Ok, weird problem here. I just got 15/2 FIOS set up. One PC, with XP, a 6 foot Cat 5e run, and a 10/100/1000 onboard ethernet controller (ASUS PC-DL) is doing 15Mbit downstream no problem. Another computer, with a 100Mbit Linksys card, is doing only 8-9Mbit down. Both machines are of reasonable spec, the faster one is a dual Xeon with 1gig of RAM, the slower a 1GHz Thunderbird with 256 megs of RAM.

I originally thought maybe the card's connection settings were incorrect, but the card is set to auto detect, as is the DLINK router.

It's a 250 foot cable run but I tested for physical deterioration by moving the problematic PC onto the 6 foot cable, and that did not resolve the speed problem. I originally had a 10Mbit card in the box, and it was giving me 5Mbit down, and then upgrading it to a 100Mbit card only bought me 9Mbit.

It seems like this machine is averaging around half the advertised speed, is it possible the DLINK router is unable to autodetect the duplex setting? Or maybe there is some weird PCI latency issue with the machine, or some weird BIOS setting? I'm not sure how to proceed on troubleshooting, I can't yank the gigabit card and throw it into this box because it is onboard...maybe I could disable the 1000mbit card and throw the 100mbit card into the one that works, and see if it still happens. I also tried two different WiFi cards, a Netgear and a DLINK, and got around 5mbit with those, so I returned them to the store.

Obviously it's not a WAN problem, because the other machine can do 15 down, unless maybe the PPPoE link is somehow throttling me by MAC address, but I do not believe that to be the case.

This machine just won't do 100 even though it thinks it is doing 100. Pinging the gateway from the true 100mbit machine gives me ping times all <1ms, pinging the gateway from this broken machine gives me an initial ping of usually around 12ms, and then an average of 3ms or so. This is what leads me to believe its a duplex detection problem, it's almost as if its waiting for the entire round trip to ping back out.

Any ideas or suggestions would be appreciated.

Of all the stupid @#$@. Almost as soon as I got home, I solved this problem by disabling AVAST ANTIVIRUS, of all things. Guess who's getting uninstalled and/or traded in for something more lightweight like AVG

If you think Avast is bad Symantic will be less.

Symantec will do a hostile system takeover, lol.

Yeah these days the concept of "antivirus" sure does look a lot like "virus." I've never had a virus or trojan tie me up with spontaneous R&D projects for a few days like Avast just did...