I apologize the last sentence of my previous email should be "...but no OPTIONS pings on client's side" Now I have installed kamailio 4.2 on server and client is behind NAT with enabled NATSIPPING and the result is the same like on private network = no OPTIONS ping. The only changes in default kamailio.cfg are: #!define WITH_MYSQL #!define WITH_AUTH #!define WITH_USRLOCDB #!define WITH_NAT #!define WITH_NATSIPPING alias="89.187.145.51" listen=tcp:89.187.145.51:5060 listen=tcp:127.0.0.1:5060 modparam("rtpproxy", "rtpproxy_sock", "udp:127.0.0.1:7722") # ----- nathelper params ----- modparam("nathelper", "natping_interval", 10) modparam("nathelper", "ping_nated_only", 0) modparam("nathelper", "sipping_bflag", FLB_NATSIPPING) modparam("nathelper", "sipping_method", "OPTIONS") modparam("nathelper", "sipping_from", "sip:pinger@89.187.145.51") # params needed for NAT traversal in other modules modparam("nathelper|registrar", "received_avp", "$avp(RECEIVED)") modparam("usrloc", "nat_bflag", FLB_NATB) and route[REGISTRAR] {       if (!is_method("REGISTER")) return;       if(isflagset(FLT_NATS)) {                   setbflag(FLB_NATB);                   setbflag(FLB_NATSIPPING);                    }         if (!save("location"))         sl_reply_error();         exit; } After registration the Cflag is 192 so in my opinion nat_bflag and sipping_ bflag are set but no OPTIONS pings on clint's side. I understand that it is  trivial problem but would somebody be so kind to help me to solve it? Thank you Petr ---------- Původní zpráva ---------- Od: Petr Wozniak &lt;Petr.Wozniak(a)seznam.cz&gt; Komu: miconda(a)gmail.com, Kamailio (SER) - Users Mailing List <sr-users@ lists.sip-router.org> Datum: 10. 11. 2014 18:03:23 Předmět: Re: [SR-Users] beginner's problem with sipping " Thank you very much Daniel.   I have adjusted the parameter for nat_uac_test() to 128 without success.   Then I disable NATDETECT route and only load modules nathelper and rtpproxy and set their parameters to modparam("nathelper", "natping_interval", 10) modparam("nathelper", "ping_nated_only", 0) modparam("nathelper", "sipping_bflag", FLB_NATSIPPING) modparam("nathelper", "sipping_method", "OPTIONS") modparam("nathelper", "sipping_from", "sip:pinger@192.168.1.44")   modparam("nathelper|registrar", "received_avp", "$avp(RECEIVED)")   and   route[REGISTRAR] {       if (is_method("REGISTER")) {                setbflag(FLB_NATSIPPING);                if (!save("location"))                sl_reply_error();                exit; } }       cflag after registration is 128 so in my opinion FLB_NATSIPPIG flag is set but OPTIONS pings on client's side.   kamailio.cfg please you find attached   Thank you   Regards   Petr ---------- Původní zpráva ---------- Od: Daniel-Constantin Mierla &lt;miconda(a)gmail.com&gt; Komu: Kamailio (SER) - Users Mailing List &lt;sr-users(a)lists.sip-router.org&gt; Datum: 10. 11. 2014 9:22:38 Předmět: Re: [SR-Users] beginner's problem with sipping " Hello, if you are in a private network, you need to adjust the parameter for nat_ uac_test() function to ignore private addresses in check tests -- see the readme of nathelper module. Cheers, Daniel On 09/11/14 19:33, Petr Wozniak wrote: " Dear sr-users,   I am beginner and apologize for bothering you with such a trivial problem. I would like to test sip UDP and TCP keepalive pinging. Kamailio and client  are on the same network (192.168.1.44 and 192.168.1.20) that implies not behind NAT. So in kamailio.cfg I have set   modparam("nathelper", "ping_nated_only", 0)   My simple kamailio.cfg please you find enclosed. are sending from kamailio. If somebody would be so kind to help me I will be very glad.   Thank you in advance   Regards   Petr _______________________________________________ SIP Express Router (SER) and Kamailio (OpenSER) - sr-users mailing list <a href='mailto:sr-users@lists.sip-router.org'>sr-users@lists.sip-router.org</a> <a href='http://lists.sip-router.org/cgi-bin/mailman/listinfo/sr-users'… " -- Daniel-Constantin Mierla <a href='http://twitter.com/#!/miconda'>http://twitter.com/#!/micon… - <a href='http://www.linkedin.com/in/miconda'>http://www.linkedin.co… Kamailio Advanced Training, Nov 24-27, Berlin - <a href='http://www.asipto.com'>http://www.asipto.com</a> _______________________________________________ SIP Express Router (SER) and Kamailio (OpenSER) - sr-users mailing list sr-users(a)lists.sip-router.org http://lists.sip-router.org/cgi-bin/mailman/listinfo/sr-users" _______________________________________________ SIP Express Router (SER) and Kamailio (OpenSER) - sr-users mailing list sr-users(a)lists.sip-router.org http://lists.sip-router.org/cgi-bin/mailman/listinfo/sr-users"