Re: Objection to draft-ietf-6man-rfc4291bis-07.txt

Lorenzo Colitti <lorenzo@google.com> Thu, 02 March 2017 15:36 UTC

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From: Lorenzo Colitti <lorenzo@google.com>
Date: Fri, 3 Mar 2017 00:35:40 +0900
Message-ID: <CAKD1Yr1SbdE-i-oGhi2kEFBWTOi_-FzgVdMYkMWjCEtw0MRRMg@mail.gmail.com>
Subject: Re: Objection to draft-ietf-6man-rfc4291bis-07.txt
To: Tore Anderson <tore@fud.no>
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On Thu, Mar 2, 2017 at 11:36 PM, Tore Anderson <tore@fud.no>; wrote:

> But if you're coding up an host OS IPv6 stack you can't differentiate
> between IPv4-translatable IPv6 addresses and «normal» IPv6 addresses.
> After all there's no flag or property that tells the host stack that a
> given IPv6 address is IPv4-translatable or not.
>

Agreed. But note: I'm not suggesting that hosts should refuse to manually
configure arbitrary-length prefix lengths. Hosts allow this today and I
have no problem with that.

What I'm saying is that the IID length for unicast addresses, with a few
exceptions, should continue to be fixed at 64 bits. Those exceptions should
be unicast addresses that start with binary 000 (RFC 4291) point-to-point
links that use /127 (RFC 6164), IPv6-translatable addresses (RFC 6052), and
probably not much else.

The reason the fixed 64-bit length is important is that it ensures that
subnets never run out of addresses, and that's an extremely desirable
property.