diff --git a/device.go b/device.go
index 5f468b2..e116731 100644
--- a/device.go
+++ b/device.go
@@ -8,6 +8,7 @@ package main
 
 import (
 	"./ratelimiter"
+	"./tun"
 	"runtime"
 	"sync"
 	"sync/atomic"
@@ -80,7 +81,7 @@ type Device struct {
 	}
 
 	tun struct {
-		device TUNDevice
+		device tun.TUNDevice
 		mtu    int32
 	}
 }
@@ -250,7 +251,7 @@ func (device *Device) PutMessageBuffer(msg *[MaxMessageSize]byte) {
 	device.pool.messageBuffers.Put(msg)
 }
 
-func NewDevice(tun TUNDevice, logger *Logger) *Device {
+func NewDevice(tunDevice tun.TUNDevice, logger *Logger) *Device {
 	device := new(Device)
 
 	device.isUp.Set(false)
@@ -258,7 +259,7 @@ func NewDevice(tun TUNDevice, logger *Logger) *Device {
 
 	device.log = logger
 
-	device.tun.device = tun
+	device.tun.device = tunDevice
 	mtu, err := device.tun.device.MTU()
 	if err != nil {
 		logger.Error.Println("Trouble determining MTU, assuming default:", err)
diff --git a/main.go b/main.go
index 523a927..a04cd15 100644
--- a/main.go
+++ b/main.go
@@ -7,6 +7,7 @@
 package main
 
 import (
+	"./tun"
 	"fmt"
 	"os"
 	"os/signal"
@@ -125,10 +126,10 @@ func main() {
 
 	// open TUN device (or use supplied fd)
 
-	tun, err := func() (TUNDevice, error) {
+	tun, err := func() (tun.TUNDevice, error) {
 		tunFdStr := os.Getenv(ENV_WG_TUN_FD)
 		if tunFdStr == "" {
-			return CreateTUN(interfaceName)
+			return tun.CreateTUN(interfaceName, DefaultMTU)
 		}
 
 		// construct tun device from supplied fd
@@ -139,7 +140,7 @@ func main() {
 		}
 
 		file := os.NewFile(uintptr(fd), "")
-		return CreateTUNFromFile(file)
+		return tun.CreateTUNFromFile(file, DefaultMTU)
 	}()
 
 	if err == nil {
diff --git a/misc.go b/misc.go
index aeda813..af61718 100644
--- a/misc.go
+++ b/misc.go
@@ -41,13 +41,6 @@ func (a *AtomicBool) Set(val bool) {
 	atomic.StoreInt32(&a.flag, flag)
 }
 
-/* Integer manipulation */
-
-func toInt32(n uint32) int32 {
-	mask := uint32(1 << 31)
-	return int32(-(n & mask) + (n & ^mask))
-}
-
 func min(a, b uint) uint {
 	if a > b {
 		return b
diff --git a/tun.go b/tun.go
index d2fb708..9752636 100644
--- a/tun.go
+++ b/tun.go
@@ -7,30 +7,12 @@
 package main
 
 import (
-	"os"
+	"./tun"
 	"sync/atomic"
 )
 
 const DefaultMTU = 1420
 
-type TUNEvent int
-
-const (
-	TUNEventUp = 1 << iota
-	TUNEventDown
-	TUNEventMTUUpdate
-)
-
-type TUNDevice interface {
-	File() *os.File                 // returns the file descriptor of the device
-	Read([]byte, int) (int, error)  // read a packet from the device (without any additional headers)
-	Write([]byte, int) (int, error) // writes a packet to the device (without any additional headers)
-	MTU() (int, error)              // returns the MTU of the device
-	Name() (string, error)          // fetches and returns the current name
-	Events() chan TUNEvent          // returns a constant channel of events related to the device
-	Close() error                   // stops the device and closes the event channel
-}
-
 func (device *Device) RoutineTUNEventReader() {
 	setUp := false
 	logDebug := device.log.Debug
@@ -41,7 +23,7 @@ func (device *Device) RoutineTUNEventReader() {
 	device.state.starting.Done()
 
 	for event := range device.tun.device.Events() {
-		if event&TUNEventMTUUpdate != 0 {
+		if event&tun.TUNEventMTUUpdate != 0 {
 			mtu, err := device.tun.device.MTU()
 			old := atomic.LoadInt32(&device.tun.mtu)
 			if err != nil {
@@ -56,13 +38,13 @@ func (device *Device) RoutineTUNEventReader() {
 			}
 		}
 
-		if event&TUNEventUp != 0 && !setUp {
+		if event&tun.TUNEventUp != 0 && !setUp {
 			logInfo.Println("Interface set up")
 			setUp = true
 			device.Up()
 		}
 
-		if event&TUNEventDown != 0 && setUp {
+		if event&tun.TUNEventDown != 0 && setUp {
 			logInfo.Println("Interface set down")
 			setUp = false
 			device.Down()
diff --git a/tun/tun.go b/tun/tun.go
new file mode 100644
index 0000000..a39ced5
--- /dev/null
+++ b/tun/tun.go
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * Copyright (C) 2017-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ * Copyright (C) 2017-2018 Mathias N. Hall-Andersen <mathias@hall-andersen.dk>.
+ */
+
+package tun
+
+import "os"
+
+type TUNEvent int
+
+const (
+	TUNEventUp = 1 << iota
+	TUNEventDown
+	TUNEventMTUUpdate
+)
+
+type TUNDevice interface {
+	File() *os.File                 // returns the file descriptor of the device
+	Read([]byte, int) (int, error)  // read a packet from the device (without any additional headers)
+	Write([]byte, int) (int, error) // writes a packet to the device (without any additional headers)
+	MTU() (int, error)              // returns the MTU of the device
+	Name() (string, error)          // fetches and returns the current name
+	Events() chan TUNEvent          // returns a constant channel of events related to the device
+	Close() error                   // stops the device and closes the event channel
+}
diff --git a/tun_darwin.go b/tun/tun_darwin.go
similarity index 86%
rename from tun_darwin.go
rename to tun/tun_darwin.go
index e5a01a7..fcbb4f9 100644
--- a/tun_darwin.go
+++ b/tun/tun_darwin.go
@@ -4,11 +4,10 @@
  * Copyright (C) 2017-2018 Mathias N. Hall-Andersen <mathias@hall-andersen.dk>.
  */
 
-package main
+package tun
 
 import (
-	"./rwcancel"
-	"encoding/binary"
+	"../rwcancel"
 	"errors"
 	"fmt"
 	"golang.org/x/net/ipv6"
@@ -34,7 +33,7 @@ type sockaddrCtl struct {
 	scReserved [5]uint32
 }
 
-type NativeTun struct {
+type nativeTun struct {
 	name        string
 	fd          *os.File
 	rwcancel    *rwcancel.RWCancel
@@ -45,7 +44,7 @@ type NativeTun struct {
 
 var sockaddrCtlSize uintptr = 32
 
-func (tun *NativeTun) RoutineRouteListener(tunIfindex int) {
+func (tun *nativeTun) routineRouteListener(tunIfindex int) {
 	var (
 		statusUp  bool
 		statusMTU int
@@ -97,7 +96,7 @@ func (tun *NativeTun) RoutineRouteListener(tunIfindex int) {
 	}
 }
 
-func CreateTUN(name string) (TUNDevice, error) {
+func CreateTUN(name string, mtu int) (TUNDevice, error) {
 	ifIndex := -1
 	if name != "utun" {
 		_, err := fmt.Sscanf(name, "utun%d", &ifIndex)
@@ -151,21 +150,21 @@ func CreateTUN(name string) (TUNDevice, error) {
 		return nil, fmt.Errorf("SYS_CONNECT: %v", errno)
 	}
 
-	tun, err := CreateTUNFromFile(os.NewFile(uintptr(fd), ""))
+	tun, err := CreateTUNFromFile(os.NewFile(uintptr(fd), ""), mtu)
 
 	if err == nil && name == "utun" {
 		fname := os.Getenv("WG_TUN_NAME_FILE")
 		if fname != "" {
-			ioutil.WriteFile(fname, []byte(tun.(*NativeTun).name+"\n"), 0400)
+			ioutil.WriteFile(fname, []byte(tun.(*nativeTun).name+"\n"), 0400)
 		}
 	}
 
 	return tun, err
 }
 
-func CreateTUNFromFile(file *os.File) (TUNDevice, error) {
+func CreateTUNFromFile(file *os.File, mtu int) (TUNDevice, error) {
 
-	tun := &NativeTun{
+	tun := &nativeTun{
 		fd:     file,
 		events: make(chan TUNEvent, 10),
 		errors: make(chan error, 1),
@@ -201,10 +200,9 @@ func CreateTUNFromFile(file *os.File) (TUNDevice, error) {
 		return nil, err
 	}
 
-	go tun.RoutineRouteListener(tunIfindex)
+	go tun.routineRouteListener(tunIfindex)
 
-	// set default MTU
-	err = tun.setMTU(DefaultMTU)
+	err = tun.setMTU(mtu)
 	if err != nil {
 		tun.Close()
 		return nil, err
@@ -213,7 +211,7 @@ func CreateTUNFromFile(file *os.File) (TUNDevice, error) {
 	return tun, nil
 }
 
-func (tun *NativeTun) Name() (string, error) {
+func (tun *nativeTun) Name() (string, error) {
 
 	var ifName struct {
 		name [16]byte
@@ -236,15 +234,15 @@ func (tun *NativeTun) Name() (string, error) {
 	return tun.name, nil
 }
 
-func (tun *NativeTun) File() *os.File {
+func (tun *nativeTun) File() *os.File {
 	return tun.fd
 }
 
-func (tun *NativeTun) Events() chan TUNEvent {
+func (tun *nativeTun) Events() chan TUNEvent {
 	return tun.events
 }
 
-func (tun *NativeTun) doRead(buff []byte, offset int) (int, error) {
+func (tun *nativeTun) doRead(buff []byte, offset int) (int, error) {
 	select {
 	case err := <-tun.errors:
 		return 0, err
@@ -258,7 +256,7 @@ func (tun *NativeTun) doRead(buff []byte, offset int) (int, error) {
 	}
 }
 
-func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
+func (tun *nativeTun) Read(buff []byte, offset int) (int, error) {
 	for {
 		n, err := tun.doRead(buff, offset)
 		if err == nil || !rwcancel.ErrorIsEAGAIN(err) {
@@ -270,7 +268,7 @@ func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
 	}
 }
 
-func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
+func (tun *nativeTun) Write(buff []byte, offset int) (int, error) {
 
 	// reserve space for header
 
@@ -293,7 +291,7 @@ func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
 	return tun.fd.Write(buff)
 }
 
-func (tun *NativeTun) Close() error {
+func (tun *nativeTun) Close() error {
 	var err3 error
 	err1 := tun.rwcancel.Cancel()
 	err2 := tun.fd.Close()
@@ -313,7 +311,7 @@ func (tun *NativeTun) Close() error {
 	return err3
 }
 
-func (tun *NativeTun) setMTU(n int) error {
+func (tun *nativeTun) setMTU(n int) error {
 
 	// open datagram socket
 
@@ -335,7 +333,7 @@ func (tun *NativeTun) setMTU(n int) error {
 
 	var ifr [32]byte
 	copy(ifr[:], tun.name)
-	binary.LittleEndian.PutUint32(ifr[16:20], uint32(n))
+	*(*uint32)(unsafe.Pointer(&ifr[unix.IFNAMSIZ])) = uint32(n)
 	_, _, errno := unix.Syscall(
 		unix.SYS_IOCTL,
 		uintptr(fd),
@@ -350,7 +348,7 @@ func (tun *NativeTun) setMTU(n int) error {
 	return nil
 }
 
-func (tun *NativeTun) MTU() (int, error) {
+func (tun *nativeTun) MTU() (int, error) {
 
 	// open datagram socket
 
diff --git a/tun_freebsd.go b/tun/tun_freebsd.go
similarity index 91%
rename from tun_freebsd.go
rename to tun/tun_freebsd.go
index 5461c45..b4cf57d 100644
--- a/tun_freebsd.go
+++ b/tun/tun_freebsd.go
@@ -3,10 +3,10 @@
  * Copyright (C) 2017-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
  */
 
-package main
+package tun
 
 import (
-	"./rwcancel"
+	"../rwcancel"
 	"bytes"
 	"errors"
 	"fmt"
@@ -48,7 +48,7 @@ type ifstat struct {
 	Ascii   [_IFSTATMAX]byte
 }
 
-type NativeTun struct {
+type nativeTun struct {
 	name        string
 	fd          *os.File
 	rwcancel    *rwcancel.RWCancel
@@ -57,7 +57,7 @@ type NativeTun struct {
 	routeSocket int
 }
 
-func (tun *NativeTun) RoutineRouteListener(tunIfindex int) {
+func (tun *nativeTun) routineRouteListener(tunIfindex int) {
 	var (
 		statusUp  bool
 		statusMTU int
@@ -221,7 +221,7 @@ func tunDestroy(name string) error {
 	return nil
 }
 
-func CreateTUN(name string) (TUNDevice, error) {
+func CreateTUN(name string, mtu int) (TUNDevice, error) {
 	if len(name) > unix.IFNAMSIZ-1 {
 		return nil, errors.New("interface name too long")
 	}
@@ -306,12 +306,12 @@ func CreateTUN(name string) (TUNDevice, error) {
 		return nil, fmt.Errorf("failed to rename %s to %s: %s", assignedName, name, errno.Error())
 	}
 
-	return CreateTUNFromFile(tunfile)
+	return CreateTUNFromFile(tunfile, mtu)
 }
 
-func CreateTUNFromFile(file *os.File) (TUNDevice, error) {
+func CreateTUNFromFile(file *os.File, mtu int) (TUNDevice, error) {
 
-	tun := &NativeTun{
+	tun := &nativeTun{
 		fd:     file,
 		events: make(chan TUNEvent, 10),
 		errors: make(chan error, 1),
@@ -347,10 +347,9 @@ func CreateTUNFromFile(file *os.File) (TUNDevice, error) {
 		return nil, err
 	}
 
-	go tun.RoutineRouteListener(tunIfindex)
+	go tun.routineRouteListener(tunIfindex)
 
-	// set default MTU
-	err = tun.setMTU(DefaultMTU)
+	err = tun.setMTU(mtu)
 	if err != nil {
 		tun.Close()
 		return nil, err
@@ -359,7 +358,7 @@ func CreateTUNFromFile(file *os.File) (TUNDevice, error) {
 	return tun, nil
 }
 
-func (tun *NativeTun) Name() (string, error) {
+func (tun *nativeTun) Name() (string, error) {
 	name, err := tunName(tun.fd.Fd())
 	if err != nil {
 		return "", err
@@ -368,15 +367,15 @@ func (tun *NativeTun) Name() (string, error) {
 	return name, nil
 }
 
-func (tun *NativeTun) File() *os.File {
+func (tun *nativeTun) File() *os.File {
 	return tun.fd
 }
 
-func (tun *NativeTun) Events() chan TUNEvent {
+func (tun *nativeTun) Events() chan TUNEvent {
 	return tun.events
 }
 
-func (tun *NativeTun) doRead(buff []byte, offset int) (int, error) {
+func (tun *nativeTun) doRead(buff []byte, offset int) (int, error) {
 	select {
 	case err := <-tun.errors:
 		return 0, err
@@ -390,7 +389,7 @@ func (tun *NativeTun) doRead(buff []byte, offset int) (int, error) {
 	}
 }
 
-func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
+func (tun *nativeTun) Read(buff []byte, offset int) (int, error) {
 	for {
 		n, err := tun.doRead(buff, offset)
 		if err == nil || !rwcancel.ErrorIsEAGAIN(err) {
@@ -402,7 +401,7 @@ func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
 	}
 }
 
-func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
+func (tun *nativeTun) Write(buff []byte, offset int) (int, error) {
 
 	// reserve space for header
 
@@ -425,7 +424,7 @@ func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
 	return tun.fd.Write(buff)
 }
 
-func (tun *NativeTun) Close() error {
+func (tun *nativeTun) Close() error {
 	var err4 error
 	err1 := tun.rwcancel.Cancel()
 	err2 := tun.fd.Close()
@@ -449,7 +448,7 @@ func (tun *NativeTun) Close() error {
 	return err4
 }
 
-func (tun *NativeTun) setMTU(n int) error {
+func (tun *nativeTun) setMTU(n int) error {
 	// open datagram socket
 
 	var fd int
@@ -486,7 +485,7 @@ func (tun *NativeTun) setMTU(n int) error {
 	return nil
 }
 
-func (tun *NativeTun) MTU() (int, error) {
+func (tun *nativeTun) MTU() (int, error) {
 	// open datagram socket
 
 	fd, err := unix.Socket(
diff --git a/tun_linux.go b/tun/tun_linux.go
similarity index 86%
rename from tun_linux.go
rename to tun/tun_linux.go
index db9cb51..acfb942 100644
--- a/tun_linux.go
+++ b/tun/tun_linux.go
@@ -6,15 +6,14 @@
 
 /* Copyright 2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. */
 
-package main
+package tun
 
 /* Implementation of the TUN device interface for linux
  */
 
 import (
-	"./rwcancel"
+	"../rwcancel"
 	"bytes"
-	"encoding/binary"
 	"errors"
 	"fmt"
 	"golang.org/x/net/ipv6"
@@ -32,7 +31,7 @@ const (
 	ifReqSize       = unix.IFNAMSIZ + 64
 )
 
-type NativeTun struct {
+type nativeTun struct {
 	fd                      *os.File
 	fdCancel                *rwcancel.RWCancel
 	index                   int32         // if index
@@ -46,11 +45,11 @@ type NativeTun struct {
 	statusListenersShutdown chan struct{}
 }
 
-func (tun *NativeTun) File() *os.File {
+func (tun *nativeTun) File() *os.File {
 	return tun.fd
 }
 
-func (tun *NativeTun) RoutineHackListener() {
+func (tun *nativeTun) routineHackListener() {
 	defer tun.hackListenerClosed.Unlock()
 	/* This is needed for the detection to work across network namespaces
 	 * If you are reading this and know a better method, please get in touch.
@@ -90,7 +89,7 @@ func createNetlinkSocket() (int, error) {
 	return sock, nil
 }
 
-func (tun *NativeTun) RoutineNetlinkListener() {
+func (tun *nativeTun) routineNetlinkListener() {
 	defer func() {
 		unix.Close(tun.netlinkSock)
 		tun.hackListenerClosed.Lock()
@@ -160,7 +159,7 @@ func (tun *NativeTun) RoutineNetlinkListener() {
 	}
 }
 
-func (tun *NativeTun) isUp() (bool, error) {
+func (tun *nativeTun) isUp() (bool, error) {
 	inter, err := net.InterfaceByName(tun.name)
 	return inter.Flags&net.FlagUp != 0, err
 }
@@ -194,11 +193,10 @@ func getIFIndex(name string) (int32, error) {
 		return 0, errno
 	}
 
-	index := binary.LittleEndian.Uint32(ifr[unix.IFNAMSIZ:])
-	return toInt32(index), nil
+	return *(*int32)(unsafe.Pointer(&ifr[unix.IFNAMSIZ])), nil
 }
 
-func (tun *NativeTun) setMTU(n int) error {
+func (tun *nativeTun) setMTU(n int) error {
 
 	// open datagram socket
 
@@ -218,7 +216,7 @@ func (tun *NativeTun) setMTU(n int) error {
 
 	var ifr [ifReqSize]byte
 	copy(ifr[:], tun.name)
-	binary.LittleEndian.PutUint32(ifr[16:20], uint32(n))
+	*(*uint32)(unsafe.Pointer(&ifr[unix.IFNAMSIZ])) = uint32(n)
 	_, _, errno := unix.Syscall(
 		unix.SYS_IOCTL,
 		uintptr(fd),
@@ -233,7 +231,7 @@ func (tun *NativeTun) setMTU(n int) error {
 	return nil
 }
 
-func (tun *NativeTun) MTU() (int, error) {
+func (tun *nativeTun) MTU() (int, error) {
 
 	// open datagram socket
 
@@ -263,10 +261,10 @@ func (tun *NativeTun) MTU() (int, error) {
 		return 0, errors.New("failed to get MTU of TUN device: " + strconv.FormatInt(int64(errno), 10))
 	}
 
-	return int(*(*int32)(unsafe.Pointer(&ifr[16]))), nil
+	return int(*(*int32)(unsafe.Pointer(&ifr[unix.IFNAMSIZ]))), nil
 }
 
-func (tun *NativeTun) Name() (string, error) {
+func (tun *nativeTun) Name() (string, error) {
 
 	var ifr [ifReqSize]byte
 	_, _, errno := unix.Syscall(
@@ -287,7 +285,7 @@ func (tun *NativeTun) Name() (string, error) {
 	return tun.name, nil
 }
 
-func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
+func (tun *nativeTun) Write(buff []byte, offset int) (int, error) {
 
 	if tun.nopi {
 		buff = buff[offset:]
@@ -315,7 +313,7 @@ func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
 	return tun.fd.Write(buff)
 }
 
-func (tun *NativeTun) doRead(buff []byte, offset int) (int, error) {
+func (tun *nativeTun) doRead(buff []byte, offset int) (int, error) {
 	select {
 	case err := <-tun.errors:
 		return 0, err
@@ -333,7 +331,7 @@ func (tun *NativeTun) doRead(buff []byte, offset int) (int, error) {
 	}
 }
 
-func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
+func (tun *nativeTun) Read(buff []byte, offset int) (int, error) {
 	for {
 		n, err := tun.doRead(buff, offset)
 		if err == nil || !rwcancel.ErrorIsEAGAIN(err) {
@@ -345,11 +343,11 @@ func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
 	}
 }
 
-func (tun *NativeTun) Events() chan TUNEvent {
+func (tun *nativeTun) Events() chan TUNEvent {
 	return tun.events
 }
 
-func (tun *NativeTun) Close() error {
+func (tun *nativeTun) Close() error {
 	var err1 error
 	if tun.statusListenersShutdown != nil {
 		close(tun.statusListenersShutdown)
@@ -371,7 +369,7 @@ func (tun *NativeTun) Close() error {
 	return err3
 }
 
-func CreateTUN(name string) (TUNDevice, error) {
+func CreateTUN(name string, mtu int) (TUNDevice, error) {
 
 	// open clone device
 
@@ -401,7 +399,7 @@ func CreateTUN(name string) (TUNDevice, error) {
 		return nil, errors.New("interface name too long")
 	}
 	copy(ifr[:], nameBytes)
-	binary.LittleEndian.PutUint16(ifr[16:], flags)
+	*(*uint16)(unsafe.Pointer(&ifr[unix.IFNAMSIZ])) = flags
 
 	_, _, errno := unix.Syscall(
 		unix.SYS_IOCTL,
@@ -413,12 +411,12 @@ func CreateTUN(name string) (TUNDevice, error) {
 		return nil, errno
 	}
 
-	return CreateTUNFromFile(fd)
+	return CreateTUNFromFile(fd, mtu)
 }
 
-func CreateTUNFromFile(fd *os.File) (TUNDevice, error) {
-	tun := &NativeTun{
-		fd:                      fd,
+func CreateTUNFromFile(file *os.File, mtu int) (TUNDevice, error) {
+	tun := &nativeTun{
+		fd:                      file,
 		events:                  make(chan TUNEvent, 5),
 		errors:                  make(chan error, 5),
 		statusListenersShutdown: make(chan struct{}),
@@ -426,7 +424,7 @@ func CreateTUNFromFile(fd *os.File) (TUNDevice, error) {
 	}
 	var err error
 
-	tun.fdCancel, err = rwcancel.NewRWCancel(int(fd.Fd()))
+	tun.fdCancel, err = rwcancel.NewRWCancel(int(file.Fd()))
 	if err != nil {
 		tun.fd.Close()
 		return nil, err
@@ -457,12 +455,10 @@ func CreateTUNFromFile(fd *os.File) (TUNDevice, error) {
 	}
 
 	tun.hackListenerClosed.Lock()
-	go tun.RoutineNetlinkListener()
-	go tun.RoutineHackListener() // cross namespace
+	go tun.routineNetlinkListener()
+	go tun.routineHackListener() // cross namespace
 
-	// set default MTU
-
-	err = tun.setMTU(DefaultMTU)
+	err = tun.setMTU(mtu)
 	if err != nil {
 		tun.Close()
 		return nil, err
diff --git a/tun_openbsd.go b/tun/tun_openbsd.go
similarity index 86%
rename from tun_openbsd.go
rename to tun/tun_openbsd.go
index 932404e..74b25e5 100644
--- a/tun_openbsd.go
+++ b/tun/tun_openbsd.go
@@ -3,10 +3,10 @@
  * Copyright (C) 2017-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
  */
 
-package main
+package tun
 
 import (
-	"./rwcancel"
+	"../rwcancel"
 	"errors"
 	"fmt"
 	"golang.org/x/net/ipv6"
@@ -27,7 +27,7 @@ type ifreq_mtu struct {
 
 const _TUNSIFMODE = 0x8004745d
 
-type NativeTun struct {
+type nativeTun struct {
 	name        string
 	fd          *os.File
 	rwcancel    *rwcancel.RWCancel
@@ -36,7 +36,7 @@ type NativeTun struct {
 	routeSocket int
 }
 
-func (tun *NativeTun) RoutineRouteListener(tunIfindex int) {
+func (tun *nativeTun) routineRouteListener(tunIfindex int) {
 	var (
 		statusUp  bool
 		statusMTU int
@@ -100,7 +100,7 @@ func errorIsEBUSY(err error) bool {
 	return false
 }
 
-func CreateTUN(name string) (TUNDevice, error) {
+func CreateTUN(name string, mtu int) (TUNDevice, error) {
 	ifIndex := -1
 	if name != "tun" {
 		_, err := fmt.Sscanf(name, "tun%d", &ifIndex)
@@ -140,21 +140,21 @@ func CreateTUN(name string) (TUNDevice, error) {
 		return nil, fmt.Errorf("error %s", errno.Error())
 	}
 
-	tun, err := CreateTUNFromFile(tunfile)
+	tun, err := CreateTUNFromFile(tunfile, mtu)
 
 	if err == nil && name == "tun" {
 		fname := os.Getenv("WG_TUN_NAME_FILE")
 		if fname != "" {
-			ioutil.WriteFile(fname, []byte(tun.(*NativeTun).name+"\n"), 0400)
+			ioutil.WriteFile(fname, []byte(tun.(*nativeTun).name+"\n"), 0400)
 		}
 	}
 
 	return tun, err
 }
 
-func CreateTUNFromFile(file *os.File) (TUNDevice, error) {
+func CreateTUNFromFile(file *os.File, mtu int) (TUNDevice, error) {
 
-	tun := &NativeTun{
+	tun := &nativeTun{
 		fd:     file,
 		events: make(chan TUNEvent, 10),
 		errors: make(chan error, 1),
@@ -190,10 +190,9 @@ func CreateTUNFromFile(file *os.File) (TUNDevice, error) {
 		return nil, err
 	}
 
-	go tun.RoutineRouteListener(tunIfindex)
+	go tun.routineRouteListener(tunIfindex)
 
-	// set default MTU
-	err = tun.setMTU(DefaultMTU)
+	err = tun.setMTU(mtu)
 	if err != nil {
 		tun.Close()
 		return nil, err
@@ -202,7 +201,7 @@ func CreateTUNFromFile(file *os.File) (TUNDevice, error) {
 	return tun, nil
 }
 
-func (tun *NativeTun) Name() (string, error) {
+func (tun *nativeTun) Name() (string, error) {
 	gostat, err := tun.fd.Stat()
 	if err != nil {
 		tun.name = ""
@@ -213,15 +212,15 @@ func (tun *NativeTun) Name() (string, error) {
 	return tun.name, nil
 }
 
-func (tun *NativeTun) File() *os.File {
+func (tun *nativeTun) File() *os.File {
 	return tun.fd
 }
 
-func (tun *NativeTun) Events() chan TUNEvent {
+func (tun *nativeTun) Events() chan TUNEvent {
 	return tun.events
 }
 
-func (tun *NativeTun) doRead(buff []byte, offset int) (int, error) {
+func (tun *nativeTun) doRead(buff []byte, offset int) (int, error) {
 	select {
 	case err := <-tun.errors:
 		return 0, err
@@ -235,7 +234,7 @@ func (tun *NativeTun) doRead(buff []byte, offset int) (int, error) {
 	}
 }
 
-func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
+func (tun *nativeTun) Read(buff []byte, offset int) (int, error) {
 	for {
 		n, err := tun.doRead(buff, offset)
 		if err == nil || !rwcancel.ErrorIsEAGAIN(err) {
@@ -247,7 +246,7 @@ func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
 	}
 }
 
-func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
+func (tun *nativeTun) Write(buff []byte, offset int) (int, error) {
 
 	// reserve space for header
 
@@ -270,7 +269,7 @@ func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
 	return tun.fd.Write(buff)
 }
 
-func (tun *NativeTun) Close() error {
+func (tun *nativeTun) Close() error {
 	var err3 error
 	err1 := tun.rwcancel.Cancel()
 	err2 := tun.fd.Close()
@@ -290,7 +289,7 @@ func (tun *NativeTun) Close() error {
 	return err3
 }
 
-func (tun *NativeTun) setMTU(n int) error {
+func (tun *nativeTun) setMTU(n int) error {
 	// open datagram socket
 
 	var fd int
@@ -327,7 +326,7 @@ func (tun *NativeTun) setMTU(n int) error {
 	return nil
 }
 
-func (tun *NativeTun) MTU() (int, error) {
+func (tun *nativeTun) MTU() (int, error) {
 	// open datagram socket
 
 	fd, err := unix.Socket(