Comment 2 for bug 1224618

Please configure dnsmasq to log its activity so you can atleast verify what IT thinks about the dhcp traffic.

# openstack-config --set /etc/quantum/dhcp_agent.ini DEFAULT dnsmasq_config_file /etc/quantum/dnsmasq.conf

And this goes in the config file:
log-facility = /data/log/quantum/dnsmasq.log
log-dhcp

You should now be able to see if the instance is offered a IP and what actually happens with the offer.

Tsharking the bridge or namespaced interface could be interesting aswell.