[TriLUG] Any help diagnosing an intermittent network issue?

[Wes Garrison]

Shooting from the hip, this sounds like an auto-negotiation problem.

If both are set to auto, perhaps try hard setting them to 100/full duplex
and see what happens?

On Sat, Oct 25, 2014 at 2:27 PM, R Radford <rradford at mindspring.com> wrote:

> I have my laptop (running Ubuntu 14.04) corrected via wifi to my home
> router - that connect is up and stable.
>
> I then connect the wired network of the laptop to my Raspberry Pi.  I have
> configured both the RPi and my laptop as static on a different subnet.
>
> On most days, all is well - I can ssh to my RPi, and I have ICS set up
> between the RPi through my laptop to my wifi, so I can grab updates on my
> RPi and ssh to it.
>
> However some days the connection between my laptop and the RPi is very
> unstable.  I plug in the Ethernet cable between the two, watch the
> interface (eth0) come up and can connect, but then it drops a few seconds
> later.  Running a watch command on "ifconfig eth0" shows that it toggles
> between up and down every few seconds.
>
> There are no errors listed on the ifconfig, and nothing is in dmesg
> indicating an error.
>
> Ifconfig output when everything is fine:
>
> rradford at asimov:~$ ifconfig
> eth0      Link encap:Ethernet  HWaddr 2c:27:d7:06:56:54
>           inet addr:10.42.0.1  Bcast:10.42.0.255  Mask:255.255.255.0
>           inet6 addr: fe80::2e27:d7ff:fe06:5654/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:8607 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:132232 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:1000
>           RX bytes:8871528 (8.8 MB)  TX bytes:21755527 (21.7 MB)
>
> lo        Link encap:Local Loopback
>           inet addr:127.0.0.1  Mask:255.0.0.0
>           inet6 addr: ::1/128 Scope:Host
>           UP LOOPBACK RUNNING  MTU:65536  Metric:1
>           RX packets:847951 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:847951 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:0
>           RX bytes:134296144 (134.2 MB)  TX bytes:134296144 (134.2 MB)
>
> wlan0     Link encap:Ethernet  HWaddr 68:a3:c4:d5:57:7a
>           inet addr:192.168.0.82  Bcast:192.168.0.255  Mask:255.255.255.0
>           inet6 addr: fe80::6aa3:c4ff:fed5:577a/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:344266 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:290361 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:1000
>           RX bytes:260820609 (260.8 MB)  TX bytes:61832612 (61.8 MB)
>
> Static interface on the RPi is configured via network-manager GUI.  The
> eth0 interface is not in /etc/network/interfaces.
>
> Watching the eth0 on the RPi does not show any issues.
>
> I don't understand why the interface bounces up and down every few seconds
> (and usually finally gives up) on some days, but with no changes works fine
> another day. I know this will be very difficult to debug remotely, so what
> I am looking for is help on where I should look to help diagnose this
> problem.
>
> Btw, this was working reliably with no problems before the 14.04 upgrade a
> few months ago, if that matters.
>
> Any assistance or ideas are greatly appreciated.
>
> Thanx,
> Rodney
>
> PS: I hope this doesn't get posted twice by accident (first post was from
> an unregistered address so I am sending it again).
> --
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-- 
_________________________________
Wesley S. Garrison
Network Engineer
Xitech Communications, Inc.
phone:  (919) 260-0803
pager:   (919) 869-1744
fax:       (919) 928-5746
__________________________________
"Lead us not into temptation, but deliver us from email."