Subject: IPv4/IPv6 transition with Route Through RRs

From: Willie Gillespie <[email-masked]>
Date: Mon, 07 Jan 2008 21:54:07 -0700

Basic abstract of the e-mail:
In RFC 1183, an experimental DNS RR type is defined called the Route 
Through (RT) RR.  Although not its original purpose, could this be 
expanded and used to ease the IPv4 to IPv6 transition?
---

A simple state table gives us 9 possibilities:
# | Endpoint A | Endpoint B
---------------------------
1 | IPv4 only  | IPv4 only
2 | IPv4 only  | IPv4/6
3 | IPv4 only  | IPv6 only
4 | IPv4/6     | IPv4 only
5 | IPv4/6     | IPv4/6
6 | IPv4/6     | IPv6 only
7 | IPv6 only  | IPv4 only
8 | IPv6 only  | IPv4/6
9 | IPv6 only  | IPv6 only

You might argue that some of the entries on the list are duplicates 
since #4 is just #2 reversed, etc.  But I'll leave it as is for now.

Assuming some way to route the native networks:
Case #1: No connectivity problems.
Case #2: Can connect with the IPv4 addresses.
Case #3: Uh-oh.  Need some way to connect.  See below.
Case #4: Can connect with the IPv4 addresses.
Case #5: Can connect with either the IPv4 or IPv6 addresses.  (Which one 
is a different topic and should be branched off from this thread.)
Case #6: Can connect with the IPv6 addresses.
Case #7: Uh-oh.  Need some way to connect.  See below.
Case #8: Can connect with the IPv6 addresses.
Case #9: No connectivity problems.

So, concerning Case #3 and Case #7, which is basically a IPv4 host on 
one end and a IPv6 host on the other:

If a IPv6-only host wants to connect to a IPv4-only host, could an RT 
record be used to point the IPv6 machine to a suitable IPv6-to-IPv4 gateway?
* Perhaps a company would rather not (or cannot) change over their 
production IPv4 machines, but don't want to leave IPv6 customers in the 
dark.  They would perform a simple DNS addition along with a gateway of 
sorts. (Maybe the "gateway" is a paid service of the ISP?) The "gateway" 
would have an IPv6 address and know how to simply bridge/relay traffic 
to and from a particular IPv4 address.  This would make it very simple 
to "upgrade" existing IPv4 services to allow IPv6 traffic, without 
modifying existing systems.

(1) Would something like the above work?
(2) If yes, what would it take to implement?
(3) If no, what is a workable idea that can be implemented? (no reason 
to respond unless you can suggest an alternative or improvement)
I view those as separate, yet related, discussions.

On the other hand, if an IPv4-only host wants to connect to a IPv6-only 
host, could an RT record be used to point the IPv4 machine to a suitable 
IPv4-to-IPv6 gateway?
* This scenario is a little trickier since one probably couldn't be able 
to provide a IPv4-to-IPv6 bridging service for all of their hosts. 
Plus, I doubt the IPv4 hosts are going to be updated to look for RT 
records anyway.  So, this RT idea doesn't really cover this situation... 
  Perhaps a relay system could be built where a single IPv4 address maps 
different ports to different IPv6 boxes.  For example, port 25 -> IPv6 
SMTP server, and port 80 -> IPv6 HTTP server.  Either way, that's just a 
thought and perhaps should be split off into a different thread. 
There's probably already a name I don't know for what I just described 
there.

(4) What is the best way to handle IPv4 connecting to IPv6 services? 
[new thread]

Well, that turned out to be much longer than I thought and took me much 
too long to write.  Let's break this into a bunch of smaller threads so 
we don't have to read so much with any replies.

Willie

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---

From: Willie Gillespie <[email-masked]>
Date: Tue, 08 Jan 2008 00:31:01 -0700

Willie Gillespie wrote:
<snip>
> (1) Would something like the above work?

Okay, so I was trying to think way too hard and overlooked the more 
simple solution.  What I described here doesn't need any fancy 
experimental DNS record, it would just need an AAAA record pointing to 
the "gateway" machine and it would work as expected.

Still, probably the easiest transition for current IPv4 services to make 
if they are afraid of touching their production machines.  An ISP could 
probably offer that service inline fairly easily and sell it to their 
customers until they were ready to dual-stack or whatnot.

Anyway, I guess question (4) still stands.... sorry for the unnecessary 
reading.

Willie