[153443] in North American Network Operators' Group
RE: IPv6 /64 links (was Re: ipv6 book recommendations?)
daemon@ATHENA.MIT.EDU (Chuck Church)
Wed Jun 6 10:59:43 2012
From: "Chuck Church" <chuckchurch@gmail.com>
To: <Jean-Francois.TremblayING@videotron.com>
In-Reply-To: <OF81E9E43F.7BD2CCFA-ON85257A15.004EFFD7-85257A15.00502F69@videotron.com>
Date: Wed, 6 Jun 2012 10:58:05 -0400
Cc: 'NANOG list' <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
Does anyone know the reason /64 was proposed as the size for all L2 =
domains?
I've looked for this answer before, never found a good one. I thought I
read there are some L2 technologies that use a 64 bit hardware address,
might have been Bluetooth. Guaranteeing that ALL possible hosts could =
live
together in the same L2 domain seems like overkill, even for this group.
/80 would make more sense, it does match up with Ethernet MACs. Not as =
easy
to compute, for humans nor processors that like things in 32 or 64 bit
chunks however. Anyone have a definite answer?
Thanks,
Chuck
-----Original Message-----
From: Jean-Francois.TremblayING@videotron.com
[mailto:Jean-Francois.TremblayING@videotron.com]=20
Sent: Wednesday, June 06, 2012 10:36 AM
To: anton@huge.geek.nz
Cc: NANOG list
Subject: IPv6 /64 links (was Re: ipv6 book recommendations?)
Anton Smith <anton@huge.geek.nz> a =E9crit sur 06/06/2012 09:53:02 AM :
> Potentially silly question but, as Bill points out a LAN always=20
> occupies a /64.
>=20
> Does this imply that we would have large L2 segments with a large=20
> number of hosts on them? What about the age old discussion about=20
> keeping broadcast segments small?
The /64 only removes the limitation on the number of *addresses* on the =
L2
domain. Limitations still apply for the amount of ARP and ND noise. A
maximum number of hosts is reached when that noise floor represents a
significant portion of the link bandwidth. If ARP/ND proxying is used, =
the
limiting factor may instead be the CPU on the gateway.=20
The ND noise generated is arguably higher than ARP because of DAD, but I
don't remember seeing actual numbers on this (anybody?).=20
I've seen links with up to 15k devices where ARP represented a =
significant
part of the link usage, but most weren't (yet) IPv6.=20
/JF
