[Kamailio-Users] handling of DNS-SRV in kamailio-1.4.3 & 1.5.0

[Klaus Feichtinger]

Hello,

I have to relay SIP requests to a special "redundant" destination (= FQDN - e.g. "test.kamailio.loc") that consists of 3 hosts with different priorities.

After startup Kamailio creates a DNS-SRV request to the DNS server and receives a response with following answer (e.g.):
   _sip._udp.test.kamailio.loc: type SRV, class IN, priority 10, weight 100, port 5060, target host1.test.kamailio.loc
   _sip._udp.test.kamailio.loc: type SRV, class IN, priority 20, weight 90, port 5060, target host2.test.kamailio.loc
   _sip._udp.test.kamailio.loc: type SRV, class IN, priority 30, weight 80, port 5060, target host3.test.kamailio.loc

In worst case - if the prime and secondary host (host1 and host2) are unavailable - I expect that kamailio tries relaying the request to the third host in the list. But it doesn't. It makes retransmission of the original invite to the second host and does not try reaching the third host. 

For tuning the switchover to the alternative target(2) I have set the module parameter "fr_timer" for TM to 3 seconds (modparam("tm", "fr_timer", 3)).


Is this behaviour of Kamailio-1.4.3 and Kamailio-1.5.0 (I've tested it with both versions) as expected (= limited to support only two answers in a DNS SRV reply)? Does anybody have experience with this scenario? Can anybody give me a hint?

regards,

Klaus F.
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