[Rdo-list] DNS resolver problems w/ instack-virt-setup

Lars Kellogg-Stedman lars at redhat.com
Fri Apr 17 17:09:02 UTC 2015

On Fri, Apr 17, 2015 at 06:15:37PM +0200, Marius Cornea wrote:
> is set on the virbr0 interface on the host (default
> libvirt net) where under/overcloud VMs are running.

It is also the address of the virbr0 interface *on the overcloud

> ( subnet).  The overcloud nodes have one interface in the
> brbm bridge and route the traffic through the undercloud node. You can
> check that default gw on overcloud nodes is (eth1 of instack
> VM).

That confirms what I said in my previous email:

> That's not a useful address for either of these nodes, on which
> external connectivity -- at least on the controller -- is via
> eth0/br-ex on the network. 

> The undercloud node masquerades all traffic coming from
> so the overcloud nodes can get external connectivity,
> including to which handles the dns queries.

It doesn't.  First, because is set on the virbr0
interface on the overcloud controller node, traffic to this address
never leaves the host.

While the undercloud node does have masquerade rules in place:

  # iptables -t nat -S | grep -i masquerade

It doesn't have ip forwarding enabled:

  # sysctl -a | grep ip_forward
  net.ipv4.ip_forward = 0

No forwarding, so no masquerading.

Lars Kellogg-Stedman <lars at redhat.com> | larsks @ {freenode,twitter,github}
Cloud Engineering / OpenStack          | http://blog.oddbit.com/

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