IPv6 /64 links (was Re: ipv6 book recommendations?)

Karl Auer kauer at biplane.com.au
Thu Jun 7 17:09:46 CDT 2012

On Thu, 2012-06-07 at 16:42 -0400, Ricky Beam wrote:
> On Wed, 06 Jun 2012 17:17:37 -0400, Karl Auer wrote:
> > a) DAD only happens when an IPv6 node is starting up. ARP happens
> > whenever a node needs to talk to another node that it hasn't seen in
> > while.
> DAD is a special case of ND.  It happens every time the system selects
> an address. (i.e. startup with non-SLAAC address, and when privacy
> extensions generates an address.)

Er - OK. I should have said "happens when an address is assigned to an
interface". It is still, however, way less traffic than ARP, which was
my point. Possible exception - a network where everyone is using privacy

> > b) DAD only goes to solicited node multicast addresses
> This assumes a network of devices that do multicast filtering,
> correctly.

Yes, it does. It assumes a properly provisioned and configured IPv6
network. While that may not be common now, it will become more common.
And it is a self-correcting problem - people who don't want lots of
noise will implement their networks correctly, those who don't care will
do as they wish. No change there :-)

BTW, I'm assuming here that by "multicast filtering" you mean "switching
that properly snoops on MLD and sends multicast packets only to the
correct listeners".

> > c) Similarly, ND (the direct equivalent of ARP) goes only to
> solicited node multicast addresses, ARP goes to every node on the
> link.
> Effectively the same as broadcast in the IPv6 world.  If everyone is  
> running IPv6, then everyone will see the packet. (things not running
> ipv6 can filter it out, but odds are it'll be put on the cable.)

On this point I think you are wrong. Except for router advertisements,
most NDP packets are sent to a solicited node multicast address, and so
do NOT go to all nodes. It is "the same as broadcast" only in a network
with switches that do not do MLD snooping.

> > So I'm not sure how DAD traffic would exceed ARP traffic.
> I wouldn't expect it to.

Nor would I - which was the point of my response to an original poster
who said it might.

Regards, K.

Karl Auer (kauer at biplane.com.au)

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