Subject: RE: (ngtrans) Teredo comment -- symmetric NAT

From: "Christian Huitema" <[email-masked]>
Date: Thu, 26 Sep 2002 11:27:09 -0700

> The TEREDO spec consistently states that "symmetric NATs" are not
> supported,
> but it offers no workaround suggestions and no promise of future
support.
> 16 spare bits would provide a good fit for an extra protocol port
number;
> perhaps a port number that would be associated with the "Server IPv4"
> address. I am thinking that this might potentially open the door for
> symmetric NAT support and perhaps other useful functions.

Symmetric NAT can only be traversed by an explicit tunnel, which is
outside the scope of the Teredo design. Section 7 of the draft explains
how to use the Teredo formats to implement a tunnel service that could
reuse the Teredo packet formats, but I agree with you, it is not
developed; IMHO, it belongs in another draft. One point however is
clear: the tunnel service will provide addresses that are rooted in a
prefix managed by the tunnel server, not Teredo addresses. More bits in
the Teredo prefix would not be particularly useful.

-- Christian Huitema