kstratton> I just went through some painful debug session(s) with my kstratton> ISP. For some reason, after forcing 10 base T half duplex kstratton> through my windows box directly to my modem (I do not kstratton> expect ISPs to support linux),everything suddenly worked kstratton> (after reconnection and re-enabling of course). Can you give more details on the cable modem box you're using and the PC as well? Such as what network card in the PC you are using? kstratton> How often does this kind of thing happen? I have seen this kstratton> kind of thing before only once before, and I was using an kstratton> old hub that only supported 10 base T, not a home router kstratton> that is supposed to autodetect the port type. I remember kstratton> that the modem only supports 10 base T, but I am not 100% kstratton> certain. Sun and Cisco were notirious for having problems figuring our autonegotiation on the Sun hme (Happy Meal Ethernet) cards. They'd end up 100Full on one side and 100 Half Duplex on the other. It would work, just very slowly... kstratton> Does anybody have an explanation of what most likely kstratton> happened? Do not hesitate to skimp on technical details or kstratton> references if is convenient. I desperately want to kstratton> understand what happened. -- Something didn't autonegotiate properly. Did you try powering off both devices and then powering them on starting with the cable box? Also, alot of Cable Companies lock the cable box to the first MAC (ethernet hardware address) they see coming over the link. So if you boot up with a PC, and then try to move to something else like a NAT box or a linux box acting as a NAT box, things can go wonky. Usually a hard reset of the Cablemodem will do the trick, but sometimes you need to contact the ISP and ask them to reset it for you. In your case, it really sounds like a problem with Autonegotiation. Some devices just don't do a good job, esp older equipment from before the Gigabit ethernet stage. Just to expand on Frank's email, the people who designed the Gigiabit Ethernet standard over Copper (802.xxx I can't remember) saw all the problems with the 100/10 devices and autonegotiation and explicity made AutoNeg part of the spec in a very well detailed way, so that these problems won't happen again. As a matter of fact, Gigabit ports are much smarter and don't require crossover cables either, you can just plug them into back to back, they figure out what's going on automatically and adjust. The joys of big ASICs! John