Fail to open a socket for multicast

Question

Hi,

I have problems to open an multicast socket in Erlang to receive messages:

88> gen_udp:open(5353,[{reuseaddr, true}, {ip,{224,0,0,251}},{multicast_ttl,4},{multicast_loop,false},binary]).
{error,eaddrnotavail}

I checkt diffrent IP addresses and ports and the option {active, false}, but nothing helps. What could be the reason?

Thanks, Matthias.

Answer 1

Have you tried adding the option {add_membership, {Addr, LAddr}} where:

1. Addr is the multicast group in question (e.g. 224.0.0.251)
2. LAddr is a local interface (e.g. 0.0.0.0 for the default one)

1> gen_udp:open(5353,[{reuseaddr, true}, {add_membership, {{224, 0,0, 251}, {0, 0, 0, 0}}}, {ip,{224,0,0,251}},{multicast_ttl,4},{multicast_loop,false},binary]).

{ok,#Port<0.454>}

Answer 2

Hi,

After your helpful comments, I test something new. Please have a look:

12> gen_udp:open(1234,[{reuseaddr,true}, {add_membership,{{224,0,0,1},{0,0,0,0}}}, {ip,{224,0,0,1}}, {multicast_ttl,4}, {multicast_loop,false}, binary]).
{error,eaddrnotavail}
13> gen_udp:open(1234,[{reuseaddr, true}, {add_membership,{{224,0,0,1},{0,0,0,0}}},{multicast_ttl,4}, {multicast_loop,false}, binary]).
{ok,#Port<0.474>}

What's wrong? I think I need to get the line 12> running. Is the line 13> sufficient to write a listener.

Thanks, Matthias