Help debugging network problem
 

Hi gurus,

I have a machine running 2.6.24-19-server from the amd64 version of
8.04LTS, and I have a strange networking problem. Periodically (every
few minutes) the network connection will stop working. The strange
thing is that 50% of the time, any active SSH connections to the machine
continue to work, I can ping the machine from the outside, but new
connections don't happen.

As an example:

In one window I ran tcpdump, while in the other window I attempted to
use apt-get to install a package. Apt said it was attempting to contact
http://us.archive.ubuntu.com, but no packets showed up in tcpdump.
Eventually
apt quit with "Could not resolve 'us.archive.ubuntu.com'", and when I
quit tcpdump it said: "664 packets dropped by kernel"

The network will work for a few minutes, then seize up for a few
minutes, then magically start working again -- for a few minutes.
During the network blackout, I can bring things back by ifdown/ifup the
interface. Then things will work again -- for a few minutes.

The ethernet is built in to a SuperMicro X7DWE, and is an Intel
82563EB. I tried both the e1000 driver that came with the stock kernel,
and compiled the newer version that came on the motherboard driver CD.

Anybody have any idea why the kernel would drop packets? Is this a
driver issue, a hardware failure, or something completely different?


Thanks for your help!

Michael

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Help debugging network problem
 

Michael Peek wrote:
> Hi gurus,
>
> I have a machine running 2.6.24-19-server from the amd64 version of
> 8.04LTS, and I have a strange networking problem. Periodically (every
> few minutes) the network connection will stop working. The strange
> thing is that 50% of the time, any active SSH connections to the machine
> continue to work, I can ping the machine from the outside, but new
> connections don't happen.
>
> As an example:
>
> In one window I ran tcpdump, while in the other window I attempted to
> use apt-get to install a package. Apt said it was attempting to contact
> http://us.archive.ubuntu.com, but no packets showed up in tcpdump.
> Eventually
> apt quit with "Could not resolve 'us.archive.ubuntu.com'", and when I
> quit tcpdump it said: "664 packets dropped by kernel"
>
> The network will work for a few minutes, then seize up for a few
> minutes, then magically start working again -- for a few minutes.
> During the network blackout, I can bring things back by ifdown/ifup the
> interface. Then things will work again -- for a few minutes.
>
> The ethernet is built in to a SuperMicro X7DWE, and is an Intel
> 82563EB. I tried both the e1000 driver that came with the stock kernel,
> and compiled the newer version that came on the motherboard driver CD.
>
> Anybody have any idea why the kernel would drop packets? Is this a
> driver issue, a hardware failure, or something completely different?
>
>
> Thanks for your help!
>
> Michael
>
Possibly your router is too close to a cordless phone, microwave or
any other appliance that uses nearly the same radio band.

Are you using any encryption (WEP, WPA)for your connection? Have you
tried manually changing channels on your router to not interfere with
another router close by,... eg: your neighbor?

Just a few thoughts off the top of my head.


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Help debugging network problem
 

Michael Peek wrote:
> Hi gurus,
>
> I have a machine running 2.6.24-19-server from the amd64 version of
> 8.04LTS, and I have a strange networking problem. Periodically
> (every few minutes) the network connection will stop working. The
> strange thing is that 50% of the time, any active SSH connections
> to the machine continue to work, I can ping the machine from the
> outside, but new connections don't happen.
>
> As an example:
>
> In one window I ran tcpdump, while in the other window I attempted
> to use apt-get to install a package. Apt said it was attempting to
> contact http://us.archive.ubuntu.com, but no packets showed up in
> tcpdump. Eventually apt quit with "Could not resolve
> 'us.archive.ubuntu.com'", and when I quit tcpdump it said: "664
> packets dropped by kernel"
>
> The network will work for a few minutes, then seize up for a few
> minutes, then magically start working again -- for a few minutes.
> During the network blackout, I can bring things back by
> ifdown/ifup the interface. Then things will work again -- for a
> few minutes.
>
> The ethernet is built in to a SuperMicro X7DWE, and is an Intel
> 82563EB. I tried both the e1000 driver that came with the stock
> kernel, and compiled the newer version that came on the motherboard
> driver CD.
>
> Anybody have any idea why the kernel would drop packets? Is this a
> driver issue, a hardware failure, or something completely
> different?
>
>
> Thanks for your help!
>
> Michael
>
I just noticed you are using wired. My bad.


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Help debugging network problem
 

scott wrote:
> Michael Peek wrote:
>> Hi gurus,
>>
>> I have a machine running 2.6.24-19-server from the amd64 version of
>> 8.04LTS, and I have a strange networking problem. Periodically
>> (every few minutes) the network connection will stop working. The
>> strange thing is that 50% of the time, any active SSH connections
>> to the machine continue to work, I can ping the machine from the
>> outside, but new connections don't happen.
>>
>> As an example:
>>
>> In one window I ran tcpdump, while in the other window I attempted
>> to use apt-get to install a package. Apt said it was attempting to
>> contact http://us.archive.ubuntu.com, but no packets showed up in
>> tcpdump. Eventually apt quit with "Could not resolve
>> 'us.archive.ubuntu.com'", and when I quit tcpdump it said: "664
>> packets dropped by kernel"
>>
>> The network will work for a few minutes, then seize up for a few
>> minutes, then magically start working again -- for a few minutes.
>> During the network blackout, I can bring things back by
>> ifdown/ifup the interface. Then things will work again -- for a
>> few minutes.
>>
>> The ethernet is built in to a SuperMicro X7DWE, and is an Intel
>> 82563EB. I tried both the e1000 driver that came with the stock
>> kernel, and compiled the newer version that came on the motherboard
>> driver CD.
>>
>> Anybody have any idea why the kernel would drop packets? Is this a
>> driver issue, a hardware failure, or something completely
>> different?
>>
>>
>> Thanks for your help!
>>
>> Michael
>>
> I just noticed you are using wired. My bad.
>
>

Not sure if this will solve anything, but have you tried upgrading your
kernel? 2.6.24-21 is the latest for 8.04. Worth a shot.

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Help debugging network problem
 

scott wrote:
>> The network will work for a few minutes, then seize up for a few
>> minutes, then magically start working again
>>
>> Michael
>>
> Possibly your router is too close to a cordless phone, microwave or
> any other appliance that uses nearly the same radio band.
> Scott


20081108 0922 GMT-6

I would bet on Scotts diagnosis.

My dad purchased a new laptop. He has a Motorola SBG900 wireless cable
modem. Everything was fine until the phone rang and then ---- no
connection. They didn't put it together but when I was visiting weekend
I noticed the problem and tracked it down pretty quick. I had personally
not seen a phone do that until then.

AT&T cordless phones found at Walmart have been a major cause of
problems among many of my clients.

Though I was unable to get get a signal though from the modem to the pc
when the phone was in use on any channel, I would definitely try it as
it depends on which phone you have.

Wade

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Help debugging network problem
 

Luke Militello wrote:
>>> The network will work for a few minutes, then seize up for a few
>>> minutes, then magically start working again --
>>>
>>> Anybody have any idea why the kernel would drop packets? Is this a
>>> driver issue, a hardware failure,

20081108 1011 GMT-6

Assuming you have checked the cables between the server and your net
connection, did you try another server to connect to?

Wade
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Linux since June 2005

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