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<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">Thanks for your answers.</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">I thought I could make an example with your suggestions, for documentation (I see others are interested at the moment).</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">Using add_contact_alias, when the 200 OK for an INVITE is received, e.g. from 10.0.9.49:61756:</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">SIP/2.0 200 OK</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">[…]</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">Contact: <sip:giacomo@10.0.9.49:61750;transport=tcp></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">add_contact_alias detects that received ip:port is different than the one in the Contact, so it appends an alias before relaying the 200 OK:</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">SIP/2.0 200 OK</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">[…]</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">Contact: <sip:giacomo@10.0.9.49:61750;alias=10.0.9.49~61756~2;transport=tcp></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">This will then be used when generating the ACK:</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">ACK sip:giacomo@10.0.9.49:61750;alias=10.0.9.49~61756~2;transport=tcp SIP/2.0</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">[…]</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">which Kamailio will change with handle_uri_alias(), removing the alias and setting the received ip:port as destination:</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">ACK sip:giacomo@10.0.9.49:61750;transport=tcp SIP/2.0</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">sent correctly to 10.0.9.49:61756.</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">With fix_nated_contact, same scenario, Kamailio would modify the Contact before relaying the 200 OK:</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">SIP/2.0 200 OK</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">[…]</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">Contact: <sip:giacomo@10.0.9.49:61756;transport=tcp></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">Which will then be used as R-URI for the ACK:</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">ACK sip:giacomo@10.0.9.49:61756;transport=tcp SIP/2.0</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">[…]</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">And sent without modifications to 10.0.9.49:61756.</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">As stated in other references, the difference is that with the add_contact_alias approach the invited client sees its published Contact in the ACK’s R-URI.</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">I hope this is useful.</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">Regards,</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D">Giacomo</span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1F497D"> </span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt; font-family:"Tahoma","sans-serif"; color:windowtext">From:</span></b><span lang="EN-US" style="font-size:10.0pt; font-family:"Tahoma","sans-serif"; color:windowtext"> Klaus Darilion [mailto:klaus.mailinglists@pernau.at]
<br>
<b>Sent:</b> 11 March 2012 13:10<br>
<b>To:</b> SIP Router - Kamailio (OpenSER) and SIP Express Router (SER) - Users Mailing List<br>
<b>Cc:</b> Giacomo Vacca<br>
<b>Subject:</b> Re: [SR-Users] Best approach for TCP/TLS connection re-use for nated Contacts</span></p>
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<p class="MsoNormal"> </p>
<p class="MsoNormal"><br>
Am 09.03.2012 20:56, schrieb Giacomo Vacca: </p>
<p class="MsoNormal">One of the solutions I’ve found is using <i>always </i>add_contact_alias() in onreply_route when handling the 200 OK, and then use handle_ruri_alias() when defining the destination for the ACK.</p>
<p class="MsoNormal"><br>
Yes, that the pragmatic approach I always use. IMO it is also a bit of security. I do not like to blindly trust user provided data (e.g. contact header), thus I always use the IP:port from where the message was received.<br>
<br>
regards<br>
Klaus</p>
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