From: <Harald.T.Alvestrand@uninett.no>
Message-Id: <199601181853.NAA04647@CS.UTK.EDU>
To: iesg@cnri.reston.va.us
cc: drums@cs.utk.edu, ipng@sunroof.eng.sun.com
Subject: A suggestion for IPv6 domain literals
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Date: Thu, 18 Jan 1996 19:53:00 +0100
Sender: Harald.T.Alvestrand@uninett.no

Ladies and Gentlemen,
I've followed the debate on the IPNG list about the merits of notation
for IPv6 addresses with great interest.

It seems clear that:
- Mail HAS to work when the DNS is down. In particular, you need to send
  mail with a source address that can be replied to *somehow* when you're=

  into such deep trouble that you don't find your own host's name.
  Addresses must then be such that they don't wreck mailers that have nev=
er
  heard of IPv6; this is the "relay" and the "cc" problem.
  This was also the consensus from the DRUMS WG in Dallas.
- In *all* other cases, it's either a strict local matter between source =
and
  sink (telnet 1080:0:0:0:8:800:200C:417A) or inappropriate and should be=

  discouraged (http://1080:0:0:0:8:800:200C:417A:8000/weird-port-no.html)=
=2E

I have a trial suggestion for you, mostly based on Christian's suggestion=
,
but with a little spice added for variety.

SUGGESTION 1: Add to the legal formats for writing IPv6 addresses in
RFC 1884 section 2.2 a pure hex representation: 32 hex digits, no
punctuation.

SUGGESTION 2: Change the definition of "domain" in RFC 821 and 822 to be:=


domain =3D domain-literal | dns-name

dns-name =3D name *("." name)
domain-literal =3D "[" name *("." name) "]"

While this is somewhat more permissive than current RFC 821 syntax (it
allows namelike objects inside a domain literal), it is much more
restrictive than current RFC 822 syntax. Spice to taste.

SUGGESTION 3: Write in the text (not grammar) rules that inside a domain
literal, the following forms are acceptable:

  number "." number "." number "." number (IPv4 address)

  "ipv6" "." 32 hexchar (IPv6 address)

DISCUSSION:

In order to remain just a little compatible with the IPv6 decision to go
with Hex rather than Decimal, I think we *have* to allow A-F in the domai=
n
literal. Extending this to handle A-Z is trivial, once you touch that par=
t
of the parsing code.

The "ipv6" tag is left in to give surprised people an idea of what is goi=
ng
on, and on the general principle that "if you want two today, you'd bette=
r
leave an escape hatch in case you ever need a third".

Comments?
(I don't want to do much of this on 3 mailing lists, but I don't want
either the IPv6 or the DRUMS people to feel left out, so I left both in.
Sorry for those in the microscopic subset that are on both!)

             Harald A