[ovs-discuss] using routers to separate networks

Ben Pfaff blp at nicira.com
Wed May 4 18:47:32 UTC 2011


On Wed, May 04, 2011 at 11:36:20AM -0700, Tom Brown wrote:
> On Wed, May 4, 2011 at 11:00, Ben Pfaff <blp at nicira.com> wrote:
> 
> > On Tue, May 03, 2011 at 05:37:45PM -0700, Tom Brown wrote:
> > > Each vm in the network is supposed to sit behind a router and use dhcp to
> > > obtain an ip address from the dhcp server running on the router. However,
> > > I'm finding that the dhcp request coming out of the vms is seen by dhcp
> > > server on the host machine's network (our company dhcp server).
> >
> > Looking at your diagram, the only connections from each vm to the
> > "outside world" are through a router or a br network device.  To me
> > this suggests a few possibilities:
> >
> >        * The br network devices are forwarding the DHCP requests.
> >
> Thanks for your reply. I believe the issue to be that the br network devices
> are forwarding the DHCP requests. I'm not doing anything with the router
> that would forward broadcast/DHCP packets. There are no additional network
> devices not shown in the diagram.
> 
> I wasn't expecting the br devices to forward the DHCP requests through br0.
> How do I prevent that from happening?

I wouldn't expect it to forward them, either.  DHCP requests are
normally addressed to 255.255.255.255, which should not be forwarded.

Do you have an IP address configured on br0 or br1?  If you don't,
then you can just "ifconfig br0 down".  If this makes a difference,
then it at least proves that br0 is responsible for forwarding the
request, for whatever reason.



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