[client] Add flag to configure MTU (#4213)

Author: lixmal

client/cmd/root.go

@@ -39,6 +39,7 @@ const (
 	extraIFaceBlackListFlag  = "extra-iface-blacklist"
 	dnsRouteIntervalFlag     = "dns-router-interval"
 	enableLazyConnectionFlag = "enable-lazy-connection"
+	mtuFlag                  = "mtu"
 )
 
 var (
@@ -72,6 +73,7 @@ var (
 	anonymizeFlag           bool
 	dnsRouteInterval        time.Duration
 	lazyConnEnabled         bool
+	mtu                     uint16
 	profilesDisabled        bool
 	updateSettingsDisabled  bool
 

client/cmd/root_test.go

@@ -54,6 +54,7 @@ func TestSetFlagsFromEnvVars(t *testing.T) {
 	cmd.PersistentFlags().StringVar(&interfaceName, interfaceNameFlag, iface.WgInterfaceDefault, "WireGuard interface name")
 	cmd.PersistentFlags().BoolVar(&rosenpassEnabled, enableRosenpassFlag, false, "Enable Rosenpass feature Rosenpass.")
 	cmd.PersistentFlags().Uint16Var(&wireguardPort, wireguardPortFlag, iface.DefaultWgPort, "WireGuard interface listening port")
+	cmd.PersistentFlags().Uint16Var(&mtu, mtuFlag, iface.DefaultMTU, "Set MTU (Maximum Transmission Unit) for the WireGuard interface")
 
 	t.Setenv("NB_EXTERNAL_IP_MAP", "abc,dec")
 	t.Setenv("NB_INTERFACE_NAME", "test-name")

client/cmd/up.go

@@ -63,6 +63,7 @@ func init() {
 	upCmd.PersistentFlags().BoolVarP(&foregroundMode, "foreground-mode", "F", false, "start service in foreground")
 	upCmd.PersistentFlags().StringVar(&interfaceName, interfaceNameFlag, iface.WgInterfaceDefault, "WireGuard interface name")
 	upCmd.PersistentFlags().Uint16Var(&wireguardPort, wireguardPortFlag, iface.DefaultWgPort, "WireGuard interface listening port")
+	upCmd.PersistentFlags().Uint16Var(&mtu, mtuFlag, iface.DefaultMTU, "Set MTU (Maximum Transmission Unit) for the WireGuard interface")
 	upCmd.PersistentFlags().BoolVarP(&networkMonitor, networkMonitorFlag, "N", networkMonitor,
 		`Manage network monitoring. Defaults to true on Windows and macOS, false on Linux and FreeBSD. `+
 			`E.g. --network-monitor=false to disable or --network-monitor=true to enable.`,
@@ -357,6 +358,11 @@ func setupSetConfigReq(customDNSAddressConverted []byte, cmd *cobra.Command, pro
 		req.WireguardPort = &p
 	}
 
+	if cmd.Flag(mtuFlag).Changed {
+		m := int64(mtu)
+		req.Mtu = &m
+	}
+
 	if cmd.Flag(networkMonitorFlag).Changed {
 		req.NetworkMonitor = &networkMonitor
 	}
@@ -436,6 +442,13 @@ func setupConfig(customDNSAddressConverted []byte, cmd *cobra.Command, configFil
 		ic.WireguardPort = &p
 	}
 
+	if cmd.Flag(mtuFlag).Changed {
+		if err := iface.ValidateMTU(mtu); err != nil {
+			return nil, err
+		}
+		ic.MTU = &mtu
+	}
+
 	if cmd.Flag(networkMonitorFlag).Changed {
 		ic.NetworkMonitor = &networkMonitor
 	}
@@ -533,6 +546,14 @@ func setupLoginRequest(providedSetupKey string, customDNSAddressConverted []byte
 		loginRequest.WireguardPort = &wp
 	}
 
+	if cmd.Flag(mtuFlag).Changed {
+		if err := iface.ValidateMTU(mtu); err != nil {
+			return nil, err
+		}
+		m := int64(mtu)
+		loginRequest.Mtu = &m
+	}
+
 	if cmd.Flag(networkMonitorFlag).Changed {
 		loginRequest.NetworkMonitor = &networkMonitor
 	}

client/iface/bind/ice_bind.go

@@ -56,10 +56,11 @@ type ICEBind struct {
 	muUDPMux         sync.Mutex
 	udpMux           *UniversalUDPMuxDefault
 	address          wgaddr.Address
+	mtu              uint16
 	activityRecorder *ActivityRecorder
 }
 
-func NewICEBind(transportNet transport.Net, filterFn FilterFn, address wgaddr.Address) *ICEBind {
+func NewICEBind(transportNet transport.Net, filterFn FilterFn, address wgaddr.Address, mtu uint16) *ICEBind {
 	b, _ := wgConn.NewStdNetBind().(*wgConn.StdNetBind)
 	ib := &ICEBind{
 		StdNetBind:       b,
@@ -69,6 +70,7 @@ func NewICEBind(transportNet transport.Net, filterFn FilterFn, address wgaddr.Ad
 		endpoints:        make(map[netip.Addr]net.Conn),
 		closedChan:       make(chan struct{}),
 		closed:           true,
+		mtu:              mtu,
 		address:          address,
 		activityRecorder: NewActivityRecorder(),
 	}
@@ -80,6 +82,10 @@ func NewICEBind(transportNet transport.Net, filterFn FilterFn, address wgaddr.Ad
 	return ib
 }
 
+func (s *ICEBind) MTU() uint16 {
+	return s.mtu
+}
+
 func (s *ICEBind) Open(uport uint16) ([]wgConn.ReceiveFunc, uint16, error) {
 	s.closed = false
 	s.closedChanMu.Lock()
@@ -158,6 +164,7 @@ func (s *ICEBind) createIPv4ReceiverFn(pc *ipv4.PacketConn, conn *net.UDPConn, r
 			Net:       s.transportNet,
 			FilterFn:  s.filterFn,
 			WGAddress: s.address,
+			MTU:       s.mtu,
 		},
 	)
 	return func(bufs [][]byte, sizes []int, eps []wgConn.Endpoint) (n int, err error) {

client/iface/bind/udp_mux_ios.go

@@ -4,4 +4,4 @@ package bind
 
 func (m *UDPMuxDefault) notifyAddressRemoval(addr string) {
 	// iOS doesn't support nbnet hooks, so this is a no-op
-}
+}

client/iface/bind/udp_mux_universal.go

@@ -18,6 +18,7 @@ import (
 	"github.com/pion/stun/v2"
 	"github.com/pion/transport/v3"
 
+	"github.com/netbirdio/netbird/client/iface/bufsize"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 )
 
@@ -44,6 +45,7 @@ type UniversalUDPMuxParams struct {
 	Net                   transport.Net
 	FilterFn              FilterFn
 	WGAddress             wgaddr.Address
+	MTU                   uint16
 }
 
 // NewUniversalUDPMuxDefault creates an implementation of UniversalUDPMux embedding UDPMux
@@ -84,7 +86,7 @@ func NewUniversalUDPMuxDefault(params UniversalUDPMuxParams) *UniversalUDPMuxDef
 // just ignore other packets printing an warning message.
 // It is a blocking method, consider running in a go routine.
 func (m *UniversalUDPMuxDefault) ReadFromConn(ctx context.Context) {
-	buf := make([]byte, 1500)
+	buf := make([]byte, m.params.MTU+bufsize.WGBufferOverhead)
 	for {
 		select {
 		case <-ctx.Done():

client/iface/bufsize/bufsize.go

@@ -0,0 +1,9 @@
+package bufsize
+
+const (
+	// WGBufferOverhead represents the additional buffer space needed beyond MTU
+	// for WireGuard packet encapsulation (WG header + UDP + IP + safety margin)
+	// Original hardcoded buffers were 1500, default MTU is 1280, so overhead = 220
+	// TODO: Calculate this properly based on actual protocol overhead instead of using hardcoded difference
+	WGBufferOverhead = 220
+)

client/iface/device.go

@@ -17,6 +17,7 @@ type WGTunDevice interface {
 	Up() (*bind.UniversalUDPMuxDefault, error)
 	UpdateAddr(address wgaddr.Address) error
 	WgAddress() wgaddr.Address
+	MTU() uint16
 	DeviceName() string
 	Close() error
 	FilteredDevice() *device.FilteredDevice

client/iface/device/device_android.go

@@ -21,7 +21,7 @@ type WGTunDevice struct {
 	address    wgaddr.Address
 	port       int
 	key        string
-	mtu        int
+	mtu        uint16
 	iceBind    *bind.ICEBind
 	tunAdapter TunAdapter
 	disableDNS bool
@@ -33,7 +33,7 @@ type WGTunDevice struct {
 	configurer     WGConfigurer
 }
 
-func NewTunDevice(address wgaddr.Address, port int, key string, mtu int, iceBind *bind.ICEBind, tunAdapter TunAdapter, disableDNS bool) *WGTunDevice {
+func NewTunDevice(address wgaddr.Address, port int, key string, mtu uint16, iceBind *bind.ICEBind, tunAdapter TunAdapter, disableDNS bool) *WGTunDevice {
 	return &WGTunDevice{
 		address:    address,
 		port:       port,
@@ -58,7 +58,7 @@ func (t *WGTunDevice) Create(routes []string, dns string, searchDomains []string
 		searchDomainsToString = ""
 	}
 
-	fd, err := t.tunAdapter.ConfigureInterface(t.address.String(), t.mtu, dns, searchDomainsToString, routesString)
+	fd, err := t.tunAdapter.ConfigureInterface(t.address.String(), int(t.mtu), dns, searchDomainsToString, routesString)
 	if err != nil {
 		log.Errorf("failed to create Android interface: %s", err)
 		return nil, err
@@ -137,6 +137,10 @@ func (t *WGTunDevice) WgAddress() wgaddr.Address {
 	return t.address
 }
 
+func (t *WGTunDevice) MTU() uint16 {
+	return t.mtu
+}
+
 func (t *WGTunDevice) FilteredDevice() *FilteredDevice {
 	return t.filteredDevice
 }

client/iface/device/device_darwin.go

@@ -21,7 +21,7 @@ type TunDevice struct {
 	address wgaddr.Address
 	port    int
 	key     string
-	mtu     int
+	mtu     uint16
 	iceBind *bind.ICEBind
 
 	device         *device.Device
@@ -30,7 +30,7 @@ type TunDevice struct {
 	configurer     WGConfigurer
 }
 
-func NewTunDevice(name string, address wgaddr.Address, port int, key string, mtu int, iceBind *bind.ICEBind) *TunDevice {
+func NewTunDevice(name string, address wgaddr.Address, port int, key string, mtu uint16, iceBind *bind.ICEBind) *TunDevice {
 	return &TunDevice{
 		name:    name,
 		address: address,
@@ -42,7 +42,7 @@ func NewTunDevice(name string, address wgaddr.Address, port int, key string, mtu
 }
 
 func (t *TunDevice) Create() (WGConfigurer, error) {
-	tunDevice, err := tun.CreateTUN(t.name, t.mtu)
+	tunDevice, err := tun.CreateTUN(t.name, int(t.mtu))
 	if err != nil {
 		return nil, fmt.Errorf("error creating tun device: %s", err)
 	}
@@ -111,6 +111,10 @@ func (t *TunDevice) WgAddress() wgaddr.Address {
 	return t.address
 }
 
+func (t *TunDevice) MTU() uint16 {
+	return t.mtu
+}
+
 func (t *TunDevice) DeviceName() string {
 	return t.name
 }