[SR-Users] Another NAT question

[Moacir Ferreira]

Daniel, It is more like I made a stupid request, sorry... Kamailio
is everything, but simple! I did some readings and, after rereading your
e-mail, it is more like that it is easier to get my routing needs done if I
have a dual homed server with a public interface and a private interface. Anyway, please consider that I am a dummy on Kamailio and
that I am using the kamailio.cfg template we get from the source code as a
starting point. The first step on the routing logic is to do a sanity check via
“route(REQINIT)”. Just after this sanity check, the next step is to verify if
the UA is NATed via “route(NATDETECT)”. Now, when calling the real routing
function “route(RELAY)”, all NAT decision has already been taken earlier and all
problems fixed! Now, supposing that I flagged all internal users during the
authentication “route(AUTH)” using the source IP ($si), how can I then use the
flag to build the following logic: Any internal to any internal -> Treat as no NATed (this
is natural as Kamailio will not “see” any NAT during the internal UAs registration
process); Any external to any external, follows the standard NAT detection
decision (this is also natural as Kamailio can “see” who is NATed or not); Any internal to external (or vice-versa), treat as NATed
(this is the challenge!); Although a dummy still, I like learning and reading… So if
you have any example, documentation that can send me the link, etc., please
send me. Next time I bother you I will have a more “reasonable” question to
post or better, I will have found the solution myself. Cheers! Moacir

> Date: Mon, 15 Oct 2012 09:10:30 +0200
> From: miconda at gmail.com
> To: sr-users at lists.sip-router.org
> CC: moacirferreira at hotmail.com
> Subject: Re: [SR-Users] Another NAT question
> 
> Hello,
> 
> you can detect that the call is coming from public/external interface 
> and goes to private/internal interface.
> 
> There are couple of ways to do it, one is to set a branch flag when they 
> register, saying it is from external or internal. Then based on src ip 
> ($si) or rcv io ($Ri) of the invite and the branch flag from location, 
> you decide to enforce the rtpproxy or not.
> 
> Alternative is to look at the forced socket or destination ip after 
> lookup location and get the info from there about the message flow.
> 
> Cheers,
> Daniel
> 
> On 10/13/12 11:43 PM, Moacir Ferreira wrote:
> > Hi,
> >   
> > I have a scenario where I got a firewall with 3 interfaces: internal, DMZ and external. All the traffic from internal going to external is NATed. However, the traffic between internal and DMZ is NOT NATed. The external and DMZ are using public IP addresses. On the DMZ I have a Kamailio server running with RTPProxy + NAT Helper.
> >   
> > Everything works fine when public (from the internet) users (UAs) are behind NAT as Kamailio will force the RTP to go via RTPProxy. However, when the public user has a public IP, it will fail to establish the RTP to a user who registered on Kamailio coming from the internal firewall interface.
> >   
> > The reason is that, as I don't do NAT between internal and DMZ firewall interfaces, Kamailio will not RTPRroxy in between the UAs because, from the way Kamailio detects NAT, they are not behind NAT. So the public user UA tries to reach a private IP address. If the "inside" user tries to call a public user (a user on the Internet with a public IP), it works.
> >
> > Yes, I could do NAT in between the internal and DMZ firewall interfaces. However, this would force all RTP traffic of my UAs at the LAN go to Kamailio RTPProxy, an bad effect that I would like to avoid.
> >
> > So my question is: what would be the best approach to solve this issue using Kamailio and RTPProxy in such scenario?
> >
> > Cheers!
> > Moacir 		 	   		
> > _______________________________________________
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> 
> -- 
> Daniel-Constantin Mierla - http://www.asipto.com
> http://twitter.com/#!/miconda - http://www.linkedin.com/in/miconda
> Kamailio Advanced Training, Berlin, Nov 5-8, 2012 - http://asipto.com/u/kat
> Kamailio Advanced Training, Miami, USA, Nov 12-14, 2012 - http://asipto.com/u/katu
> 
 		 	   		  
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