On Ubuntu 14.04 Trusty, I had LXC running, but recently I upgraded from 1.0.7 to 1.1.2 as per the instructions here on Launchpad. However, I found that I could not start my containers any more. After stepping through the container startup logs (starting the container with logging output) I could see that it was because the network bridge hadn't been created on startup by
/usr/lib/x86_64-linux-gnu/lxc/lxc-net, the network startup script for LXC.
I managed to get the bridge up by following LXC NET fails to create bridge on Ubuntu Server 14.04 | community.flockport.com
However, that still indicated a problem with dnsmasq (no DNS resolution) and lxcbr0 (the default LXC container bridge) not having any NAT rules. The instructions are more of a quick fix to alleviate the symptoms without fixing the problem. I can't ping out of the containers, and it seems to me that the network setup script isn't being run at startup. What can I check next?