Re: [SR-Users] about kamailio.cfg NAT test

I may be misinterpreting this, but RFC3261 section 18.2.2 ( Sending Responses ): - The server transport uses the value of the top Via header field in - order to determine where to send a response. It MUST follow the - following process: - - o If the "sent-protocol" is a reliable transport protocol such as - TCP or SCTP, or TLS over those, the response MUST be sent using - the existing connection to the source of the original request - that created the transaction, if that connection is still open. - This requires the server transport to maintain an association - between server transactions and transport connections. If that - connection is no longer open, the server SHOULD open a - connection to the IP address in the "received" parameter, if - present, using the port in the "sent-by" value, or the default - port for that transport, if no port is specified. If that - connection attempt fails, the server SHOULD use the procedures - in [4] for servers in order to determine the IP address and - port to open the connection and send the response to. The message is constructed by the application, and the TCP source port is determined afterwards, so there's no way that the application can know what that port will be ahead of time. When using TCP, it should be expected that message source port will be different than the port indicated in the Via. With that said, there's nothing wrong here. nat_uac_test(flags) bit value 16 is : * 16 - Test if the source port is different from the port in the "Via" header This tests exactly what it states, so it's not a false positive. It's probably a bad idea to use bit value 16 to check for NAT if using TCP. Ben Kaufman ben.kaufman(a)altigen.com -----Original Message----- From: Daniel-Constantin Mierla <miconda(a)gmail.com> Sent: Tuesday, March 24, 2020 10:47 AM To: Ben Kaufman <ben.kaufman(a)altigen.com>om>; Kamailio (SER) - Users Mailing List <sr-users(a)lists.kamailio.org>rg>; Juha Heinanen <jh(a)tutpro.com> Subject: Re: [SR-Users] about kamailio.cfg NAT test Yes, tcp is typically using ephemeral source port, in the way that is allocated by the tcp stack/kernel, not easy to be specified by the client app. But the client app can get the local (ephemeral) port after connect() using getsockname() and use it to build the SIP message that is going to be sent through the connection. I expect this is the way how (most of the) sip phone apps do it when the port in SIP headers is matching the source port of the connection. Cheers, Daniel On 24.03.20 15:15, Ben Kaufman wrote: -- Daniel-Constantin Mierla -- www.asipto.com www.twitter.com/miconda -- www.linkedin.com/in/miconda STATEMENT OF CONFIDENTIALITY: The information contained in this electronic message and any attachments to this message are intended for the exclusive use of the addressee(s) and may contain confidential or privileged information. If you are not the intended recipient, or the person responsible for delivering the e-mail to the intended recipient, be advised you have received this message in error and that any use, dissemination, forwarding, printing, or copying is strictly prohibited. Please notify AltiGen Communications immediately at either (888)258-4436 or via email to administrator(a)altigen.com, and destroy all copies of this message and any attachments.