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

David Farmer <> Tue, 28 February 2017 20:34 UTC

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From: David Farmer <>
Date: Tue, 28 Feb 2017 14:33:58 -0600
Message-ID: <>
Subject: Re: Objection to draft-ietf-6man-rfc4291bis-07.txt
To: Lorenzo Colitti <>
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On Tue, Feb 28, 2017 at 10:29 AM, Lorenzo Colitti <>

> 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 don't disagree with your answers, and you may not think the manual config
question is important, but others seem too.

> 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?

And you don't have too.  But, your saying no one else can ever have a
reason to do that, and I'm not so sure about that.  And something on the
other side of the Internet can't make any assumption about what I'm doing
anyway.  You are saying it can't be done because the 64 bit boundary is
even more important than CIDR and addresses on the other side of the
Internet are supposed to be opaque.  Where as I disagree, CIDR and the
opaqueness of addresses across the Internet are more fundamental properties
than 64 bit boundary.  Which is why I say the 64 bit boundary is really a
RECOMMENDATION.  And CIDR and the opaqueness of addresses across the
Internet are REQUIREMENTS.

> 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
> future).

Which is why it time to get this right and saying it is now and forever 64
isn't right.

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

adjective: constant
1. occurring continuously over a period of time.
- remaining the same over a period of time.

noun: constant; plural noun: constants
1. a situation or state of affairs that does not change.

a quantity or parameter that does not change its value whatever the value
of the variables, under a given set of conditions.

a number expressing a relation or property that remains the same in all
circumstances, or for the same substance under the same conditions.


A mathematical constant is a special number, usually a real number, that is
"significantly interesting in some way". Constants arise in many areas of
mathematics, with constants such as e and π occurring in such diverse
contexts as geometry, number theory, and calculus.

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.

David Farmer     
Networking & Telecommunication Services
Office of Information Technology
University of Minnesota
2218 University Ave SE        Phone: 612-626-0815
Minneapolis, MN 55414-3029   Cell: 612-812-9952