"Media disconnected", "network cable not plugged in". What is going on?

April 20, 2008 5:01 AM

All network cards in our LAN suddenly claim to be disconnected. Wireless still works just fine. Can you help?

Background: Our LAN consists of 5 computers, all running WinXP, all using the wireless network to connect to the internet. This configuration has been working perfectly for a very long time.
I'm the only one who uses the wired network cards with a crossover cable to transfer files between 2 of these computers.

All of a sudden, computer A and computer B kept saying the network cable was unplugged when I tried to transfer files. I've been transferring files every weekend for a year, without problems. I had only made a transfer the previous day and everything worked fine.

Both computers' WinXP claimed the network cards were working properly, but ipconfig stated "media disconnected". Hence, when inserting the network cable, the computers kept saying "network cable unplugged".
Rebooting (and rebooting the router/modem) didn't help. There are no virusses or spyware on these computers and they're all updated regularly. The other computers displayed the exact same symptoms.

The only thing that had changed in the last couple of weeks was the introduction of computer C. Transferring files had worked the previous days (and the weeks before), and I gained internet access on that computer by alternately using a cable and the wireless network USB stick of computer B. This is the only thing I can imagine that was different than normal in our network, but I don't see why this would have caused these problems.

I left that evening with computer B to the city where I study. I normally use the wired network there to connect to the internet but the network card kept being disconnected.

I found a DHCPnack error in my logs, but this would be a consequence of these problems rather than a cause, or not?

Googling this problem suggested Media Sense to be the culprit, trying WinsockxpFix.exe or LSPFix.exe. These latter two didn't work, I didn't disable Media Sense yet because I don't fully understand the consequences. Can I just disable it?

I'm stumped! What was the cause for these problems and how do I fix it? Can you help?

posted by lioness to computers & internet (16 comments total)

I'd try a different cable. "Media disconnected" means there is no voltage on the cable, meaning it's probably the culprit.
posted by disclaimer at 5:21 AM on April 20, 2008

Sorry, I forgot to add that different cables give the same result. That was the first thing I tried.
posted by lioness at 6:12 AM on April 20, 2008

This is a long shot, but perhaps some excessive amount of current along the crossover cable fried one or both NICs? Perhaps built up capacitance in the case of a very long crossover cable? Also if just one NIC is bad (most likely the one in your "Computer B", since you had a similar problem at school), the other PC would show a disconnected cable since both NICs are required to be working for the crossover cable to complete a network connection. Try testing both your crossovers between two known good computers to make sure they are not the problem. Then try Computer A and Computer B independently with one of the known good computers. Also see if you can ping the loopback adapter on both computers. Disable the wireless adapters and type "ping 127.0.0.1" from the command prompt and see if you get a response.
posted by Rafaelloello at 6:22 AM on April 20, 2008

One more question, are you statically assigning the IP addresses to the network cards? You must be, because there can't be any DHCP server inside a crossover cable. Make doubly sure that the ip assignments are on a completely different network than your wireless network and that there is no conflict.
posted by Rafaelloello at 6:30 AM on April 20, 2008

Where does Computer C come into this, as far as wiring goes?
posted by odinsdream at 6:40 AM on April 20, 2008

All 5 computers claim to have disconnected network cards, while 2 never even had a cable connected. The 2 users of these computers only use the wireless internet. So I'm quite sure it's not a problem with the NIC's themselves.

What puzzled me was that even with a different modem/router the problem persisted.

I can ping myself (with disabled wireless) without problems, every packet arrives.

Thank you both for thinking with me!
posted by lioness at 6:41 AM on April 20, 2008

Rafaelloello:
Every time I want to transfer some files (almost every weekend), I give a static ip address to computer B.

Computer A only uses wireless, so I leave that static ip configured for the wired network card. Computer B uses wireless here and wired in another city, so I always delete these settings after transferring.

The ip addresses are very different, for example 192.1.1.1 wireless and 10.0.0.1 wired.

odinsdream:
Computer C doesn't have his own wireless card. So I sometimes used the wireless USB stick from computer B to gain acces to the internet and sometimes a cable, depending on which room these two laptops were in. This all worked for several weeks without problems, though.

Computers D and E (that were never wired) are my friends' computers, which I never touched. That led me to believe it was a more general networking problem.
posted by lioness at 7:02 AM on April 20, 2008

If the problem is with a crossover connection between two computers, then the modem/router doesn't factor into it at all.
posted by doomtop at 7:04 AM on April 20, 2008

I'd vote that something has hosed the TCP/IP stack on all the machines on your network (which is basically what you are trying to fix with the Winsock and LSP tools you mention).

Since we're talking about wired networking here, how about you try a Linux LiveCD to connect the two machines together? Most magazines these days come with some distro loaded as a LiveCD on the DVD they package with the mag, so you could boot both machines to Linux and then set static IP's and see if they talk to each other over your crossover cable.. If so, it's a problem with the software on the machines (and really starts to make me wonder about viruses, spyware etc).
posted by ranglin at 7:09 AM on April 20, 2008

Are you getting lights on the network ports of the problem computers? I'm betting not- the "network cable disconnected" message is pretty low level, if you have electrical connectivity you won't get the message.

Find a known good straight through cable and connect the problem PCs (one at a time) to one of the wired ports on your router. Do you get lights and does the PC recognize that it's connected to something? I would bet that one of the PCs has a blown network card.
posted by gjc at 7:40 AM on April 20, 2008

doomtop:
I noticed the problem while using the crossover cable, but it's not a crossover connection problem. The problem persists while trying to connect to the internet.

ranglin:
My apologies if this is an ignorant question, but I'm not at all familiar with networking problems. If the problem was the TCP/IP stack, shouldn't the wireless cards be 'broken' too?
And wouldn't Winsock and LSP have fixed that? (LSPFix states "No problems found".)

I don't have the time to download, burn and try Knoppix, as I almost have to leave to the other city, but I can try that upon returning (Friday). I really doubt however that a virus or spyware is the cause, computers A, B and C are with a 100% certainty. I asked my flatmates to scan their computer (D and E), but they'll only return tonight. However, I drilled them about computer safety, so normally these computers should be clean as wel.

I'm normally the techgirl of our appartment and this is the first problem I'm not able to solve by myself, so I'm really frustrated about it.

gjc:
Not all computers have network lights, is there another way besides those lights to see wether they are connected?
Again sorry for my ignorance, but can one blown card mess up all the other cards in the network?
posted by lioness at 8:19 AM on April 20, 2008

Re: getting a light from the network card: If there is no light at the computer network jack, try looking for a light at the router end - if your connected to port 1 on the router, if the computer network card is working, the light for port 1 should be lit.
posted by disclaimer at 9:39 AM on April 20, 2008

... and to follow on - if a network card is shorting out or causing a lot of traffic issues, it could very well disrupt network operation - especially if it's not well made.
posted by disclaimer at 9:40 AM on April 20, 2008

gjc, you're spot on!
Computer B's network card didn't make the router light up and when I disabled the card, the other computers were able to get wired access.
And thank you, disclaimer, for guiding me!

Computer B (=my laptop) was in repair for a busted internal power jack, I'm afraid the repair guy fried my network card. Alas, I have no way to prove it worked before bringing it into the shop. Dammit!

My eternal gratitude for finding out what was wrong!
posted by lioness at 1:24 PM on April 20, 2008

Glad you've solved the problem, but I'm a little confused here...

Weren't all the computers connected to the router via wireless access? And didn't you say that all the computers were demonstrating the same symptoms over the wired link (which was the crossover cable)?

I think a lot of us here assumed something more sinister than broken hardware because we assumed that not only did computer A not talk to B, but also B didn't talk to C, C to D etc (over the wired crossover link). Why would the network card on computer B cause problems on computer C & D? Or am I confusing your description somehow?

Anyway, just trying to clarify, although not sure if you'll be back into the thread, since it all seems to be sorted out... :)
posted by ranglin at 5:52 PM on April 20, 2008

And I want to know why my high up answer wasn't picked as best answer even though I was first to tell you where the problem likely lied:

Also if just one NIC is bad (most likely the one in your "Computer B", since you had a similar problem at school)

Just kidding. Glad you solved it.
posted by Rafaelloello at 8:53 PM on April 21, 2008