[Openstack] [Quantum/Neutron] VM cannot get IP address from DHCP server

David Kang dkang at isi.edu
Wed Jul 24 03:41:55 UTC 2013

 A Redhat manual suggests the following rule to enable forwarding packets
among VMs and external network.

iptables -t filter -I FORWARD -i qr-+ -o qg-+ -j ACCEPT
iptables -t filter -I FORWARD -i qg-+ -o qr-+ -j ACCEPT
iptables -t filter -I FORWARD -i qr-+ -o qr-+ -j ACCEPT

 But it doesn't work for me.
Any suggestion?


----- Original Message -----
> On 07/23/2013 12:22 PM, David Kang wrote:
> >
> >  Hi,
> >
> >   We are running OpenStack Folsom on CentOS 6.4.
> > Quantum-linuxbridge-agent is used.
> > By default, the Quantum node has the following entries in its
> > /etc/sysconfig/iptables file.
> >
> > -A INPUT -j REJECT --reject-with icmp-host-prohibited
> > -A FORWARD -j REJECT --reject-with icmp-host-prohibited
> >
> >  With those two lines, VM cannot get IP address from the DHCP server
> >  running on the Quantum node.
> > More specifically, the first line prevents a VM from getting IP
> > address from DHCP server.
> > The second line prevents a VM from talking to other VMs and external
> > worlds.
> > Is there a better way to make the Quantum network work well
> > than just commenting them out?
> Since Quantum isn't adding them, and you want the system to act as a
> DHCP server
> and gateway, I think you have two choices:
> 1. Delete them
> 2. Craft rules to sit above them (using -I) to allow certain packets
> #2 gets tricky as you'll need to account for DHCP, metadata, etc. in
> the INPUT
> chain, and in the FORWARD chain you could maybe start by allowing all
> traffic
> from your bridge. You would need to do some more work there.
> I believe any DHCP iptables rules will be on the compute hosts, and
> will be put
> in place for anti-spoofing. Since this is the network node you won't
> see them here.
> -Brian

Dr. Dong-In "David" Kang
Computer Scientist

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