question: private MulticastSocket createSocket ( ) throws IOException { MulticastSocket sock = new MulticastSocket ( mcastPort ) ; sock . setLoopbackMode ( false ) ; if ( sockItf != null ) sock . setInterface ( sockItf ) ; if ( sock . getLoopbackMode ( ) ) U . warn ( log , "Loopback mode is disabled which prevents nodes on the same machine from discovering " + "each other." ) ; sock . joinGroup ( mcastGrp ) ; if ( ttl != - 1 ) sock . setTimeToLive ( ttl ) ; return sock ; }
target:  Creates multicast socket and joins multicast group.