Hi, I am struggling with a cellular operator which removes the rport from the SIP messages sent by the client. During the troubleshooting process I have been playing with the NDLB parameters I found mentioned at the fs-wiki <param name="NDLB-force-rport" value="true"/> <param name="NDLB-received-in-nat-reg-contact" value="true"/> as well as with sip-force-contact at the extension xml config file. <variables> <variable name="sip-force-contact" value="NDLB-connectile-dysfunction"/> </variables> I Want to make freeswitch replying to the source port instead of the port supplied by the client, that is to port 12543 instead of to the 7608 as you can see below some pcap dumps of the case. I am not sure if that would solve thep roblem and am open to other suggestions as well. Thanks in advance, Tzury pcap dumps below: ### REGISTER ### User Datagram Protocol, Src Port: 12543 (12543), Dst Port: sip (5060) REGISTER sip:example.net SIP/2.0 v: SIP/2.0/UDP 212.154.128.222:7608;branch=z9hG4bKPj41fa0abd044c35c75598d561b2f93167 Max-Forwards: 70 f: <sip:1013@example.net>;tag=9194adecbf8e8179530eb589e83631db t: <sip:1013@example.net> i: ebf2e3c254517938f90f33d8fd89326d CSeq: 17355 REGISTER m: <sip:1013@212.154.128.222:7608> Expires: 300 l: 0 ### 401 UNAUTHORIZED ### SIP/2.0 401 Unauthorized Via: SIP/2.0/UDP 212.154.128.222:7608;branch=z9hG4bKPj41fa0abd044c35c75598d561b2f93167 From: <sip:1013@example.net>;tag=9194adecbf8e8179530eb589e83631db To: <sip:1013@example.net>;tag=166HraN0B149g Call-ID: ebf2e3c254517938f90f33d8fd89326d CSeq: 17355 REGISTER User-Agent: FreeSWITCH-mod_sofia/1.0.3-exported Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, PRACK, MESSAGE, SUBSCRIBE, NOTIFY, REFER, UPDATE, REGISTER, INFO, PUBLISH Supported: timer, precondition, path, replaces WWW-Authenticate: Digest realm="example.net", nonce="f2f1370c-bc7c-11de-b000-fbe81e221ab4", algorithm=MD5, qop="auth" Content-Length: 0