Re: A 3rd try at a proposal for draft-ietf-6man-rfc4291bis-07

Lorenzo Colitti <> Tue, 07 March 2017 06:04 UTC

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From: Lorenzo Colitti <>
Date: Tue, 7 Mar 2017 15:03:56 +0900
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Subject: Re: A 3rd try at a proposal for draft-ietf-6man-rfc4291bis-07
To: David Farmer <>
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On Tue, Mar 7, 2017 at 1:56 PM, David Farmer <> wrote:

> To be clear no where in the text I provided does it say that an IID other
> than 64 is allow.  It say 128 bit quantities from manual configuration and
> DHCPv6 can be associated with with subnet prefixes of any length.  That is
> a fine distinction, but no finer that you claiming that requiring that
> 64-bit IIDs, and you implying 64-bit subnet prefixes too, doesn't make IPv6
> classful. Are you saying that every implementation of IPv6 that allows
> manual config of subnet prefixes other that /64 have it wrong?
> Furthermore, if subnet prefixes other than /64 aren't allowed then how do
> we have RFC6164
> I contend that the whole concept of an IID is optional, please note that
> RFC4291 and it's predecessor say: "At a minimum, a node may consider that
> unicast addresses (including its own) have no internal structure", So I
> contend that RFC4291 merely says that if you use an IID it must be 64 bits.
> It doesn't directly say that 128bit IPv6 addresses can't be associated with
> subnet prefixes other than /64.  In fact it also says, "IPv6 unicast
> addresses are aggregatable with prefixes of arbitrary bit-length, similar
> to IPv4 addresses under Classless Inter-Domain Routing."  Which to me
> implies that subnets other than /64 have to be valid.  Furthermore, RAs are
> allowed to be any length, especially if they don't set the "A" flag, why is
> this if not to allow subnet prefixes of any length?

Sure. Now let's write all that down in a document so that these subtle (and
likely controversial) issues can be fully explained and debated. Because:

   1. If these issues are subtle even for us, how can we hope that non-IETF
   participants (or even just non-WG participants) will understand them?
   2. If we don't write them down and just make a change to RFC 4291, how
   can we know that any decision we make is properly justified.
   3. If we don't write them down and just make a change to RFC 4291, how
   will future IETF participants and network administrators and host
   implementers know how to interpret the text we write? I don't think asking
   them to make sense of the 6man archives is reasonable.

I can't help fill in the [...] because I personally don't see what you can
>> do with a /113 that you can't do with a /64 (other than conserve addresses,
>> which has always been a non-goal), but there seem to be several
>> participants who do see a problem. What I'm saying is that if we want to
>> change the standard, the people who see a problem with it should articulate
>> that problem in a way that it's possible to find a solution using informed
>> and documented engineering trade-offs rather than opinions.
> Just because you can't see it doesn't mean that other can't and don't have
> valid uses.

Absolutely agreed. Let's write those uses down, and use them to inform our
decision as to how (and whether) we should change the standard.