about gen_udp for erlang multibrodcast -

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i have erlang code, don't understand code { add_membership, { addr, { 0, 0, 0, 0 } } }, what's meaning of 0.0.0.0. 

addr = {226,0,0,1}, opts = [ { active, true },        { ip, addr },        { add_membership, { addr, { 0, 0, 0, 0 } } },        { multicast_loop, true },        { reuseaddr, true },        list ], { ok, recvsocket } = gen_udp:open (port, opts),

anyone can tell me meaning of 0.0.0.0?

0.0.0.0 wildcard ip address. machine might have several ip addresses, e.g. if has several network interface cards.

with add_membership option register multicast address (addr) , incoming packets network interface (0.0.0.0) forwarded application. can add specific ip address instead of 0.0.0.0 if want allow multicast packets particular interface.


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