Flags used in Socket.receiveMessage and Socket.sendMessage. The flags listed in the enum are some commonly available flags, but the values used for them are the same as on the platform, and any other flags are passed in/out as is. So to use a platform specific flag, just include the right system header and pass in the flag.
Request to send/receive out of band data.
Read data from the socket without removing it from the queue.
Don't use a gateway to send out the packet, only send to hosts on directly connected networks.