Ubuntu thinks its connected to the network, but nothing works?

[cfogelberg]

Hello,

I have a strange network problem on my laptop that recurs from time to time. Any help you can offer in solving it is much appreciated!!

Possibly the problem is caused by configuration changes at the remote end of my connection but I know that there is a local solution because Windows can always connect even when Ubuntu can't. Further, the problem has occurred at a wide range of times (early in the morning, late at night, during the weekend, middle of a weekday etc).

I have a Dell XPS M1330, and it dual boots Vista and Ubuntu 9.04. The connection has always worked when using Vista. However, from time to time it fails in Ubuntu, and for all services/ports (http, ssh, ftp, skype, etc.). If I reboot the machine into Vista when this happens then everything works. E.g. this morning:

* Boot in Ubuntu - nothing works
* Boot in Vista - everything works
* Boot in Ubuntu - nothing works
* Boot in Vista - everything works

In all cases Ubuntu says that it is connected, and pops up connected/disconnected messages whenever I plug/unplug the cable. So it seems to be sort of half connecting at least, and Windows can connect fully, so...?

The internet connection is on the Oxford university network and is just an ethernet socket in the wall. Address allocation is through DHCP. I don't know anything else about the connection or set up.

Sometimes my wireless connection in Ubuntu is flakey, especially after resuming from suspend. To try and eliminate this as a problem with the wired connection I have rebooted the laptop and also tried disabling/enabling the wired connection (disabling/enabling the wireless connection usually fixes it).

I also had a look at dmesg when I last booted into Ubuntu, and there wasn't anything funny looking there. I don't have the output to hand and will post it if it will help and as soon as I have a working connection in Ubuntu again

Any solutions or suggestions people have would be much appreciated, and if you would like further information please let me know.

Thanks,
Christo

[Iowan]

I presume Ubuntu gets an IP address (check via ifconfig -a). Does it get valid DNS (check /etc/resolv.conf)?

[cfogelberg]

I presume Ubuntu gets an IP address (check via ifconfig -a). Does it get valid DNS (check /etc/resolv.conf)?

Hi,

Thanks for getting back to me. This could be a slow problem to resolve because it happens so unpredictably. It has been working now for a few days. When I run ifconfig and check resolv.conf when it is working I get:

ifconfig -a (only eth2 shown, this is the ethernet card):

eth2 Link encap:Ethernet HWaddr 00:15:c5:82:a9:27
inet addr:129.67.90.52 Bcast:129.67.91.255 Mask:255.255.252.0
inet6 addr: fec0::b:215:c5ff:fe82:a927/64 Scope:Site
inet6 addr: 2002:8143:5985:b:215:c5ff:fe82:a927/64 Scope:Global
inet6 addr: fe80::215:c5ff:fe82:a927/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:171185 errors:0 dropped:0 overruns:0 frame:0
TX packets:23225 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:47555784 (47.5 MB) TX bytes:3954497 (3.9 MB)
Interrupt:17

/etc/resolv.conf:

# Generated by NetworkManager
domain gradacc.ox.ac.uk
search gradacc.ox.ac.uk
nameserver 129.67.1.1
nameserver 163.1.2.1
nameserver 129.67.1.180

When it next stops working will look at these and see if there are any differences. Will either post them here or post a resolution if I figure one out.

Thanks again,
Christo