diff --git a/netcard.go b/netcard.go
index 0060e02..6d4f77c 100644
--- a/netcard.go
+++ b/netcard.go
@@ -272,7 +272,7 @@ func (nc *NetCard) runWrite() {
 		for _, buf := range bufs {
 
 			var wbuf []byte
-			wbuf = append(wbuf, buf[0:20]...)
+			wbuf = append(wbuf, buf[0:8]...)
 			wbuf = append(wbuf, waterutil.IPv4Payload(buf)...)
 			log.Printf("get wframes decode len: %d, write buf: %d", len(buf), len(wbuf))
 			log.Printf("get decode frames decode source: %s dst: %s", waterutil.IPv4Source(buf), waterutil.IPv4Destination(buf))