[SR-Users] Asterisk and Kamailio Failover-Failback

Hi everyone, currently i am running 2 Asterisk Servers that share the same dialplan and sip users, also they connect through DUNDi. Right now i need that the users on certain network register to one of the 2 servers and in case it fails, then kamailio should tell the phone to log in to the backup server. After the main server for that location is restored the phones should connect again to the main server. something like this: Location A Location B network: 192.168.1.0/24 network: 192.168.2.0/24 main asterisk server: 192.168.1.1 main asterisk server: 192.168.2.1 backup asterisk server: 192.168.2.1 backup asterisk server: 192.168.1.1 Unless there's a failover situation the phones on Location A (network: 192.168.1.0/24) should login to their main server, same with Location B , as soon the problem is fixed they should failback to their main server again, as i said both asterisk server share the same dialplan and sip-users. I don't want to let kamailio handle the user registration, i just need it to tell the phones which asterisk server should they contact based on their IP and main/backup server status. I tried to do it using DNS-SRV instead of Kamalio, it worked, but the phones never failback, also, DNS-SRV doesn't tell what server should be used based on the network the request came from. I've been trying to do this and really need help, any example would be appreciated, thanks in advance. Also i'd like to know if this is possible using H.323 protocol suit instead of SIP.