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.

1 Answer 1


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

See: https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Virtualization_Host_Configuration_and_Guest_Installation_Guide/ch11s02.html for more details.

  • From that link, it sounds like the problem is the dhcp client in the guest. What was the guest operating system that you were running? Also, since the link mentions that the problem doesn't exist with virtio, would setting libvirt_use_virtio_for_bridges=True have resolved the issue? Nov 14, 2012 at 3:04
  • @LorinHochstein: I wasn't getting leases with the Cirros test image or the latest Ubuntu images, so I don't think this is limited to only a obscure guests. I do have libvirt_use_virtio_for_bridges=True so I don't think that would fix it. Nov 14, 2012 at 13:16
  • I'm very surprised to hear that this would break with Ubuntu 12.10 and cirros/latest ubuntu images, since I would guess that the Ubuntu packagers would test this scenario first. Can you send me some more details about your setup so I can try to replicate the issue and submit a bug report to the project? Nov 14, 2012 at 16:07
  • @LorinHochstein: Seems to exist already at bugs.launchpad.net/nova/+bug/1029430 , someone was asking about this in #openstack too, which was why I posted this. See (github.com/mseknibilel/OpenStack-Folsom-Install-guide/issues/14) for more info on my setup. Nov 14, 2012 at 16:49
  • @Kyle - Thank you kind sir, my AIO OpenStack install was picking up IPs from my router instead of dnsmasq, took me ages to finally find your post, have +1'd!
    – Dan Higham
    Jan 1, 2013 at 14:30

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