diff --git a/cmd/main.go b/cmd/main.go
index 9c1b72e..804a1a3 100644
--- a/cmd/main.go
+++ b/cmd/main.go
@@ -7,39 +7,53 @@ import (
 )
 
 var usage = `
+	通过伪造ping，把udp流量通过远程服务器转发到目的服务器上。用于突破某些运营商封锁UDP流量。
+	By forging ping, the udp traffic is forwarded to the destination server through the remote server. Used to break certain operators to block UDP traffic.
+
 Usage:
 
     pingtunnel -type server
 
-    pingtunnel -type client -l LOCAL_IP:4455 -s SERVER_IP -t 4455
+    pingtunnel -type client -l LOCAL_IP:4455 -s SERVER_IP -t SERVER_IP:4455
 
+    -type     服务器或者客户端
+              client or server
+
+    -l        本地的地址，发到这个端口的流量将转发到服务器
+              Local address, traffic sent to this port will be forwarded to the server
+
+    -s        服务器的地址，流量将通过隧道转发到这个服务器
+              The address of the server, the traffic will be forwarded to this server through the tunnel
+
+    -t        远端服务器转发的目的地址，流量将转发到这个地址
+              Destination address forwarded by the remote server, traffic will be forwarded to this address
+
+    -timeout  本地记录连接超时的时间，单位是秒
+              The time when the local record connection timed out, in seconds
 `
 
 func main() {
-	fmt.Println("start...")
 
-	t := flag.String("type", "client", "client or server")
-	listen := flag.String("l", ":4455", "listen addr")
-	target := flag.Int("t", 4455, "target port")
-	server := flag.String("s", "127.0.0.1", "server addr")
+	t := flag.String("type", "", "client or server")
+	listen := flag.String("l", "", "listen addr")
+	target := flag.String("t", "", "target addr")
+	server := flag.String("s", "", "server addr")
+	timeout := flag.Int("timeout", 60, "conn timeout")
 	flag.Usage = func() {
 		fmt.Printf(usage)
 	}
 
 	flag.Parse()
 
-	if flag.NArg() != 0 {
+	if (*t != "client" && *t != "server") || (*t == "client" && (len(*listen) == 0 || len(*target) == 0 || len(*server) == 0)) {
 		flag.Usage()
 		return
 	}
 
-	fmt.Printf("type %s\n", *t)
-	fmt.Printf("listen %s\n", *listen)
-	fmt.Printf("server %s\n", *server)
-	fmt.Printf("target port %d\n", *target)
+	fmt.Println("start...")
 
 	if *t == "server" {
-		s, err := pingtunnel.NewServer()
+		s, err := pingtunnel.NewServer(*timeout)
 		if err != nil {
 			fmt.Printf("ERROR: %s\n", err.Error())
 			return
@@ -48,13 +62,19 @@ func main() {
 		s.Run()
 	}
 	if *t == "client" {
-		c, err := pingtunnel.NewClient(*listen, *server, *target)
+
+		fmt.Printf("type %s\n", *t)
+		fmt.Printf("listen %s\n", *listen)
+		fmt.Printf("server %s\n", *server)
+		fmt.Printf("target %s\n", *target)
+
+		c, err := pingtunnel.NewClient(*listen, *server, *target, *timeout)
 		if err != nil {
 			fmt.Printf("ERROR: %s\n", err.Error())
 			return
 		}
-		fmt.Printf("Client Listen %s (%s) Server %s (%s) TargetPort %d:\n", c.Addr(), c.IPAddr(),
-			c.ServerAddr(), c.ServerIPAddr(), c.TargetPort())
+		fmt.Printf("Client Listen %s (%s) Server %s (%s) TargetPort %s:\n", c.Addr(), c.IPAddr(),
+			c.ServerAddr(), c.ServerIPAddr(), c.TargetAddr())
 		c.Run()
 	}
 }
diff --git a/src/pingtunnel/client.go b/src/pingtunnel/client.go
index 3be3f5d..b1e43b5 100644
--- a/src/pingtunnel/client.go
+++ b/src/pingtunnel/client.go
@@ -7,7 +7,7 @@ import (
 	"time"
 )
 
-func NewClient(addr string, server string, target int) (*Client, error) {
+func NewClient(addr string, server string, target string, timeout int) (*Client, error) {
 
 	ipaddr, err := net.ResolveUDPAddr("udp", addr)
 	if err != nil {
@@ -24,24 +24,33 @@ func NewClient(addr string, server string, target int) (*Client, error) {
 		addr:         addr,
 		ipaddrServer: ipaddrServer,
 		addrServer:   server,
-		targetPort:   (uint16)(target),
+		targetAddr:   target,
+		timeout:      timeout,
 	}, nil
 }
 
 type Client struct {
+	timeout int
+
 	ipaddr *net.UDPAddr
 	addr   string
 
 	ipaddrServer *net.IPAddr
 	addrServer   string
 
-	targetPort uint16
+	targetAddr string
 
 	conn       *icmp.PacketConn
 	listenConn *net.UDPConn
 
-	localConnToIdMap map[string]uint32
-	localIdToConnMap map[uint32]*net.UDPAddr
+	localAddrToConnMap map[string]*ClientConn
+	localIdToConnMap   map[string]*ClientConn
+}
+
+type ClientConn struct {
+	ipaddr     *net.UDPAddr
+	id         string
+	activeTime time.Time
 }
 
 func (p *Client) Addr() string {
@@ -52,8 +61,8 @@ func (p *Client) IPAddr() *net.UDPAddr {
 	return p.ipaddr
 }
 
-func (p *Client) TargetPort() uint16 {
-	return p.targetPort
+func (p *Client) TargetAddr() string {
+	return p.targetAddr
 }
 
 func (p *Client) ServerIPAddr() *net.IPAddr {
@@ -82,16 +91,21 @@ func (p *Client) Run() {
 	defer listener.Close()
 	p.listenConn = listener
 
-	p.localConnToIdMap = make(map[string]uint32)
-	p.localIdToConnMap = make(map[uint32]*net.UDPAddr)
+	p.localAddrToConnMap = make(map[string]*ClientConn)
+	p.localIdToConnMap = make(map[string]*ClientConn)
 
 	go p.Accept()
 
 	recv := make(chan *Packet, 1000)
 	go recvICMP(*p.conn, recv)
 
+	interval := time.NewTicker(time.Second)
+	defer interval.Stop()
+
 	for {
 		select {
+		case <-interval.C:
+			p.checkTimeoutConn()
 		case r := <-recv:
 			p.processPacket(r)
 		}
@@ -119,33 +133,58 @@ func (p *Client) Accept() error {
 			}
 		}
 
-		uuid := p.localConnToIdMap[srcaddr.String()]
-		if uuid == 0 {
-			uuid = UniqueId()
-			p.localConnToIdMap[srcaddr.String()] = uuid
-			p.localIdToConnMap[uuid] = srcaddr
-			fmt.Printf("client accept new local %d %s\n", uuid, srcaddr.String())
+		now := time.Now()
+		clientConn := p.localAddrToConnMap[srcaddr.String()]
+		if clientConn == nil {
+			uuid := UniqueId()
+			clientConn = &ClientConn{ipaddr: srcaddr, id: uuid, activeTime: now}
+			p.localAddrToConnMap[srcaddr.String()] = clientConn
+			p.localIdToConnMap[uuid] = clientConn
+			fmt.Printf("client accept new local %s %s\n", uuid, srcaddr.String())
 		}
 
-		sendICMP(*p.conn, p.ipaddrServer, p.targetPort, uuid, (uint32)(DATA), bytes[:n])
+		clientConn.activeTime = now
+		sendICMP(*p.conn, p.ipaddrServer, p.targetAddr, clientConn.id, (uint32)(DATA), bytes[:n])
 	}
 }
 
 func (p *Client) processPacket(packet *Packet) {
 
-	fmt.Printf("processPacket %d %s %d\n", packet.id, packet.src.String(), len(packet.data))
+	fmt.Printf("processPacket %s %s %d\n", packet.id, packet.src.String(), len(packet.data))
 
-	addr := p.localIdToConnMap[packet.id]
-	if addr == nil {
-		fmt.Printf("processPacket no conn %d \n", packet.id)
+	clientConn := p.localIdToConnMap[packet.id]
+	if clientConn == nil {
+		fmt.Printf("processPacket no conn %s \n", packet.id)
 		return
 	}
 
+	addr := clientConn.ipaddr
+
+	now := time.Now()
+	clientConn.activeTime = now
+
 	_, err := p.listenConn.WriteToUDP(packet.data, addr)
 	if err != nil {
 		fmt.Printf("WriteToUDP Error read udp %s\n", err)
-		p.localConnToIdMap[addr.String()] = 0
-		p.localIdToConnMap[packet.id] = nil
+		p.Close(clientConn)
 		return
 	}
 }
+
+func (p *Client) Close(clientConn *ClientConn) {
+	if p.localIdToConnMap[clientConn.id] != nil {
+		delete(p.localIdToConnMap, clientConn.id)
+		delete(p.localAddrToConnMap, clientConn.ipaddr.String())
+	}
+}
+
+func (p *Client) checkTimeoutConn() {
+	now := time.Now()
+	for id, conn := range p.localIdToConnMap {
+		diff := now.Sub(conn.activeTime)
+		if diff > time.Second*(time.Duration(p.timeout)) {
+			fmt.Printf("close inactive conn %s %s\n", id, conn.ipaddr.String())
+			p.Close(conn)
+		}
+	}
+}
diff --git a/src/pingtunnel/pingtunnel.go b/src/pingtunnel/pingtunnel.go
index ac9f8b0..2dc8796 100644
--- a/src/pingtunnel/pingtunnel.go
+++ b/src/pingtunnel/pingtunnel.go
@@ -1,12 +1,16 @@
 package pingtunnel
 
 import (
+	"crypto/md5"
+	"crypto/rand"
+	"encoding/base64"
 	"encoding/binary"
+	"encoding/hex"
 	"fmt"
 	"golang.org/x/net/icmp"
 	"golang.org/x/net/ipv4"
+	"io"
 	"net"
-	"sync/atomic"
 	"syscall"
 	"time"
 )
@@ -19,9 +23,9 @@ const (
 
 // An Echo represents an ICMP echo request or reply message body.
 type MyMsg struct {
-	ID     uint32
 	TYPE   uint32
-	TARGET uint16
+	ID     string
+	TARGET string
 	Data   []byte
 }
 
@@ -30,37 +34,61 @@ func (p *MyMsg) Len(proto int) int {
 	if p == nil {
 		return 0
 	}
-	return 10 + len(p.Data)
+	return 4 + p.LenString(p.ID) + p.LenString(p.TARGET) + len(p.Data)
+}
+
+func (p *MyMsg) LenString(s string) int {
+	return 2 + len(s)
 }
 
 // Marshal implements the Marshal method of MessageBody interface.
 func (p *MyMsg) Marshal(proto int) ([]byte, error) {
+
 	b := make([]byte, p.Len(proto))
-	binary.BigEndian.PutUint32(b[:4], uint32(p.ID))
-	binary.BigEndian.PutUint32(b[4:8], uint32(p.TYPE))
-	binary.BigEndian.PutUint16(b[8:10], uint16(p.TARGET))
-	copy(b[10:], p.Data)
+
+	binary.BigEndian.PutUint32(b[:4], uint32(p.TYPE))
+
+	id := p.MarshalString(p.ID)
+	copy(b[4:], id)
+
+	target := p.MarshalString(p.TARGET)
+	copy(b[4+p.LenString(p.ID):], target)
+
+	copy(b[4+p.LenString(p.ID)+p.LenString(p.TARGET):], p.Data)
+
 	return b, nil
 }
 
+func (p *MyMsg) MarshalString(s string) []byte {
+	b := make([]byte, p.LenString(s))
+	binary.BigEndian.PutUint16(b[:2], uint16(len(s)))
+	copy(b[2:], []byte(s))
+	return b
+}
+
 // Marshal implements the Marshal method of MessageBody interface.
 func (p *MyMsg) Unmarshal(b []byte) error {
-	p.ID = binary.BigEndian.Uint32(b[:4])
-	p.TYPE = binary.BigEndian.Uint32(b[4:8])
-	p.TARGET = binary.BigEndian.Uint16(b[8:10])
-	p.Data = make([]byte, len(b[10:]))
-	copy(p.Data, b[10:])
+
+	p.TYPE = binary.BigEndian.Uint32(b[:4])
+
+	p.ID = p.UnmarshalString(b[4:])
+
+	p.TARGET = p.UnmarshalString(b[4+p.LenString(p.ID):])
+
+	p.Data = make([]byte, len(b[4+p.LenString(p.ID)+p.LenString(p.TARGET):]))
+	copy(p.Data, b[4+p.LenString(p.ID)+p.LenString(p.TARGET):])
+
 	return nil
 }
 
-var uuid uint32
-
-func UniqueId() uint32 {
-	newValue := atomic.AddUint32(&uuid, 1)
-	return (uint32)(newValue)
+func (p *MyMsg) UnmarshalString(b []byte) string {
+	len := binary.BigEndian.Uint16(b[:2])
+	data := make([]byte, len)
+	copy(data, b[2:])
+	return string(data)
 }
 
-func sendICMP(conn icmp.PacketConn, server *net.IPAddr, target uint16, connId uint32, msgType uint32, data []byte) {
+func sendICMP(conn icmp.PacketConn, server *net.IPAddr, target string, connId string, msgType uint32, data []byte) {
 
 	m := &MyMsg{
 		ID:     connId,
@@ -130,7 +158,22 @@ func recvICMP(conn icmp.PacketConn, recv chan<- *Packet) {
 
 type Packet struct {
 	data   []byte
-	id     uint32
-	target uint16
+	id     string
+	target string
 	src    *net.IPAddr
 }
+
+func UniqueId() string {
+	b := make([]byte, 48)
+
+	if _, err := io.ReadFull(rand.Reader, b); err != nil {
+		return ""
+	}
+	return GetMd5String(base64.URLEncoding.EncodeToString(b))
+}
+
+func GetMd5String(s string) string {
+	h := md5.New()
+	h.Write([]byte(s))
+	return hex.EncodeToString(h.Sum(nil))
+}
diff --git a/src/pingtunnel/server.go b/src/pingtunnel/server.go
index 3052ef9..31ceb8e 100644
--- a/src/pingtunnel/server.go
+++ b/src/pingtunnel/server.go
@@ -4,25 +4,28 @@ import (
 	"fmt"
 	"golang.org/x/net/icmp"
 	"net"
-	"strconv"
 	"time"
 )
 
-func NewServer() (*Server, error) {
+func NewServer(timeout int) (*Server, error) {
 	return &Server{
+		timeout: timeout,
 	}, nil
 }
 
 type Server struct {
+	timeout int
+
 	conn *icmp.PacketConn
 
-	localConnMap map[uint32]*Conn
+	localConnMap map[string]*ServerConn
 }
 
-type Conn struct {
+type ServerConn struct {
 	ipaddrTarget *net.UDPAddr
 	conn         *net.UDPConn
-	id           uint32
+	id           string
+	activeTime   time.Time
 }
 
 func (p *Server) Run() {
@@ -34,13 +37,18 @@ func (p *Server) Run() {
 	}
 	p.conn = conn
 
-	p.localConnMap = make(map[uint32]*Conn)
+	p.localConnMap = make(map[string]*ServerConn)
 
 	recv := make(chan *Packet, 1000)
 	go recvICMP(*p.conn, recv)
 
+	interval := time.NewTicker(time.Second)
+	defer interval.Stop()
+
 	for {
 		select {
+		case <-interval.C:
+			p.checkTimeoutConn()
 		case r := <-recv:
 			p.processPacket(r)
 		}
@@ -49,13 +57,15 @@ func (p *Server) Run() {
 
 func (p *Server) processPacket(packet *Packet) {
 
-	fmt.Printf("processPacket %d %s %d\n", packet.id, packet.src.String(), len(packet.data))
+	fmt.Printf("processPacket %s %s %d\n", packet.id, packet.src.String(), len(packet.data))
+
+	now := time.Now()
 
 	id := packet.id
 	udpConn := p.localConnMap[id]
 	if udpConn == nil {
 
-		addr := ":" + strconv.Itoa((int)(packet.target))
+		addr := packet.target
 		ipaddrTarget, err := net.ResolveUDPAddr("udp", addr)
 		if err != nil {
 			fmt.Printf("Error ResolveUDPAddr for udp addr: %s %s\n", addr, err.Error())
@@ -67,11 +77,13 @@ func (p *Server) processPacket(packet *Packet) {
 			fmt.Printf("Error listening for udp packets: %s\n", err.Error())
 			return
 		}
-		udpConn = &Conn{conn: targetConn, ipaddrTarget: ipaddrTarget, id: id}
+		udpConn = &ServerConn{conn: targetConn, ipaddrTarget: ipaddrTarget, id: id, activeTime: now}
 		p.localConnMap[id] = udpConn
 		go p.Recv(udpConn, id, packet.src)
 	}
 
+	udpConn.activeTime = now
+
 	_, err := udpConn.conn.Write(packet.data)
 	if err != nil {
 		fmt.Printf("WriteToUDP Error %s\n", err)
@@ -80,9 +92,9 @@ func (p *Server) processPacket(packet *Packet) {
 	}
 }
 
-func (p *Server) Recv(conn *Conn, id uint32, src *net.IPAddr) {
+func (p *Server) Recv(conn *ServerConn, id string, src *net.IPAddr) {
 
-	fmt.Printf("server waiting target response %s\n", conn.ipaddrTarget.String())
+	fmt.Printf("server waiting target response %s -> %s %s\n", conn.ipaddrTarget.String(), conn.id, conn.conn.LocalAddr().String())
 
 	bytes := make([]byte, 10240)
 
@@ -102,13 +114,29 @@ func (p *Server) Recv(conn *Conn, id uint32, src *net.IPAddr) {
 			}
 		}
 
-		sendICMP(*p.conn, src, 0, id, (uint32)(DATA), bytes[:n])
+		now := time.Now()
+		conn.activeTime = now
+
+		sendICMP(*p.conn, src, "", id, (uint32)(DATA), bytes[:n])
 	}
 }
 
-func (p *Server) Close(conn *Conn) {
+func (p *Server) Close(conn *ServerConn) {
 	if p.localConnMap[conn.id] != nil {
 		conn.conn.Close()
-		p.localConnMap[conn.id] = nil
+		delete(p.localConnMap, conn.id)
 	}
 }
+
+func (p *Server) checkTimeoutConn() {
+
+	now := time.Now()
+	for id, conn := range p.localConnMap {
+		diff := now.Sub(conn.activeTime)
+		if diff > time.Second*(time.Duration(p.timeout)) {
+			fmt.Printf("close inactive conn %s %s\n", id, conn.ipaddrTarget.String())
+			p.Close(conn)
+		}
+	}
+
+}