[SR-Users] Error when using dispatcher module

Kamailio 3.1.2 I am using Kamailio in front of Freeswitch as simple sip router. To do multi-tenant in Freeswitch I created SIP domain (fs2000.ly.net) and used as sip domain inside my sip phone. This domain does not map to any real IP and no entry in our DNS server. If I sent the call directly to Freeswitch, it works fine and registered with Freeswitch. When I tried to go through Kamailio using dispatcher to route the call to freeswitch, I got this error: ERROR: <core> [resolve.c:1540]: ERROR: sip_hostport2su: could not resolve hostname: "fs2000.ly.net" The strange thing is that sometime the call did go through kamailio and registered with freeswitch. Whenever I restart Kamailio, I got above error and then the error went away by itself. Sometime took a minute and sometime took several hours. And sometime the error come back without restart. Does anybody know why? Why dispatcher want to resolve the hostname when it only lookup dispatcher for destination IP? Gary