create_socket.rb

def create_socket(multicast_addr, multicast_port, ifindex)
  # Create, bind, and return a UDP multicast socket
  UDPSocket.new(Socket::AF_INET6).tap do | s |
    ip = IPAddr.new(multicast_addr).hton + [ifindex].pack('I')
    s.setsockopt(Socket::IPPROTO_IPV6, Socket::IPV6_JOIN_GROUP, ip)
    s.setsockopt(Socket::IPPROTO_IPV6, Socket::IPV6_MULTICAST_HOPS, [1].pack('I'))
    s.setsockopt(Socket::IPPROTO_IPV6, Socket::IPV6_MULTICAST_IF, [ifindex].pack('I'))
    s.bind("::", multicast_port)
  end
end