[svlug] Occasional network problem (ubuntu machine to router)

Erik Steffl steffl at bigfoot.com
Wed Apr 1 17:09:24 PST 2009


Andrew Wilcox wrote:
> Is the CPU usage abnormally high when the network problems happen?
> Are you running something like beagle or something that would
> intermittantly use a lot of CPU?

   doesn't seem to be related to CPU but wasn't focusing on that,

> If this is a (very) low-end machine, that could cause packet drops.
> I've seen it happen before on low-end machines that are overloaded.

   it's a dual core pentium 2.40GHz, 1GB RAM, not very low end, used for 
desktop stuff (browsing, email, videos etc.)

   I only noticed this problem once since I wrote the email, it fixed 
itself after (while running ping 192.168.1.1 which is router address):

   - initial condition: lot of pings are lost

   - unplug network cable from router

   - plug it into a different port on router (ping starts saying that 
the network is unreachable)

   - plug it to the original port - and voila it works fine

   (at other times it fixes itself without me touching it)

   any ideas how to troubleshoot this? There's nothing in the logs...

	erik

> Hope that helps,
> Andrew
> 
> On Sat, Mar 28, 2009 at 4:49 AM, Erik Steffl <steffl at tsoft.com> wrote:
>> In last few days I started to get occasional (lasts 5 - 20 min or so)
>> network problems between router and a ubuntu machine. The problem is
>> that network performance goes sharply down, when I run ping from machine
>> to router most of the packets are lost (it varies how bad it is).
>>
>> I didn't see anything suspicious in the logs, disconnecting and
>> reconnecting (both software and unplugging/re-plugging the network
>> cable) doesn't make any difference.
>>
>> Other computer connected to the same router works fine.
>>
>> The problem fixes itself after some time (and the network works fine).
>>
>> Any ideas how to troubleshoot this? Given that it either works or
>> (almost) doesn't it seems like it's not wire problem (I don't touch the
>> network cable so it seems unlikely that it would work most of the time
>> but not all the time and that it would fix itself without any
>> intervention). It only happens in last few days, didn't do any HW changes.
>>
>> System:
>>
>>   Ubuntu 8.10
>>
>> [   11.170407] eth1: RealTek RTL8139 at 0xb000, 00:50:ba:4d:1a:58, IRQ 18
>> [   11.170414] eth1:  Identified 8139 chip type 'RTL-8139C'
>> [   11.190809] 8139cp: 10/100 PCI Ethernet driver v1.3 (Mar 22, 2004)
>>
>>   Router: Netgear RangeMax WNR834B v2
>>
>>   thanks,
>>
>>        erik
>>
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>>
> 
> 
> 





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