[OpenSIPS-Users] Preload Route denied for SIP REGISTER. Why should I use an alias? What is the fundamentals behind it?

[Rodrigo Pimenta Carvalho]

Dear OpenSIPS-Users.


I have studied the fundamentals about my questions, reading RFC 3261 (topics 16.4 and 16.12) and then I have just figured out what is the problem.


My OpenSISP is behind a NAT, so it knows its local IP, but it doesn't know its public IP.  When this OpenSIPS receives a SIP REGISTER, such request has the public IP in its Route header. In this case, the OpenSIPS tries to forward the request to the "next proxy", as if such IP was of a valid outbound proxy. When the forwarded message reach the NAT, it come back to the OpenSIPS. This is a kind of loop that run until the proxy rises the "too many hops" error.


To solve this issue, I have to implement one of the following ideas, if possible:


- Fix the Route header, substituting the public IP with the local IP.


or


- Tell to the OpenSIPS, via opensips.cfg file, that he is always the last server that has to receive the SIP requests and not forward SIP REGISTER.


I will read the OpenSIPS documentation, specially the NATHELPER module, to see if one of these ideas is possible.


Any comment from someone will be very helpful!! I still have to find a direction.


Best regards.


RODRIGO PIMENTA CARVALHO
Inatel Competence Center
Software
Ph: +55 35 3471 9200 RAMAL 979


________________________________
De: users-bounces at lists.opensips.org <users-bounces at lists.opensips.org> em nome de Rodrigo Pimenta Carvalho <pimenta at inatel.br>
Enviado: segunda-feira, 7 de dezembro de 2015 17:26
Para: users at lists.opensips.org
Assunto: [OpenSIPS-Users] Preload Route denied for SIP REGISTER. Why should I use an alias? What is the fundamentals behind it?



Dear OpenSIPS-users.


I'm working with OpenSIPS and softphones successfully, since some months ago. All my softphones can register on OpenSIPS very well.

All was ok while this SIP proxy and the softphones was all running in the same local network.


Today, I have just created  a new isolated network and I put my OpenSIPS there. That is, now my OpenSIPS is behind a NAT from the point of view of all softphones. In this case, when a softphone tries to register on OpenSIPS, it get the answer: "Status: 403 Preload Route denied".


I have studied about this issue today (RR Module) including the answer found here: http://comments.gmane.org/gmane.comp.voip.opensips.user/24120 .


According to that answer I could comment, in opensips.cfg file,  the part that uses the function loose_route(). However it caused the "too many hops" problem.


Then, after reading more discussions, I have put an alias in my OpenSIPS.cfg script. It solved the issue, but I'm not sure if it is a good solution.


Could someone explain a bit about the issue I'm dealing with, please? I'm missing some fundamentals here, for sure. What could be an alternative solution?


Is there some way of "fixing" some header in the SIP REGISTER request, by means of OpenSIPS, so that it could accept the SIP REGISTER without issues?


Any hint will be very helpful!!

Thanks alot!




RODRIGO PIMENTA CARVALHO
Inatel Competence Center
Software
Ph: +55 35 3471 9200 RAMAL 979
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