Connecting to a SIP server cluster

My Asterisk server is connecting to “”, which resolves to multiple IP addresses: 300 IN A 300 IN A 300 IN A 300 IN A

If one of these machines is down (i.e. it’s not replying to the SIP packets or it’s sending back ICMP Port Unreachable), Asterisk keeps trying the same server. Shouldn’t Asterisk move on to the next server automatically in this case? It seems to only way to do this at the moment is to run the “reload” command, which causes it to do a DNS lookup and it may then pick one of the other servers.