Everything is working fine, but with some clients (like Grandstream phone) the RTCP session wants to go tot he private address of the phone. Here is the log of one of these strange calls:

 

Apr 27 16:54:38 rtp1 rtpengine[2273]: INFO: [312ed76c31f21b71452e91e5184ad25b@172.16.2.210:5060]: [core] --------- Port  178.238.213.14:11088 <>    81.183.216.3:5068 , SSRC 77c19488, 625 p, 107500 b, 0 e, 29 ts

Apr 27 16:54:38 rtp1 rtpengine[2273]: INFO: [312ed76c31f21b71452e91e5184ad25b@172.16.2.210:5060]: [core] --------- Port  178.238.213.14:11089 <>      10.0.5.192:5069  (RTCP), SSRC 0, 0 p, 0 b, 0 e, 43 ts

 

As you can see the RTP itself is okay, but the RTCP will somehow go to the private address. If we tracing the sdp messages in sngrep, then we can see that Kamailio transforming IP addresses for the backend servers to the public (and the private address of the rtpengine) addresses.

This is almost certainly because the client has not sent any RTCP, and therefore rtpengine was not able to learn the correct public non-NAT address for the RTCP port, leaving you with the address that was advertised in the SDP.

Cheers