Ethernet Only Working in 10Mbps Full/Half Duplex

[Skrying]

I've had this odd issue for the last few days. The ethernet on my motherboard will only work when I force it into 10Mbps Full or Half Duplex setting. The motherboard is an Asus M4A785TD-V EVO with a Realtek RTL8112L ethernet controller. This issue appeared suddenly when I booted into my Windows 7 partition from Ubuntu 10.04. When using any other speed faster than 10Mbps it will repeatedly drop and reconnect rapidly. Previously it was working just fine Auto Negotiation but that will no longer work.

Any ideas? I've tried reinstalling drivers and swapped out cables. No luck though.

[just brew it!]

Bad network switch? We've had a few go bad at work... all sorts of weird stuff starts happening, including the sort of symptoms you're describing.

[notfred]

What speed would it autonegotiate to before? If it was Gigabit then it could be a wiring/connector problem. I had a bad wiring run where only some pairs were good and some network cards would autonegotiate up to Gigabit and then fail because of the bad pairs (Gigabit requires all the pairs working, slower speeds don't). Forcing the speed down to 100Mbps Full and making sure that autonegotiate was still on at that speed fixed it as it stopped it from using the bad pairs.

The fact that it only works at 10Mbps makes me think one end has lost autonegotiate capability. If you are forcing the speed on one end, you need to make sure that the adaptor still does autonegotiate but only advertises the speed you are forcing it to. If you don't then the other end sends the autonegotiate sequence and gets nothing back so it assumes it is talking to an old dumb 10Mbps half duplex. Setting your speed to 10Mbps gets you connected and you'll only notice a duplex mismatch (i.e. setting full when the other end is half) if you start looking at the collisions counter or if you benchmark and notice the very poor throughput.

[Aranarth]

I agree with notfred and Justbrewit.

I would first swap the cable out. If you cannot then check to make sure it had not been chewed up or that it has something heavy on it like a table leg or that it has been rolled over by a chair with casters etc.

Next I would try a different port on the switch or a whole different switch all together.

Most switches these days are intelligent and they do not require all ports to run at the same speed. However most hubs are not buffered and do require everyone to talk at the same speed. If you are using a hub its time to let the poor beast go and get a switch.

If your main board has multiple Ethernet ports try a different one or use a separate nic altogether.

I would try disconnecting everyone else from the switch if possible and just have a connection to your broadband "modem".
Sometimes all you can do is the process or elimination till you find the culprit.

Oh yeah, don't forget to try rebooting your switch as well.

[Skrying]

I have no control over the other end as this is connected to a dorm network. Previously the speed would auto negotiate to 100Mbps (speed of the network). I haven't heard about anyone else having issues but I haven't exactly went around asking about it. I'm only here for 5 more days so I'll likely hold off on moving things around until I move in to my summer place.

[Contingency]

If you have another computer, you can isolate the switch from troubleshooting by cabling both PCs together.

[pavelow]

Hi.. I'm having the exact same problem, as soon as i installed Ubuntu 10.04 dual boot with win7 (wubi) my NIC (RT8111D) board is 790XTA-UD4 hasn't been able to go above 10Mbps. I'm running it with a gigabit switch and the same cable tested with another computer works fine @gigabit speed... i think it has something to do with Ubuntu 10.04 not with the hardware...

[pavelow]

fixed it... Just unplugged the offending machine from the wall socket for a few minutes, plugged it back in and then i had Gigabit Ethernet again.

[axeman]

I had an experience some time ago where gigabit realtek chips worked like absolute crap in linux, sad to hear they haven't fixed it two years later, although part of the issue is realtek network chips are quite terrible as far as the hardware implementation goes, or so I hear. I don't remember what the chip number was, but it was a PCIe based NIC, and the linux driver for realtek PCIe devices was not very stable at all. I compiled a version of the driver that realtek supplied, which worked a bit better, but still had some issues, I can't remember exactly what. I bought a couple of cards with marvell ethernet chips on them and no issues.