Subject: IPv6 address text representation

From: Andrew Main <[email-masked]>
Date: Thu, 8 May 2003 09:56:27 +0100

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.

Comments are invited.  Obviously this list has a direct interest in seeing
that the IPv6 address presentation format has been handled correctly.
I'd also particularly like comments on the historical material from
people who were there at the time; at the moment it's all based on
archaeological analysis of the RFCs.

>A New Internet-Draft is available from the on-line Internet-Drafts directories.
>
>
>	Title		: Textual Representation of IPv4 and IPv6 Addresses
>	Author(s)	: A. Main
>	Filename	: draft-main-ipaddr-text-rep-00.txt
>	Pages		: 11
>	Date		: 2003-5-2
>	
>Historically, the conventional textual representations of IPv4 and
>IPv6 addresses have been poorly specified.  This document gives
>precise definitions of these conventions, together with advice for
>implementors.
>
>A URL for this Internet-Draft is:
>http://www.ietf.org/internet-drafts/draft-main-ipaddr-text-rep-00.txt

-zefram
-- 
Andrew Main (Zefram) <[email-masked]>
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From: Brian E Carpenter <[email-masked]>
Date: Fri, 09 May 2003 12:09:42 +0200

Andrew,

> 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
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From: "(Brian E Carpenter)" <[email-masked]>
Subject: (IPng 4705) draft-ietf-ipngwg-addr-arch-v2-03.txt
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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>