[153510] in North American Network Operators' Group
Re: IPv6 /64 links (was Re: ipv6 book recommendations?)
daemon@ATHENA.MIT.EDU (Owen DeLong)
Thu Jun 7 17:50:55 2012
From: Owen DeLong <owen@delong.com>
In-Reply-To: <op.wfju4quutfhldh@rbeam.xactional.com>
Date: Thu, 7 Jun 2012 14:45:22 -0700
To: "Ricky Beam" <jfbeam@gmail.com>
Cc: 'NANOG list' <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Jun 7, 2012, at 1:27 PM, Ricky Beam wrote:
> On Wed, 06 Jun 2012 10:58:05 -0400, Chuck Church =
<chuckchurch@gmail.com> wrote:
>> Does anyone know the reason /64 was proposed as the size for all L2 =
domains?
>=20
> 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.
>=20
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
