Re: [v6ops] privacy point re. unsolicited NA / router neighbor cache

On Tue., 23 Jul. 2019, 23:33 Sander Steffann, <sander@steffann.nl> wrote:

> Hi,
>
> > The general idea that on-link multicast is a positive aspect of IPv6
> > is nice, but wrong.
>
> Well, a little bit :)
>
> There is still the advantage that the NIC can apply its MAC address
> filter. L2 destination FF:FF:FF:FF:FF:FF can't be filtered there, but
> 33:33:* can :)

It's no surprise that Steve Deering also wrote RFC 1112, "Host Extensions
for IP Multicasting", which says,

"7.4. Extensions to an Ethernet Local Network Module
...
It is highly desirable to take advantage of any address
   filtering capabilities that the Ethernet hardware interface may have,
   so that the host receives only those packets that are destined to it."
...

IPv4 and IPX uses/used link-layer broadcasts. Appletalk used link-layer
multicasts, however, from memory, it used the same or a few multicast
address for everything.

IPv6 improves Appletalk by using much more specific link-layer multicast
addresses for different purposes, which allows NIC filtering to be much
more fine grained.

If a host is only running protocols that use link-layer multicasts, then it
could switch off broadcast reception in its NIC (IFF_BROADCAST interface
flag).

For example, an IPv6 only host attached to a link that also has IPv4 hosts
would be able to drop in its NIC hardware IPv4 ARPs and DHCPv4 DISCOVERS,
rather than processing and then dropping them at higher layers in the stack.

Regards,
Mark.

> Cheers,
> Sander
>
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