diff --git a/README.md b/README.md
index 114a255..e9fd2db 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@
 ## Usage
 > If you are running in windows, remember to select the `wintun.dll` of your arch in `lower/wintun` and place it alongside the compiled exe
 ```bash
-wg [-c config.yaml] [-d|w] [-g] [-h] [-m mtu] [-p]
+wg [-c config.yaml] [-d|w] [-g] [-h] [-m mtu] [-p] [-l log.txt]
 ```
 #### Instructions
 ```bash
@@ -16,8 +16,10 @@ wg [-c config.yaml] [-d|w] [-g] [-h] [-m mtu] [-p]
   -d    print debug logs
   -g    generate key pair
   -h    display this help
+  -l string
+        write log to file (default "-")
   -m int
-        set the mtu of wg (default 32700)
+        set the mtu of wg (default 1432)
   -p    show my publickey
   -w    only show logs above warn level
 ```
diff --git a/main.go b/main.go
index 464c024..7cec9f4 100644
--- a/main.go
+++ b/main.go
@@ -24,6 +24,7 @@ func main() {
 	mtu := flag.Int("m", 1500-68, "set the mtu of wg")
 	debug := flag.Bool("d", false, "print debug logs")
 	warn := flag.Bool("w", false, "only show logs above warn level")
+	logfile := flag.String("l", "-", "write log to file")
 	flag.Parse()
 	if *debug {
 		logrus.SetLevel(logrus.DebugLevel)
@@ -50,6 +51,14 @@ func main() {
 		fmt.Println("PrivateKey:", helper.BytesToString(prvk[:57]))
 		os.Exit(0)
 	}
+	if *logfile != "-" {
+		f, err := os.Create(*logfile)
+		if err != nil {
+			panic(err)
+		}
+		defer f.Close()
+		logrus.SetOutput(f)
+	}
 	if helper.IsNotExist(*file) {
 		f := new(bytes.Buffer)
 		var r string
diff --git a/main_win.go b/main_win.go
index ca6bade..b0645c6 100644
--- a/main_win.go
+++ b/main_win.go
@@ -26,7 +26,7 @@ const (
 	colorReset     = "\x1b[0m"
 )
 
-// LogFormat specialize for zbp
+// LogFormat ...
 type LogFormat struct{}
 
 // Format implements logrus.Formatter
diff --git a/upper/services/tunnel/tunnel.go b/upper/services/tunnel/tunnel.go
index 497cc77..d510e39 100644
--- a/upper/services/tunnel/tunnel.go
+++ b/upper/services/tunnel/tunnel.go
@@ -1,7 +1,7 @@
 package tunnel
 
 import (
-	"errors"
+	"io"
 	"net"
 
 	"github.com/sirupsen/logrus"
@@ -72,7 +72,7 @@ func (s *Tunnel) Read(p []byte) (int, error) {
 			return copy(p, d[:len(p)]), nil
 		}
 	}
-	return 0, errors.New("reading reaches nil")
+	return 0, io.EOF
 }
 
 func (s *Tunnel) Stop() {
diff --git a/upper/services/tunnel/tunnel_test.go b/upper/services/tunnel/tunnel_test.go
index 0a3451c..9721aad 100644
--- a/upper/services/tunnel/tunnel_test.go
+++ b/upper/services/tunnel/tunnel_test.go
@@ -3,6 +3,7 @@ package tunnel
 import (
 	"crypto/rand"
 	"encoding/hex"
+	"io"
 	"testing"
 
 	curve "github.com/fumiama/go-x25519"
@@ -84,6 +85,17 @@ func TestTunnel(t *testing.T) {
 		t.Fatal("error: recv 4096 bytes data")
 	}
 
+	sendb = make([]byte, 65535)
+	rand.Read(sendb)
+	n, _ := tunnme.Write(sendb)
+	t.Log("write", n, "bytes")
+	buf = make([]byte, 65535)
+	n, _ = io.ReadFull(&tunnpeer, buf)
+	t.Log("read", n, "bytes")
+	if string(sendb) != string(buf) {
+		t.Fatal("error: recv 65535 bytes data")
+	}
+
 	tunnme.Stop()
 	tunnpeer.Stop()
 }