why a cat5 <5m non-erroring link with auto on both ends that negotiates 100/full would sometimes (once,twice per week) drop down (10/half) and then back up again shortly after? Forcing both ends 'fixes' it (stops the flaps).. Seen that one before?
Cheers On 20 August 2010 14:46, John Neiberger <[email protected]> wrote: > Someone in the other thread mentioned that they were surprised to see > that so many people were against manually configuring speed and > duplex, so I thought I would explain why this is a bad idea most of > the time. > > The Fast Ethernet standard does not mention how devices are supposed > to behave when manually configured. It only deals with Nway > autonegotiation. The problem is that there are two possible behaviors > when settings are manually configured: > > #1: Participate in Nway, but only offer the configured settings > #2: Disable Nway entirely and run at the configured settings > > Cisco's older switches, like the XL series, used behavior #1, as do > most PC/Server NICs that I've run across for that past eight years or > so. Beginning around the time the 2950s came out, Cisco decided to > switch to behavior #2. If you connect two devices that use behavior > #1, you'll be fine. If you connect two devices that use behavior #2, > you'll be fine. But what happens if you connect a "#1" device to a > "#2" device? You get a duplex mismatch! The device that still > participates in Nway is going to expect to see an autonegotiating link > partner. When it doesn't detect one, it follows the standard and > assumes it is connected to a hub or some device that can't do full > duplex and it falls back to half duplex, often without telling you. > This creates input errors on the full duplex side and late collisions > on the half duplex side. If you have hard-set your speed and duplex on > a Cisco switch and you're seeing a lot of input errors, you likely > have a duplex mismatch because of this problem. Setting BOTH sides to > auto usually resolves this issue. > > Auto is the only reliable way to go these days unless you know ahead > of time which of the two behaviors your devices are choosing. If you > don't know, autonegotiation is the most likely way to get a good > connection at 100/full. > > I hope that helps clear some of that up. > > -John > _______________________________________________ > cisco-nsp mailing list [email protected] > https://puck.nether.net/mailman/listinfo/cisco-nsp > archive at http://puck.nether.net/pipermail/cisco-nsp/ > _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
