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Try nova console-log <VM-Name> and find if there's any related issue. If there is, you will see some related debug info.

Also, recheck your configurations. I've asked a similar question here, and finally found it was due to a configuration fault. Check the configurations according to your guide or Official Installation Guide at link text

If it's still not, search for "Neutron DHCP error" in google. You'll find so many issues related to this. Then try to find problems on your own. Here's suggestions provided by vincent-legoll(and it really helped solving my problem!)

You'll have to use tcpdump starting from inside your VM to see where the DHCP packets get lost. Go from there, then on the compute node, then to the network node (beware of the network namespaces : ip netns XXXXX exec tcpdump [...]). Be careful to take eventual encapsulation (GRE) into account when tcpdump'ing.

You'll have to ensure the dnsmasq processes are properly running(*) on your network node, that they get the DHCP requests, that they answer properly. Then follow the response packet back to the VM, verifying at each network step that they get through.

When you'll have found where they get blocked, you'll know where to search for the cause of that.

(*) they should be configured properly, and running in the right network namespace, etc...

Try nova console-log <VM-Name> and find if there's any related issue. If there is, you will see some related debug info.

Also, recheck your configurations. I've asked a similar question here, and finally found it was due to a configuration fault. Check the configurations according to your guide or Official Installation Guide at link textOpenStack Installation Guide for Ubuntu 14.04

If it's still not, search for "Neutron DHCP error" in google. You'll find so many issues related to this. Then try to find problems on your own. Here's suggestions provided by vincent-legoll(and it really helped solving my problem!)

You'll have to use tcpdump starting from inside your VM to see where the DHCP packets get lost. Go from there, then on the compute node, then to the network node (beware of the network namespaces : ip netns XXXXX exec tcpdump [...]). Be careful to take eventual encapsulation (GRE) into account when tcpdump'ing.

You'll have to ensure the dnsmasq processes are properly running(*) on your network node, that they get the DHCP requests, that they answer properly. Then follow the response packet back to the VM, verifying at each network step that they get through.

When you'll have found where they get blocked, you'll know where to search for the cause of that.

(*) they should be configured properly, and running in the right network namespace, etc...