Hi, using Kamailio 3.2.0-dev5 (x86_64/linux) 552425. Related conf: ------------------------------ modparam("registrar", "use_path", 1) modparam("registrar", "path_mode", 1) modparam("nathelper", "natping_interval", 10) modparam("nathelper", "sipping_method", "OPTIONS") # No flag is set for NAT pinging... ------------------------------ REGISTER arrives coming from an outbound proxy which added Path header: ------------------ REGISTER sip:REGISTRAR SIP/2.0 Path: <sip:PROXY;transport=udp;lr> Contact: <sip:pepe@192.168.1.232:23652;transport=udp>;expires=3600 ----------------- Registration is performed, and since that, Kamailio starts sending ugly UDP datagrams to the Contact URI of the REGISTER: U 2011/08/31 13:32:21.558022 REGISTRAR -> 192.168.1.232:45329 \x00\x00\x00\x00 So first question is: why is the UDP "ping" sent to the REGISTER Contact URI instead of sending it to the Path URI? NOTE: I know that I can add custom/propietary ";received" param in Path URI and set in the registrar server: modparam("registrar", "path_use_received", 1) but honestly that should be non needed. Second question. Wouldn't be better if the UDP "ping" contains CRLF+CRLF rather than \x00\x00\x00\x00 ? At least, CRLF+CRLF is already defined as a SIP TCP ping. Regards. -- Iñaki Baz Castillo &lt;ibc(a)aliax.net&gt;