Assuming IPv6 is enabled: If a DatagramChannel created with the no-arg open method is used to send IPv4 multicast datagrams then it is platform specific as to whether the IP_MULTICAST_XXX socket options are effective or not. The same thing arises with the IP_TOS socket option when sending IPv4 unicast or multicast datagrams. On Linux and Windows it is possible to set IP_MULTICAST_XXX and IP_TOS socket options on IPv6 sockets so that they are effective for IPv4 addresses. DatagramChannel should be updated to try to set the IPv4 socket options, this will be important for a future MulticastSocket implementation that uses a DatagramChannel under the covers.