[153539] in North American Network Operators' Group
Re: IPv6 /64 links (was Re: ipv6 book recommendations?)
daemon@ATHENA.MIT.EDU (Dave Hart)
Thu Jun 7 23:09:29 2012
In-Reply-To: <1339116492.2754.162.camel@karl>
From: Dave Hart <davehart@gmail.com>
Date: Fri, 8 Jun 2012 03:08:33 +0000
To: Karl Auer <kauer@biplane.com.au>
Cc: nanog@nanog.org
Reply-To: davehart_gmail_exchange_tee@davehart.net
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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.
