Kireeti Kompella <[email protected]> writes:

> The solution is simple: route if IP, bridge if not.  Yes, one could
>  do IRB, but why?  IRB brings in complications, especially for
>  multicast.  I'm sure someone suggested this already, so put me down
>  as supporting this view.

I'm not sure I understand the difference.

>From an *NVE* perspective, when it receives a packet (which will have
an L2 header), it can look at the Ethertype, and if its IP, it can
route it. Otherwise, it can provide normal L2 service. So, in this
sense, "route if IP, bridge if not" is straightforward. And more to
the point, I assume that if the packet gets L2 service, the entire VN
is treated as a *single* broadcast domain. All nodes can reach all
other nodes. Right?

Just so I understand, how is this different than IRB?  What does IRB
imply that the above does not?

But this is different than what (I believe) Lucy is arguing for. In
the case of a multi-subnet VN, you have one VN, but it contains
different subnets. Each subnet is intended to be one broadcast domain
(i.e., equivalent of a VLAN), so that when sending LL multicast and
the like on a specific subnet, such packets are *not* delivered to all
nodes in the VN, but only those that are part of subnet.

This is a more complex type of service to provide. And I'm not sure we
need this type of service to be provided by one VN. A (seemingly
simpler) alternative would be to put each subnet in its own VN and
allow inter-subnet traffic to be handed as inter-VN traffic. So long
as that case is optimized (i.e., the ingress NVE can tunnel directly
to the egress NVE without adding triangular routing), this would seem
to be a cleaner way to implement this.

Thomas

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