I have a setup with 2 FreeSwitch servers and a single Kamailio sevrer in front with the dispatcher module. Everything works when directly connected to FreeSwitch. When I connect to Kamailio I'm only able to call one way between 2 extensions. The log from FreeSwitch says: 2011-09-29 15:51:53.625761 [ERR] sofia_reg.c:2136 Cannot locate any authentication credentials to complete an authentication request for realm '"10.0.1.7"' I guess it because, somehow, that one of the extension has a local IP. Both extensions can register and call into FreeSwitch and hear hold music etc. It's just one of the extension who can't call the other extension. I don't know if the error should be fixed on FreeSwitch or on Kamailio. And how... Can anyone help me out?