diff --git a/src/constants.go b/src/constants.go
index 4e8d521..0384741 100644
--- a/src/constants.go
+++ b/src/constants.go
@@ -4,15 +4,17 @@ import (
 	"time"
 )
 
+/* Specification constants */
+
 const (
 	RekeyAfterMessages      = (1 << 64) - (1 << 16) - 1
+	RejectAfterMessages     = (1 << 64) - (1 << 4) - 1
 	RekeyAfterTime          = time.Second * 120
 	RekeyAttemptTime        = time.Second * 90
-	RekeyTimeout            = time.Second * 5 // TODO: Exponential backoff
+	RekeyTimeout            = time.Second * 5
 	RejectAfterTime         = time.Second * 180
-	RejectAfterMessages     = (1 << 64) - (1 << 4) - 1
 	KeepaliveTimeout        = time.Second * 10
-	CookieRefreshTime       = time.Minute * 2
+	CookieRefreshTime       = time.Second * 120
 	MaxHandshakeAttemptTime = time.Second * 90
 )
 
@@ -20,11 +22,13 @@ const (
 	RekeyAfterTimeReceiving = RekeyAfterTime - KeepaliveTimeout - RekeyTimeout
 )
 
+/* Implementation specific constants */
+
 const (
 	QueueOutboundSize      = 1024
 	QueueInboundSize       = 1024
 	QueueHandshakeSize     = 1024
 	QueueHandshakeBusySize = QueueHandshakeSize / 8
 	MinMessageSize         = MessageTransportSize // keep-alive
-	MaxMessageSize         = 4096
+	MaxMessageSize         = 4096                 // TODO: make depend on the MTU?
 )
diff --git a/src/device.go b/src/device.go
index 2a2ad62..a26cc7b 100644
--- a/src/device.go
+++ b/src/device.go
@@ -64,7 +64,7 @@ func NewDevice(tun TUNDevice, logLevel int) *Device {
 	defer device.mutex.Unlock()
 
 	device.log = NewLogger(logLevel)
-	device.mtu = tun.MTU()
+	// device.mtu = tun.MTU()
 	device.peers = make(map[NoisePublicKey]*Peer)
 	device.indices.Init()
 	device.ratelimiter.Init()
diff --git a/src/timers.go b/src/timers.go
index 70e0766..6393955 100644
--- a/src/timers.go
+++ b/src/timers.go
@@ -229,6 +229,7 @@ func (peer *Peer) RoutineHandshakeInitiator() {
 
 		run = func() bool {
 			for {
+
 				// clear completed signal
 
 				select {
diff --git a/src/tun.go b/src/tun.go
index 60732c4..85735a6 100644
--- a/src/tun.go
+++ b/src/tun.go
@@ -1,8 +1,8 @@
 package main
 
 type TUNDevice interface {
-	Read([]byte) (int, error)
-	Write([]byte) (int, error)
-	Name() string
-	MTU() int
+	Read([]byte) (int, error)  // read a packet from the device (without any additional headers)
+	Write([]byte) (int, error) // writes a packet to the device (without any additional headers)
+	MTU() (int, error)         // returns the MTU of the device
+	Name() string              // returns the current name
 }
diff --git a/src/tun_linux.go b/src/tun_linux.go
index d16a966..63c3886 100644
--- a/src/tun_linux.go
+++ b/src/tun_linux.go
@@ -14,25 +14,52 @@ import (
 
 const CloneDevicePath = "/dev/net/tun"
 
-const (
-	IFF_NO_PI = 0x1000
-	IFF_TUN   = 0x1
-	IFNAMSIZ  = 0x10
-	TUNSETIFF = 0x400454CA
-)
-
 type NativeTun struct {
 	fd   *os.File
 	name string
-	mtu  int
 }
 
 func (tun *NativeTun) Name() string {
 	return tun.name
 }
 
-func (tun *NativeTun) MTU() int {
-	return tun.mtu
+func (tun *NativeTun) MTU() (int, error) {
+
+	// open datagram socket
+
+	fd, err := syscall.Socket(
+		syscall.AF_INET,
+		syscall.SOCK_DGRAM,
+		0,
+	)
+
+	if err != nil {
+		return 0, err
+	}
+
+	// do ioctl call
+
+	var ifr [64]byte
+	var flags uint16
+	copy(ifr[:], tun.name)
+	binary.LittleEndian.PutUint16(ifr[16:], flags)
+	_, _, errno := syscall.Syscall(
+		syscall.SYS_IOCTL,
+		uintptr(fd),
+		uintptr(syscall.SIOCGIFMTU),
+		uintptr(unsafe.Pointer(&ifr[0])),
+	)
+	if errno != 0 {
+		return 0, errors.New("Failed to get MTU of TUN device")
+	}
+
+	// convert result to signed 32-bit int
+
+	val := binary.LittleEndian.Uint32(ifr[16:20])
+	if val >= (1 << 31) {
+		return int(val-(1<<31)) - (1 << 31), nil
+	}
+	return int(val), nil
 }
 
 func (tun *NativeTun) Write(d []byte) (int, error) {
@@ -44,36 +71,43 @@ func (tun *NativeTun) Read(d []byte) (int, error) {
 }
 
 func CreateTUN(name string) (TUNDevice, error) {
-	// Open clone device
+
+	// open clone device
+
 	fd, err := os.OpenFile(CloneDevicePath, os.O_RDWR, 0)
 	if err != nil {
 		return nil, err
 	}
 
-	// Prepare ifreq struct
-	var ifr [128]byte
-	var flags uint16 = IFF_TUN | IFF_NO_PI
+	// prepare ifreq struct
+
+	var ifr [64]byte
+	var flags uint16 = syscall.IFF_TUN | syscall.IFF_NO_PI
 	nameBytes := []byte(name)
-	if len(nameBytes) >= IFNAMSIZ {
+	if len(nameBytes) >= syscall.IFNAMSIZ {
 		return nil, errors.New("Name size too long")
 	}
 	copy(ifr[:], nameBytes)
 	binary.LittleEndian.PutUint16(ifr[16:], flags)
 
-	// Create new device
-	_, _, errno := syscall.Syscall(syscall.SYS_IOCTL,
-		uintptr(fd.Fd()), uintptr(TUNSETIFF),
-		uintptr(unsafe.Pointer(&ifr[0])))
+	// create new device
+
+	_, _, errno := syscall.Syscall(
+		syscall.SYS_IOCTL,
+		uintptr(fd.Fd()),
+		uintptr(syscall.TUNSETIFF),
+		uintptr(unsafe.Pointer(&ifr[0])),
+	)
 	if errno != 0 {
 		return nil, errors.New("Failed to create tun, ioctl call failed")
 	}
 
-	// Read name of interface
+	// read (new) name of interface
+
 	newName := string(ifr[:])
 	newName = newName[:strings.Index(newName, "\000")]
 	return &NativeTun{
 		fd:   fd,
 		name: newName,
-		mtu:  0,
 	}, nil
 }