On Fri, Jun 8, 2012 at 12:48 AM, Karl Auer <kauer@biplane.com.au> wrote:
Yes - whether with ARP or ND, any node has to filter out the packets that do not apply to it (whether it's done by the NIC or the host CPU is another question, not relevant here).
It is relevant to the question of the scalability of large L2 networks. With IPv4, ARP presents not only a network capacity issue, but also a host capacity issue as every node expends software resources processing every broadcast ARP. With ND, only a tiny fraction of hosts expend any software capacity processing a given multicast packet, thanks to ethernet NIC's hardware filtering of received multicasts -- with or without multicast-snooping switches.
The original post posited that ND could cause as much traffic as ARP. My point is that it probably doesn't, because the ND packets will only be seen on the specific switch ports belonging to those nodes that are listening to the relevant multicast groups, and only those nodes will actually receive the ND packets. In contrast to ARP, which is broadcast, always, to all nodes, and thus goes out every switch port in the broadcast domain.
This is pretty much the *point* of using multicast instead of broadcast.
I agree.