networking hosed after upgrading to 10.04

[Tom H]

On Mon, May 30, 2011 at 11:48 PM, scar <scar at drigon.com> wrote:
>
> i finally decided to upgrade an old machine from 9.10 to 10.04, and
> there is something strange going on with the networking.
>
> this machine is only connected to my LAN using one ethernet port, and i
> also had previously set up a bridge for use with a virtual machine i
> have installed, so a rather simple setup but not standard.  i just used
> the KVM setup guide on ubuntu.com somewhere to setup the bridge.
>
> when the system boots up, it can't be found on the LAN, and it can't
> connect to websites either.
>
> in network manager i have several different connections that i don't
> remember having:
>
> Wired connection 1
> Auto eth0
> Auto Ethernet
> ifupdown (eth0)
> ifupdown (br0)
>
> i'm pretty sure 'auto ethernet' was the only one i used before.  it
> seems after i pick any one of these to connect to, i then have access to
> my LAN, but still can't reach any outside websites for example.
>
> also, when i was running 9.10 my motherboard blew out and i had it
> replaced under warranty.  however, a different model was sent since the
> original had been discontinued.  i remember something strange happened
> with the networking at that time too, but i was able to get it working
> with some help from my loco team, and haven't had to fuss with it since.
>
> it seems to me this chain of events may have really messed up my
> networking (this system has been upgraded since 8.10 too).  i'm
> wondering if there is a simple way to wipe the slate clean and get my
> LAN and bridge connections configured again...

The "Auto" connections are created by NM and the "Ifupdown" are
created by "/etc/network/interfaces" in conjunction with
"managed=true" in "/etc/NetworkManager/nm-system-settings.conf" in the
"ifupdown" section.

I don't understand how you can have the "Auto" and "Ifupdown" entries
simultaneously.

What's the output of "nm-tool"?

What's your bridge setup/configuration?