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-   -   Internet dead all of a sudden, nothing changed. (http://www.linuxquestions.org/questions/linux-networking-3/internet-dead-all-of-a-sudden-nothing-changed-943323/)

sofly 05-04-2012 05:35 PM

Internet dead all of a sudden, nothing changed.
 
I run a small server w/ CentOS 5.8. It's main function is as a samba fileserver.

It has a static IP, and was working until last night. I got a call that the network was down, and when I got to the office it was the only machine without a connection. It's on a wired connection that's plugged directly into the switch rack. I also moved it directly into the router, which didn't work. I've also tried the usual boring stuff (rebooting the network service in init.d, etc.). Nothing seems to be working :/

I'm no expert with logs in linux, is there a network log that I can find? What's the best troubleshooting step to see what's going wrong with the machine?

Thanks :D

frankbell 05-04-2012 09:06 PM

You can run lspci to see whether the network card is still being seen and boot to a live CD of something to see whether the networking works with it. If it doesn't, it's likely hardware.

I got a dollar to a doughnut that the single most productive thing you can do is swap out the ethernet card with a known-good card.

jefro 05-04-2012 09:13 PM

I hate to start off with this but is the ethernet cable plugged in?

Lights on back of nic?

Do you have a loopback ethernet connector or cable?

Any lights on router?

Results of commands like ifconfig netstat or arp maybe.

Skaperen 05-04-2012 11:44 PM

Does "ifconfig eth0" show "RUNNING" in the status?

sofly 05-07-2012 10:23 AM

After investigating a bit further, I'm pretty sure this is a NIC hardware issue. I haven't had time to test much. The NIC still shows on lspci, and I am seeing just the green light on the back on the CPU where the ethernet is plugged in. eth0 is running as well, which really makes me think this is hardware related. How known are NICs for just dying, but still appearing to function?

I'm going to boot to a LiveCD tonight to test it. I'll post any results, and as usual, any advice is much appreciated :)

frankbell 05-07-2012 09:27 PM

Don't overlook the simplest cause--try swapping out the ethernet cable too. I had one of those go bad on me about a year ago.

es0teric 05-08-2012 03:22 AM

Check /var/log/messages or /var/log/syslog around those timeframes, as well as dmesg. Those may provide insight.

You can also setup a ping test to another LAN box to run 1000 times or something, and see if any packet loss occurs.

sofly 05-09-2012 06:00 PM

A really weird thing happened yesterday. I was sitting in my chair wondering why the NIC would crap out on me out of nowhere. I built this machine myself, so I was about to crack it open as I noticed that the power cable was a tad loose. I had already begun setting up a new server and was going to clone all of our data over to it. When I plugged the power cable back in all the way (it had ~1/4 inch to go), the computer booted up and was running at normal speed with an internet connection.

I'm a EECS major in college, and I'm REALLY curious as to why this happened - did lack of power or signal flow somehow temporarily sieze the mobo and [for some reason] the peripherals and components weren't getting the right voltage or current? Probably going to start another thread about this...

Lesson learned - before you troubleshoot a "dead" NIC, unplug everything, open it up, make sure it's all good, plug everything back in, and give it 1 more go before you throw the flag.

frankbell 05-09-2012 09:48 PM

Wow. I'm not qualified enough as an electrician to have an idea. My guess would be that there wasn't enough contact between the surfaces to allow an adequate flow of current, but that is a guess based on complete and total ignorance. Or perhaps a bit of corrosion built up on the contacts and reseating the cable cleaned it off.

Your troubleshooting principle is excellent though. Even when it's likely not a hardware problem, five minutes of reseating cables and other simple hardware tests are quick and easy and can save hours of agonizing over software.

Glad you are running again.


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