Strange network behaviour

[carlosestensser]

I am running kubuntu oneiric, which has worked flawlessly so far, and I have a strange issue with my network connection.
I have a Motorola SBG901 modem.
Sometimes (approx. 1 out of every 4 times) I can't connect to the internet through the ethernet cable. the strange thing is that:
1. I can connect with my laptop through wifi.
2. I can connect through the eternet connection if I reboot and log in to my kubuntu natty installation which is in another partition.
3. If I reboot once again and log in to oneiric once more after having been to natty, my wired connection works in oneiric.

What should I look for in order to diagnose the problem?

Thanks in advance


Sorry if there are any grammar mistakes. I speak Spanish and I am still a bit hangover.

[SteveRiley]

Re: Strange network behaviour

Next time the problem manifests itself, before you reboot into Natty, open a console window and enter:

dmesg | grep eth0

and

ifconfig

Then post the output.

[carlosestensser]

Re: Strange network behaviour

Thanks a lot.
That's the kind of answer I was looking for.

[carlosestensser]

Re: Strange network behaviour

Here is the output of dmesg and ifconfig:

darwin-Desktop-sdc1:~$ dmesg | grep eth0
[ 15.114497] atl1c 0000:02:00.0: atl1c: eth0 NIC Link is Up<100 Mbps Full Duplex>
[ 25.660017] eth0: no IPv6 routers present

darwin-Desktop-sdc1:~$ ifconfig
eth0 Link encap:Ethernet direcciónHW 00:24:1d:b8:c3:31 
Direc. inet:192.168.0.2 Difus.:192.168.0.255 Másc:255.255.255.0
Dirección inet6: fe80::224:1dff:feb8:c331/64 Alcance:Enlace
ACTIVO DIFUSIÓN FUNCIONANDO MULTICAST MTU:1500 Métrica:1
Paquetes RX:269 errores:0 perdidos:0 overruns:0 frame:0
Paquetes TX:400 errores:0 perdidos:0 overruns:0 carrier:1
colisiones:0 long.colaTX:1000 
Bytes RX:17268 (17.2 KB) TX bytes:37320 (37.3 KB)
Interrupción:44 
lo Link encap:Bucle local 
Direc. inet:127.0.0.1 Másc:255.0.0.0
Dirección inet6: ::1/128 Alcance:Anfitrión
ACTIVO BUCLE FUNCIONANDO MTU:16436 Métrica:1
Paquetes RX:66 errores:0 perdidos:0 overruns:0 frame:0
Paquetes TX:66 errores:0 perdidos:0 overruns:0 carrier:0
colisiones:0 long.colaTX:0 
Bytes RX:19107 (19.1 KB) TX bytes:19107 (19.1 KB)

Any thoughts?

[SteveRiley]

Re: Strange network behaviour

Hmm... looks like it's configuring correctly. A couple more things to check, mainly so I can see more info:

grep "" /sys/class/net/eth0/*

Next let's see your routing table:

route

And verify whether you can ping your default gateway:

ping -c3 `netstat -rn | awk '/UG/{print $2}'`

And then, this could be long, but has even more diagnostic info:

grep eth0 /var/log/syslog

[carlosestensser]

Re: Strange network behaviour

Thanks Steve for stqying with me in these difficult moments!
Next time it happens, I'll follow your instructions.

[wizard10000]

Re: Strange network behaviour

I've seen this before - may not be the same problem, but try this:

Next time your Ethernet card won't connect shut the machine down then start it back up - a warm boot won't work. I'll bet the machine connects when you start it back up.

It's been an intermittent problem for years with some NICs under Linux - where the driver fails to initialize the card properly. A warm boot generally won't fix the problem but a cold boot will as a cold boot resets hardware where a warm boot doesn't.

My guess is that Natty's driver works properly where Oneric's driver doesn't. Your TCP-IP stack is most likely working properly, but I'll bet that a hard reset gets you connected every time.