How to multicast using gen_udp in Erlang?

Question

How do you use gen_udp in Erlang to do multicasting? I know its in the code, there is just no documentation behind it. Sending out data is obvious and simple. I

Answer 1

I try to get this example running on my PC. What could happen, if I get always the message {error,eaddrnotavail} by opening the receive socket?

Example 1: This works:

{ok, Socket} = gen_udp:open(?PORT, [{reuseaddr,true}, {ip,?SERVER_IP},
               {multicast_ttl,4}, {multicast_loop,false}, binary]),

Example 2: Getting an runtime Error:

{ok, Socket} = gen_udp:open(?PORT, [{reuseaddr,true}, {ip,?MULTICAST_IP},
               {multicast_ttl,4}, {multicast_loop,false}, binary]),

% --> {error,eaddrnotavail}

-define(SERVER_IP, {10,31,123,123}). % The IP of the current computer
-define(PORT, 5353).
-define(MULTICAST_IP, {224,0,0,251}).