Subject: The Inside-Out ISATAP Model

From: Fred Templin <[email-masked]>
Date: Sun, 10 Nov 2002 23:12:28 -0800 (PST)

Hello,

I didn't get a chance to write a draft on this ahead of the deadline,
but I would like to propose a discussion topic for the design teams
at IETF 55. The topic proposes the use of ISATAP with globally-unique
interface identifiers, i.e., with the 'u/l' bit in the company code
set to "universal" and a globally unique IPv4 address.   

This feature enables the "Inside-Out ISATAP model", which I would also
like to propose as design team discussion material. For a diagrammatic
represenation of this model, see:

  http://www.geocities.com/osprey67/inside_out.ppt

In the traditional model, ISATAP operates "intra-site" as its name
implies. Nodes within an ISATAP site connect across the global Internet
to other sites via 6to4, native IPv6 routing, etc. But, when globally
unique IPv4 addresses are used, the model can be turned "inside-out".

In the inside-out model, ISATAP treats the global Internet as a
monolithic site with IPv6 clouds hanging off the edges. As in the
traditional model, ISATAP treats the IPv4 Internet as a link layer
for IPv6, thus the interface identifier is the natural place to
embed the link layer address. Moreover, this model allows all 64
bits of the routing prefix to be used for other purposes, e.g.
v6 routing.

Note that this model does NOT displace 6to4 and/or Teredo; instead,
all three mechanisms have important and complementary roles to play
in the global scheme. I would also like to suggest further discussion
along these lines in the design teams.

Fred Templin
[email-masked]  

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From: Pekka Savola <[email-masked]>
Date: Mon, 11 Nov 2002 09:37:45 +0200 (EET)

On Sun, 10 Nov 2002, Fred Templin wrote:
[...]
> bits of the routing prefix to be used for other purposes, e.g.

Wasn't this model already exhausted with "automatic tunneling using 
compatible addresses"?  The topology is flat, you can't connect even 
routers using this mechanism.

I fail to see what new advantages ISATAP would bring here.  Instead, the 
trust model is completely different, and certain assumptions no longer 
hold.

btw. reference to section 4.7 in isatap Security Considerations should be 
4.5, I believe.

-- 
Pekka Savola                 "Tell me of difficulties surmounted,
Netcore Oy                   not those you stumble over and fall"
Systems. Networks. Security.  -- Robert Jordan: A Crown of Swords

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From: Fred Templin <[email-masked]>
Date: Mon, 11 Nov 2002 06:33:52 -0800 (PST)

Pekka,

> routers using this mechanism.

It may well have been. If it was, I either missed the discussion or
it went over my head. It seems to me that microcausms of the model
I'm describing here have been debated over the past several months
in the newsgroups, but the model itself was not mentioned from a
high-level perspective. My purpose in bringing it up now is to
inform any others like myself who had never previously considered
turning the ISATAP model inside-out, and to initiate discussion in
the design teams.   

> trust model is completely different, and certain assumptions no longer 

Whether/not there are advantages, and whether/not the trust model
issues can be worked is something that needs to be discussed in
the design teams, given sufficient interest. I don't have good
answers to these questions myself, and am not entirely certain
what other questions may remain. 
 
> btw. reference to section 4.7 in isatap Security Considerations should be 

Arg! You mentioned that before, and I had every intention of fixing
it. Thanks for pointing it out - again!

Fred Templin
[email-masked]