[TriLUG] Wierd Network Problem - Clues Appreciated

[Scott Chilcote]

Hi,

In case anyone's wondering, the problem here turned out to be a NIC gone 
bad after all.  What threw me off was that the card I had swapped it 
with for testing had problems of its own.  They seemed similar enough at 
the time, which started me down the wrong path.

I learned a couple of useful lessons while troubleshooting this problem:

1. Don't buy a $10 NIC from SmartLink (Davicom) as a replacement. It 
lists "Linux" as a compatible OS on the carton, but this turns out to be 
true only if you use the source code module they provide for 2.4.X 
kernels.  My 2.4.7 kernel refused to load it, with a screenful of 
unresolved symbols.  I tried using an existing module for the card 
instead, and noticed that my SCSI hard disks were reporting timeouts 
when I used insmod to install the module.  Turns out it crapped all over 
my boot partitions (RAID-0 setup).  Not the sort of thing I usually 
expect when trying to add a network card... Fortunately, half a day's 
work later, things are just about back to normal.  I'm going to pay the 
extra for a 3c905b/c from now on.

2. Intrex in Cary told me repeatedly that they no longer support Linux. 
  I'd made the mistake of asking whether they knew which of their 
network cards were supported under Linux.  I told the guy I didn't need 
any hand holding, but he sure wanted to make the point.  Not sure why I 
got the scalded cat response.

Thanks for all the suggestions and offers of help!

           Scott C.

Scott Chilcote wrote:
> Hi Folks,
> 
> One of the systems on my LAN started dropping packets really bad when I 
> tried communicating with machines out on the internet.  Pinging sites 
> like yahoo and ibiblio would return 3 out of 7,  2 out of 10, etc. and 
> TCP connections (email, web) just timed out.
> 
> I tried two other machines on the same LAN, and they had no problems 
> communicating with systems on the internet.  This seemed to rule out the 
> broadband router and DSL modem.
> 
> The next thing I tried was replacing the NIC and the ethernet cable on 
> the problem machine.  This turned out to make no improvement.  Then it 
> occurred to me to try pinging other systems on the LAN with this one, 
> and that worked just fine.  I put the old NIC back in, and it still 
> worked fine.  It's only getting out to the internet with this system 
> that isn't working.  I even tried it with a webserver running on a local 
> system, and the web page came up fine.
> 
> I then started wondering if there was a problem with one of the ethernet 
> connections on the DSL/Router/Switch or one of the other switches, so I 
> tried changing those around.  This made no difference.
> 
> I've more or less ruled out an OS or configuration problem on this 
> machine, too.  It's a dual-boot system with Win98se on one partition. 
> The behavior is identical under Win98se.  There have been no recent 
> configuration changes to this system other than adding a USB connected 
> UPS.  I haven't tried removing that, but I guess it's worth doing.
> 
> Another symptom happens when I try to bring up the SMC DSL Router's 
> administration web page.  The other systems can bring this page up 
> instantly.  The "problem" system takes forever to bring it up, and it 
> draws in a tiny piece at a time.  It did this even after I swapped out 
> the NIC and the ethernet cable.  This happens even though pings sent to 
> this LAN address return just fine.  This sort of indicates a TCP problem.
> 
> Has anyone seen this kind of behavior, or can you suggest something else 
> to try?  I'm guessing there's something wierd going on inside the 
> hardware of the faulty system, or there's a bizarre problem with the DSL 
> router that makes it single out this one machine.  I hate to blow $100 
> on a replacement DSL router if it isn't actually bad.
> 
> Thanks for any help!
> 
>                            Scott C.
> 
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