diff --git a/app/app/src/main/java/cn/openp2p/OpenP2PService.kt b/app/app/src/main/java/cn/openp2p/OpenP2PService.kt
index 6660496..88de756 100644
--- a/app/app/src/main/java/cn/openp2p/OpenP2PService.kt
+++ b/app/app/src/main/java/cn/openp2p/OpenP2PService.kt
@@ -203,7 +203,8 @@ class OpenP2PService : VpnService() {
                 val network = Network(id, name, gateway, nodeList)
                 println(network)
                 Log.i(OpenP2PService.LOG_TAG, "onBind");
-                builder.addDnsServer("8.8.8.8")
+                builder.addDnsServer("223.5.5.5")
+                builder.addDnsServer("2400:3200::1") // alicloud dns v6 & v4
                 builder.addRoute("10.2.3.0", 24)
 //            builder.addRoute("0.0.0.0", 0);
                 builder.setSession(LOG_TAG!!)
diff --git a/core/config.go b/core/config.go
index 8f6a8c7..15ad725 100644
--- a/core/config.go
+++ b/core/config.go
@@ -239,7 +239,7 @@ func (c *Config) delete(app AppConfig) {
 	defer c.save()
 	for i := 0; i < len(c.Apps); i++ {
 		if (app.SrcPort != 0 && c.Apps[i].Protocol == app.Protocol && c.Apps[i].SrcPort == app.SrcPort) || // normal app
-			(app.SrcPort == 0 && c.Apps[i].PeerNode == app.PeerNode) { // memapp
+			(app.SrcPort == 0 && c.Apps[i].SrcPort == 0 && c.Apps[i].PeerNode == app.PeerNode) { // memapp
 			if i == len(c.Apps)-1 {
 				c.Apps = c.Apps[:i]
 			} else {
diff --git a/core/nat.go b/core/nat.go
index 2a4e3de..3748d25 100644
--- a/core/nat.go
+++ b/core/nat.go
@@ -66,7 +66,7 @@ func natTest(serverHost string, serverPort int, localPort int) (publicIP string,
 	}
 
 	// The connection can write data to the desired address.
-	msg, err := newMessage(MsgNATDetect, 0, nil)
+	msg, err := newMessage(MsgNATDetect, MsgNAT, nil)
 	_, err = conn.WriteTo(msg, dst)
 	if err != nil {
 		return "", 0, err
@@ -164,17 +164,33 @@ func publicIPTest(publicIP string, echoPort int) (hasPublicIP int, hasUPNPorNATP
 			break
 		}
 		defer conn.Close()
-		dst, err := net.ResolveUDPAddr("udp", fmt.Sprintf("%s:%d", publicIP, echoPort))
+		dst, err := net.ResolveUDPAddr("udp", fmt.Sprintf("%s:%d", gConf.Network.ServerHost, gConf.Network.ServerPort))
 		if err != nil {
 			break
 		}
-		conn.WriteTo([]byte("echo"), dst)
+
+		// The connection can write data to the desired address.
+		msg, _ := newMessage(MsgNATDetect, MsgPublicIP, NatDetectReq{EchoPort: echoPort})
+		_, err = conn.WriteTo(msg, dst)
+		if err != nil {
+			return
+		}
 		buf := make([]byte, 1600)
 
 		// wait for echo testing
 		conn.SetReadDeadline(time.Now().Add(PublicIPEchoTimeout))
-		_, _, err = conn.ReadFromUDP(buf)
-		if err == nil {
+		nRead, _, err := conn.ReadFromUDP(buf)
+		if err != nil {
+			gLog.Println(LvERROR, "PublicIP detect error:", err)
+			break
+		}
+		natRsp := NatDetectRsp{}
+		err = json.Unmarshal(buf[openP2PHeaderSize:nRead], &natRsp)
+		if err != nil {
+			gLog.Println(LvERROR, "PublicIP detect error:", err)
+			break
+		}
+		if natRsp.Port == echoPort {
 			if i == 1 {
 				gLog.Println(LvDEBUG, "UPNP or NAT-PMP:YES")
 				hasUPNPorNATPMP = 1
diff --git a/core/protocol.go b/core/protocol.go
index c9ca1bd..6519ab2 100644
--- a/core/protocol.go
+++ b/core/protocol.go
@@ -10,7 +10,7 @@ import (
 	"time"
 )
 
-const OpenP2PVersion = "3.21.8"
+const OpenP2PVersion = "3.21.10"
 const ProductName string = "openp2p"
 const LeastSupportVersion = "3.0.0"
 const SyncServerTimeVersion = "3.9.0"
@@ -217,6 +217,12 @@ const (
 	MsgSDWANInfoRsp
 )
 
+// MsgNATDetect
+const (
+	MsgNAT = iota
+	MsgPublicIP
+)
+
 func newMessage(mainType uint16, subType uint16, packet interface{}) ([]byte, error) {
 	data, err := json.Marshal(packet)
 	if err != nil {
diff --git a/core/underlay.go b/core/underlay.go
index 5bb9997..0c0a42f 100644
--- a/core/underlay.go
+++ b/core/underlay.go
@@ -27,7 +27,7 @@ func DefaultReadBuffer(ul underlay) (*openP2PHeader, []byte, error) {
 		return nil, nil, err
 	}
 	head, err := decodeHeader(headBuf)
-	if err != nil {
+	if err != nil || head.MainType > 16 {
 		return nil, nil, err
 	}
 	dataBuf := make([]byte, head.DataLen)