Why is /etc/network/interfaces ignored?

Solution 1:

You have:

address         192.168.1.200 # the IP address of the Ethernet port

and report that this is the line that isn't working. Are you aware, from interfaces(5), that:

   Lines starting with `#' are ignored. Note  that  end-of-line  comments
   are NOT supported, comments must be on a line of their own.

Did you add the end-of-line comments for the question, or do you actually have them in your /etc/network/intefaces file? If so, try removing them.

Solution 2:

Perhaps, despite having removed the network-manager package, you still have the file /etc/NetworkManager/NetworkManager.conf containing

[ifupdown]
managed=true

which causes ifup not automatically to bring up interfaces.

If this is the cause of the problem then I suggest either dpkg --purge network-manager or setting managed=false.

I filed a bug report about this: https://bugs.launchpad.net/ubuntu/+source/ifupdown/+bug/1187693

Solution 3:

I managed to fix my problem by changing 2 files. First of all, as suggested by Eric Carvalho, I uncommented auto eth0 in /etc/networking/interfaces. (Note that this is quite odd, several tutorials online seem to suggest this shouldn't be required for Xen.)

That by itself did not fix the slow boot though. It seems that on startup it still took a few seconds before the interfaces came up and in the meantime Ubuntu was already stuck in a 60 seconds idle wait. This I fixed by modifying the delay time in /etc/init/failsafe.conf from 60 seconds to 1 second. (I found out about this file through Google, no idea which one it was exactly.)