diff --git a/config/global.go b/config/global.go
index 4bcfe7d..df62328 100644
--- a/config/global.go
+++ b/config/global.go
@@ -1,3 +1,3 @@
 package config
 
-const ShowDebugLog = false
+const ShowDebugLog = true
diff --git a/gold/head/hello.go b/gold/head/hello.go
new file mode 100644
index 0000000..bd5ccee
--- /dev/null
+++ b/gold/head/hello.go
@@ -0,0 +1,8 @@
+package head
+
+type Hello uint8
+
+const (
+	HelloPing Hello = iota
+	HelloPong
+)
diff --git a/gold/link/listen.go b/gold/link/listen.go
index 1290cbb..ea40365 100644
--- a/gold/link/listen.go
+++ b/gold/link/listen.go
@@ -226,13 +226,18 @@ func (m *Me) dispatch(packet *head.Packet, addr p2p.EndPoint, index int, finish
 		}
 		switch packet.Proto {
 		case head.ProtoHello:
-			n, err := p.WriteAndPut(head.NewPacket(head.ProtoHello, m.SrcPort(), p.peerip, m.DstPort(), nil), false)
-			if err == nil {
-				if config.ShowDebugLog {
-					logrus.Debugln("[listen] @", index, "send", n, "bytes hello ack packet")
+			switch {
+			case len(packet.Body()) == 0:
+				logrus.Warnln("[listen] @", index, "recv old hello packet, do nothing")
+			case packet.Body()[0] == byte(head.HelloPing):
+				n, err := p.WriteAndPut(head.NewPacket(head.ProtoHello, m.SrcPort(), p.peerip, m.DstPort(), []byte{byte(head.HelloPong)}), false)
+				if err == nil {
+					logrus.Infoln("[listen] @", index, "recv hello, send", n, "bytes hello ack packet")
+				} else {
+					logrus.Errorln("[listen] @", index, "send hello ack packet error:", err)
 				}
-			} else {
-				logrus.Errorln("[listen] @", index, "send hello ack packet error:", err)
+			default:
+				logrus.Infoln("[listen] @", index, "recv hello ack packet, do nothing")
 			}
 			packet.Put()
 		case head.ProtoNotify:
diff --git a/gold/link/nat.go b/gold/link/nat.go
index c661b24..85901b0 100644
--- a/gold/link/nat.go
+++ b/gold/link/nat.go
@@ -35,7 +35,7 @@ func (l *Link) keepAlive(dur int64) {
 					logrus.Infoln("[nat] re-connect me succeeded")
 				}
 			}
-			n, err := l.WriteAndPut(head.NewPacket(head.ProtoHello, l.me.srcport, l.peerip, l.me.dstport, nil), false)
+			n, err := l.WriteAndPut(head.NewPacket(head.ProtoHello, l.me.srcport, l.peerip, l.me.dstport, []byte{byte(head.HelloPing)}), false)
 			if err == nil {
 				logrus.Infoln("[nat] send", n, "bytes keep alive packet")
 			} else {