[143367] in North American Network Operators' Group
Re: IPv6 end user addressing
daemon@ATHENA.MIT.EDU (William Herrin)
Mon Aug 8 01:16:38 2011
In-Reply-To: <3E3FDD2AC2CEF442A9D2B00CF5F6D0409A733475@winexmp02>
From: William Herrin <bill@herrin.us>
Date: Mon, 8 Aug 2011 01:15:29 -0400
To: Jonathon Exley <Jonathon.Exley@kordia.co.nz>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Sun, Aug 7, 2011 at 6:09 PM, Jonathon Exley
<Jonathon.Exley@kordia.co.nz> wrote:
> This has probably been said before, but it makes me uncomfortable to thin=
k of everybody in the world being given /48 subnets by default.
> All of a sudden that wide expanse of 2^128 IP addresses shrinks to 2^48 s=
ites. Sure that's still 65535 times more than 2^32 IPv4 addresses, but woul=
dn't it be wise to apply some conservatism now to allow the IPv6 address sp=
ace to last for many more years?
> After all, there are only 4 bits of IP version field so the basic packet =
format won't last forever.
Hi Jonathan,
IPv6 uses a slightly different mental model when it comes to address alloca=
tion.
In IPv4 you assigned blocks of 32-bit addresses. In IPv6 this is no
longer the case. You do not assign blocks of 128-bit addresses.
In IPv6 you assign blocks of 64-bit LANs. Each LAN is 64-bits long as
required by technologies like SLAAC. So, a /48 is 65k LANs, _not_
however many bazillion addresses.
The question you should be asking is: is it excessive or unwise to go
around assigning 65,000 LANs to every customer? Would 256 (/56) or 1
(/64) be a better number?
Assigning 1 LAN seems questionable. We're trying to avoid NAT with
IPv6 which means a customer may want to spend a LAN on things like the
interior network of a virtual machine server. It's hard to do this if
you only have one LAN.
On the other hand, a whole lot of folks have through this through
before you and concluded that a /56 (256 LANs per customer) is a
smarter starting point than a /48.
Regards,
Bill Herrin
--=20
William D. Herrin ................ herrin@dirtside.com=A0 bill@herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004
