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Re: [v6ops] IPv6-Only Preferred DHCPv4 option

Lorenzo Colitti <lorenzo@google.com> Wed, 04 December 2019 23:57 UTC

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From: Lorenzo Colitti <lorenzo@google.com>
Date: Thu, 05 Dec 2019 08:57:19 +0900
Message-ID: <CAKD1Yr0KPfFvk7Y49WkiVnm1q0E6i1u1hi4p_x56=p+kP9g=0g@mail.gmail.com>
To: Nick Hilliard <nick@foobar.org>
Cc: Brian E Carpenter <brian.e.carpenter@gmail.com>, "v6ops@ietf.org WG" <v6ops@ietf.org>
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Subject: Re: [v6ops] IPv6-Only Preferred DHCPv4 option
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On Thu, Dec 5, 2019 at 5:43 AM Nick Hilliard <nick@foobar.org> wrote:

> > As an ex-author of an ex-draft that suggested using IPv6 to tell
> > hosts to avoid IPv4, I'm curious to know whether a draft that
> > suggests using IPv4 to tell hosts to prefer IPv6 will also be accused
> > of being an operational nightmare.
>
> I haven't read the draft yet - and won't get to it for a couple of days
> - but am also curious about why this approach is better than the other
> way around :-)
>

Here are a couple of reasons why we believe this proposal will fare better
than the IPv6-only flag:

   1. It has a clear goal and clear semantics.  There was little consensus
   on the meaning of the IPv6-only flag. Did it mean that there was no IPv4 on
   the link? That the network should not provide IPv4 addresses? Or that hosts
   should never send packets with IPv4 ethertypes? If the latter, why not drop
   the packets in the infrastructure? But then, what about link-local? And so
   on. In contrast, this option's goal is very clear (conserve IPv4 addresses)
   and its meaning is very clear: here's an IPv4 address if you want it, but
   please don't use it if you don't need it.
   2. It is using a protocol that already configures IPv4 to configure
   IPv4. The IPv6-only flag was trying to affect IPv4 using an IPv6 protocol,
   and that allows attackers to mount attacks on existing networks that have
   not deployed IPv6 and thus have no IPv6 security measures in place.

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