loopback network problems after upgrade from breezy to dapper

[Henning Sprang]

Hi
I am experiencing problems with/after an upgrade from breezy to
dapper. The dist-upgrade
itself already did not run very smooth, but after some tweaks it
looks as no packages are missing or blocked anymore. Everything runs fine,
but:

When booting, the system hangs at the message "configuring network
interfaces" and hitting ESC or ctrl-c, seems to be the only thing that gets
me around this - I tried many times, but no matter how long I wait,
it's always the same.

After that, the gnome desktop doesn't start after entering username
and password - it just hangs at a brown screen.

Looking into the text console, the output of "ifconfig" shows that
only the eth0 is up and correctly configured, and lo is missing.
Trying to start it with /etc/init.d/networking start results in the
same as at system start - just nothing happens for a long while, until
sometime I hit ctrl-c.

The interesting thing: when i put lo up manually with "ifconfig lo
up", the lo interface just comes up, I can restart gdm with
ctrl-alt-backspace, and gnome runs fine, everything's "normal".
Just, it's not exactly convenient to log into the text console each
boot and put lo up manually.

Network config for lo looks the same as on another natively installed
dapper machine, I see no error messages in any log that tells me
something goes wrong with lo, I am out of ideas now on how I could get
lo to come up with the normal network start script...

Henning