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

Ricky Beam jfbeam at gmail.com
Thu Jun 7 15:42:52 CDT 2012


On Wed, 06 Jun 2012 17:17:37 -0400, Karl Auer <kauer at biplane.com.au> 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.)

> b) DAD only goes to solicited node multicast addresses, i.e., only to
> those nodes that share the same last 24 bits as the target address. ARP
> goes to every node on the link (broadcast).

This assumes a network of devices that do multicast filtering, correctly.   
This is not a good assumption even in large enterprises.  Common  
residential gear usually doesn't understand multicast at all. (unless  
you're a uverse tv customer using ethernet and paid close attention to  
your hardware.)

> 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.)

> So I'm not sure how DAD traffic would exceed ARP traffic.

I wouldn't expect it to.  Looking at the output of my 3745, it fires 3  
ND's at startup and is then silent. (TWC has no IPv6 on my node, but v4  
ARP broadcasts amount to ~16K/s)

--Ricky



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