Thanks for the explanation! I finally got the dispatcher working in an active / passive Kamailio cluster in front of three FreePBX servers. I was using the Asipto Kamailio and Asterisk real time guide as a starting point so it had the WITHINDLG route. I ended up modifying the TOASTERISK route to call ds_select_dst and the FROMASTERSK route uses an htable for matching IPs off a mySQL view of the Kamailio dispatcher table. I also have some modifications to the REGFWD route. We'll see how performance is today as I did have to use a sqlops query to lookup the dispatcher set ID for TOASTERISK and REGFWD depending on the authentication ID. This setup is responsible for around 1000 extensions with 2000 devices for a high volume call center.