[client] Fix/v4 stun routing (#4430)

Deduplicate STUN package sending.
Originally, because every peer shared the same UDP address, the library could not distinguish which STUN message was associated with which candidate. As a result, the Pion library responded from all candidates for every STUN message.

client/iface/bind/ice_bind.go

@@ -15,6 +15,7 @@ import (
 	"golang.org/x/net/ipv6"
 	wgConn "golang.zx2c4.com/wireguard/conn"
 
+	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 	nbnet "github.com/netbirdio/netbird/util/net"
 )
@@ -44,7 +45,7 @@ type ICEBind struct {
 	RecvChan chan RecvMessage
 
 	transportNet transport.Net
-	filterFn     FilterFn
+	filterFn     udpmux.FilterFn
 	endpoints    map[netip.Addr]net.Conn
 	endpointsMu  sync.Mutex
 	// every time when Close() is called (i.e. BindUpdate()) we need to close exit from the receiveRelayed and create a
@@ -54,13 +55,13 @@ type ICEBind struct {
 	closed       bool
 
 	muUDPMux         sync.Mutex
-	udpMux           *UniversalUDPMuxDefault
+	udpMux           *udpmux.UniversalUDPMuxDefault
 	address          wgaddr.Address
 	mtu              uint16
 	activityRecorder *ActivityRecorder
 }
 
-func NewICEBind(transportNet transport.Net, filterFn FilterFn, address wgaddr.Address, mtu uint16) *ICEBind {
+func NewICEBind(transportNet transport.Net, filterFn udpmux.FilterFn, address wgaddr.Address, mtu uint16) *ICEBind {
 	b, _ := wgConn.NewStdNetBind().(*wgConn.StdNetBind)
 	ib := &ICEBind{
 		StdNetBind:       b,
@@ -115,7 +116,7 @@ func (s *ICEBind) ActivityRecorder() *ActivityRecorder {
 }
 
 // GetICEMux returns the ICE UDPMux that was created and used by ICEBind
-func (s *ICEBind) GetICEMux() (*UniversalUDPMuxDefault, error) {
+func (s *ICEBind) GetICEMux() (*udpmux.UniversalUDPMuxDefault, error) {
 	s.muUDPMux.Lock()
 	defer s.muUDPMux.Unlock()
 	if s.udpMux == nil {
@@ -158,8 +159,8 @@ func (s *ICEBind) createIPv4ReceiverFn(pc *ipv4.PacketConn, conn *net.UDPConn, r
 	s.muUDPMux.Lock()
 	defer s.muUDPMux.Unlock()
 
-	s.udpMux = NewUniversalUDPMuxDefault(
+	s.udpMux = udpmux.NewUniversalUDPMuxDefault(
-		UniversalUDPMuxParams{
+		udpmux.UniversalUDPMuxParams{
 			UDPConn:   nbnet.WrapPacketConn(conn),
 			Net:       s.transportNet,
 			FilterFn:  s.filterFn,

client/iface/bind/udp_mux_ios.go

@@ -1,7 +0,0 @@
-//go:build ios
-
-package bind
-
-func (m *UDPMuxDefault) notifyAddressRemoval(addr string) {
-	// iOS doesn't support nbnet hooks, so this is a no-op
-}

client/iface/device.go

@@ -7,14 +7,14 @@ import (
 
 	wgdevice "golang.zx2c4.com/wireguard/device"
 
-	"github.com/netbirdio/netbird/client/iface/bind"
 	"github.com/netbirdio/netbird/client/iface/device"
+	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 )
 
 type WGTunDevice interface {
 	Create() (device.WGConfigurer, error)
-	Up() (*bind.UniversalUDPMuxDefault, error)
+	Up() (*udpmux.UniversalUDPMuxDefault, error)
 	UpdateAddr(address wgaddr.Address) error
 	WgAddress() wgaddr.Address
 	MTU() uint16

client/iface/device/device_android.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/netbirdio/netbird/client/iface/bind"
 	"github.com/netbirdio/netbird/client/iface/configurer"
+	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 )
 
@@ -29,7 +30,7 @@ type WGTunDevice struct {
 	name           string
 	device         *device.Device
 	filteredDevice *FilteredDevice
-	udpMux         *bind.UniversalUDPMuxDefault
+	udpMux         *udpmux.UniversalUDPMuxDefault
 	configurer     WGConfigurer
 }
 
@@ -88,7 +89,7 @@ func (t *WGTunDevice) Create(routes []string, dns string, searchDomains []string
 	}
 	return t.configurer, nil
 }
-func (t *WGTunDevice) Up() (*bind.UniversalUDPMuxDefault, error) {
+func (t *WGTunDevice) Up() (*udpmux.UniversalUDPMuxDefault, error) {
 	err := t.device.Up()
 	if err != nil {
 		return nil, err

client/iface/device/device_darwin.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/netbirdio/netbird/client/iface/bind"
 	"github.com/netbirdio/netbird/client/iface/configurer"
+	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 )
 
@@ -26,7 +27,7 @@ type TunDevice struct {
 
 	device         *device.Device
 	filteredDevice *FilteredDevice
-	udpMux         *bind.UniversalUDPMuxDefault
+	udpMux         *udpmux.UniversalUDPMuxDefault
 	configurer     WGConfigurer
 }
 
@@ -71,7 +72,7 @@ func (t *TunDevice) Create() (WGConfigurer, error) {
 	return t.configurer, nil
 }
 
-func (t *TunDevice) Up() (*bind.UniversalUDPMuxDefault, error) {
+func (t *TunDevice) Up() (*udpmux.UniversalUDPMuxDefault, error) {
 	err := t.device.Up()
 	if err != nil {
 		return nil, err

client/iface/device/device_ios.go

@@ -14,6 +14,7 @@ import (
 
 	"github.com/netbirdio/netbird/client/iface/bind"
 	"github.com/netbirdio/netbird/client/iface/configurer"
+	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 )
 
@@ -28,7 +29,7 @@ type TunDevice struct {
 
 	device         *device.Device
 	filteredDevice *FilteredDevice
-	udpMux         *bind.UniversalUDPMuxDefault
+	udpMux         *udpmux.UniversalUDPMuxDefault
 	configurer     WGConfigurer
 }
 
@@ -83,7 +84,7 @@ func (t *TunDevice) Create() (WGConfigurer, error) {
 	return t.configurer, nil
 }
 
-func (t *TunDevice) Up() (*bind.UniversalUDPMuxDefault, error) {
+func (t *TunDevice) Up() (*udpmux.UniversalUDPMuxDefault, error) {
 	err := t.device.Up()
 	if err != nil {
 		return nil, err

client/iface/device/device_kernel_unix.go

@@ -12,8 +12,8 @@ import (
 	"golang.zx2c4.com/wireguard/device"
 	"golang.zx2c4.com/wireguard/tun/netstack"
 
-	"github.com/netbirdio/netbird/client/iface/bind"
 	"github.com/netbirdio/netbird/client/iface/configurer"
+	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 	"github.com/netbirdio/netbird/sharedsock"
 	nbnet "github.com/netbirdio/netbird/util/net"
@@ -31,9 +31,9 @@ type TunKernelDevice struct {
 
 	link       *wgLink
 	udpMuxConn net.PacketConn
-	udpMux     *bind.UniversalUDPMuxDefault
+	udpMux     *udpmux.UniversalUDPMuxDefault
 
-	filterFn bind.FilterFn
+	filterFn udpmux.FilterFn
 }
 
 func NewKernelDevice(name string, address wgaddr.Address, wgPort int, key string, mtu uint16, transportNet transport.Net) *TunKernelDevice {
@@ -79,7 +79,7 @@ func (t *TunKernelDevice) Create() (WGConfigurer, error) {
 	return configurer, nil
 }
 
-func (t *TunKernelDevice) Up() (*bind.UniversalUDPMuxDefault, error) {
+func (t *TunKernelDevice) Up() (*udpmux.UniversalUDPMuxDefault, error) {
 	if t.udpMux != nil {
 		return t.udpMux, nil
 	}
@@ -106,14 +106,14 @@ func (t *TunKernelDevice) Up() (*bind.UniversalUDPMuxDefault, error) {
 		udpConn = nbnet.WrapPacketConn(rawSock)
 	}
 
-	bindParams := bind.UniversalUDPMuxParams{
+	bindParams := udpmux.UniversalUDPMuxParams{
 		UDPConn:   udpConn,
 		Net:       t.transportNet,
 		FilterFn:  t.filterFn,
 		WGAddress: t.address,
 		MTU:       t.mtu,
 	}
-	mux := bind.NewUniversalUDPMuxDefault(bindParams)
+	mux := udpmux.NewUniversalUDPMuxDefault(bindParams)
 	go mux.ReadFromConn(t.ctx)
 	t.udpMuxConn = rawSock
 	t.udpMux = mux

client/iface/device/device_netstack.go

@@ -10,6 +10,7 @@ import (
 	"github.com/netbirdio/netbird/client/iface/bind"
 	"github.com/netbirdio/netbird/client/iface/configurer"
 	nbnetstack "github.com/netbirdio/netbird/client/iface/netstack"
+	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 	nbnet "github.com/netbirdio/netbird/util/net"
 )
@@ -26,7 +27,7 @@ type TunNetstackDevice struct {
 	device         *device.Device
 	filteredDevice *FilteredDevice
 	nsTun          *nbnetstack.NetStackTun
-	udpMux         *bind.UniversalUDPMuxDefault
+	udpMux         *udpmux.UniversalUDPMuxDefault
 	configurer     WGConfigurer
 
 	net *netstack.Net
@@ -80,7 +81,7 @@ func (t *TunNetstackDevice) create() (WGConfigurer, error) {
 	return t.configurer, nil
 }
 
-func (t *TunNetstackDevice) Up() (*bind.UniversalUDPMuxDefault, error) {
+func (t *TunNetstackDevice) Up() (*udpmux.UniversalUDPMuxDefault, error) {
 	if t.device == nil {
 		return nil, fmt.Errorf("device is not ready yet")
 	}

client/iface/device/device_usp_unix.go

@@ -12,6 +12,7 @@ import (
 
 	"github.com/netbirdio/netbird/client/iface/bind"
 	"github.com/netbirdio/netbird/client/iface/configurer"
+	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 )
 
@@ -25,7 +26,7 @@ type USPDevice struct {
 
 	device         *device.Device
 	filteredDevice *FilteredDevice
-	udpMux         *bind.UniversalUDPMuxDefault
+	udpMux         *udpmux.UniversalUDPMuxDefault
 	configurer     WGConfigurer
 }
 
@@ -74,7 +75,7 @@ func (t *USPDevice) Create() (WGConfigurer, error) {
 	return t.configurer, nil
 }
 
-func (t *USPDevice) Up() (*bind.UniversalUDPMuxDefault, error) {
+func (t *USPDevice) Up() (*udpmux.UniversalUDPMuxDefault, error) {
 	if t.device == nil {
 		return nil, fmt.Errorf("device is not ready yet")
 	}

client/iface/device/device_windows.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/netbirdio/netbird/client/iface/bind"
 	"github.com/netbirdio/netbird/client/iface/configurer"
+	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 )
 
@@ -29,7 +30,7 @@ type TunDevice struct {
 	device          *device.Device
 	nativeTunDevice *tun.NativeTun
 	filteredDevice  *FilteredDevice
-	udpMux          *bind.UniversalUDPMuxDefault
+	udpMux          *udpmux.UniversalUDPMuxDefault
 	configurer      WGConfigurer
 }
 
@@ -104,7 +105,7 @@ func (t *TunDevice) Create() (WGConfigurer, error) {
 	return t.configurer, nil
 }
 
-func (t *TunDevice) Up() (*bind.UniversalUDPMuxDefault, error) {
+func (t *TunDevice) Up() (*udpmux.UniversalUDPMuxDefault, error) {
 	err := t.device.Up()
 	if err != nil {
 		return nil, err

client/iface/device_android.go

@@ -5,14 +5,14 @@ import (
 
 	"golang.zx2c4.com/wireguard/tun/netstack"
 
-	"github.com/netbirdio/netbird/client/iface/bind"
 	"github.com/netbirdio/netbird/client/iface/device"
+	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 )
 
 type WGTunDevice interface {
 	Create(routes []string, dns string, searchDomains []string) (device.WGConfigurer, error)
-	Up() (*bind.UniversalUDPMuxDefault, error)
+	Up() (*udpmux.UniversalUDPMuxDefault, error)
 	UpdateAddr(address wgaddr.Address) error
 	WgAddress() wgaddr.Address
 	MTU() uint16

client/iface/iface.go

@@ -16,9 +16,9 @@ import (
 	wgdevice "golang.zx2c4.com/wireguard/device"
 
 	"github.com/netbirdio/netbird/client/errors"
-	"github.com/netbirdio/netbird/client/iface/bind"
 	"github.com/netbirdio/netbird/client/iface/configurer"
 	"github.com/netbirdio/netbird/client/iface/device"
+	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 	"github.com/netbirdio/netbird/client/iface/wgproxy"
 	"github.com/netbirdio/netbird/monotime"
@@ -61,7 +61,7 @@ type WGIFaceOpts struct {
 	MTU          uint16
 	MobileArgs   *device.MobileIFaceArguments
 	TransportNet transport.Net
-	FilterFn     bind.FilterFn
+	FilterFn     udpmux.FilterFn
 	DisableDNS   bool
 }
 
@@ -114,7 +114,7 @@ func (r *WGIface) ToInterface() *net.Interface {
 
 // Up configures a Wireguard interface
 // The interface must exist before calling this method (e.g. call interface.Create() before)
-func (w *WGIface) Up() (*bind.UniversalUDPMuxDefault, error) {
+func (w *WGIface) Up() (*udpmux.UniversalUDPMuxDefault, error) {
 	w.mu.Lock()
 	defer w.mu.Unlock()
 

client/iface/udpmux/conn.go

@@ -1,4 +1,4 @@
-package bind
+package udpmux
 
 /*
  Most of this code was copied from https://github.com/pion/ice and modified to fulfill NetBird's requirements
@@ -16,11 +16,12 @@ import (
 )
 
 type udpMuxedConnParams struct {
-	Mux       *UDPMuxDefault
+	Mux         *SingleSocketUDPMux
-	AddrPool  *sync.Pool
+	AddrPool    *sync.Pool
-	Key       string
+	Key         string
-	LocalAddr net.Addr
+	LocalAddr   net.Addr
-	Logger    logging.LeveledLogger
+	Logger      logging.LeveledLogger
+	CandidateID string
 }
 
 // udpMuxedConn represents a logical packet conn for a single remote as identified by ufrag
@@ -119,6 +120,10 @@ func (c *udpMuxedConn) Close() error {
 	return err
 }
 
+func (c *udpMuxedConn) GetCandidateID() string {
+	return c.params.CandidateID
+}
+
 func (c *udpMuxedConn) isClosed() bool {
 	select {
 	case <-c.closedChan:

client/iface/udpmux/doc.go

@@ -0,0 +1,64 @@
+// Package udpmux provides a custom implementation of a UDP multiplexer
+// that allows multiple logical ICE connections to share a single underlying
+// UDP socket. This is based on Pion's ICE library, with modifications for
+// NetBird's requirements.
+//
+// # Background
+//
+// In WebRTC and NAT traversal scenarios, ICE (Interactive Connectivity
+// Establishment) is responsible for discovering candidate network paths
+// and maintaining connectivity between peers. Each ICE connection
+// normally requires a dedicated UDP socket. However, using one socket
+// per candidate can be inefficient and difficult to manage.
+//
+// This package introduces SingleSocketUDPMux, which allows multiple ICE
+// candidate connections (muxed connections) to share a single UDP socket.
+// It handles demultiplexing of packets based on ICE ufrag values, STUN
+// attributes, and candidate IDs.
+//
+// # Usage
+//
+// The typical flow is:
+//
+//  1. Create a UDP socket (net.PacketConn).
+//  2. Construct Params with the socket and optional logger/net stack.
+//  3. Call NewSingleSocketUDPMux(params).
+//  4. For each ICE candidate ufrag, call GetConn(ufrag, addr, candidateID)
+//     to obtain a logical PacketConn.
+//  5. Use the returned PacketConn just like a normal UDP connection.
+//
+// # STUN Message Routing Logic
+//
+//		When a STUN packet arrives, the mux decides which connection should
+//		receive it using this routing logic:
+//
+//		Primary Routing: Candidate Pair ID
+//		  - Extract the candidate pair ID from the STUN message using
+//		    ice.CandidatePairIDFromSTUN(msg)
+//	   - The target candidate is the locally generated candidate that
+//	     corresponds to the connection that should handle this STUN message
+//		  - If found, use the target candidate ID to lookup the specific
+//		    connection in candidateConnMap
+//		  - Route the message directly to that connection
+//
+//		Fallback Routing: Broadcasting
+//		  When candidate pair ID is not available or lookup fails:
+//		  - Collect connections from addressMap based on source address
+//		  - Find connection using username attribute (ufrag) from STUN message
+//		  - Remove duplicate connections from the list
+//		  - Send the STUN message to all collected connections
+//
+// # Peer Reflexive Candidate Discovery
+//
+//	When a remote peer sends a STUN message from an unknown source address
+//	(from a candidate that has not been exchanged via signal), the ICE
+//	library will:
+//	  - Generate a new peer reflexive candidate for this source address
+//	  - Extract or assign a candidate ID based on the STUN message attributes
+//	  - Create a mapping between the new peer reflexive candidate ID and
+//	    the appropriate local connection
+//
+//	This discovery mechanism ensures that STUN messages from newly discovered
+//	peer reflexive candidates can be properly routed to the correct local
+//	connection without requiring fallback broadcasting.
+package udpmux

client/iface/udpmux/mux.go

@@ -1,4 +1,4 @@
-package bind
+package udpmux
 
 import (
 	"fmt"
@@ -22,9 +22,9 @@ import (
 
 const receiveMTU = 8192
 
-// UDPMuxDefault is an implementation of the interface
+// SingleSocketUDPMux is an implementation of the interface
-type UDPMuxDefault struct {
+type SingleSocketUDPMux struct {
-	params UDPMuxParams
+	params Params
 
 	closedChan chan struct{}
 	closeOnce  sync.Once
@@ -32,6 +32,9 @@ type UDPMuxDefault struct {
 	// connsIPv4 and connsIPv6 are maps of all udpMuxedConn indexed by ufrag|network|candidateType
 	connsIPv4, connsIPv6 map[string]*udpMuxedConn
 
+	// candidateConnMap maps local candidate IDs to their corresponding connection.
+	candidateConnMap map[string]*udpMuxedConn
+
 	addressMapMu sync.RWMutex
 	addressMap   map[string][]*udpMuxedConn
 
@@ -46,8 +49,8 @@ type UDPMuxDefault struct {
 
 const maxAddrSize = 512
 
-// UDPMuxParams are parameters for UDPMux.
+// Params are parameters for UDPMux.
-type UDPMuxParams struct {
+type Params struct {
 	Logger  logging.LeveledLogger
 	UDPConn net.PacketConn
 
@@ -147,18 +150,19 @@ func isZeros(ip net.IP) bool {
 	return true
 }
 
-// NewUDPMuxDefault creates an implementation of UDPMux
+// NewSingleSocketUDPMux creates an implementation of UDPMux
-func NewUDPMuxDefault(params UDPMuxParams) *UDPMuxDefault {
+func NewSingleSocketUDPMux(params Params) *SingleSocketUDPMux {
 	if params.Logger == nil {
 		params.Logger = getLogger()
 	}
 
-	mux := &UDPMuxDefault{
+	mux := &SingleSocketUDPMux{
-		addressMap: map[string][]*udpMuxedConn{},
+		addressMap:       map[string][]*udpMuxedConn{},
-		params:     params,
+		params:           params,
-		connsIPv4:  make(map[string]*udpMuxedConn),
+		connsIPv4:        make(map[string]*udpMuxedConn),
-		connsIPv6:  make(map[string]*udpMuxedConn),
+		connsIPv6:        make(map[string]*udpMuxedConn),
-		closedChan: make(chan struct{}, 1),
+		candidateConnMap: make(map[string]*udpMuxedConn),
+		closedChan:       make(chan struct{}, 1),
 		pool: &sync.Pool{
 			New: func() interface{} {
 				// big enough buffer to fit both packet and address
@@ -171,15 +175,15 @@ func NewUDPMuxDefault(params UDPMuxParams) *UDPMuxDefault {
 	return mux
 }
 
-func (m *UDPMuxDefault) updateLocalAddresses() {
+func (m *SingleSocketUDPMux) updateLocalAddresses() {
 	var localAddrsForUnspecified []net.Addr
 	if addr, ok := m.params.UDPConn.LocalAddr().(*net.UDPAddr); !ok {
 		m.params.Logger.Errorf("LocalAddr is not a net.UDPAddr, got %T", m.params.UDPConn.LocalAddr())
 	} else if ok && addr.IP.IsUnspecified() {
 		// For unspecified addresses, the correct behavior is to return errListenUnspecified, but
 		// it will break the applications that are already using unspecified UDP connection
-		// with UDPMuxDefault, so print a warn log and create a local address list for mux.
+		// with SingleSocketUDPMux, so print a warn log and create a local address list for mux.
-		m.params.Logger.Warn("UDPMuxDefault should not listening on unspecified address, use NewMultiUDPMuxFromPort instead")
+		m.params.Logger.Warn("SingleSocketUDPMux should not listening on unspecified address, use NewMultiUDPMuxFromPort instead")
 		var networks []ice.NetworkType
 		switch {
 
@@ -216,13 +220,13 @@ func (m *UDPMuxDefault) updateLocalAddresses() {
 	m.mu.Unlock()
 }
 
-// LocalAddr returns the listening address of this UDPMuxDefault
+// LocalAddr returns the listening address of this SingleSocketUDPMux
-func (m *UDPMuxDefault) LocalAddr() net.Addr {
+func (m *SingleSocketUDPMux) LocalAddr() net.Addr {
 	return m.params.UDPConn.LocalAddr()
 }
 
 // GetListenAddresses returns the list of addresses that this mux is listening on
-func (m *UDPMuxDefault) GetListenAddresses() []net.Addr {
+func (m *SingleSocketUDPMux) GetListenAddresses() []net.Addr {
 	m.updateLocalAddresses()
 
 	m.mu.Lock()
@@ -236,7 +240,7 @@ func (m *UDPMuxDefault) GetListenAddresses() []net.Addr {
 
 // GetConn returns a PacketConn given the connection's ufrag and network address
 // creates the connection if an existing one can't be found
-func (m *UDPMuxDefault) GetConn(ufrag string, addr net.Addr) (net.PacketConn, error) {
+func (m *SingleSocketUDPMux) GetConn(ufrag string, addr net.Addr, candidateID string) (net.PacketConn, error) {
 	// don't check addr for mux using unspecified address
 	m.mu.Lock()
 	lenLocalAddrs := len(m.localAddrsForUnspecified)
@@ -260,12 +264,14 @@ func (m *UDPMuxDefault) GetConn(ufrag string, addr net.Addr) (net.PacketConn, er
 		return conn, nil
 	}
 
-	c := m.createMuxedConn(ufrag)
+	c := m.createMuxedConn(ufrag, candidateID)
 	go func() {
 		<-c.CloseChannel()
 		m.RemoveConnByUfrag(ufrag)
 	}()
 
+	m.candidateConnMap[candidateID] = c
+
 	if isIPv6 {
 		m.connsIPv6[ufrag] = c
 	} else {
@@ -276,7 +282,7 @@ func (m *UDPMuxDefault) GetConn(ufrag string, addr net.Addr) (net.PacketConn, er
 }
 
 // RemoveConnByUfrag stops and removes the muxed packet connection
-func (m *UDPMuxDefault) RemoveConnByUfrag(ufrag string) {
+func (m *SingleSocketUDPMux) RemoveConnByUfrag(ufrag string) {
 	removedConns := make([]*udpMuxedConn, 0, 2)
 
 	// Keep lock section small to avoid deadlock with conn lock
@@ -284,10 +290,12 @@ func (m *UDPMuxDefault) RemoveConnByUfrag(ufrag string) {
 	if c, ok := m.connsIPv4[ufrag]; ok {
 		delete(m.connsIPv4, ufrag)
 		removedConns = append(removedConns, c)
+		delete(m.candidateConnMap, c.GetCandidateID())
 	}
 	if c, ok := m.connsIPv6[ufrag]; ok {
 		delete(m.connsIPv6, ufrag)
 		removedConns = append(removedConns, c)
+		delete(m.candidateConnMap, c.GetCandidateID())
 	}
 	m.mu.Unlock()
 
@@ -314,7 +322,7 @@ func (m *UDPMuxDefault) RemoveConnByUfrag(ufrag string) {
 }
 
 // IsClosed returns true if the mux had been closed
-func (m *UDPMuxDefault) IsClosed() bool {
+func (m *SingleSocketUDPMux) IsClosed() bool {
 	select {
 	case <-m.closedChan:
 		return true
@@ -324,7 +332,7 @@ func (m *UDPMuxDefault) IsClosed() bool {
 }
 
 // Close the mux, no further connections could be created
-func (m *UDPMuxDefault) Close() error {
+func (m *SingleSocketUDPMux) Close() error {
 	var err error
 	m.closeOnce.Do(func() {
 		m.mu.Lock()
@@ -347,11 +355,11 @@ func (m *UDPMuxDefault) Close() error {
 	return err
 }
 
-func (m *UDPMuxDefault) writeTo(buf []byte, rAddr net.Addr) (n int, err error) {
+func (m *SingleSocketUDPMux) writeTo(buf []byte, rAddr net.Addr) (n int, err error) {
 	return m.params.UDPConn.WriteTo(buf, rAddr)
 }
 
-func (m *UDPMuxDefault) registerConnForAddress(conn *udpMuxedConn, addr string) {
+func (m *SingleSocketUDPMux) registerConnForAddress(conn *udpMuxedConn, addr string) {
 	if m.IsClosed() {
 		return
 	}
@@ -368,81 +376,109 @@ func (m *UDPMuxDefault) registerConnForAddress(conn *udpMuxedConn, addr string)
 	log.Debugf("ICE: registered %s for %s", addr, conn.params.Key)
 }
 
-func (m *UDPMuxDefault) createMuxedConn(key string) *udpMuxedConn {
+func (m *SingleSocketUDPMux) createMuxedConn(key string, candidateID string) *udpMuxedConn {
 	c := newUDPMuxedConn(&udpMuxedConnParams{
-		Mux:       m,
+		Mux:         m,
-		Key:       key,
+		Key:         key,
-		AddrPool:  m.pool,
+		AddrPool:    m.pool,
-		LocalAddr: m.LocalAddr(),
+		LocalAddr:   m.LocalAddr(),
-		Logger:    m.params.Logger,
+		Logger:      m.params.Logger,
+		CandidateID: candidateID,
 	})
 	return c
 }
 
 // HandleSTUNMessage handles STUN packets and forwards them to underlying pion/ice library
-func (m *UDPMuxDefault) HandleSTUNMessage(msg *stun.Message, addr net.Addr) error {
+func (m *SingleSocketUDPMux) HandleSTUNMessage(msg *stun.Message, addr net.Addr) error {
-
 	remoteAddr, ok := addr.(*net.UDPAddr)
 	if !ok {
 		return fmt.Errorf("underlying PacketConn did not return a UDPAddr")
 	}
 
-	// If we have already seen this address dispatch to the appropriate destination
+	// Try to route to specific candidate connection first
-	// If you are using the same socket for the Host and SRFLX candidates, it might be that there are more than one
+	if conn := m.findCandidateConnection(msg); conn != nil {
-	// muxed connection - one for the SRFLX candidate and the other one for the HOST one.
+		return conn.writePacket(msg.Raw, remoteAddr)
-	// We will then forward STUN packets to each of these connections.
+	}
-	m.addressMapMu.RLock()
+
+	// Fallback: route to all possible connections
+	return m.forwardToAllConnections(msg, addr, remoteAddr)
+}
+
+// findCandidateConnection attempts to find the specific connection for a STUN message
+func (m *SingleSocketUDPMux) findCandidateConnection(msg *stun.Message) *udpMuxedConn {
+	candidatePairID, ok, err := ice.CandidatePairIDFromSTUN(msg)
+	if err != nil {
+		return nil
+	} else if !ok {
+		return nil
+	}
+
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	conn, exists := m.candidateConnMap[candidatePairID.TargetCandidateID()]
+	if !exists {
+		return nil
+	}
+	return conn
+}
+
+// forwardToAllConnections forwards STUN message to all relevant connections
+func (m *SingleSocketUDPMux) forwardToAllConnections(msg *stun.Message, addr net.Addr, remoteAddr *net.UDPAddr) error {
 	var destinationConnList []*udpMuxedConn
+
+	// Add connections from address map
+	m.addressMapMu.RLock()
 	if storedConns, ok := m.addressMap[addr.String()]; ok {
 		destinationConnList = append(destinationConnList, storedConns...)
 	}
 	m.addressMapMu.RUnlock()
 
-	var isIPv6 bool
+	if conn, ok := m.findConnectionByUsername(msg, addr); ok {
-	if udpAddr, _ := addr.(*net.UDPAddr); udpAddr != nil && udpAddr.IP.To4() == nil {
+		// If we have already seen this address dispatch to the appropriate destination
-		isIPv6 = true
+		// If you are using the same socket for the Host and SRFLX candidates, it might be that there are more than one
+		// muxed connection - one for the SRFLX candidate and the other one for the HOST one.
+		// We will then forward STUN packets to each of these connections.
+		if !m.connectionExists(conn, destinationConnList) {
+			destinationConnList = append(destinationConnList, conn)
+		}
 	}
 
-	// This block is needed to discover Peer Reflexive Candidates for which we don't know the Endpoint upfront.
+	// Forward to all found connections
-	// However, we can take a username attribute from the STUN message which contains ufrag.
-	// We can use ufrag to identify the destination conn to route packet to.
-	attr, stunAttrErr := msg.Get(stun.AttrUsername)
-	if stunAttrErr == nil {
-		ufrag := strings.Split(string(attr), ":")[0]
-
-		m.mu.Lock()
-		destinationConn := m.connsIPv4[ufrag]
-		if isIPv6 {
-			destinationConn = m.connsIPv6[ufrag]
-		}
-
-		if destinationConn != nil {
-			exists := false
-			for _, conn := range destinationConnList {
-				if conn.params.Key == destinationConn.params.Key {
-					exists = true
-					break
-				}
-			}
-			if !exists {
-				destinationConnList = append(destinationConnList, destinationConn)
-			}
-		}
-		m.mu.Unlock()
-	}
-
-	// Forward STUN packets to each destination connections even thought the STUN packet might not belong there.
-	// It will be discarded by the further ICE candidate logic if so.
 	for _, conn := range destinationConnList {
 		if err := conn.writePacket(msg.Raw, remoteAddr); err != nil {
 			log.Errorf("could not write packet: %v", err)
 		}
 	}
-
 	return nil
 }
 
-func (m *UDPMuxDefault) getConn(ufrag string, isIPv6 bool) (val *udpMuxedConn, ok bool) {
+// findConnectionByUsername finds connection using username attribute from STUN message
+func (m *SingleSocketUDPMux) findConnectionByUsername(msg *stun.Message, addr net.Addr) (*udpMuxedConn, bool) {
+	attr, err := msg.Get(stun.AttrUsername)
+	if err != nil {
+		return nil, false
+	}
+
+	ufrag := strings.Split(string(attr), ":")[0]
+	isIPv6 := isIPv6Address(addr)
+
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	return m.getConn(ufrag, isIPv6)
+}
+
+// connectionExists checks if a connection already exists in the list
+func (m *SingleSocketUDPMux) connectionExists(target *udpMuxedConn, conns []*udpMuxedConn) bool {
+	for _, conn := range conns {
+		if conn.params.Key == target.params.Key {
+			return true
+		}
+	}
+	return false
+}
+
+func (m *SingleSocketUDPMux) getConn(ufrag string, isIPv6 bool) (val *udpMuxedConn, ok bool) {
 	if isIPv6 {
 		val, ok = m.connsIPv6[ufrag]
 	} else {
@@ -451,6 +487,13 @@ func (m *UDPMuxDefault) getConn(ufrag string, isIPv6 bool) (val *udpMuxedConn, o
 	return
 }
 
+func isIPv6Address(addr net.Addr) bool {
+	if udpAddr, ok := addr.(*net.UDPAddr); ok {
+		return udpAddr.IP.To4() == nil
+	}
+	return false
+}
+
 type bufferHolder struct {
 	buf []byte
 }

client/iface/udpmux/mux_generic.go

@@ -1,12 +1,12 @@
 //go:build !ios
 
-package bind
+package udpmux
 
 import (
 	nbnet "github.com/netbirdio/netbird/util/net"
 )
 
-func (m *UDPMuxDefault) notifyAddressRemoval(addr string) {
+func (m *SingleSocketUDPMux) notifyAddressRemoval(addr string) {
 	// Kernel mode: direct nbnet.PacketConn (SharedSocket wrapped with nbnet)
 	if conn, ok := m.params.UDPConn.(*nbnet.PacketConn); ok {
 		conn.RemoveAddress(addr)

client/iface/udpmux/mux_ios.go

@@ -0,0 +1,7 @@
+//go:build ios
+
+package udpmux
+
+func (m *SingleSocketUDPMux) notifyAddressRemoval(addr string) {
+	// iOS doesn't support nbnet hooks, so this is a no-op
+}

client/iface/udpmux/universal.go

@@ -1,4 +1,4 @@
-package bind
+package udpmux
 
 /*
  Most of this code was copied from https://github.com/pion/ice and modified to fulfill NetBird's requirements.
@@ -29,7 +29,7 @@ type FilterFn func(address netip.Addr) (bool, netip.Prefix, error)
 // UniversalUDPMuxDefault handles STUN and TURN servers packets by wrapping the original UDPConn
 // It then passes packets to the UDPMux that does the actual connection muxing.
 type UniversalUDPMuxDefault struct {
-	*UDPMuxDefault
+	*SingleSocketUDPMux
 	params UniversalUDPMuxParams
 
 	// since we have a shared socket, for srflx candidates it makes sense to have a shared mapped address across all the agents
@@ -72,12 +72,12 @@ func NewUniversalUDPMuxDefault(params UniversalUDPMuxParams) *UniversalUDPMuxDef
 		address:    params.WGAddress,
 	}
 
-	udpMuxParams := UDPMuxParams{
+	udpMuxParams := Params{
 		Logger:  params.Logger,
 		UDPConn: m.params.UDPConn,
 		Net:     m.params.Net,
 	}
-	m.UDPMuxDefault = NewUDPMuxDefault(udpMuxParams)
+	m.SingleSocketUDPMux = NewSingleSocketUDPMux(udpMuxParams)
 
 	return m
 }
@@ -211,8 +211,8 @@ func (m *UniversalUDPMuxDefault) GetRelayedAddr(turnAddr net.Addr, deadline time
 
 // GetConnForURL add uniques to the muxed connection by concatenating ufrag and URL (e.g. STUN URL) to be able to support multiple STUN/TURN servers
 // and return a unique connection per server.
-func (m *UniversalUDPMuxDefault) GetConnForURL(ufrag string, url string, addr net.Addr) (net.PacketConn, error) {
+func (m *UniversalUDPMuxDefault) GetConnForURL(ufrag string, url string, addr net.Addr, candidateID string) (net.PacketConn, error) {
-	return m.UDPMuxDefault.GetConn(fmt.Sprintf("%s%s", ufrag, url), addr)
+	return m.SingleSocketUDPMux.GetConn(fmt.Sprintf("%s%s", ufrag, url), addr, candidateID)
 }
 
 // HandleSTUNMessage discovers STUN packets that carry a XOR mapped address from a STUN server.
@@ -233,7 +233,7 @@ func (m *UniversalUDPMuxDefault) HandleSTUNMessage(msg *stun.Message, addr net.A
 		}
 		return nil
 	}
-	return m.UDPMuxDefault.HandleSTUNMessage(msg, addr)
+	return m.SingleSocketUDPMux.HandleSTUNMessage(msg, addr)
 }
 
 // isXORMappedResponse indicates whether the message is a XORMappedAddress and is coming from the known STUN server.

client/internal/engine.go

@@ -29,9 +29,9 @@ import (
 	"github.com/netbirdio/netbird/client/firewall"
 	firewallManager "github.com/netbirdio/netbird/client/firewall/manager"
 	"github.com/netbirdio/netbird/client/iface"
-	"github.com/netbirdio/netbird/client/iface/bind"
 	"github.com/netbirdio/netbird/client/iface/device"
 	nbnetstack "github.com/netbirdio/netbird/client/iface/netstack"
+	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/internal/acl"
 	"github.com/netbirdio/netbird/client/internal/dns"
 	dnsconfig "github.com/netbirdio/netbird/client/internal/dns/config"
@@ -166,7 +166,7 @@ type Engine struct {
 
 	wgInterface WGIface
 
-	udpMux *bind.UniversalUDPMuxDefault
+	udpMux *udpmux.UniversalUDPMuxDefault
 
 	// networkSerial is the latest CurrentSerial (state ID) of the network sent by the Management service
 	networkSerial uint64
@@ -461,7 +461,7 @@ func (e *Engine) Start(netbirdConfig *mgmProto.NetbirdConfig, mgmtURL *url.URL)
 		StunTurn:             &e.stunTurn,
 		InterfaceBlackList:   e.config.IFaceBlackList,
 		DisableIPv6Discovery: e.config.DisableIPv6Discovery,
-		UDPMux:               e.udpMux.UDPMuxDefault,
+		UDPMux:               e.udpMux.SingleSocketUDPMux,
 		UDPMuxSrflx:          e.udpMux,
 		NATExternalIPs:       e.parseNATExternalIPMappings(),
 	}
@@ -1326,7 +1326,7 @@ func (e *Engine) createPeerConn(pubKey string, allowedIPs []netip.Prefix, agentV
 			StunTurn:             &e.stunTurn,
 			InterfaceBlackList:   e.config.IFaceBlackList,
 			DisableIPv6Discovery: e.config.DisableIPv6Discovery,
-			UDPMux:               e.udpMux.UDPMuxDefault,
+			UDPMux:               e.udpMux.SingleSocketUDPMux,
 			UDPMuxSrflx:          e.udpMux,
 			NATExternalIPs:       e.parseNATExternalIPMappings(),
 		},

client/internal/engine_test.go

@@ -26,10 +26,11 @@ import (
 	"google.golang.org/grpc/keepalive"
 
 	"github.com/netbirdio/management-integrations/integrations"
+
 	"github.com/netbirdio/netbird/client/iface"
-	"github.com/netbirdio/netbird/client/iface/bind"
 	"github.com/netbirdio/netbird/client/iface/configurer"
 	"github.com/netbirdio/netbird/client/iface/device"
+	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 	"github.com/netbirdio/netbird/client/iface/wgproxy"
 	"github.com/netbirdio/netbird/client/internal/dns"
@@ -84,7 +85,7 @@ type MockWGIface struct {
 	NameFunc                   func() string
 	AddressFunc                func() wgaddr.Address
 	ToInterfaceFunc            func() *net.Interface
-	UpFunc                     func() (*bind.UniversalUDPMuxDefault, error)
+	UpFunc                     func() (*udpmux.UniversalUDPMuxDefault, error)
 	UpdateAddrFunc             func(newAddr string) error
 	UpdatePeerFunc             func(peerKey string, allowedIps []netip.Prefix, keepAlive time.Duration, endpoint *net.UDPAddr, preSharedKey *wgtypes.Key) error
 	RemovePeerFunc             func(peerKey string) error
@@ -134,7 +135,7 @@ func (m *MockWGIface) ToInterface() *net.Interface {
 	return m.ToInterfaceFunc()
 }
 
-func (m *MockWGIface) Up() (*bind.UniversalUDPMuxDefault, error) {
+func (m *MockWGIface) Up() (*udpmux.UniversalUDPMuxDefault, error) {
 	return m.UpFunc()
 }
 
@@ -413,7 +414,7 @@ func TestEngine_UpdateNetworkMap(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	engine.udpMux = bind.NewUniversalUDPMuxDefault(bind.UniversalUDPMuxParams{UDPConn: conn, MTU: 1280})
+	engine.udpMux = udpmux.NewUniversalUDPMuxDefault(udpmux.UniversalUDPMuxParams{UDPConn: conn, MTU: 1280})
 	engine.ctx = ctx
 	engine.srWatcher = guard.NewSRWatcher(nil, nil, nil, icemaker.Config{})
 	engine.connMgr = NewConnMgr(engine.config, engine.statusRecorder, engine.peerStore, wgIface)

client/internal/iface_common.go

@@ -9,9 +9,9 @@ import (
 	"golang.zx2c4.com/wireguard/tun/netstack"
 	"golang.zx2c4.com/wireguard/wgctrl/wgtypes"
 
-	"github.com/netbirdio/netbird/client/iface/bind"
 	"github.com/netbirdio/netbird/client/iface/configurer"
 	"github.com/netbirdio/netbird/client/iface/device"
+	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 	"github.com/netbirdio/netbird/client/iface/wgproxy"
 	"github.com/netbirdio/netbird/monotime"
@@ -24,7 +24,7 @@ type wgIfaceBase interface {
 	Name() string
 	Address() wgaddr.Address
 	ToInterface() *net.Interface
-	Up() (*bind.UniversalUDPMuxDefault, error)
+	Up() (*udpmux.UniversalUDPMuxDefault, error)
 	UpdateAddr(newAddr string) error
 	GetProxy() wgproxy.Proxy
 	UpdatePeer(peerKey string, allowedIps []netip.Prefix, keepAlive time.Duration, endpoint *net.UDPAddr, preSharedKey *wgtypes.Key) error

client/internal/peer/worker_ice.go

@@ -9,11 +9,10 @@ import (
 	"time"
 
 	"github.com/pion/ice/v4"
-	"github.com/pion/stun/v2"
 	log "github.com/sirupsen/logrus"
 
 	"github.com/netbirdio/netbird/client/iface"
-	"github.com/netbirdio/netbird/client/iface/bind"
+	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/internal/peer/conntype"
 	icemaker "github.com/netbirdio/netbird/client/internal/peer/ice"
 	"github.com/netbirdio/netbird/client/internal/stdnet"
@@ -55,10 +54,6 @@ type WorkerICE struct {
 	sessionID ICESessionID
 	muxAgent  sync.Mutex
 
-	StunTurn []*stun.URI
-
-	sentExtraSrflx bool
-
 	localUfrag string
 	localPwd   string
 
@@ -139,7 +134,6 @@ func (w *WorkerICE) OnNewOffer(remoteOfferAnswer *OfferAnswer) {
 		w.muxAgent.Unlock()
 		return
 	}
-	w.sentExtraSrflx = false
 	w.agent = agent
 	w.agentDialerCancel = dialerCancel
 	w.agentConnecting = true
@@ -166,6 +160,21 @@ func (w *WorkerICE) OnRemoteCandidate(candidate ice.Candidate, haRoutes route.HA
 		w.log.Errorf("error while handling remote candidate")
 		return
 	}
+
+	if shouldAddExtraCandidate(candidate) {
+		// sends an extra server reflexive candidate to the remote peer with our related port (usually the wireguard port)
+		// this is useful when network has an existing port forwarding rule for the wireguard port and this peer
+		extraSrflx, err := extraSrflxCandidate(candidate)
+		if err != nil {
+			w.log.Errorf("failed creating extra server reflexive candidate %s", err)
+			return
+		}
+
+		if err := w.agent.AddRemoteCandidate(extraSrflx); err != nil {
+			w.log.Errorf("error while handling remote candidate")
+			return
+		}
+	}
 }
 
 func (w *WorkerICE) GetLocalUserCredentials() (frag string, pwd string) {
@@ -327,7 +336,7 @@ func (w *WorkerICE) punchRemoteWGPort(pair *ice.CandidatePair, remoteWgPort int)
 		return
 	}
 
-	mux, ok := w.config.ICEConfig.UDPMuxSrflx.(*bind.UniversalUDPMuxDefault)
+	mux, ok := w.config.ICEConfig.UDPMuxSrflx.(*udpmux.UniversalUDPMuxDefault)
 	if !ok {
 		w.log.Warn("invalid udp mux conversion")
 		return
@@ -354,26 +363,6 @@ func (w *WorkerICE) onICECandidate(candidate ice.Candidate) {
 			w.log.Errorf("failed signaling candidate to the remote peer %s %s", w.config.Key, err)
 		}
 	}()
-
-	if !w.shouldSendExtraSrflxCandidate(candidate) {
-		return
-	}
-
-	// sends an extra server reflexive candidate to the remote peer with our related port (usually the wireguard port)
-	// this is useful when network has an existing port forwarding rule for the wireguard port and this peer
-	extraSrflx, err := extraSrflxCandidate(candidate)
-	if err != nil {
-		w.log.Errorf("failed creating extra server reflexive candidate %s", err)
-		return
-	}
-	w.sentExtraSrflx = true
-
-	go func() {
-		err = w.signaler.SignalICECandidate(extraSrflx, w.config.Key)
-		if err != nil {
-			w.log.Errorf("failed signaling the extra server reflexive candidate: %s", err)
-		}
-	}()
 }
 
 func (w *WorkerICE) onICESelectedCandidatePair(c1 ice.Candidate, c2 ice.Candidate) {
@@ -424,22 +413,31 @@ func (w *WorkerICE) onConnectionStateChange(agent *icemaker.ThreadSafeAgent, dia
 	}
 }
 
-func (w *WorkerICE) shouldSendExtraSrflxCandidate(candidate ice.Candidate) bool {
-	if !w.sentExtraSrflx && candidate.Type() == ice.CandidateTypeServerReflexive && candidate.Port() != candidate.RelatedAddress().Port {
-		return true
-	}
-	return false
-}
-
 func (w *WorkerICE) turnAgentDial(ctx context.Context, agent *icemaker.ThreadSafeAgent, remoteOfferAnswer *OfferAnswer) (*ice.Conn, error) {
-	isControlling := w.config.LocalKey > w.config.Key
+	if isController(w.config) {
-	if isControlling {
+		return w.agent.Dial(ctx, remoteOfferAnswer.IceCredentials.UFrag, remoteOfferAnswer.IceCredentials.Pwd)
-		return agent.Dial(ctx, remoteOfferAnswer.IceCredentials.UFrag, remoteOfferAnswer.IceCredentials.Pwd)
 	} else {
 		return agent.Accept(ctx, remoteOfferAnswer.IceCredentials.UFrag, remoteOfferAnswer.IceCredentials.Pwd)
 	}
 }
 
+func shouldAddExtraCandidate(candidate ice.Candidate) bool {
+	if candidate.Type() != ice.CandidateTypeServerReflexive {
+		return false
+	}
+
+	if candidate.Port() == candidate.RelatedAddress().Port {
+		return false
+	}
+
+	// in the older version when we didn't set candidate ID extension the remote peer sent the extra candidates
+	// in newer version we generate locally the extra candidate
+	if _, ok := candidate.GetExtension(ice.ExtensionKeyCandidateID); !ok {
+		return false
+	}
+	return true
+}
+
 func extraSrflxCandidate(candidate ice.Candidate) (*ice.CandidateServerReflexive, error) {
 	relatedAdd := candidate.RelatedAddress()
 	ec, err := ice.NewCandidateServerReflexive(&ice.CandidateServerReflexiveConfig{
@@ -455,6 +453,10 @@ func extraSrflxCandidate(candidate ice.Candidate) (*ice.CandidateServerReflexive
 	}
 
 	for _, e := range candidate.Extensions() {
+		// overwrite the original candidate ID with the new one to avoid candidate duplication
+		if e.Key == ice.ExtensionKeyCandidateID {
+			e.Value = candidate.ID()
+		}
 		if err := ec.AddExtension(e); err != nil {
 			return nil, err
 		}

go.mod

@@ -261,6 +261,6 @@ replace golang.zx2c4.com/wireguard => github.com/netbirdio/wireguard-go v0.0.0-2
 
 replace github.com/cloudflare/circl => github.com/cunicu/circl v0.0.0-20230801113412-fec58fc7b5f6
 
-replace github.com/pion/ice/v4 => github.com/netbirdio/ice/v4 v4.0.0-20250827161942-426799a23107
+replace github.com/pion/ice/v4 => github.com/netbirdio/ice/v4 v4.0.0-20250908184934-6202be846b51
 
 replace github.com/libp2p/go-netroute => github.com/netbirdio/go-netroute v0.0.0-20240611143515-f59b0e1d3944

go.sum

@@ -501,8 +501,8 @@ github.com/neelance/astrewrite v0.0.0-20160511093645-99348263ae86/go.mod h1:kHJE
 github.com/neelance/sourcemap v0.0.0-20200213170602-2833bce08e4c/go.mod h1:Qr6/a/Q4r9LP1IltGz7tA7iOK1WonHEYhu1HRBA7ZiM=
 github.com/netbirdio/go-netroute v0.0.0-20240611143515-f59b0e1d3944 h1:TDtJKmM6Sf8uYFx/dMeqNOL90KUoRscdfpFZ3Im89uk=
 github.com/netbirdio/go-netroute v0.0.0-20240611143515-f59b0e1d3944/go.mod h1:sHA6TRxjQ6RLbnI+3R4DZo2Eseg/iKiPRfNmcuNySVQ=
-github.com/netbirdio/ice/v4 v4.0.0-20250827161942-426799a23107 h1:ZJwhKexMlK15B/Ld+1T8VYE2Mt1lk1kf2DlXr46EHcw=
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