When I start instances in openstack, they don't get DHCP leases. When I go into the instance and manually configure the IP that would have been assigned. Network flows fine.
With TCPDump, I can see DHCP Offers, but they seem to be ignored.
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When using the
vhost_net module, checksums are not added, so most dhcpclients seem to ignore the DHCP offers. In my case, Ubuntu 12.10 was the host operating system.
You can fix this with a mangle rule in iptables:
iptables -A POSTROUTING -t mangle -p udp --dport 68 -j CHECKSUM --checksum-fill