[ovs-discuss] IP address for switch interfaces

Ben Pfaff blp at ovn.org
Fri Jun 24 15:48:44 UTC 2016

Please don't drop the mailing list.

As I said, IP addresses must be bound to internal interfaces, not to
physical interfaces.  The FAQ addresses this in more detail.

### Q: I created a bridge and added my Ethernet port to it, using commands
   like these:

       ovs-vsctl add-br br0
       ovs-vsctl add-port br0 eth0

   and as soon as I ran the "add-port" command I lost all connectivity
   through eth0.  Help!

A: A physical Ethernet device that is part of an Open vSwitch bridge
   should not have an IP address.  If one does, then that IP address
   will not be fully functional.

   You can restore functionality by moving the IP address to an Open
   vSwitch "internal" device, such as the network device named after
   the bridge itself.  For example, assuming that eth0's IP address is, you could run the commands below to fix up the

       ifconfig eth0
       ifconfig br0

   (If your only connection to the machine running OVS is through the
   IP address in question, then you would want to run all of these
   commands on a single command line, or put them into a script.)  If
   there were any additional routes assigned to eth0, then you would
   also want to use commands to adjust these routes to go through br0.

   If you use DHCP to obtain an IP address, then you should kill the
   DHCP client that was listening on the physical Ethernet interface
   (e.g. eth0) and start one listening on the internal interface
   (e.g. br0).  You might still need to manually clear the IP address
   from the physical interface (e.g. with "ifconfig eth0").

   There is no compelling reason why Open vSwitch must work this way.
   However, this is the way that the Linux kernel bridge module has
   always worked, so it's a model that those accustomed to Linux
   bridging are already used to.  Also, the model that most people
   expect is not implementable without kernel changes on all the
   versions of Linux that Open vSwitch supports.

   By the way, this issue is not specific to physical Ethernet
   devices.  It applies to all network devices except Open vSwitch
   "internal" devices.

On Fri, Jun 24, 2016 at 11:41:01AM +0000, Pynbiang Hadem wrote:
> Thanks Ben for your reply. Do you mean to say that there is no way to assign IP addresses to interfaces, s1-eth0, s1-eth1 and s1-eth2 ? Or can it be done at the controller application level?.
> ThanksHadem 
>     On Thursday, 23 June 2016 10:15 PM, Ben Pfaff <blp at ovn.org> wrote:
>  On Thu, Jun 23, 2016 at 07:07:31AM +0000, Pynbiang Hadem wrote:
> > Assume that an openflow switch has three interfaces, s1-eth0, s1-eth1
> > and s1-eth2. Is it possible to bind an IP address to each
> > interface?. 
> If you are talking about an OVS bridge, no.  IP addresses must be bound
> to internal interfaces, not to physical interfaces.  If you need three
> IP addresses, common practice would be to use three internal interfaces.
> > If so, what kind of data-structure is used by OpenFlow for the
> > binding?.  ThanksHadem
> I don't understand this question.

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