Dear List, I have Kamailio 3.1 installed in Amazon EC 2 server. Everything is working fine except that every REGISTER / MESSAGE was looped for twice or 3 times. And I am sure this is not caused by UA. I have attached the ngrep log in this message. And also, my main modification to the kamailio.cfg is like below: Your help will be great great appreciated. Thank you!! Coca ---------------------------------- #!define WITH_MYSQL #!define WITH_NAT alias="mydomain.org" alias="xx.xx.xx.xx" advertised_address="xx.xx.xx.xx" ... ... route { # per request initial checks route(REQINIT); # NAT detection route(NAT); # handle requests within SIP dialogs route(WITHINDLG); ### only initial requests (no To tag) # CANCEL processing if (is_method("CANCEL")) { if (t_check_trans()) t_relay(); exit; } t_check_trans(); # authentication route(AUTH); # record routing for dialog forming requests (in case they are routed) # - remove preloaded route headers remove_hf("Route"); if (is_method("INVITE|SUBSCRIBE")) { #record_route(); /* for NAT support */ record_route_preset("xx.xx.xx.xx"); } # account only INVITEs if (is_method("INVITE")) { setflag(FLT_ACC); # do accounting } # dispatch requests to foreign domains route(SIPOUT); ### requests for my local domains # handle presence related requests route(PRESENCE); # handle registrations route(REGISTRAR); if ($rU==$null) { # request with no Username in RURI sl_send_reply("484","Address Incomplete"); exit; } # dispatch destinations to PSTN route(PSTN); # user location service route(LOCATION); route(RELAY); } # Handle SIP registrations route[REGISTRAR] { if (is_method("REGISTER")) { if(isflagset(FLT_NATS)) { setbflag(FLB_NATB); # uncomment next line to do SIP NAT pinging setbflag(FLB_NATSIPPING); } if (!save("location")) sl_reply_error(); exit; } }