Trouble configuring unicast

I have a stack set up for testing on a single box, and I am successfully 
sending and receiving messages between the members of the group when i 
multicast them, i.e. when i use send without specifying an address for 
the destination.

I am using a Receiver to receive the request from the channel.

However if I specify an address for the recipient in the message - so it 
should only go to the recipient (I have validated the address is 
correct) then the message is not received. I'm assuming that if you 
specify a single address a UNICAST transport will be used.

I guess I must have something wrong in my stack config, but can't work 
out what it is:

"UDP(mcast_addr=228.8.8.8;mcast_port=45566;ip_ttl=32;bind_addr=localhost):"+
"PING(timeout=2000;num_initial_members=3):"+
"FD(timeout=3000):"+
"VERIFY_SUSPECT(timeout=1500):"+
"pbcast.NAKACK(gc_lag=10;retransmit_timeout=600,1200,2400,4800):"+
"UNICAST(timeout=600,1200,2400,4800):"+
"pbcast.STABLE(desired_avg_gossip=10000):"+
"FRAG:"+ 
"pbcast.GMS(join_timeout=5000;join_retry_timeout=2000;shun=true;print_local_addr=true)";

Any idea?

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