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

Lorenzo Colitti <> Tue, 28 February 2017 16:30 UTC

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From: Lorenzo Colitti <>
Date: Wed, 1 Mar 2017 01:29:51 +0900
Message-ID: <>
Subject: Re: Objection to draft-ietf-6man-rfc4291bis-07.txt
To: David Farmer <>
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On Wed, Mar 1, 2017 at 12:46 AM, David Farmer <> wrote:

> However many OSes also allow configurations other than just /64, is this
> OK? Is that how RFC4291 should be interpreted? Honestly, I don't read it
> that way,

IMO the important question is not "should an OS refuse to configure a /65
when manually configuring an address". I think the much more important
questions are, "can the OS assume that it can use the full 64 bits to form
an IID", and "will this link ever run out of IPv6 addresses". The answers
to those should be yes and no.

> I think we should be saying OS MAY allow configurations other than /64, at
> least with manual configuration, and maybe DHCPv6 too.

I really don't want to use a network that provides a /120 and requires
DHCPv6 to connect. Not only does it offer subpar functionality, it does so
for no good reason. At least in IPv4 there was a reason: there weren't
enough addresses. Would you want to use such a network?

Another thing I think we should avoid is to remove the fixed 64 barrier and
open the door to having this debate again and again, once for every new
IPv6-over-foo document and once for every new address configuration
protocol (today we have SLAAC and DHCPv6, who knows what we'll have in the

We have defined this as a parameter not as a constant.

I really don't understand this statement. How can you say that it's a
parameter, given that every RFC that has been published on this topic
starting from 1998 states that (most) IIDs are 64 bits long?

Most of the code in most implementations treated this a parameter, but
there is code that just takes the 64-bit length at face value, and is well
within its rights to do so, because it's specified by the standard.