[ovs-dev] [PATCH] vswitch: Consistently set Nicira OUI.

Jesse Gross jesse at nicira.com
Mon Feb 1 16:43:01 PST 2010

On Mon, Feb 1, 2010 at 7:12 PM, Ben Pfaff <blp at nicira.com> wrote:

> On Mon, Feb 01, 2010 at 06:30:24PM -0500, Jesse Gross wrote:
> > In places where a random Ethernet address needs to be generated we
> > are inconsistent about setting an OUI.  This sets an OUI everywhere
> > to allow the source of packets to be easily identified.
> I have mixed feelings about this.  Yes, it makes it easier to identify
> packets coming from Open vSwitch, but I'm not sure that that is too
> useful (has anyone on the list ever had a need for it?) and it kind of
> gives up control over Nicira's OUI.
> Also, there are only 22 bits of randomness instead of 46 if we fix all
> those bits.
> The dpid is a little different, since it isn't used as a source MAC
> anywhere as far as I know.

Right now it is used inconsistently - for example the datapath sets it on
internal ports, which is usually but not always overridden by userspace.  As
far as "giving up" the OUI goes, using it in one place gives it up just as
much as using it all the time.  Also a few extra bits are fixed so there are
still many additional addresses available for allocation.

It's true that the DPID that is never used as a MAC address but MAC
addresses are used as DPIDs, so they are in the same address space and a
collision would cause a problem.

The bottom line is that we should be consistent everywhere because otherwise
we end up with the worst of both worlds.  Personally I prefer have the OUI
set since it is nicer when looking at packet traces.  It's also friendlier
to the rest of the world.  VMware sets their OUI on addresses they generate.
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