[97649] in North American Network Operators' Group
Re: The Choice: IPv4 Exhaustion or Transition to IPv6
daemon@ATHENA.MIT.EDU (Steven M. Bellovin)
Thu Jun 28 18:10:37 2007
Date: Thu, 28 Jun 2007 17:59:33 -0400
From: "Steven M. Bellovin" <smb@cs.columbia.edu>
To: Valdis.Kletnieks@vt.edu
Cc: Bora Akyol <bora.akyol@aprius.com>,
brett watson <brett@the-watsons.org>, nanog@merit.edu
In-Reply-To: <19138.1183067213@turing-police.cc.vt.edu>
Errors-To: owner-nanog@merit.edu
On Thu, 28 Jun 2007 17:46:53 -0400
Valdis.Kletnieks@vt.edu wrote:
> On Thu, 28 Jun 2007 13:08:52 PDT, Bora Akyol said:
> > At a very low, hardware centric level, IPv6 would be a lot easier to
> > implement if
> >
> > 1) The addresses were 64 bits instead of 128 bits.
> > 2) The extension headers architecture was completely revamped to be
> > more hardware friendly.
>
> Wow, a blast from the past. The *current* IPv6 design was selected
> to a good extent because it was *easier* to do in hardware than some
> of the other contenders. You think 64 versus 128 is tough - think
> about the ASIC fun and games to support *variable length* addresses
> (not necessarily even a multiple of 4 bytes, in some of the
> proposals. Could be 7, could be 11, check the address length field
> for details. Yee. Hah).
I'm not going to revist all of the design issues; as I said, at this
point IPv6 is what is is. On that point, you're mostly right; there
were indeed a class of CLNP-derived solutions that were rejected. That
said, some of us -- including me -- wanted to use the two high-order
bits of the address to select among {64,128,192,256}-bit addresses.
Settling on 128 bits was a compromise between that group and advocates
of a 64-bit fixed-length address. History since then persuades me that
sticking with 64 bits would have been a very bad mistake.
--Steve Bellovin, http://www.cs.columbia.edu/~smb
