diff --git a/client.go b/client.go
index ecbbcc4c..d1ae457f 100644
--- a/client.go
+++ b/client.go
@@ -54,7 +54,11 @@ var (
 	postedCancels               = expvar.NewInt("postedCancels")
 )
 
-const extensionBytes = "\x00\x00\x00\x00\x00\x10\x00\x00"
+// Justification for set bits follows.
+//
+// Extension protocol: http://www.bittorrent.org/beps/bep_0010.html
+// DHT: http://www.bittorrent.org/beps/bep_0005.html
+const extensionBytes = "\x00\x00\x00\x00\x00\x10\x00\x01"
 
 // Currently doesn't really queue, but should in the future.
 func (cl *Client) queuePieceCheck(t *torrent, pieceIndex pp.Integer) {
@@ -531,6 +535,13 @@ func (me *Client) runConnection(sock net.Conn, torrent *torrent, discovery peerS
 			Bitfield: torrent.bitfield(),
 		})
 	}
+	if conn.PeerExtensionBytes[7]&0x01 != 0 && me.dHT != nil {
+		addr, _ := me.dHT.LocalAddr().(*net.UDPAddr)
+		conn.Post(pp.Message{
+			Type: pp.Port,
+			Port: uint16(addr.Port),
+		})
+	}
 	err = me.connectionLoop(torrent, conn)
 	if err != nil {
 		err = fmt.Errorf("during Connection loop with peer %q: %s", conn.PeerID, err)
@@ -860,6 +871,16 @@ func (me *Client) connectionLoop(t *torrent, c *connection) error {
 			if err != nil {
 				log.Printf("peer extension map: %#v", c.PeerExtensionIDs)
 			}
+		case pp.Port:
+			if me.dHT == nil {
+				break
+			}
+			addr, _ := c.Socket.RemoteAddr().(*net.TCPAddr)
+			_, err = me.dHT.Ping(&net.UDPAddr{
+				IP:   addr.IP,
+				Zone: addr.Zone,
+				Port: int(msg.Port),
+			})
 		default:
 			err = fmt.Errorf("received unknown message type: %#v", msg.Type)
 		}
diff --git a/peer_protocol/protocol.go b/peer_protocol/protocol.go
index db32ac59..607edf59 100644
--- a/peer_protocol/protocol.go
+++ b/peer_protocol/protocol.go
@@ -33,6 +33,7 @@ const (
 	Request                   // 6
 	Piece                     // 7
 	Cancel                    // 8
+	Port                      // 9
 	Extended      = 20
 
 	HandshakeExtendedID = 0
@@ -50,6 +51,7 @@ type Message struct {
 	Bitfield             []bool
 	ExtendedID           byte
 	ExtendedPayload      []byte
+	Port                 uint16
 }
 
 func (msg Message) MarshalBinary() (data []byte, err error) {
@@ -92,6 +94,8 @@ func (msg Message) MarshalBinary() (data []byte, err error) {
 				return
 			}
 			_, err = buf.Write(msg.ExtendedPayload)
+		case Port:
+			err = binary.Write(buf, binary.BigEndian, msg.Port)
 		default:
 			err = fmt.Errorf("unknown message type: %v", msg.Type)
 		}
@@ -187,6 +191,8 @@ func (d *Decoder) Decode(msg *Message) (err error) {
 			break
 		}
 		msg.ExtendedPayload, err = ioutil.ReadAll(r)
+	case Port:
+		err = binary.Read(r, binary.BigEndian, &msg.Port)
 	default:
 		err = fmt.Errorf("unknown message type %#v", c)
 	}
diff --git a/peer_protocol/protocol_test.go b/peer_protocol/protocol_test.go
index d2fc8d4b..580d26b2 100644
--- a/peer_protocol/protocol_test.go
+++ b/peer_protocol/protocol_test.go
@@ -121,3 +121,34 @@ func TestMarshalKeepalive(t *testing.T) {
 		t.Fatalf("marshalled keepalive is %q, expected %q", bs, expected)
 	}
 }
+
+func TestMarshalPortMsg(t *testing.T) {
+	b, err := (Message{
+		Type: Port,
+		Port: 0xaabb,
+	}).MarshalBinary()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(b) != "\x00\x00\x00\x03\x09\xaa\xbb" {
+		t.FailNow()
+	}
+}
+
+func TestUnmarshalPortMsg(t *testing.T) {
+	var m Message
+	d := Decoder{
+		R:         bufio.NewReader(bytes.NewBufferString("\x00\x00\x00\x03\x09\xaa\xbb")),
+		MaxLength: 8,
+	}
+	err := d.Decode(&m)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if m.Type != Port {
+		t.FailNow()
+	}
+	if m.Port != 0xaabb {
+		t.FailNow()
+	}
+}