// and iptables will be smart enough to pick the correct underlying set (v4 or v6, based on context),
// reducing the # of rules we need.
//
// BUT netlink lib doesn't support adding things to `list:set` types yet, and current tagged release
// doesn't support creating `list:set` types yet (is in main branch tho).
// So this will actually create 2 underlying ipsets, one for v4 and one for v6

			// since Linux 4.11.
			_ = syscall.SetsockoptInt(fd, syscall.IPPROTO_TCP, unix.TCP_FASTOPEN_CONNECT, 1)

			// Enable TCP quick ACK, John Nagle says
			// "Set TCP_QUICKACK. If you find a case where that makes things worse, let me know."
			_ = syscall.SetsockoptInt(fd, syscall.IPPROTO_TCP, unix.TCP_QUICKACK, 1)

			/// Enable keep-alive
			{
				_ = unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_KEEPALIVE, 1)