The MulticastSocket implementation on Windows uses the two stacks implementation. The two stacks implementation creates a socket on the IPv4 stack and another on the IPv6 stack. Operations are then performed on both sockets as appropriate. If the socket is bound to a specific address, then the IP version of the socket that matches that address is retained, and the other closed.
This is a complicated implementation, which will hopefully be replaced soon, but in the meantime there is a serious bug with handling the IP_MULTICAST_IF[2] socket option. The code does not correctly cater for the fact that one of the file descriptors may be closed, leading to SocketExceptions with a message of: "An operation was attempted on something that is not a socket (Error setting socket option)" Webrev: https://cr.openjdk.java.net/~chegar/8236441/webrev.00/ JIRA: https://bugs.openjdk.java.net/browse/JDK-8236441 -Chris.
