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

Thu Jun 7 21:45:22 UTC 2012

On Jun 7, 2012, at 1:27 PM, Ricky Beam wrote:

> On Wed, 06 Jun 2012 10:58:05 -0400, Chuck Church <chuckchurch at gmail.com> wrote:
>> Does anyone know the reason /64 was proposed as the size for all L2 domains?
> 
> There is one, and only one, reason for the ::/64 split: SLAAC.  IPv6 is a classless addressing system.  You can make your LAN ::/117 if you want to; SLAAC will not work there.
> 
Nope...

There's also ND and the solicited node address.

> The reason the requirement is (currently) 64 is to accomodate EUI-64 hardware addresses -- firewire, bluetooth, fibre channel, etc.  Originally, SLAAC was designed for ethernet and its 48bit hardware address. (required LAN mask was ::/80.)  The purpose wasn't to put the whole internet into one LAN.  It was to make address selection "brainless", esp. for embeded systems with limited memory/cpu/etc... they can form an address by simply appending their MAC to the prefix, and be 99.99999% sure it won't be in use. (i.e. no DAD required.)  However, that was optimizing a problem that never existed -- existing tiny systems of the day were never destined to have an IPv6 stack, "modern" IPv6 hardware can select an address and perform DAD efficiently in well under 1K. (which is noise vs. the size of the rest of the IPv6 stack.)

Modern embedded IPv6 systems in short order will have IPv6 implemented in the chip ala the Wizard W5100 chip that is very popular for IPv4 in embedded systems and micro-controllers today.

> SLAAC has been a flawed idea from the first letter... if for no other reason than it makes people think "64bit network + 64bit host" -- and that is absolutely wrong. (one cannot make such assumptions about networks they do not control. it's even worse when people design hardware thinking that.)

While one cannot assume 64+64 on networks you don't control and CIDR is the rule for IPv6, having a common 64+64 subnet size widely deployed has a number of advantages.

I am interested to hear what people are using in lieu of ND and ARP on NBMA and/or BMA multipoint IPv6 networks with netmasks longer than /64.

Owen