SIP-NAT issues (was: RE: [Asterisk-Users] Free World Dialup behind NAT)

[Jamie Carl]

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I've been trying this too.  I've had a look at the SIP packets and the
SDP section gives the internal IP address for RTP destination.

INVITE sip:10001 at fwd.pulver.com SIP/2.0
Via: SIP/2.0/UDP 10.50.1.2:5060;branch=z9hG4bK47758f0a
From: "asterisk" <sip:asterisk at 10.50.1.2>;tag=as6f148dbb
To: <sip:10001 at fwd.pulver.com>
Contact: <sip:asterisk at 10.50.1.2>
Call-ID: 671df30d248a69495aaa784f64aa6fc3 at 10.50.1.2
CSeq: 102 INVITE
User-Agent: Asterisk PBX
Content-Type: application/sdp
Content-Length: 183

v=0
o=root 10741 10741 IN IP4 10.50.1.2
s=session                 ^^^^^^^^^
c=IN IP4 10.50.1.2
         ^^^^^^^^^^  <--  Here's the problem
t=0 0
m=audio 11296 RTP/AVP 0 101
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16

So call setup works, but the remote endpoint is sending the RTP stream
to the wrong address.  Is there any way around this??

I have "nat=yes" in my sip.conf file, but there seems to be NO public
information in this header at all.  So i'm thinking, what does "nat=yes"
actually do?


Regards,

Jamie Carl
Email:	me at jazz-inc.net
PH:		+61-414-365-466

-----Original Message-----
From: Shaun Ewing [mailto:shaun at ewing.dropbear.id.au]
Sent: Sunday, 25 May 2003 2:07 PM
To: asterisk-users at lists.digium.com
Subject: Re: [Asterisk-Users] Free World Dialup behind NAT


*This message was transferred with a trial version of CommuniGate(tm)
Pro*

----- Original Message -----
From: "Oliver Brandt" <oliver_mlisten at gmx.de>

<SNIP>

> Anyway, I set up an acount and as long as my * box dials into the
> internet itself it works fine. But as soon as I try to connect from
> behind the NAT I can't here the other person (he can here me though).
>
> My setup:
> ATA -> * -> NAT -> Freeworld -> other person

I had the same problem.

I tried everything I could think of (forwarding ports, etc) with no
luck.

It seemed (by looking at sip debug) that Asterisk was including its
internal
IP address in the outgoing headers. My guess is that the udp reply
packets
are being sent to that internal address - but as the person isn't on
your
network they're going into a black hole.

The only way I could solve it was by using one of my public IP addresses
(my
ISP gives up to 4).

Previously my config was similar to yours, but now it is:

Softphone -> * -> FWD -> other person
                 -> * -> LAN (other phones).

Once I had the * box on the public Internet and not behind NAT it worked
perfectly.

It would be interesting to see if there is a way to get around this
without
having an IP - I'm not too keen on having this box on the public
Internet;
I'd feel much more secure with it behind the firewall.

--Shaun

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