use resolved addr

transport/internet/sockopt_windows.go

@@ -40,7 +40,10 @@ func applyOutboundSocketOptions(network string, address string, fd uintptr, conf
 		if err != nil {
 			return errors.New("failed to find the interface").Base(err)
 		}
-		isV4 := (network == "tcp4" || network == "udp4")
+		// easy way to check if the address is ipv4
+		isV4 := strings.Contains(address, ".")
+		// note: DO NOT trust the passed network variable, it can be udp6 even if the address is ipv4
+		// because operating system might(always) use ipv6 socket to process ipv4
 		if isV4 {
 			var bytes [4]byte
 			binary.BigEndian.PutUint32(bytes[:], uint32(inf.Index))

transport/internet/system_dialer.go

@@ -60,10 +60,14 @@ func (d *DefaultSystemDialer) Dial(ctx context.Context, src net.Address, dest ne
 			}
 		}
 		var lc net.ListenConfig
+		destAddr, err := net.ResolveUDPAddr("udp", dest.NetAddr())
+		if err != nil {
+			return nil, err
+		}
 		lc.Control = func(network, address string, c syscall.RawConn) error {
 			return c.Control(func(fd uintptr) {
 				if sockopt != nil {
-					if err := applyOutboundSocketOptions(network, "", fd, sockopt); err != nil {
+					if err := applyOutboundSocketOptions(network, destAddr.String(), fd, sockopt); err != nil {
 						errors.LogInfo(ctx, err, "failed to apply socket options")
 					}
 				}
@@ -73,10 +77,6 @@ func (d *DefaultSystemDialer) Dial(ctx context.Context, src net.Address, dest ne
 		if err != nil {
 			return nil, err
 		}
-		destAddr, err := net.ResolveUDPAddr("udp", dest.NetAddr())
-		if err != nil {
-			return nil, err
-		}
 		return &PacketConnWrapper{
 			Conn: packetConn,
 			Dest: destAddr,