Of late, when I plug into a particular LAN port the only way I can get my Win XP machine to recognise it is if I change the Link Speed and Duplex settings on the network card (using Device Manager) to use 10 Mbps Full Duplex instead of Auto Detect or 100 Mbps Full Duplex. The same machine(and cable) gets on to the network just fine on other LAN ports, and other machines work at the 100 Mbps setting on this LAN port. I’m quite curious as to what could cause this anomaly. Any body care to venture a guess?
LAN port where? On router? Hub? The wall? Are the “other LAN ports” part of the same device or are they completely separate from the troublemaker?
Depending on the answer, one issue that I remember seeing way back when I managed by grad research group’s computers was that sometimes when two devices were paired up and they were both set to auto-detect they would not play nice together. In that situation we would have to set one of them to 10 or 100 and then the other would detect that.
LAN port on the wall. “Other LAN ports” are the different LAN ports on the wall, but part of the same network. The thing that really confuses me is that the problem went away for a few weeks, but is now back. Nothing(even remotely relevant) has changed in this time period in my computer.
Probably just a bad or pinched cable.
The nice thing about Cat5 is that a damaged cable run will usually not fail outright, but be able to degrade to run at a slower speed.
You can just put in a ticket to have your IT guy put a Fluke tester (or equivalent) on the cable, it’ll tell you what the problem is.
It is most likely a fault on that port back at the switch. As Blakeyrat says, have them test the wiring and in addition to that, the port.
It’s definitely not the LAN cable between the wall port and the computer. I’ve tried it with different LAN cables. If it were the wall wiring, wouldn’t the same problem show up on the other computers with which I’ve tested it? I’m not interested in fixing the fault as much as understanding the reason why it may be happening.
I have two questions really.
a) Why can I connect to the network when I change the setting to 10 Mbps but not at 100 Mbps?
b) Why does this problem only crop up with the combination of this one port and my computer?
ETA: Thanks all for the responses.
It is probably a combination of a low quality NIC on that specific computer and some minor fault on the cabling.
I had exactly the same problem with a computer of mine. Only in my case I didn’t have to manually change the network speed, it would automatically drop to 10Mbps.
It was a rather long run of cable and my theory is that this specific NIC wasn’t powerful enough and the length of the cable made the signal to attenuate too much. I installed a second NIC on that computer and it could connect at 100Mbps alright.
I would go with the idea of a marginal NIC. It may be that there is noise on that particular port that the other NICs in the other machines can handle but this particular NIC can’t. I’d look in the immediate vicinity of the port and see if there are any strong EM sources nearby. A lot of interference and a cable with slightly damaged shielding might be just enough to cause a problem. For example if the troublesome port is next to where the power cable goes, I would definitely consider that possibility. Both ideas are long shots, but it’s a very strange problem.