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4 Replies Last post: Sep 12, 2007 3:14 AM by h2o  
 
rauckenthaler
7 posts since
Apr 27, 2007

Jul 24, 2007 4:39 AM

OpenSBC behind NAT/router

Hi all,

I have a bit of a tricky problem and am not sure if OpenSBC can handle this setup. The network config is as follows

Office: Office Home
SBC (10.17.20.4) Router/NAT Router/NAT SIPPhone

Now the office NAT has port forwarding rules to send the SIP traffic to the SBC. The SIPPhone can send the invite to the SBC which internally forwards it to a voice service. The SBC sends back the 200 OK and ACK follows. So the SIP sginalling works, but the SDP offer/answer is not quite right.

Obvioulsy the SDP in the invite has the wrong (sipphone-local) ip address. The SBc should be able to correct that. But the SDP answer from the SBC also shows it''s internal IP address(10.17.20.4).

Now the question i have is if it is possible to configure the SBC to use the public ip address in the SDP. Furthermore, i''d like to know if it is possible to configure a port-range for the RTP traffic so that i can put some forwarding onto the NAT/router.

A last question would be, whether i''m able to get this setup to work?

does somebody have some experience or give some advice?

cheers

roland
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joegen
136 posts since
Apr 28, 2007
1. Jul 24, 2007 5:41 AM in response to: rauckenthaler
Re: OpenSBC behind NAT/router
openSBc isn''t really made for this setup. OpenSBC is intended to be
used either as a bridge between multi-homed networks or as a far end NAT
traversal server. These two setup requires that OpenSBC itself is not
the subject of NAT.

You may try "Static RTP Media Address" in the general parameters
config. Set the value to the public address of your NAT router. As
for the port number, OpenSBC starts at 30000 onwards for RTP and no,
there isn''t any provision to set the port range. This however can
easily be achieved with some code modification. Let me know if you want
to stretch it a bit further.
 
rauckenthaler
7 posts since
Apr 27, 2007
2. Aug 6, 2007 3:48 AM in response to: joegen
Re: OpenSBC behind NAT/router
Hi Joegen,

Last week i was back in the office and able to do some tests. I set the "Static RTP Media Address" to the public ip address and now the RTP seems to get streamed from the client the the public ip address. I still need to check if the NAT router will forward the RTP packets.

However i have also found that the Contact in the 200OK shows that internal IP adress rather than the public ip-address of the SBC behind the NAT. Is there a config field to "force" the SBC to pass back a specific IP address in the contact header of the 200OK?
Guest
Guest
3. Aug 7, 2007 9:39 AM in response to: rauckenthaler
Re: [OpenSBC] OpenSBC behind NAT/router
Hi Roland,

There is no provision yet to set the contact address for opensbc to bind
to the external NAT IP. However most SIP implementations already
support RFC 3581 (see http://www.opensipstack.org/rfc/rfc3581.txt ) so
there might not be a need to change the contact uri.

Joegen

Roland Auckenthaler wrote:

Hi Joegen,

Last week i was back in the office and able to do some tests. I set the "Static RTP Media Address" to the public ip address and now the RTP seems to get streamed from the client the the public ip address. I still need to check if the NAT router will forward the RTP packets.

However i have also found that the Contact in the 200OK shows that internal IP adress rather than the public ip-address of the SBC behind the NAT. Is there a config field to "force" the SBC to pass back a specific IP address in the contact header of the 200OK?
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h2o
3 posts since
Aug 29, 2007
4. Sep 12, 2007 3:14 AM in response to: joegen
Re: OpenSBC behind NAT/router

Hi joegen!


Would you tell me how can I setup the RTP port range thet OpenSBC uses?

Is it the line 193 in the B2BMediaInterface.cxx in OpenSIPStack?

It would be helpful to have an option on the WEB interface to set this.


Kind Regards,


Zoltan Perhacs

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