[106999] in North American Network Operators' Group
Re: It's Ars Tech's turn to bang the IPv4 exhaustion drum
daemon@ATHENA.MIT.EDU (Alain Durand)
Tue Aug 19 13:46:32 2008
Date: Tue, 19 Aug 2008 13:45:49 -0400
From: Alain Durand <alain_durand@cable.comcast.com>
To: Nathan Ward <nanog@daork.net>,
nanog list <nanog@nanog.org>
In-Reply-To: <C389A4AC-3477-4F3F-9A73-84195143EF27@daork.net>
Errors-To: nanog-bounces@nanog.org
On 8/19/08 1:36 PM, "Nathan Ward" <nanog@daork.net> wrote:
> 64 bits is not a magical boundary.
>
> 112 bits is widely recommended for linknets, for example.
>
> 64 bits is common, because of EUI-64 and friends. That's it.
> There is nothing, anywhere, that says that the first 64 bits is for
> routing.
Actually, there is text that says so:
RFC4291: IPv6 Addressing Architecture, section 2.5.1
" For all unicast addresses, except those that start with the binary
value 000, Interface IDs are required to be 64 bits long and to be
constructed in Modified EUI-64 format."
The fact that most implementations ignore this is a different story.
In practice, many routers require the packet to go twice in the hardware if
the prefix length is > 64 bits, so even though it is a total waste of space,
it is not stupid to use /64 for point-to-point links and even for loopbacks!
- Alain.
