Re: IPv6 address text representation

[Brian E Carpenter <brian@xxxxxxxxxxxxxxx>]

Andrew,

Andrew Main wrote:
> 
> The update of the URI syntax RFC, draft-fielding-uri-rfc2396bis,
> gives a precise ABNF syntax for IPv6 address textual format, on which
> Roy Fielding and I collaborated.  This really ought to be in the IPv6
> Addressing Architecture document -- RFC2373 had a faulty attempt at an
> ABNF grammar -- but the URI work came too late to get the grammar into the
> Addressing Architecture update that was being worked on at the time, now
> published as RFC3513.  Bob Hinden suggested that the IP address textual
> representation work could be published as a standalone document instead.
> 
> I've submitted a draft of this standalone document; it's
> draft-main-ipaddr-text-rep-00.  In working out the syntax details with
> Roy, I ended up with a lot of historical material and rationale, which
> I think makes such a narrow-topic document worthwhile.

Agreed. I'm glad someone finally got the ABNF right. 

In your history, I think you might mention the <dotnum> BNF
in [MTP] which was inherited by RFC 821. 

Embarassingly, I can add to the history by admitting that the faulty
ABNF in [IPV6-AA-2] was mine (see the message appended below).

A few other comments on the draft.

Should it be Informational? Wouldn't it be better to have it available
as a normative reference?

I suggest adding after the first paragraph of the Introduction something
like:

  It is generally considered undesirable for numeric IP addresses to
  be stored anywhere but in the DNS system, to avoid operational problems
  when hosts or networks are renumbered for any reason [RFC 1900].  
  However, this does not remove the need to represent addresses textually
  in documents, user interfaces, configuration files, and some protocols.

> 4.3 Delimitation
...
>    In contexts where an IP address needs to be distinguished from
>    similar-looking data that can appear in the same place, there is
>    precedent (from email addresses and URLs) for enclosing an IP address
>    in brackets ("[]") as a distinguisher.

You could usefully refer here to RFC 821, RFC 2732, and [URI].

   Brian

---------

Date: Mon, 27 Oct 1997 13:56:49 GMT
Message-Id: <9710271356.AA35978@hursley.ibm.com>
From: "(Brian E Carpenter)" <brian@hursley.ibm.com>
Subject: (IPng 4705) draft-ietf-ipngwg-addr-arch-v2-03.txt
To: ipng@sunroof.eng.sun.com
Reply-To: brian@hursley.ibm.com
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Just some minor points on draft-ietf-ipngwg-addr-arch-v2-03.txt

1. Given the difficulty we have in persuading the URL and SMTP
folks to do the right thing with the textual representation,
I suggest including a BNF syntax version as an annex.
A rough cut is annexed to this email.

2. I know why we say 

> o An anycast address must not be assigned to an IPv6 host, that
> is, it may be assigned to an IPv6 router only.

but is this really going to be tenable? It certainly isn't
enforceable.

3. For the record: I know I lost this one, but I still
think it is wrong to invert the universal/local bit in EUI-64.

     Brian Carpenter

In the variant of BNF used for URL syntax:

  IPv6address = hexpart [ ":" IPv4address ]
  IPv4address = 1*digit "." 1*digit "." 1*digit "." 1*digit

  hexpart = hexseq | hexseq "::" [ hexseq ] | "::" [ hexseq ]
  hexseq  = hex4 *( ":" hex4)
  hex4    = 1*hex

  hex   = digit | "A" | "a" | "B"  <etc>
  digit = "1" | "2" | "3" <etc>

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