Re: [Ekiga-list] symmetric nat traversal

[yannick <sevmek free fr>]

Le vendredi 28 novembre 2008 à 19:15 +0100, Martin Uecker a écrit :
> On Fri, Nov 28, 2008 at 04:17:35PM +0100, Piotr Morgwai Kotarbiński wrote:
> > The document is 5 years old and last modification of the project page
> > occurred also in 2003, so I'm not sure if anybody is working on it
> > still... I'll try to contact the author or other members of the
> > project and ask what's the status.
> > 
> > Thanks
> > 
> >   Morg
> > 
> 
> It seems that Miredo [http://www.remlab.net/miredo/] has symmetric
> NAT traversal support. It might be possible to acquire an IPv6
> address using teredo (Miredo) on both clients and then communicate
> with ipv6. In general, this would be a much more elegant solution
> then to implement NAT traversal in each and every program. Since
> Teredo is also supported on Windows, this might also work for
> Windows users.
> 

"Teredo is not compatible with all NAT devices. Using the terminology of
RFC 3489, full cone, restricted and port-restricted NAT devices are
supported, while symmetric NATs are not. National Chiao Tung University
proposed SymTeredo which enhanced the original Teredo protocol to
support symmetric NATs, and the Microsoft and Miredo implementations
implement certain unspecified non-standard extensions to improve support
for symmetric NATs. However, connectivity between a Teredo client behind
a symmetric NAT, and a Teredo client behind a port-restricted or
symmetric NAT remains seemingly impossible.

Indeed, Teredo assumes that when two clients exchange encapsulated IPv6
packets, the mapped/external UDP port numbers used will be the same as
those that were used to contact the Teredo server (and building the
Teredo IPv6 address). Without this assumption, it would not be possible
to establish a direct communication between the two clients, and a
costly relay would have to be used to perform triangle routing. A Teredo
implementation tries to detect the type of NAT at startup, and will
refuse to operate if the NAT appears to be symmetric. (This limitation
can sometimes be worked around by manually configuring a port forwarding
rule on the NAT box, which requires administrative access to the
device)."

http://en.wikipedia.org/wiki/Teredo_tunneling#Limitations

Well, according to wikipedia, it seems toredo has the same limitations
as Ekiga currently has...

> 
> Martin
> 
> 
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