Hi Ben,

On Tue, Nov 24, 2015 at 6:12 PM, Ben Pfaff <b...@ovn.org> wrote:
> I'm having trouble figuring out which one we should do.  The reason that
> I'm torn between choices is because of layering.  I like the way that,
> currently, the switch and router datapaths are (almost) independent of
> each other, in the sense that they don't have to know anything about
> what they're attached to.  However, we've already got one violation of
> this principle: logical routers statically discover MAC-IP bindings on
> their attached switches.  For now, that's pretty much necessary, since
> logical routers don't support ARP yet (I'm fixing that, don't worry),

By "support ARP" do you mean logical routers broadcast ARP requests to
lswitch ports and then process ARP replies (from the owner of the IP)
to get IP-MAC bindings?
In such case even if this kind of dynamic ARP is supported, it would
still be valuable to continue supporting the static MAC-IP bindings,
which is the major scenario of CMS such as openstack, where IP-MAC
binding is known during VM provisioning (and similar use case for
containers). I think dynamic ARP introduce higher costs, and requires
periodical refreshing, so it is better to be triggered only when
static binding is not available.

Or do you mean any other kind of ARP support?

> but in the long run we could eliminate it.  Or we could decide that this
> idea of layering and separation is not valuable (in this case); I don't
> have a strong opinion yet.
>

Thanks for this background of the choices. I think it is ok to keep
current implementation until we figure out which option is better.

-- 
Best regards,
Han
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