[client] Add IPv6 support to usersace bind (#5147)

client/iface/bind/dual_stack_conn.go

@@ -0,0 +1,169 @@
+package bind
+
+import (
+	"errors"
+	"net"
+	"sync"
+	"time"
+
+	"github.com/hashicorp/go-multierror"
+	log "github.com/sirupsen/logrus"
+
+	nberrors "github.com/netbirdio/netbird/client/errors"
+)
+
+var (
+	errNoIPv4Conn  = errors.New("no IPv4 connection available")
+	errNoIPv6Conn  = errors.New("no IPv6 connection available")
+	errInvalidAddr = errors.New("invalid address type")
+)
+
+// DualStackPacketConn wraps IPv4 and IPv6 UDP connections and routes writes
+// to the appropriate connection based on the destination address.
+// ReadFrom is not used in the hot path - ICEBind receives packets via
+// BatchReader.ReadBatch() directly. This is only used by udpMux for sending.
+type DualStackPacketConn struct {
+	ipv4Conn net.PacketConn
+	ipv6Conn net.PacketConn
+
+	readFromWarn sync.Once
+}
+
+// NewDualStackPacketConn creates a new dual-stack packet connection.
+func NewDualStackPacketConn(ipv4Conn, ipv6Conn net.PacketConn) *DualStackPacketConn {
+	return &DualStackPacketConn{
+		ipv4Conn: ipv4Conn,
+		ipv6Conn: ipv6Conn,
+	}
+}
+
+// ReadFrom reads from the available connection (preferring IPv4).
+// NOTE: This method is NOT used in the data path. ICEBind receives packets via
+// BatchReader.ReadBatch() directly for both IPv4 and IPv6, which is much more efficient.
+// This implementation exists only to satisfy the net.PacketConn interface for the udpMux,
+// but the udpMux only uses WriteTo() for sending STUN responses - it never calls ReadFrom()
+// because STUN packets are filtered and forwarded via HandleSTUNMessage() from the receive path.
+func (d *DualStackPacketConn) ReadFrom(b []byte) (n int, addr net.Addr, err error) {
+	d.readFromWarn.Do(func() {
+		log.Warn("DualStackPacketConn.ReadFrom called - this is unexpected and may indicate an inefficient code path")
+	})
+
+	if d.ipv4Conn != nil {
+		return d.ipv4Conn.ReadFrom(b)
+	}
+	if d.ipv6Conn != nil {
+		return d.ipv6Conn.ReadFrom(b)
+	}
+	return 0, nil, net.ErrClosed
+}
+
+// WriteTo writes to the appropriate connection based on the address type.
+func (d *DualStackPacketConn) WriteTo(b []byte, addr net.Addr) (n int, err error) {
+	udpAddr, ok := addr.(*net.UDPAddr)
+	if !ok {
+		return 0, &net.OpError{
+			Op:   "write",
+			Net:  "udp",
+			Addr: addr,
+			Err:  errInvalidAddr,
+		}
+	}
+
+	if udpAddr.IP.To4() == nil {
+		if d.ipv6Conn != nil {
+			return d.ipv6Conn.WriteTo(b, addr)
+		}
+		return 0, &net.OpError{
+			Op:   "write",
+			Net:  "udp6",
+			Addr: addr,
+			Err:  errNoIPv6Conn,
+		}
+	}
+
+	if d.ipv4Conn != nil {
+		return d.ipv4Conn.WriteTo(b, addr)
+	}
+	return 0, &net.OpError{
+		Op:   "write",
+		Net:  "udp4",
+		Addr: addr,
+		Err:  errNoIPv4Conn,
+	}
+}
+
+// Close closes both connections.
+func (d *DualStackPacketConn) Close() error {
+	var result *multierror.Error
+	if d.ipv4Conn != nil {
+		if err := d.ipv4Conn.Close(); err != nil {
+			result = multierror.Append(result, err)
+		}
+	}
+	if d.ipv6Conn != nil {
+		if err := d.ipv6Conn.Close(); err != nil {
+			result = multierror.Append(result, err)
+		}
+	}
+	return nberrors.FormatErrorOrNil(result)
+}
+
+// LocalAddr returns the local address of the IPv4 connection if available,
+// otherwise the IPv6 connection.
+func (d *DualStackPacketConn) LocalAddr() net.Addr {
+	if d.ipv4Conn != nil {
+		return d.ipv4Conn.LocalAddr()
+	}
+	if d.ipv6Conn != nil {
+		return d.ipv6Conn.LocalAddr()
+	}
+	return nil
+}
+
+// SetDeadline sets the deadline for both connections.
+func (d *DualStackPacketConn) SetDeadline(t time.Time) error {
+	var result *multierror.Error
+	if d.ipv4Conn != nil {
+		if err := d.ipv4Conn.SetDeadline(t); err != nil {
+			result = multierror.Append(result, err)
+		}
+	}
+	if d.ipv6Conn != nil {
+		if err := d.ipv6Conn.SetDeadline(t); err != nil {
+			result = multierror.Append(result, err)
+		}
+	}
+	return nberrors.FormatErrorOrNil(result)
+}
+
+// SetReadDeadline sets the read deadline for both connections.
+func (d *DualStackPacketConn) SetReadDeadline(t time.Time) error {
+	var result *multierror.Error
+	if d.ipv4Conn != nil {
+		if err := d.ipv4Conn.SetReadDeadline(t); err != nil {
+			result = multierror.Append(result, err)
+		}
+	}
+	if d.ipv6Conn != nil {
+		if err := d.ipv6Conn.SetReadDeadline(t); err != nil {
+			result = multierror.Append(result, err)
+		}
+	}
+	return nberrors.FormatErrorOrNil(result)
+}
+
+// SetWriteDeadline sets the write deadline for both connections.
+func (d *DualStackPacketConn) SetWriteDeadline(t time.Time) error {
+	var result *multierror.Error
+	if d.ipv4Conn != nil {
+		if err := d.ipv4Conn.SetWriteDeadline(t); err != nil {
+			result = multierror.Append(result, err)
+		}
+	}
+	if d.ipv6Conn != nil {
+		if err := d.ipv6Conn.SetWriteDeadline(t); err != nil {
+			result = multierror.Append(result, err)
+		}
+	}
+	return nberrors.FormatErrorOrNil(result)
+}

client/iface/bind/dual_stack_conn_bench_test.go

@@ -0,0 +1,119 @@
+package bind
+
+import (
+	"net"
+	"testing"
+)
+
+var (
+	ipv4Addr = &net.UDPAddr{IP: net.ParseIP("127.0.0.1"), Port: 12345}
+	ipv6Addr = &net.UDPAddr{IP: net.ParseIP("::1"), Port: 12345}
+	payload  = make([]byte, 1200)
+)
+
+func BenchmarkWriteTo_DirectUDPConn(b *testing.B) {
+	conn, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
+	if err != nil {
+		b.Fatal(err)
+	}
+	defer conn.Close()
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = conn.WriteTo(payload, ipv4Addr)
+	}
+}
+
+func BenchmarkWriteTo_DualStack_IPv4Only(b *testing.B) {
+	conn, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
+	if err != nil {
+		b.Fatal(err)
+	}
+	defer conn.Close()
+
+	ds := NewDualStackPacketConn(conn, nil)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = ds.WriteTo(payload, ipv4Addr)
+	}
+}
+
+func BenchmarkWriteTo_DualStack_IPv6Only(b *testing.B) {
+	conn, err := net.ListenUDP("udp6", &net.UDPAddr{IP: net.IPv6zero, Port: 0})
+	if err != nil {
+		b.Skipf("IPv6 not available: %v", err)
+	}
+	defer conn.Close()
+
+	ds := NewDualStackPacketConn(nil, conn)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = ds.WriteTo(payload, ipv6Addr)
+	}
+}
+
+func BenchmarkWriteTo_DualStack_Both_IPv4Traffic(b *testing.B) {
+	conn4, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
+	if err != nil {
+		b.Fatal(err)
+	}
+	defer conn4.Close()
+
+	conn6, err := net.ListenUDP("udp6", &net.UDPAddr{IP: net.IPv6zero, Port: 0})
+	if err != nil {
+		b.Skipf("IPv6 not available: %v", err)
+	}
+	defer conn6.Close()
+
+	ds := NewDualStackPacketConn(conn4, conn6)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = ds.WriteTo(payload, ipv4Addr)
+	}
+}
+
+func BenchmarkWriteTo_DualStack_Both_IPv6Traffic(b *testing.B) {
+	conn4, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
+	if err != nil {
+		b.Fatal(err)
+	}
+	defer conn4.Close()
+
+	conn6, err := net.ListenUDP("udp6", &net.UDPAddr{IP: net.IPv6zero, Port: 0})
+	if err != nil {
+		b.Skipf("IPv6 not available: %v", err)
+	}
+	defer conn6.Close()
+
+	ds := NewDualStackPacketConn(conn4, conn6)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = ds.WriteTo(payload, ipv6Addr)
+	}
+}
+
+func BenchmarkWriteTo_DualStack_Both_MixedTraffic(b *testing.B) {
+	conn4, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
+	if err != nil {
+		b.Fatal(err)
+	}
+	defer conn4.Close()
+
+	conn6, err := net.ListenUDP("udp6", &net.UDPAddr{IP: net.IPv6zero, Port: 0})
+	if err != nil {
+		b.Skipf("IPv6 not available: %v", err)
+	}
+	defer conn6.Close()
+
+	ds := NewDualStackPacketConn(conn4, conn6)
+	addrs := []net.Addr{ipv4Addr, ipv6Addr}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = ds.WriteTo(payload, addrs[i&1])
+	}
+}

client/iface/bind/dual_stack_conn_test.go

@@ -0,0 +1,191 @@
+package bind
+
+import (
+	"net"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestDualStackPacketConn_RoutesWritesToCorrectSocket(t *testing.T) {
+	ipv4Conn := &mockPacketConn{network: "udp4"}
+	ipv6Conn := &mockPacketConn{network: "udp6"}
+	dualStack := NewDualStackPacketConn(ipv4Conn, ipv6Conn)
+
+	tests := []struct {
+		name       string
+		addr       *net.UDPAddr
+		wantSocket string
+	}{
+		{
+			name:       "IPv4 address",
+			addr:       &net.UDPAddr{IP: net.ParseIP("192.168.1.1"), Port: 1234},
+			wantSocket: "udp4",
+		},
+		{
+			name:       "IPv6 address",
+			addr:       &net.UDPAddr{IP: net.ParseIP("2001:db8::1"), Port: 1234},
+			wantSocket: "udp6",
+		},
+		{
+			name:       "IPv4-mapped IPv6 goes to IPv4",
+			addr:       &net.UDPAddr{IP: net.ParseIP("::ffff:192.168.1.1"), Port: 1234},
+			wantSocket: "udp4",
+		},
+		{
+			name:       "IPv4 loopback",
+			addr:       &net.UDPAddr{IP: net.ParseIP("127.0.0.1"), Port: 1234},
+			wantSocket: "udp4",
+		},
+		{
+			name:       "IPv6 loopback",
+			addr:       &net.UDPAddr{IP: net.ParseIP("::1"), Port: 1234},
+			wantSocket: "udp6",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ipv4Conn.writeCount = 0
+			ipv6Conn.writeCount = 0
+
+			n, err := dualStack.WriteTo([]byte("test"), tt.addr)
+			require.NoError(t, err)
+			assert.Equal(t, 4, n)
+
+			if tt.wantSocket == "udp4" {
+				assert.Equal(t, 1, ipv4Conn.writeCount, "expected write to IPv4")
+				assert.Equal(t, 0, ipv6Conn.writeCount, "expected no write to IPv6")
+			} else {
+				assert.Equal(t, 0, ipv4Conn.writeCount, "expected no write to IPv4")
+				assert.Equal(t, 1, ipv6Conn.writeCount, "expected write to IPv6")
+			}
+		})
+	}
+}
+
+func TestDualStackPacketConn_IPv4OnlyRejectsIPv6(t *testing.T) {
+	dualStack := NewDualStackPacketConn(&mockPacketConn{network: "udp4"}, nil)
+
+	// IPv4 works
+	_, err := dualStack.WriteTo([]byte("test"), &net.UDPAddr{IP: net.ParseIP("192.168.1.1"), Port: 1234})
+	require.NoError(t, err)
+
+	// IPv6 fails
+	_, err = dualStack.WriteTo([]byte("test"), &net.UDPAddr{IP: net.ParseIP("2001:db8::1"), Port: 1234})
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "no IPv6 connection")
+}
+
+func TestDualStackPacketConn_IPv6OnlyRejectsIPv4(t *testing.T) {
+	dualStack := NewDualStackPacketConn(nil, &mockPacketConn{network: "udp6"})
+
+	// IPv6 works
+	_, err := dualStack.WriteTo([]byte("test"), &net.UDPAddr{IP: net.ParseIP("2001:db8::1"), Port: 1234})
+	require.NoError(t, err)
+
+	// IPv4 fails
+	_, err = dualStack.WriteTo([]byte("test"), &net.UDPAddr{IP: net.ParseIP("192.168.1.1"), Port: 1234})
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "no IPv4 connection")
+}
+
+// TestDualStackPacketConn_ReadFromIsNotUsedInHotPath documents that ReadFrom
+// only reads from one socket (IPv4 preferred). This is fine because the actual
+// receive path uses wireguard-go's BatchReader directly, not ReadFrom.
+func TestDualStackPacketConn_ReadFromIsNotUsedInHotPath(t *testing.T) {
+	ipv4Conn := &mockPacketConn{
+		network:  "udp4",
+		readData: []byte("from ipv4"),
+		readAddr: &net.UDPAddr{IP: net.ParseIP("192.168.1.1"), Port: 1234},
+	}
+	ipv6Conn := &mockPacketConn{
+		network:  "udp6",
+		readData: []byte("from ipv6"),
+		readAddr: &net.UDPAddr{IP: net.ParseIP("2001:db8::1"), Port: 1234},
+	}
+
+	dualStack := NewDualStackPacketConn(ipv4Conn, ipv6Conn)
+
+	buf := make([]byte, 100)
+	n, addr, err := dualStack.ReadFrom(buf)
+
+	require.NoError(t, err)
+	// reads from IPv4 (preferred) - this is expected behavior
+	assert.Equal(t, "from ipv4", string(buf[:n]))
+	assert.Equal(t, "192.168.1.1", addr.(*net.UDPAddr).IP.String())
+}
+
+func TestDualStackPacketConn_LocalAddrPrefersIPv4(t *testing.T) {
+	ipv4Addr := &net.UDPAddr{IP: net.ParseIP("0.0.0.0"), Port: 51820}
+	ipv6Addr := &net.UDPAddr{IP: net.ParseIP("::"), Port: 51820}
+
+	tests := []struct {
+		name     string
+		ipv4     net.PacketConn
+		ipv6     net.PacketConn
+		wantAddr net.Addr
+	}{
+		{
+			name:     "both available returns IPv4",
+			ipv4:     &mockPacketConn{localAddr: ipv4Addr},
+			ipv6:     &mockPacketConn{localAddr: ipv6Addr},
+			wantAddr: ipv4Addr,
+		},
+		{
+			name:     "IPv4 only",
+			ipv4:     &mockPacketConn{localAddr: ipv4Addr},
+			ipv6:     nil,
+			wantAddr: ipv4Addr,
+		},
+		{
+			name:     "IPv6 only",
+			ipv4:     nil,
+			ipv6:     &mockPacketConn{localAddr: ipv6Addr},
+			wantAddr: ipv6Addr,
+		},
+		{
+			name:     "neither returns nil",
+			ipv4:     nil,
+			ipv6:     nil,
+			wantAddr: nil,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			dualStack := NewDualStackPacketConn(tt.ipv4, tt.ipv6)
+			assert.Equal(t, tt.wantAddr, dualStack.LocalAddr())
+		})
+	}
+}
+
+// mock
+
+type mockPacketConn struct {
+	network    string
+	writeCount int
+	readData   []byte
+	readAddr   net.Addr
+	localAddr  net.Addr
+}
+
+func (m *mockPacketConn) ReadFrom(b []byte) (n int, addr net.Addr, err error) {
+	if m.readData != nil {
+		return copy(b, m.readData), m.readAddr, nil
+	}
+	return 0, nil, nil
+}
+
+func (m *mockPacketConn) WriteTo(b []byte, addr net.Addr) (n int, err error) {
+	m.writeCount++
+	return len(b), nil
+}
+
+func (m *mockPacketConn) Close() error                       { return nil }
+func (m *mockPacketConn) LocalAddr() net.Addr                { return m.localAddr }
+func (m *mockPacketConn) SetDeadline(t time.Time) error      { return nil }
+func (m *mockPacketConn) SetReadDeadline(t time.Time) error  { return nil }
+func (m *mockPacketConn) SetWriteDeadline(t time.Time) error { return nil }

client/iface/bind/ice_bind.go

@@ -14,7 +14,6 @@ import (
 	"github.com/pion/stun/v3"
 	"github.com/pion/transport/v3"
 	log "github.com/sirupsen/logrus"
-	"golang.org/x/net/ipv4"
 	"golang.org/x/net/ipv6"
 	wgConn "golang.zx2c4.com/wireguard/conn"
 
@@ -28,22 +27,7 @@ type receiverCreator struct {
 }
 
 func (rc receiverCreator) CreateReceiverFn(pc wgConn.BatchReader, conn *net.UDPConn, rxOffload bool, msgPool *sync.Pool) wgConn.ReceiveFunc {
-	if ipv4PC, ok := pc.(*ipv4.PacketConn); ok {
-		return rc.iceBind.createIPv4ReceiverFn(ipv4PC, conn, rxOffload, msgPool)
-	}
-	// IPv6 is currently not supported in the udpmux, this is a stub for compatibility with the
-	// wireguard-go ReceiverCreator interface which is called for both IPv4 and IPv6.
-	return func(bufs [][]byte, sizes []int, eps []wgConn.Endpoint) (n int, err error) {
-		buf := bufs[0]
-		size, ep, err := conn.ReadFromUDPAddrPort(buf)
-		if err != nil {
-			return 0, err
-		}
-		sizes[0] = size
-		stdEp := &wgConn.StdNetEndpoint{AddrPort: ep}
-		eps[0] = stdEp
-		return 1, nil
-	}
+	return rc.iceBind.createReceiverFn(pc, conn, rxOffload, msgPool)
 }
 
 // ICEBind is a bind implementation with two main features:
@@ -73,6 +57,8 @@ type ICEBind struct {
 
 	muUDPMux sync.Mutex
 	udpMux   *udpmux.UniversalUDPMuxDefault
+	ipv4Conn *net.UDPConn
+	ipv6Conn *net.UDPConn
 }
 
 func NewICEBind(transportNet transport.Net, filterFn udpmux.FilterFn, address wgaddr.Address, mtu uint16) *ICEBind {
@@ -118,6 +104,12 @@ func (s *ICEBind) Close() error {
 
 	close(s.closedChan)
 
+	s.muUDPMux.Lock()
+	s.ipv4Conn = nil
+	s.ipv6Conn = nil
+	s.udpMux = nil
+	s.muUDPMux.Unlock()
+
 	return s.StdNetBind.Close()
 }
 
@@ -175,19 +167,18 @@ func (b *ICEBind) Send(bufs [][]byte, ep wgConn.Endpoint) error {
 	return nil
 }
 
-func (s *ICEBind) createIPv4ReceiverFn(pc *ipv4.PacketConn, conn *net.UDPConn, rxOffload bool, msgsPool *sync.Pool) wgConn.ReceiveFunc {
+func (s *ICEBind) createReceiverFn(pc wgConn.BatchReader, conn *net.UDPConn, rxOffload bool, msgsPool *sync.Pool) wgConn.ReceiveFunc {
 	s.muUDPMux.Lock()
 	defer s.muUDPMux.Unlock()
 
-	s.udpMux = udpmux.NewUniversalUDPMuxDefault(
-		udpmux.UniversalUDPMuxParams{
-			UDPConn:   nbnet.WrapPacketConn(conn),
-			Net:       s.transportNet,
-			FilterFn:  s.filterFn,
-			WGAddress: s.address,
-			MTU:       s.mtu,
-		},
-	)
+	// Detect IPv4 vs IPv6 from connection's local address
+	if localAddr := conn.LocalAddr().(*net.UDPAddr); localAddr.IP.To4() != nil {
+		s.ipv4Conn = conn
+	} else {
+		s.ipv6Conn = conn
+	}
+	s.createOrUpdateMux()
+
 	return func(bufs [][]byte, sizes []int, eps []wgConn.Endpoint) (n int, err error) {
 		msgs := getMessages(msgsPool)
 		for i := range bufs {
@@ -195,12 +186,13 @@ func (s *ICEBind) createIPv4ReceiverFn(pc *ipv4.PacketConn, conn *net.UDPConn, r
 			(*msgs)[i].OOB = (*msgs)[i].OOB[:cap((*msgs)[i].OOB)]
 		}
 		defer putMessages(msgs, msgsPool)
+
 		var numMsgs int
 		if runtime.GOOS == "linux" || runtime.GOOS == "android" {
 			if rxOffload {
 				readAt := len(*msgs) - (wgConn.IdealBatchSize / wgConn.UdpSegmentMaxDatagrams)
-				//nolint
-				numMsgs, err = pc.ReadBatch((*msgs)[readAt:], 0)
+				//nolint:staticcheck
+				_, err = pc.ReadBatch((*msgs)[readAt:], 0)
 				if err != nil {
 					return 0, err
 				}
@@ -222,12 +214,12 @@ func (s *ICEBind) createIPv4ReceiverFn(pc *ipv4.PacketConn, conn *net.UDPConn, r
 			}
 			numMsgs = 1
 		}
+
 		for i := 0; i < numMsgs; i++ {
 			msg := &(*msgs)[i]
 
 			// todo: handle err
-			ok, _ := s.filterOutStunMessages(msg.Buffers, msg.N, msg.Addr)
-			if ok {
+			if ok, _ := s.filterOutStunMessages(msg.Buffers, msg.N, msg.Addr); ok {
 				continue
 			}
 			sizes[i] = msg.N
@@ -248,6 +240,38 @@ func (s *ICEBind) createIPv4ReceiverFn(pc *ipv4.PacketConn, conn *net.UDPConn, r
 	}
 }
 
+// createOrUpdateMux creates or updates the UDP mux with the available connections.
+// Must be called with muUDPMux held.
+func (s *ICEBind) createOrUpdateMux() {
+	var muxConn net.PacketConn
+
+	switch {
+	case s.ipv4Conn != nil && s.ipv6Conn != nil:
+		muxConn = NewDualStackPacketConn(
+			nbnet.WrapPacketConn(s.ipv4Conn),
+			nbnet.WrapPacketConn(s.ipv6Conn),
+		)
+	case s.ipv4Conn != nil:
+		muxConn = nbnet.WrapPacketConn(s.ipv4Conn)
+	case s.ipv6Conn != nil:
+		muxConn = nbnet.WrapPacketConn(s.ipv6Conn)
+	default:
+		return
+	}
+
+	// Don't close the old mux - it doesn't own the underlying connections.
+	// The sockets are managed by WireGuard's StdNetBind, not by us.
+	s.udpMux = udpmux.NewUniversalUDPMuxDefault(
+		udpmux.UniversalUDPMuxParams{
+			UDPConn:   muxConn,
+			Net:       s.transportNet,
+			FilterFn:  s.filterFn,
+			WGAddress: s.address,
+			MTU:       s.mtu,
+		},
+	)
+}
+
 func (s *ICEBind) filterOutStunMessages(buffers [][]byte, n int, addr net.Addr) (bool, error) {
 	for i := range buffers {
 		if !stun.IsMessage(buffers[i]) {
@@ -260,9 +284,14 @@ func (s *ICEBind) filterOutStunMessages(buffers [][]byte, n int, addr net.Addr)
 			return true, err
 		}
 
-		muxErr := s.udpMux.HandleSTUNMessage(msg, addr)
-		if muxErr != nil {
-			log.Warnf("failed to handle STUN packet")
+		s.muUDPMux.Lock()
+		mux := s.udpMux
+		s.muUDPMux.Unlock()
+
+		if mux != nil {
+			if muxErr := mux.HandleSTUNMessage(msg, addr); muxErr != nil {
+				log.Warnf("failed to handle STUN packet: %v", muxErr)
+			}
 		}
 
 		buffers[i] = []byte{}

client/iface/bind/ice_bind_test.go

@@ -0,0 +1,324 @@
+package bind
+
+import (
+	"fmt"
+	"net"
+	"net/netip"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/pion/transport/v3/stdnet"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+
+	"github.com/netbirdio/netbird/client/iface/wgaddr"
+)
+
+func TestICEBind_CreatesReceiverForBothIPv4AndIPv6(t *testing.T) {
+	iceBind := setupICEBind(t)
+
+	ipv4Conn, ipv6Conn := createDualStackConns(t)
+	defer ipv4Conn.Close()
+	defer ipv6Conn.Close()
+
+	rc := receiverCreator{iceBind}
+	pool := createMsgPool()
+
+	// Simulate wireguard-go calling CreateReceiverFn for IPv4
+	ipv4RecvFn := rc.CreateReceiverFn(ipv4.NewPacketConn(ipv4Conn), ipv4Conn, false, pool)
+	require.NotNil(t, ipv4RecvFn)
+
+	iceBind.muUDPMux.Lock()
+	assert.NotNil(t, iceBind.ipv4Conn, "should store IPv4 connection")
+	assert.Nil(t, iceBind.ipv6Conn, "IPv6 not added yet")
+	assert.NotNil(t, iceBind.udpMux, "mux should be created after first connection")
+	iceBind.muUDPMux.Unlock()
+
+	// Simulate wireguard-go calling CreateReceiverFn for IPv6
+	ipv6RecvFn := rc.CreateReceiverFn(ipv6.NewPacketConn(ipv6Conn), ipv6Conn, false, pool)
+	require.NotNil(t, ipv6RecvFn)
+
+	iceBind.muUDPMux.Lock()
+	assert.NotNil(t, iceBind.ipv4Conn, "should still have IPv4 connection")
+	assert.NotNil(t, iceBind.ipv6Conn, "should now have IPv6 connection")
+	assert.NotNil(t, iceBind.udpMux, "mux should still exist")
+	iceBind.muUDPMux.Unlock()
+
+	mux, err := iceBind.GetICEMux()
+	require.NoError(t, err)
+	require.NotNil(t, mux)
+}
+
+func TestICEBind_WorksWithIPv4Only(t *testing.T) {
+	iceBind := setupICEBind(t)
+
+	ipv4Conn, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
+	require.NoError(t, err)
+	defer ipv4Conn.Close()
+
+	rc := receiverCreator{iceBind}
+	recvFn := rc.CreateReceiverFn(ipv4.NewPacketConn(ipv4Conn), ipv4Conn, false, createMsgPool())
+	require.NotNil(t, recvFn)
+
+	iceBind.muUDPMux.Lock()
+	assert.NotNil(t, iceBind.ipv4Conn)
+	assert.Nil(t, iceBind.ipv6Conn)
+	assert.NotNil(t, iceBind.udpMux)
+	iceBind.muUDPMux.Unlock()
+
+	mux, err := iceBind.GetICEMux()
+	require.NoError(t, err)
+	require.NotNil(t, mux)
+}
+
+func TestICEBind_WorksWithIPv6Only(t *testing.T) {
+	iceBind := setupICEBind(t)
+
+	ipv6Conn, err := net.ListenUDP("udp6", &net.UDPAddr{IP: net.IPv6zero, Port: 0})
+	if err != nil {
+		t.Skipf("IPv6 not available: %v", err)
+	}
+	defer ipv6Conn.Close()
+
+	rc := receiverCreator{iceBind}
+	recvFn := rc.CreateReceiverFn(ipv6.NewPacketConn(ipv6Conn), ipv6Conn, false, createMsgPool())
+	require.NotNil(t, recvFn)
+
+	iceBind.muUDPMux.Lock()
+	assert.Nil(t, iceBind.ipv4Conn)
+	assert.NotNil(t, iceBind.ipv6Conn)
+	assert.NotNil(t, iceBind.udpMux)
+	iceBind.muUDPMux.Unlock()
+
+	mux, err := iceBind.GetICEMux()
+	require.NoError(t, err)
+	require.NotNil(t, mux)
+}
+
+// TestICEBind_SendsToIPv4AndIPv6PeersSimultaneously verifies that we can communicate
+// with peers on different address families through the same DualStackPacketConn.
+func TestICEBind_SendsToIPv4AndIPv6PeersSimultaneously(t *testing.T) {
+	// two "remote peers" listening on different address families
+	ipv4Peer := listenUDP(t, "udp4", "127.0.0.1:0")
+	defer ipv4Peer.Close()
+
+	ipv6Peer, err := net.ListenUDP("udp6", &net.UDPAddr{IP: net.IPv6loopback, Port: 0})
+	if err != nil {
+		t.Skipf("IPv6 not available: %v", err)
+	}
+	defer ipv6Peer.Close()
+
+	// our local dual-stack connection
+	ipv4Local := listenUDP(t, "udp4", "127.0.0.1:0")
+	defer ipv4Local.Close()
+
+	ipv6Local := listenUDP(t, "udp6", "[::1]:0")
+	defer ipv6Local.Close()
+
+	dualStack := NewDualStackPacketConn(ipv4Local, ipv6Local)
+
+	// send to both peers
+	_, err = dualStack.WriteTo([]byte("to-ipv4"), ipv4Peer.LocalAddr())
+	require.NoError(t, err)
+
+	_, err = dualStack.WriteTo([]byte("to-ipv6"), ipv6Peer.LocalAddr())
+	require.NoError(t, err)
+
+	// verify IPv4 peer got its packet from the IPv4 socket
+	buf := make([]byte, 100)
+	_ = ipv4Peer.SetReadDeadline(time.Now().Add(time.Second))
+	n, addr, err := ipv4Peer.ReadFrom(buf)
+	require.NoError(t, err)
+	assert.Equal(t, "to-ipv4", string(buf[:n]))
+	assert.Equal(t, ipv4Local.LocalAddr().(*net.UDPAddr).Port, addr.(*net.UDPAddr).Port)
+
+	// verify IPv6 peer got its packet from the IPv6 socket
+	_ = ipv6Peer.SetReadDeadline(time.Now().Add(time.Second))
+	n, addr, err = ipv6Peer.ReadFrom(buf)
+	require.NoError(t, err)
+	assert.Equal(t, "to-ipv6", string(buf[:n]))
+	assert.Equal(t, ipv6Local.LocalAddr().(*net.UDPAddr).Port, addr.(*net.UDPAddr).Port)
+}
+
+// TestICEBind_HandlesConcurrentMixedTraffic sends packets concurrently to both IPv4
+// and IPv6 peers. Verifies no packets get misrouted (IPv4 peer only gets v4- packets,
+// IPv6 peer only gets v6- packets). Some packet loss is acceptable for UDP.
+func TestICEBind_HandlesConcurrentMixedTraffic(t *testing.T) {
+	ipv4Peer := listenUDP(t, "udp4", "127.0.0.1:0")
+	defer ipv4Peer.Close()
+
+	ipv6Peer, err := net.ListenUDP("udp6", &net.UDPAddr{IP: net.IPv6loopback, Port: 0})
+	if err != nil {
+		t.Skipf("IPv6 not available: %v", err)
+	}
+	defer ipv6Peer.Close()
+
+	ipv4Local := listenUDP(t, "udp4", "127.0.0.1:0")
+	defer ipv4Local.Close()
+
+	ipv6Local := listenUDP(t, "udp6", "[::1]:0")
+	defer ipv6Local.Close()
+
+	dualStack := NewDualStackPacketConn(ipv4Local, ipv6Local)
+
+	const packetsPerFamily = 500
+
+	ipv4Received := make(chan string, packetsPerFamily)
+	ipv6Received := make(chan string, packetsPerFamily)
+
+	startGate := make(chan struct{})
+	var wg sync.WaitGroup
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		buf := make([]byte, 100)
+		for i := 0; i < packetsPerFamily; i++ {
+			n, _, err := ipv4Peer.ReadFrom(buf)
+			if err != nil {
+				return
+			}
+			ipv4Received <- string(buf[:n])
+		}
+	}()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		buf := make([]byte, 100)
+		for i := 0; i < packetsPerFamily; i++ {
+			n, _, err := ipv6Peer.ReadFrom(buf)
+			if err != nil {
+				return
+			}
+			ipv6Received <- string(buf[:n])
+		}
+	}()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		<-startGate
+		for i := 0; i < packetsPerFamily; i++ {
+			_, _ = dualStack.WriteTo([]byte(fmt.Sprintf("v4-%04d", i)), ipv4Peer.LocalAddr())
+		}
+	}()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		<-startGate
+		for i := 0; i < packetsPerFamily; i++ {
+			_, _ = dualStack.WriteTo([]byte(fmt.Sprintf("v6-%04d", i)), ipv6Peer.LocalAddr())
+		}
+	}()
+
+	close(startGate)
+
+	time.AfterFunc(5*time.Second, func() {
+		_ = ipv4Peer.SetReadDeadline(time.Now())
+		_ = ipv6Peer.SetReadDeadline(time.Now())
+	})
+
+	wg.Wait()
+	close(ipv4Received)
+	close(ipv6Received)
+
+	ipv4Count := 0
+	for pkt := range ipv4Received {
+		require.True(t, len(pkt) >= 3 && pkt[:3] == "v4-", "IPv4 peer got misrouted packet: %s", pkt)
+		ipv4Count++
+	}
+
+	ipv6Count := 0
+	for pkt := range ipv6Received {
+		require.True(t, len(pkt) >= 3 && pkt[:3] == "v6-", "IPv6 peer got misrouted packet: %s", pkt)
+		ipv6Count++
+	}
+
+	assert.Equal(t, packetsPerFamily, ipv4Count)
+	assert.Equal(t, packetsPerFamily, ipv6Count)
+}
+
+func TestICEBind_DetectsAddressFamilyFromConnection(t *testing.T) {
+	tests := []struct {
+		name     string
+		network  string
+		addr     string
+		wantIPv4 bool
+	}{
+		{"IPv4 any", "udp4", "0.0.0.0:0", true},
+		{"IPv4 loopback", "udp4", "127.0.0.1:0", true},
+		{"IPv6 any", "udp6", "[::]:0", false},
+		{"IPv6 loopback", "udp6", "[::1]:0", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			addr, err := net.ResolveUDPAddr(tt.network, tt.addr)
+			require.NoError(t, err)
+
+			conn, err := net.ListenUDP(tt.network, addr)
+			if err != nil {
+				t.Skipf("%s not available: %v", tt.network, err)
+			}
+			defer conn.Close()
+
+			localAddr := conn.LocalAddr().(*net.UDPAddr)
+			isIPv4 := localAddr.IP.To4() != nil
+			assert.Equal(t, tt.wantIPv4, isIPv4)
+		})
+	}
+}
+
+// helpers
+
+func setupICEBind(t *testing.T) *ICEBind {
+	t.Helper()
+	transportNet, err := stdnet.NewNet()
+	require.NoError(t, err)
+
+	address := wgaddr.Address{
+		IP:      netip.MustParseAddr("100.64.0.1"),
+		Network: netip.MustParsePrefix("100.64.0.0/10"),
+	}
+	return NewICEBind(transportNet, nil, address, 1280)
+}
+
+func createDualStackConns(t *testing.T) (*net.UDPConn, *net.UDPConn) {
+	t.Helper()
+	ipv4Conn, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: 0})
+	require.NoError(t, err)
+
+	ipv6Conn, err := net.ListenUDP("udp6", &net.UDPAddr{IP: net.IPv6zero, Port: 0})
+	if err != nil {
+		ipv4Conn.Close()
+		t.Skipf("IPv6 not available: %v", err)
+	}
+	return ipv4Conn, ipv6Conn
+}
+
+func createMsgPool() *sync.Pool {
+	return &sync.Pool{
+		New: func() any {
+			msgs := make([]ipv6.Message, 1)
+			for i := range msgs {
+				msgs[i].Buffers = make(net.Buffers, 1)
+				msgs[i].OOB = make([]byte, 0, 40)
+			}
+			return &msgs
+		},
+	}
+}
+
+func listenUDP(t *testing.T, network, addr string) *net.UDPConn {
+	t.Helper()
+	udpAddr, err := net.ResolveUDPAddr(network, addr)
+	require.NoError(t, err)
+	conn, err := net.ListenUDP(network, udpAddr)
+	require.NoError(t, err)
+	return conn
+}

client/internal/peer/worker_ice.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net"
 	"net/netip"
+	"strconv"
 	"sync"
 	"time"
 
@@ -286,8 +287,8 @@ func (w *WorkerICE) connect(ctx context.Context, agent *icemaker.ThreadSafeAgent
 		RosenpassAddr:              remoteOfferAnswer.RosenpassAddr,
 		LocalIceCandidateType:      pair.Local.Type().String(),
 		RemoteIceCandidateType:     pair.Remote.Type().String(),
-		LocalIceCandidateEndpoint:  fmt.Sprintf("%s:%d", pair.Local.Address(), pair.Local.Port()),
-		RemoteIceCandidateEndpoint: fmt.Sprintf("%s:%d", pair.Remote.Address(), pair.Remote.Port()),
+		LocalIceCandidateEndpoint:  net.JoinHostPort(pair.Local.Address(), strconv.Itoa(pair.Local.Port())),
+		RemoteIceCandidateEndpoint: net.JoinHostPort(pair.Remote.Address(), strconv.Itoa(pair.Remote.Port())),
 		Relayed:                    isRelayed(pair),
 		RelayedOnLocal:             isRelayCandidate(pair.Local),
 	}
@@ -328,13 +329,7 @@ func (w *WorkerICE) closeAgent(agent *icemaker.ThreadSafeAgent, cancel context.C
 func (w *WorkerICE) punchRemoteWGPort(pair *ice.CandidatePair, remoteWgPort int) {
 	// wait local endpoint configuration
 	time.Sleep(time.Second)
-	addrString := pair.Remote.Address()
-	parsed, err := netip.ParseAddr(addrString)
-	if (err == nil) && (parsed.Is6()) {
-		addrString = fmt.Sprintf("[%s]", addrString)
-		//IPv6 Literals need to be wrapped in brackets for Resolve*Addr()
-	}
-	addr, err := net.ResolveUDPAddr("udp", fmt.Sprintf("%s:%d", addrString, remoteWgPort))
+	addr, err := net.ResolveUDPAddr("udp", net.JoinHostPort(pair.Remote.Address(), strconv.Itoa(remoteWgPort)))
 	if err != nil {
 		w.log.Warnf("got an error while resolving the udp address, err: %s", err)
 		return
@@ -386,12 +381,44 @@ func (w *WorkerICE) onICESelectedCandidatePair(agent *icemaker.ThreadSafeAgent,
 	}
 }
 
+func (w *WorkerICE) logSuccessfulPaths(agent *icemaker.ThreadSafeAgent) {
+	sessionID := w.SessionID()
+	stats := agent.GetCandidatePairsStats()
+	localCandidates, _ := agent.GetLocalCandidates()
+	remoteCandidates, _ := agent.GetRemoteCandidates()
+
+	localMap := make(map[string]ice.Candidate)
+	for _, c := range localCandidates {
+		localMap[c.ID()] = c
+	}
+	remoteMap := make(map[string]ice.Candidate)
+	for _, c := range remoteCandidates {
+		remoteMap[c.ID()] = c
+	}
+
+	for _, stat := range stats {
+		if stat.State == ice.CandidatePairStateSucceeded {
+			local, lok := localMap[stat.LocalCandidateID]
+			remote, rok := remoteMap[stat.RemoteCandidateID]
+			if !lok || !rok {
+				continue
+			}
+			w.log.Debugf("successful ICE path %s: [%s %s %s] <-> [%s %s %s] rtt=%.3fms",
+				sessionID,
+				local.NetworkType(), local.Type(), local.Address(),
+				remote.NetworkType(), remote.Type(), remote.Address(),
+				stat.CurrentRoundTripTime*1000)
+		}
+	}
+}
+
 func (w *WorkerICE) onConnectionStateChange(agent *icemaker.ThreadSafeAgent, dialerCancel context.CancelFunc) func(ice.ConnectionState) {
 	return func(state ice.ConnectionState) {
 		w.log.Debugf("ICE ConnectionState has changed to %s", state.String())
 		switch state {
 		case ice.ConnectionStateConnected:
 			w.lastKnownState = ice.ConnectionStateConnected
+			w.logSuccessfulPaths(agent)
 			return
 		case ice.ConnectionStateFailed, ice.ConnectionStateDisconnected, ice.ConnectionStateClosed:
 			// ice.ConnectionStateClosed happens when we recreate the agent. For the P2P to TURN switch important to

sharedsock/sock_linux.go

@@ -154,9 +154,20 @@ func (s *SharedSocket) updateRouter() {
 	}
 }
 
-// LocalAddr returns an IPv4 address using the supplied port
+// LocalAddr returns the local address, preferring IPv4 for backward compatibility.
 func (s *SharedSocket) LocalAddr() net.Addr {
-	// todo check impact on ipv6 discovery
+	if s.conn4 != nil {
+		return &net.UDPAddr{
+			IP:   net.IPv4zero,
+			Port: s.port,
+		}
+	}
+	if s.conn6 != nil {
+		return &net.UDPAddr{
+			IP:   net.IPv6zero,
+			Port: s.port,
+		}
+	}
 	return &net.UDPAddr{
 		IP:   net.IPv4zero,
 		Port: s.port,