Comment 5 for bug 1244589

I've just encountered this too (Ubuntu host kernel). This fixed it for me:

$ sudo ip netns exec qdhcp-90bcac39-7d49-4bcb-a212-865c9c55bce6 ethtool --offload ns-2306c732-8c tx off rx off

(substitute your DHCP namespace accordingly)

Note that offloading checksums on the (virtual) interface in the namespace is clearly not going to work, and should be a no-op in the kernel. Indications I'm getting is that in a 3.2.0 kernel the packet gets checksummed in the host kernel correctly, and in 3.8.0 it doesn't (both stock kernels for Ubuntu 12.04). In my case it seems that Linux guests are fine with the dodgy packets but other more sensitive OSes drop them.

I've done basic due diligence here but it could do with a bit more investigation to confirm.

I'm seeing this on Grizzly devstack with Neutron using linuxbridge, but I don't think that the bug itself is an Openstack one and the version of Openstack concerned won't matter if that's the case.