Hello, In my setup, Kamailio acts as a registration server and route the calls to different asterisk boxes. The clients using IPV6 private ip and IPV4 public ip address are rejected by the asterisk server. On printing the contact header, I am getting the private ip (ipv6). Is there a way to change the contact header with public ip in all scenarios. I tried updating the contact header as below and unfortunately not working. Is there a better way to handle the scenario. As of now we don/t have a plan to implement ipv6 network. $var(p1) = "<sip:"; $var(p2) = "@"; $var(p3) = ":"; $var(p4) = ";ob>"; $var(x) = "" + $var(p1) + $fU + $var(p2) + $si + $var(p3) + $sp + $var(p4); remove_hf("Contact"); append_hf("Contact: $var(x)\r\n”); Thanks & Regards Cibin