[ovs-discuss] Multiple OVSs or multiple datapaths with one OVS

[Ben Pfaff]

I'm not sure it's well documented.

Separate bridges act independently.  That's why they're separate.  If
they were connected there's be no point in supporting more than one
bridge.

As I said before, datapaths are an implementation detail.  You only
need to be concerned with bridges.  "2 bridges with a single vswitchd
daemon" behaves quite differently from "2 separate bridges associated
with separate vswitchd processes" since the former works and the
latter does not.

On Fri, Apr 12, 2013 at 03:16:17PM -0700, Aishwarya wrote:
> I guess I am a little confused about the concept of datapath. Do you have
> any documentation that explains this?
> 
> I guess what I really need to know is that whether having 2 bridges with a
> single vswitchd daemon will behave the same as having 2 separate bridges
> associated with separate vswitchd processes. Is there any difference
> between the 2 at all in final behavior. The first one will also simulate
> complete independence between the bridges right?
> 
> 
> On Fri, Apr 12, 2013 at 3:09 PM, Ben Pfaff <blp at nicira.com> wrote:
> 
> > You can use multiple bridges with 1.10 or later, including master, but
> > those bridges use a single kernel datapath.
> >
> > Why do you care whether you use multiple kernel datapaths?
> >
> > On Fri, Apr 12, 2013 at 02:55:30PM -0700, Aishwarya wrote:
> > > I am using the master branch which is OVS 1.10 or higher. So does that
> > mean
> > > I will not be able to test multiple datapaths with a single ovs-vswitchd
> > > daemon with 1.10 and higher? You answered yes to #2 above? Is this true
> > > with 1.10 too?
> > >
> > > Thanks.
> > >
> > >
> > > On Fri, Apr 12, 2013 at 2:43 PM, Ben Pfaff <blp at nicira.com> wrote:
> > >
> > > > On Fri, Apr 12, 2013 at 02:27:09PM -0700, Aishwarya wrote:
> > > > > 1) Running 2 OVS user space daemons on the same machine, and
> > creating a
> > > > > bridge per OVS process.
> > > > >
> > > > > 2) Running a single OVS and creating 2 different bridges with the
> > same
> > > > OVS
> > > > > process.
> > > > >
> > > > > Couple of questions:
> > > > > 1. Is (1) even supported?
> > > >
> > > > It won't work, out of the box, if you use the OVS kernel module.  You
> > > > might be able to get it to work with some effort, especially if you
> > > > use the userspace datapath only.
> > > >
> > > > > 2. My use case is that I basically want to be able to test with
> > multiple
> > > > > datapaths on the same machine. With my experimentation, I feel (2)
> > should
> > > > > satisfy this. Is that true?
> > > >
> > > > Yes.
> > > >
> > > > > 3. Does a single bridge correspond to a single datapath? If not,
> > what is
> > > > > the real difference between the concept of a bridge and datapath?
> > > >
> > > > A bridge is an Ethernet or OpenFlow concept.  A datapath is an
> > > > implementation detail.  Before OVS 1.10 there was a one-to-one
> > > > relationship between bridges and datapaths; in OVS 1.10 and later
> > > > there is only one datapath even if there are many bridges.
> > > >
> >