Re: [Ekiga-list] NAT issues with VoIP clients

[Jānis Rukšāns <thedogfarted gmail com>]

On Thu, Mar 18, 2010 at 3:28 PM, My Name <legenyes hotmail com> wrote:

> The article says, "For that, before registering, A and B must discover their
> public IP addresses (corresponding to NATA and NATB respectively) and send
> it to ekiga.net, so that they can be contacted afterwards (*TODO why
> ekiga.net cannot simply use ip/port from ip packet header?*)".
>
> Indeed, this requires explanation.  This is surely the job of the SIP
> server.

It is possible with rport and friends but it works in a bit different
way. The server cannot use IP/port from the packet because there can
be one or more proxy between the client and server and the IP/port in
the packet will be that of the last proxy. Thus the client still has
to discover it's public IP but it can be done w/o STUN.

First the client sends a REGISTER with private IP in *both* Contact
and Via, Via also containing rport parameter. The server will reject
the request, adding received and rport parameters with the IP and port
from the packet. This is done by each proxy in the path, therefore
when the client receives the response, the top (and only one) Via
contains the external IP and port. Now the client can resubmit the
REGISTER with the external IP and port in the Contact (but private IP
in Via), which should be accepted. With some more magic (which
requires the private address in Via) this can work with almost any
type of NAT.

Notice that this is how Linphone and Nokia N900 (and probably other
clients) work. However ekiga.net rejects REGISTERs with private Via,
which breaks these clients.

> I certainly do not need a separate STUN server to use a Web
> browser.  The Web site has no trouble determining my external IP address.

You don't need STUN to use a web browser because with web browser
you're making only outgoing connections - from the browser to the
server. NEVER the other way around, it is not even possible. The web
site has no trouble determining your external IP because it doesn't
have to. Among other reasons why people are using HTTP proxies, Tor
and similar tech is to hide their IP address - the web server can do
without it. So don't compare apples to oranges.

-- 
Ian