diff --git a/gold/head/packet.go b/gold/head/packet.go
index 420b66f..4d19c7b 100644
--- a/gold/head/packet.go
+++ b/gold/head/packet.go
@@ -77,14 +77,17 @@ func (p *Packet) Unmarshal(data []byte) (complete bool, err error) {
 		p.rembytes = p.DataSZ
 	}
 
-	p.Flags = binary.LittleEndian.Uint16(data[10:12])
+	flags := binary.LittleEndian.Uint16(data[10:12])
 
-	p.Src = make(net.IP, 4)
-	copy(p.Src, data[12:16])
-	p.Dst = make(net.IP, 4)
-	copy(p.Dst, data[16:20])
-	copy(p.Hash[:], data[20:52])
-	p.rembytes -= uint16(copy(p.Data[p.Flags<<3:], data[52:]))
+	if flags&0x1fff == 0 {
+		p.Flags = flags
+		p.Src = make(net.IP, 4)
+		copy(p.Src, data[12:16])
+		p.Dst = make(net.IP, 4)
+		copy(p.Dst, data[16:20])
+		copy(p.Hash[:], data[20:52])
+	}
+	p.rembytes -= uint16(copy(p.Data[flags<<3:], data[52:]))
 
 	complete = p.rembytes == 0
 
@@ -93,14 +96,14 @@ func (p *Packet) Unmarshal(data []byte) (complete bool, err error) {
 
 // Marshal 将自身数据编码为 []byte
 // offset 必须为 8 的倍数，表示偏移的 8 位
-func (p *Packet) Marshal(src net.IP, offset uint16, dontfrag, hasmore bool) []byte {
+func (p *Packet) Marshal(src net.IP, datasz, offset uint16, dontfrag, hasmore bool) []byte {
 	p.TTL--
 	if p.TTL == 0 {
 		return nil
 	}
 
-	p.DataSZ = uint16(len(p.Data))
 	if src != nil {
+		p.DataSZ = datasz
 		p.Src = src
 		offset >>= 3
 		if dontfrag {
diff --git a/gold/link/link.go b/gold/link/link.go
index 19c7661..38fe9a7 100644
--- a/gold/link/link.go
+++ b/gold/link/link.go
@@ -78,6 +78,8 @@ func (l *Link) Write(p *head.Packet, istransfer bool) (n int, err error) {
 	if len(p.Data) <= int(l.me.mtu) {
 		return l.write(p, 0, istransfer, false)
 	}
+	p.FillHash()
+	p.Data = l.Encode(p.Data)
 	data := p.Data
 	totl := len(data)
 	i := 0
@@ -121,11 +123,9 @@ func (l *Link) write(p *head.Packet, offset uint16, istransfer, hasmore bool) (n
 		if p.Flags&0x4000 == 0x4000 && len(p.Data) > int(l.me.mtu) {
 			return len(p.Data), errors.New("drop dont fragmnet big trans packet")
 		}
-		d = p.Marshal(nil, 0, false, false)
+		d = p.Marshal(nil, 0, 0, false, false)
 	} else {
-		p.FillHash()
-		p.Data = l.Encode(p.Data)
-		d = p.Marshal(l.me.me, offset, false, hasmore)
+		d = p.Marshal(l.me.me, uint16(len(p.Data)), offset, false, hasmore)
 	}
 	if d == nil {
 		return 0, errors.New("[link] ttl exceeded")