[SR-Users] Another NAT question

Moacir Ferreira moacirferreira at hotmail.com
Sun Nov 4 22:52:58 CET 2012

I am "reading" a lot... However, I can’t still get the “logic” to overcome my problem using
Kamailio routing logic. I was willing to have a dual-homed Kamailo+RTPproxy on a
single server, where one interface goes to the Internet and another one goes to
my private network. However, the private network is using the RFC1918 address
space. Kamailio's NAT detection mechanism forces the RTPproxy between two UAs if
they are using RFC1918 address space even if the 2 UAs are at the IP subnet that the Kamailio server is.
So, if I have a “private” network using RFC1918 addresses, made of several remote sites, all the RTP traffic
would have to go to the Kamailio/RTPproxy, causing a large and undesirable traffic on
the WAN links. By other hand, should I don’t care about getting all my RTP LAN/WAN traffic being sent to Kamailio because I am using RFC1918 address space, I could not find an "workable example" of configuring a
dual-homed Kamailio+RTPProxy that properly sets the rtpproxy_manage flags to make it work.

Looking at your IPv4/IPv6 example, we can see that it could be possible to tag a SIP transaction and decide latter if it were to go from external to internal, internal to internal or external to external. The example is quite easy to understand because you can separate IPv6 from IPv4 transactions. However, what about the private address space?
Any help would be really appreciated. If you can't help, what forum can I post my questions and get some answers?


> 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         	
> > _______________________________________________
> > SIP Express Router (SER) and Kamailio (OpenSER) - sr-users mailing list
> > sr-users at lists.sip-router.org
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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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