Merge branch 'main' into fix/exit-node-v6-deselect-propagation

# Conflicts:
#	client/internal/routemanager/manager.go

client/cmd/kubernetes.go

@@ -0,0 +1,301 @@
+package cmd
+
+import (
+	"context"
+	"crypto/tls"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/url"
+	"os"
+	"path/filepath"
+	"slices"
+	"strings"
+
+	"github.com/goccy/go-yaml"
+	log "github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
+
+	"github.com/netbirdio/netbird/client/proto"
+)
+
+const (
+	KubernetesDNSSuffix = "netbird-kubeapi-proxy"
+)
+
+var kubernetesCmd = &cobra.Command{
+	Use:   "kubernetes",
+	Short: "Kubernetes cluster commands.",
+	Long:  "Kubernetes cluster commands.",
+}
+
+var kubernetesListCmd = &cobra.Command{
+	Use:   "list",
+	RunE:  kubernetesList,
+	Short: "List Kubernetes clusters.",
+	Long:  "List Kubernetes clusters by discovering NetBird peers running netbird-kubeapi-proxy.",
+}
+
+var kubernetesWriteKubeconfigCmd = &cobra.Command{
+	Use:   "write-kubeconfig",
+	RunE:  kubernetesWriteKubeconfig,
+	Args:  cobra.ExactArgs(1),
+	Short: "Write kubeconfig for a Kubernetes cluster.",
+	Long:  "Updates kubeconfig in place to allow token-less access to the Kubernetes cluster through NetBird.",
+}
+
+func init() {
+	kubernetesWriteKubeconfigCmd.Flags().String("kubeconfig", "", "path to kubeconfig file")
+}
+
+func kubernetesList(cmd *cobra.Command, _ []string) error {
+	conn, err := getClient(cmd)
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+	client := proto.NewDaemonServiceClient(conn)
+	statusResp, err := client.Status(cmd.Context(), &proto.StatusRequest{GetFullPeerStatus: true})
+	if err != nil {
+		return err
+	}
+
+	kcs, err := getKubernetesClusters(cmd.Context(), statusResp.FullStatus.Peers, "")
+	if err != nil {
+		return err
+	}
+	if len(kcs) == 0 {
+		cmd.Println("No Kubernetes clusters available.")
+		return nil
+	}
+	cmd.Println("Available Kubernetes clusters:")
+	for _, k := range kcs {
+		cmd.Printf("\n  - Name: %s\n    FQDN: %s\n    Version: %s\n", k.name, k.url.Host, k.version)
+	}
+	return nil
+}
+
+func kubernetesWriteKubeconfig(cmd *cobra.Command, args []string) error {
+	kubeconfigPath, err := resolveKubeconfigPath(cmd)
+	if err != nil {
+		return err
+	}
+
+	conn, err := getClient(cmd)
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+	client := proto.NewDaemonServiceClient(conn)
+	statusResp, err := client.Status(cmd.Context(), &proto.StatusRequest{GetFullPeerStatus: true})
+	if err != nil {
+		return err
+	}
+
+	clusterName := args[0]
+	kcs, err := getKubernetesClusters(cmd.Context(), statusResp.FullStatus.Peers, clusterName)
+	if err != nil {
+		return err
+	}
+	if len(kcs) == 0 {
+		return fmt.Errorf("kubernetes cluster named %s not found", clusterName)
+	}
+	if len(kcs) > 1 {
+		return fmt.Errorf("too many Kubernetes clusters returned")
+	}
+	err = writeKubeconfig(kubeconfigPath, kcs[0])
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+type kubernetesCluster struct {
+	name    string
+	url     *url.URL
+	version string
+}
+
+func getKubernetesClusters(ctx context.Context, peers []*proto.PeerState, nameFilter string) ([]kubernetesCluster, error) {
+	transport := http.DefaultTransport.(*http.Transport).Clone()
+	transport.TLSClientConfig = &tls.Config{
+		InsecureSkipVerify: true,
+	}
+	httpClient := &http.Client{
+		Transport: transport,
+	}
+	resolver := net.Resolver{
+		// Required so both DNS records are returned.
+		// https://github.com/golang/go/issues/17093
+		PreferGo: true,
+	}
+
+	kcs := []kubernetesCluster{}
+	attempted := map[string]struct{}{}
+	for _, peer := range peers {
+		fqdns, err := resolver.LookupAddr(ctx, peer.IP)
+		if err != nil {
+			return nil, err
+		}
+		for _, fqdn := range fqdns {
+			if _, ok := attempted[fqdn]; ok {
+				continue
+			}
+			attempted[fqdn] = struct{}{}
+			comps := strings.Split(fqdn, ".")
+			if len(comps) < 2 {
+				continue
+			}
+			if comps[1] != KubernetesDNSSuffix {
+				continue
+			}
+			if nameFilter != "" && nameFilter != comps[0] {
+				continue
+			}
+			clusterURL, clusterVersion, err := fingerprintClusters(ctx, httpClient, fqdn)
+			if err != nil {
+				log.Debugf("could not fingerprint Kubernetes cluster %s %q", fqdn, err)
+				continue
+			}
+			kc := kubernetesCluster{
+				name:    comps[0],
+				url:     clusterURL,
+				version: clusterVersion,
+			}
+			if nameFilter != "" {
+				return []kubernetesCluster{kc}, nil
+			}
+			kcs = append(kcs, kc)
+		}
+	}
+	return kcs, nil
+}
+
+func fingerprintClusters(ctx context.Context, httpClient *http.Client, fqdn string) (*url.URL, string, error) {
+	clusterURL, err := url.Parse("https://" + fqdn)
+	if err != nil {
+		return nil, "", err
+	}
+	versionURL, err := clusterURL.Parse("/version")
+	if err != nil {
+		return nil, "", err
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, versionURL.String(), nil)
+	if err != nil {
+		return nil, "", err
+	}
+	resp, err := httpClient.Do(req)
+	if err != nil {
+		return nil, "", err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return nil, "", fmt.Errorf("expected %d response but got %s", http.StatusOK, resp.Status)
+	}
+	b, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, "", err
+	}
+	versionData := map[string]string{}
+	err = json.Unmarshal(b, &versionData)
+	if err != nil {
+		return nil, "", err
+	}
+	version, ok := versionData["gitVersion"]
+	if !ok {
+		return nil, "", errors.New("no version found in response")
+	}
+	return clusterURL, version, nil
+}
+
+func resolveKubeconfigPath(cmd *cobra.Command) (string, error) {
+	if cmd.Flags().Changed("kubeconfig") {
+		path, err := cmd.Flags().GetString("kubeconfig")
+		if err != nil {
+			return "", err
+		}
+		return path, nil
+	}
+	if env := os.Getenv("KUBECONFIG"); env != "" {
+		return env, nil
+	}
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return "", fmt.Errorf("could not determine home directory: %w", err)
+	}
+	return filepath.Join(home, ".kube", "config"), nil
+}
+
+func writeKubeconfig(kubeconfigPath string, kc kubernetesCluster) error {
+	b, err := os.ReadFile(kubeconfigPath)
+	if err != nil && !errors.Is(err, os.ErrNotExist) {
+		return err
+	}
+	var cfg map[string]any
+	if err := yaml.Unmarshal(b, &cfg); err != nil {
+		return err
+	}
+	if cfg == nil {
+		cfg = map[string]any{
+			"apiVersion": "v1",
+			"kind":       "Config",
+		}
+	}
+
+	cfg["clusters"] = appendWithName(cfg["clusters"], map[string]any{
+		"name": kc.name,
+		"cluster": map[string]any{
+			"server":                   kc.url.String(),
+			"insecure-skip-tls-verify": true,
+		},
+	})
+	cfg["users"] = appendWithName(cfg["users"], map[string]any{
+		"name": "netbird",
+		"user": map[string]any{
+			"token": "none",
+		},
+	})
+	cfg["contexts"] = appendWithName(cfg["contexts"], map[string]any{
+		"name": kc.name,
+		"context": map[string]any{
+			"cluster":   kc.name,
+			"user":      "netbird",
+			"namespace": "default",
+		},
+	})
+	cfg["current-context"] = kc.name
+
+	out, err := yaml.Marshal(cfg)
+	if err != nil {
+		return err
+	}
+	if err := os.WriteFile(kubeconfigPath, out, 0o600); err != nil {
+		return err
+	}
+	return nil
+}
+
+func appendWithName(data any, add map[string]any) any {
+	if data == nil {
+		return []any{add}
+	}
+	v, ok := data.([]any)
+	if !ok {
+		return []any{add}
+	}
+	i := slices.IndexFunc(v, func(item any) bool {
+		m, ok := item.(map[string]any)
+		if !ok {
+			return false
+		}
+		return m["name"] == add["name"]
+	})
+	if i == -1 {
+		return append(v, add)
+	}
+	v[i] = add
+	return v
+}

client/cmd/kubernetes_test.go

@@ -0,0 +1,120 @@
+package cmd
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/spf13/cobra"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFingerprintClusters(t *testing.T) {
+	t.Parallel()
+
+	srv := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		//nolint: errcheck
+		w.Write([]byte(`{"gitVersion": "foobar"}`))
+	}))
+	defer srv.Close()
+
+	clusterURL, clusterVersion, err := fingerprintClusters(t.Context(), srv.Client(), srv.Listener.Addr().String())
+	require.NoError(t, err)
+	require.Equal(t, srv.URL, clusterURL.String())
+	require.Equal(t, "foobar", clusterVersion)
+}
+
+func TestResolveKubeconfigPath(t *testing.T) {
+	home, err := os.UserHomeDir()
+	if err != nil {
+		t.Fatalf("could not determine home directory: %v", err)
+	}
+	defaultPath := filepath.Join(home, ".kube", "config")
+	path, err := resolveKubeconfigPath(&cobra.Command{})
+	require.NoError(t, err)
+	require.Equal(t, defaultPath, path)
+
+	flagPath := "flag-path"
+	cmd := &cobra.Command{}
+	cmd.Flags().String("kubeconfig", "", "")
+	err = cmd.Flags().Set("kubeconfig", flagPath)
+	require.NoError(t, err)
+	path, err = resolveKubeconfigPath(cmd)
+	require.NoError(t, err)
+	require.Equal(t, flagPath, path)
+
+	envPath := "env-path"
+	t.Setenv("KUBECONFIG", envPath)
+	path, err = resolveKubeconfigPath(&cobra.Command{})
+	require.NoError(t, err)
+	require.Equal(t, envPath, path)
+}
+
+func TestWriteKubeconfig(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name     string
+		existing string
+	}{
+		{
+			name: "empty file",
+		},
+		{
+			name: "existing content",
+			existing: `apiVersion: v1
+clusters:
+- cluster:
+    insecure-skip-tls-verify: true
+    server: https://foobar.com
+  name: foo
+current-context: test
+kind: Config
+users: []
+`,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			kubeconfigPath := filepath.Join(t.TempDir(), "config")
+			err := os.WriteFile(kubeconfigPath, []byte(tt.existing), 0o644)
+			require.NoError(t, err)
+
+			kc := kubernetesCluster{
+				name: "foo",
+				url:  &url.URL{Scheme: "https", Host: "example.com"},
+			}
+			err = writeKubeconfig(kubeconfigPath, kc)
+			require.NoError(t, err)
+
+			b, err := os.ReadFile(kubeconfigPath)
+			require.NoError(t, err)
+			expected := `apiVersion: v1
+clusters:
+- cluster:
+    insecure-skip-tls-verify: true
+    server: https://example.com
+  name: foo
+contexts:
+- context:
+    cluster: foo
+    namespace: default
+    user: netbird
+  name: foo
+current-context: foo
+kind: Config
+users:
+- name: netbird
+  user:
+    token: none
+`
+			require.Equal(t, expected, string(b))
+		})
+	}
+
+}

client/cmd/root.go

@@ -169,6 +169,11 @@ func init() {
 	debugCmd.AddCommand(forCmd)
 	debugCmd.AddCommand(persistenceCmd)
 
+	// kubernetes commands
+	rootCmd.AddCommand(kubernetesCmd)
+	kubernetesCmd.AddCommand(kubernetesListCmd)
+	kubernetesCmd.AddCommand(kubernetesWriteKubeconfigCmd)
+
 	// profile commands
 	profileCmd.AddCommand(profileListCmd)
 	profileCmd.AddCommand(profileAddCmd)

client/embed/embed.go

@@ -279,6 +279,10 @@ func (c *Client) Start(startCtx context.Context) error {
 
 	select {
 	case <-startCtx.Done():
+		// Cancel the client context before stopping: Engine.Start blocks on the
+		// signal stream while holding the engine mutex and only unblocks on
+		// cancellation. Stopping first would deadlock on that mutex.
+		cancel()
 		if stopErr := client.Stop(); stopErr != nil {
 			return fmt.Errorf("stop error after context done. Stop error: %w. Context done: %w", stopErr, startCtx.Err())
 		}

client/embed/embed_test.go

@@ -0,0 +1,168 @@
+package embed
+
+import (
+	"context"
+	"net"
+	"testing"
+	"time"
+
+	"github.com/golang/mock/gomock"
+	"github.com/stretchr/testify/require"
+	"google.golang.org/grpc"
+
+	"github.com/netbirdio/netbird/management/internals/controllers/network_map/controller"
+	"github.com/netbirdio/netbird/management/internals/controllers/network_map/update_channel"
+	"github.com/netbirdio/netbird/management/internals/modules/peers"
+	"github.com/netbirdio/netbird/management/internals/modules/peers/ephemeral/manager"
+	"github.com/netbirdio/netbird/management/internals/server/config"
+	nbgrpc "github.com/netbirdio/netbird/management/internals/shared/grpc"
+	mgmt "github.com/netbirdio/netbird/management/server"
+	"github.com/netbirdio/netbird/management/server/activity"
+	nbcache "github.com/netbirdio/netbird/management/server/cache"
+	"github.com/netbirdio/netbird/management/server/groups"
+	"github.com/netbirdio/netbird/management/server/integrations/integrated_validator/validator"
+	"github.com/netbirdio/netbird/management/server/integrations/port_forwarding"
+	"github.com/netbirdio/netbird/management/server/job"
+	"github.com/netbirdio/netbird/management/server/permissions"
+	"github.com/netbirdio/netbird/management/server/settings"
+	"github.com/netbirdio/netbird/management/server/store"
+	"github.com/netbirdio/netbird/management/server/telemetry"
+	"github.com/netbirdio/netbird/management/server/types"
+	mgmtProto "github.com/netbirdio/netbird/shared/management/proto"
+	"github.com/netbirdio/netbird/util"
+)
+
+const testSetupKey = "A2C8E62B-38F5-4553-B31E-DD66C696CEBB"
+
+// TestClientStartTimeoutRollback reproduces a deadlock between Engine.Start and
+// Engine.Stop. The signal endpoint accepts gRPC connections but never serves the
+// SignalExchange service, so Engine.Start parks in WaitStreamConnected while
+// holding the engine mutex. When the Start context expires, the rollback path
+// calls ConnectClient.Stop, which must not block forever acquiring that mutex.
+func TestClientStartTimeoutRollback(t *testing.T) {
+	signalAddr := startBlackholeSignal(t)
+	mgmAddr := startManagement(t, signalAddr)
+
+	wgPort := 0
+	client, err := New(Options{
+		DeviceName:    "embed-rollback-test",
+		SetupKey:      testSetupKey,
+		ManagementURL: "http://" + mgmAddr,
+		WireguardPort: &wgPort,
+	})
+	require.NoError(t, err, "embed client creation must succeed")
+
+	startCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	startErr := make(chan error, 1)
+	go func() {
+		startErr <- client.Start(startCtx)
+	}()
+
+	select {
+	case err := <-startErr:
+		require.ErrorIs(t, err, context.DeadlineExceeded)
+	case <-time.After(60 * time.Second):
+		t.Fatal("client.Start did not return after its context expired: Engine.Stop deadlocked against Engine.Start waiting for the signal stream")
+	}
+}
+
+// startBlackholeSignal starts a gRPC server without the SignalExchange service
+// registered. Connections succeed, but the signal stream can never be
+// established, which keeps Engine.Start parked in WaitStreamConnected.
+func startBlackholeSignal(t *testing.T) string {
+	t.Helper()
+
+	lis, err := net.Listen("tcp", "localhost:0")
+	require.NoError(t, err)
+
+	s := grpc.NewServer()
+	go func() {
+		if err := s.Serve(lis); err != nil {
+			t.Error(err)
+		}
+	}()
+	t.Cleanup(s.Stop)
+
+	return lis.Addr().String()
+}
+
+func startManagement(t *testing.T, signalAddr string) string {
+	t.Helper()
+
+	cfg := &config.Config{
+		Stuns:      []*config.Host{},
+		TURNConfig: &config.TURNConfig{},
+		Relay: &config.Relay{
+			Addresses:      []string{"127.0.0.1:1234"},
+			CredentialsTTL: util.Duration{Duration: time.Hour},
+			Secret:         "222222222222222222",
+		},
+		Signal: &config.Host{
+			Proto: "http",
+			URI:   signalAddr,
+		},
+		Datadir:    t.TempDir(),
+		HttpConfig: nil,
+	}
+
+	lis, err := net.Listen("tcp", "localhost:0")
+	require.NoError(t, err)
+
+	s := grpc.NewServer()
+
+	testStore, cleanUp, err := store.NewTestStoreFromSQL(context.Background(), "../testdata/store.sql", cfg.Datadir)
+	require.NoError(t, err)
+	t.Cleanup(cleanUp)
+
+	eventStore := &activity.InMemoryEventStore{}
+
+	permissionsManager := permissions.NewManager(testStore)
+	peersManager := peers.NewManager(testStore, permissionsManager)
+	jobManager := job.NewJobManager(nil, testStore, peersManager)
+
+	cacheStore, err := nbcache.NewStore(context.Background(), 100*time.Millisecond, 300*time.Millisecond, 100)
+	require.NoError(t, err)
+
+	iv, err := validator.NewIntegratedValidator(context.Background(), peersManager, nil, eventStore, cacheStore)
+	require.NoError(t, err)
+	metrics, err := telemetry.NewDefaultAppMetrics(context.Background())
+	require.NoError(t, err)
+
+	ctrl := gomock.NewController(t)
+	t.Cleanup(ctrl.Finish)
+	settingsMockManager := settings.NewMockManager(ctrl)
+	settingsMockManager.EXPECT().
+		GetSettings(gomock.Any(), gomock.Any(), gomock.Any()).
+		Return(&types.Settings{}, nil).
+		AnyTimes()
+	settingsMockManager.EXPECT().
+		GetExtraSettings(gomock.Any(), gomock.Any()).
+		Return(&types.ExtraSettings{}, nil).
+		AnyTimes()
+
+	groupsManager := groups.NewManagerMock()
+
+	updateManager := update_channel.NewPeersUpdateManager(metrics)
+	requestBuffer := mgmt.NewAccountRequestBuffer(context.Background(), testStore)
+	networkMapController := controller.NewController(context.Background(), testStore, metrics, updateManager, requestBuffer, mgmt.MockIntegratedValidator{}, settingsMockManager, "netbird.selfhosted", port_forwarding.NewControllerMock(), manager.NewEphemeralManager(testStore, peersManager), cfg)
+	accountManager, err := mgmt.BuildManager(context.Background(), cfg, testStore, networkMapController, jobManager, nil, "", eventStore, nil, false, iv, metrics, port_forwarding.NewControllerMock(), settingsMockManager, permissionsManager, false, cacheStore)
+	require.NoError(t, err)
+
+	secretsManager, err := nbgrpc.NewTimeBasedAuthSecretsManager(updateManager, cfg.TURNConfig, cfg.Relay, settingsMockManager, groupsManager)
+	require.NoError(t, err)
+
+	mgmtServer, err := nbgrpc.NewServer(cfg, accountManager, settingsMockManager, jobManager, secretsManager, nil, nil, &mgmt.MockIntegratedValidator{}, networkMapController, nil, nil)
+	require.NoError(t, err)
+	mgmtProto.RegisterManagementServiceServer(s, mgmtServer)
+
+	go func() {
+		if err := s.Serve(lis); err != nil {
+			t.Error(err)
+		}
+	}()
+	t.Cleanup(s.Stop)
+
+	return lis.Addr().String()
+}

client/firewall/iptables/acl_linux.go

@@ -3,6 +3,7 @@ package iptables
 import (
 	"errors"
 	"fmt"
+	"maps"
 	"net"
 	"slices"
 
@@ -421,12 +422,17 @@ func (m *aclManager) updateState() {
 	currentState.Lock()
 	defer currentState.Unlock()
 
+	// Clone the maps so the persisted state holds a private snapshot. The
+	// live maps keep being mutated by subsequent rule operations while the
+	// state manager marshals the state from its periodic-save goroutine.
+	// Sharing them by reference races the two and aborts the process with a
+	// concurrent map iteration and write.
 	if m.v6 {
-		currentState.ACLEntries6 = m.entries
-		currentState.ACLIPsetStore6 = m.ipsetStore
+		currentState.ACLEntries6 = maps.Clone(m.entries)
+		currentState.ACLIPsetStore6 = m.ipsetStore.clone()
 	} else {
-		currentState.ACLEntries = m.entries
-		currentState.ACLIPsetStore = m.ipsetStore
+		currentState.ACLEntries = maps.Clone(m.entries)
+		currentState.ACLIPsetStore = m.ipsetStore.clone()
 	}
 
 	if err := m.stateManager.UpdateState(currentState); err != nil {

client/firewall/iptables/router_linux.go

@@ -4,6 +4,7 @@ package iptables
 
 import (
 	"fmt"
+	"maps"
 	"net/netip"
 	"strconv"
 	"strings"
@@ -749,11 +750,17 @@ func (r *router) updateState() {
 	currentState.Lock()
 	defer currentState.Unlock()
 
+	// Clone the rule map so the persisted state holds a private snapshot. The
+	// live map keeps being mutated by subsequent rule operations while the
+	// state manager marshals the state from its periodic-save goroutine.
+	// Sharing it by reference races the two and aborts the process with a
+	// concurrent map iteration and write. The ipset counter guards itself
+	// during marshaling, so it can be shared directly.
 	if r.v6 {
-		currentState.RouteRules6 = r.rules
+		currentState.RouteRules6 = maps.Clone(r.rules)
 		currentState.RouteIPsetCounter6 = r.ipsetCounter
 	} else {
-		currentState.RouteRules = r.rules
+		currentState.RouteRules = maps.Clone(r.rules)
 		currentState.RouteIPsetCounter = r.ipsetCounter
 	}
 

client/firewall/iptables/rulestore_linux.go

@@ -1,6 +1,9 @@
 package iptables
 
-import "encoding/json"
+import (
+	"encoding/json"
+	"maps"
+)
 
 type ipList struct {
 	ips map[string]struct{}
@@ -19,6 +22,14 @@ func (s *ipList) addIP(ip string) {
 	s.ips[ip] = struct{}{}
 }
 
+// clone returns a deep copy of the ipList with its own ips map.
+func (s *ipList) clone() *ipList {
+	if s == nil {
+		return nil
+	}
+	return &ipList{ips: maps.Clone(s.ips)}
+}
+
 // MarshalJSON implements json.Marshaler
 func (s *ipList) MarshalJSON() ([]byte, error) {
 	return json.Marshal(struct {
@@ -55,6 +66,19 @@ func newIpsetStore() *ipsetStore {
 	}
 }
 
+// clone returns a deep copy of the ipsetStore with its own ipsets map and
+// independent ipList entries.
+func (s *ipsetStore) clone() *ipsetStore {
+	if s == nil {
+		return nil
+	}
+	cloned := &ipsetStore{ipsets: make(map[string]*ipList, len(s.ipsets))}
+	for name, list := range s.ipsets {
+		cloned.ipsets[name] = list.clone()
+	}
+	return cloned
+}
+
 func (s *ipsetStore) ipset(ipsetName string) (*ipList, bool) {
 	r, ok := s.ipsets[ipsetName]
 	return r, ok

client/internal/dns/server.go

@@ -777,13 +777,24 @@ func (s *DefaultServer) applyHostConfig() {
 // context is released rather than leaked until GC.
 func (s *DefaultServer) registerFallback() {
 	originalNameservers := s.hostManager.getOriginalNameservers()
-	if len(originalNameservers) == 0 {
+
+	serverIP := s.service.RuntimeIP()
+	var servers []netip.AddrPort
+	for _, ns := range originalNameservers {
+		if ns == serverIP {
+			log.Debugf("skipping original nameserver %s as it is the same as the server IP %s", ns, serverIP)
+			continue
+		}
+		servers = append(servers, netip.AddrPortFrom(ns, DefaultPort))
+	}
+
+	if len(servers) == 0 {
 		log.Debugf("no fallback upstreams to register; clearing PriorityFallback handler")
 		s.clearFallback()
 		return
 	}
 
-	log.Infof("registering original nameservers %v as upstream handlers with priority %d", originalNameservers, PriorityFallback)
+	log.Infof("registering original nameservers %v as upstream handlers with priority %d", servers, PriorityFallback)
 
 	handler, err := newUpstreamResolver(
 		s.ctx,
@@ -797,11 +808,6 @@ func (s *DefaultServer) registerFallback() {
 		return
 	}
 	handler.selectedRoutes = s.selectedRoutes
-
-	var servers []netip.AddrPort
-	for _, ns := range originalNameservers {
-		servers = append(servers, netip.AddrPortFrom(ns, DefaultPort))
-	}
 	handler.addRace(servers)
 
 	prev := s.fallbackHandler

client/internal/engine.go

@@ -880,62 +880,25 @@ func (e *Engine) handleSync(update *mgmProto.SyncResponse) error {
 		e.handleAutoUpdateVersion(update.NetworkMap.PeerConfig.AutoUpdate)
 	}
 
-	if update.GetNetbirdConfig() != nil {
-		wCfg := update.GetNetbirdConfig()
-		err := e.updateTURNs(wCfg.GetTurns())
-		if err != nil {
-			return fmt.Errorf("update TURNs: %w", err)
-		}
+	if err := e.updateNetbirdConfig(update.GetNetbirdConfig()); err != nil {
+		return err
+	}
 
-		err = e.updateSTUNs(wCfg.GetStuns())
-		if err != nil {
-			return fmt.Errorf("update STUNs: %w", err)
-		}
-
-		var stunTurn []*stun.URI
-		stunTurn = append(stunTurn, e.STUNs...)
-		stunTurn = append(stunTurn, e.TURNs...)
-		e.stunTurn.Store(stunTurn)
-
-		err = e.handleRelayUpdate(wCfg.GetRelay())
-		if err != nil {
-			return err
-		}
-
-		err = e.handleFlowUpdate(wCfg.GetFlow())
-		if err != nil {
-			return fmt.Errorf("handle the flow configuration: %w", err)
-		}
-
-		if err := e.PopulateNetbirdConfig(wCfg, nil); err != nil {
-			log.Warnf("Failed to update DNS server config: %v", err)
-		}
-
-		// todo update signal
+	// Posture checks are bound to the network map presence:
+	//   NetworkMap != nil, checks present -> apply the received checks
+	//   NetworkMap != nil, checks nil     -> posture checks were removed, clear them
+	//   NetworkMap == nil                 -> config-only update (e.g. relay token rotation),
+	//                                        leave the previously applied checks untouched
+	nm := update.GetNetworkMap()
+	if nm == nil {
+		return nil
 	}
 
 	if err := e.updateChecksIfNew(update.Checks); err != nil {
 		return err
 	}
 
-	nm := update.GetNetworkMap()
-	if nm == nil {
-		return nil
-	}
-
-	// Persist sync response under the dedicated lock (syncRespMux), not under syncMsgMux.
-	// A non-nil syncStore is what marks persistence as enabled. Hold the lock for
-	// the whole Set so the store cannot be cleared (disabled / engine close)
-	// mid-call and have this write resurrect a file that was just removed.
-	e.syncRespMux.RLock()
-	if e.syncStore != nil {
-		if err := e.syncStore.Set(update); err != nil {
-			log.Errorf("failed to persist sync response: %v", err)
-		} else {
-			log.Debugf("sync response persisted with serial %d", nm.GetSerial())
-		}
-	}
-	e.syncRespMux.RUnlock()
+	e.persistSyncResponse(update)
 
 	// only apply new changes and ignore old ones
 	if err := e.updateNetworkMap(nm); err != nil {
@@ -947,6 +910,64 @@ func (e *Engine) handleSync(update *mgmProto.SyncResponse) error {
 	return nil
 }
 
+// updateNetbirdConfig applies the management-provided NetBird configuration:
+// STUN/TURN and relay servers, flow logging and DNS settings. A nil config is a no-op,
+// which is the case for sync updates carrying only a network map.
+func (e *Engine) updateNetbirdConfig(wCfg *mgmProto.NetbirdConfig) error {
+	if wCfg == nil {
+		return nil
+	}
+
+	if err := e.updateTURNs(wCfg.GetTurns()); err != nil {
+		return fmt.Errorf("update TURNs: %w", err)
+	}
+
+	if err := e.updateSTUNs(wCfg.GetStuns()); err != nil {
+		return fmt.Errorf("update STUNs: %w", err)
+	}
+
+	var stunTurn []*stun.URI
+	stunTurn = append(stunTurn, e.STUNs...)
+	stunTurn = append(stunTurn, e.TURNs...)
+	e.stunTurn.Store(stunTurn)
+
+	if err := e.handleRelayUpdate(wCfg.GetRelay()); err != nil {
+		return err
+	}
+
+	if err := e.handleFlowUpdate(wCfg.GetFlow()); err != nil {
+		return fmt.Errorf("handle the flow configuration: %w", err)
+	}
+
+	if err := e.PopulateNetbirdConfig(wCfg, nil); err != nil {
+		log.Warnf("Failed to update DNS server config: %v", err)
+	}
+
+	// todo update signal
+
+	return nil
+}
+
+// persistSyncResponse stores the full sync response so it can be restored on the next
+// startup. Persistence is enabled only when syncStore is set. The dedicated syncRespMux
+// (not syncMsgMux) is held for the whole Set so the store cannot be cleared (disabled /
+// engine close) mid-call and have this write resurrect a file that was just removed.
+func (e *Engine) persistSyncResponse(update *mgmProto.SyncResponse) {
+	e.syncRespMux.RLock()
+	defer e.syncRespMux.RUnlock()
+
+	if e.syncStore == nil {
+		return
+	}
+
+	if err := e.syncStore.Set(update); err != nil {
+		log.Errorf("failed to persist sync response: %v", err)
+		return
+	}
+
+	log.Debugf("sync response persisted with serial %d", update.GetNetworkMap().GetSerial())
+}
+
 func (e *Engine) handleRelayUpdate(update *mgmProto.RelayConfig) error {
 	if update != nil {
 		// when we receive token we expect valid address list too

client/internal/routemanager/manager.go

@@ -9,6 +9,7 @@ import (
 	"net/url"
 	"runtime"
 	"slices"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -700,6 +701,15 @@ func resolveURLsToIPs(urls []string) []net.IP {
 
 // updateRouteSelectorFromManagement updates the route selector based on the isSelected status from the management server
 func (m *DefaultManager) updateRouteSelectorFromManagement(clientRoutes route.HAMap) {
+	m.mirrorV6ExitPairSelections(clientRoutes)
+
+	// An explicit user "deselect all" must not be overridden by management auto-apply.
+	// Auto-applying an exit node here would call SelectRoutes, which clears the
+	// deselect-all flag and re-enables every route the user turned off.
+	if m.routeSelector.IsDeselectAll() {
+		return
+	}
+
 	exitNodeInfo := m.collectExitNodeInfo(clientRoutes)
 	if len(exitNodeInfo.allIDs) == 0 {
 		return
@@ -709,6 +719,24 @@ func (m *DefaultManager) updateRouteSelectorFromManagement(clientRoutes route.HA
 	m.logExitNodeUpdate(exitNodeInfo)
 }
 
+// mirrorV6ExitPairSelections keeps every synthesized "-v6" exit route's selection
+// consistent with its v4 base. The v4/v6 exit pair is a single toggle, so the v6
+// entry always follows the base: deselecting the v4 exit node also drops its ::/0
+// pair, and any stale (orphaned) explicit selection on the v6 entry is reset. This
+// runs before selection is read so both collectExitNodeInfo and FilterSelectedExitNodes
+// see consistent state, including pairs loaded from persisted selector state.
+func (m *DefaultManager) mirrorV6ExitPairSelections(clientRoutes route.HAMap) {
+	routesByNetID := make(map[route.NetID][]*route.Route, len(clientRoutes))
+	for haID, routes := range clientRoutes {
+		routesByNetID[haID.NetID()] = routes
+	}
+
+	for v6ID := range route.V6ExitMergeSet(routesByNetID) {
+		baseID := route.NetID(strings.TrimSuffix(string(v6ID), route.V6ExitSuffix))
+		m.routeSelector.SyncPairedSelection(baseID, v6ID)
+	}
+}
+
 type exitNodeInfo struct {
 	allIDs               []route.NetID
 	selectedByManagement []route.NetID

client/internal/routemanager/manager_v6exit_test.go

@@ -0,0 +1,47 @@
+package routemanager
+
+import (
+	"net/netip"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/netbirdio/netbird/client/internal/routeselector"
+	"github.com/netbirdio/netbird/route"
+)
+
+// TestUpdateRouteSelectorFromManagement_MirrorsV6ExitPair reproduces the bug seen
+// in netbird-engine.log: persisted selector state has the v4 exit node deselected
+// but its synthesized "-v6" pair explicitly selected (orphaned), so the ::/0 route
+// leaked onto the tunnel. The management update must mirror the v4 deselect onto the
+// v6 pair so FilterSelectedExitNodes drops it.
+func TestUpdateRouteSelectorFromManagement_MirrorsV6ExitPair(t *testing.T) {
+	const (
+		v4ID = route.NetID("Exit Node (raspberrypi)")
+		v6ID = route.NetID("Exit Node (raspberrypi)-v6")
+	)
+	all := []route.NetID{v4ID, v6ID}
+
+	rs := routeselector.NewRouteSelector()
+	// Orphan the v6 selection: select the pair, then deselect only the v4 base.
+	require.NoError(t, rs.SelectRoutes([]route.NetID{v4ID, v6ID}, true, all))
+	require.NoError(t, rs.DeselectRoutes([]route.NetID{v4ID}, all))
+	require.True(t, rs.IsSelected(v6ID), "precondition: orphaned v6 selection survives v4 deselect")
+
+	m := &DefaultManager{routeSelector: rs}
+
+	v4Route := &route.Route{NetID: v4ID, Network: netip.MustParsePrefix("0.0.0.0/0")}
+	v6Route := &route.Route{NetID: v6ID, Network: netip.MustParsePrefix("::/0")}
+	clientRoutes := route.HAMap{
+		"Exit Node (raspberrypi)|0.0.0.0/0": {v4Route},
+		"Exit Node (raspberrypi)-v6|::/0":   {v6Route},
+	}
+
+	m.updateRouteSelectorFromManagement(clientRoutes)
+
+	assert.False(t, rs.IsSelected(v6ID), "v6 pair must follow the v4 base deselect after the management update")
+
+	filtered := rs.FilterSelectedExitNodes(clientRoutes)
+	assert.Empty(t, filtered, "deselected v4 exit node must not leak its ::/0 pair onto the tunnel")
+}

client/internal/routemanager/selector_management_test.go

@@ -0,0 +1,71 @@
+package routemanager
+
+import (
+	"net/netip"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/netbirdio/netbird/client/internal/routeselector"
+	"github.com/netbirdio/netbird/route"
+)
+
+func exitNodeRoutes(netID route.NetID, skipAutoApply bool) route.HAMap {
+	haID := route.HAUniqueID(string(netID) + "|0.0.0.0/0")
+	return route.HAMap{
+		haID: []*route.Route{
+			{
+				ID:            "r-" + route.ID(netID),
+				NetID:         netID,
+				Network:       netip.MustParsePrefix("0.0.0.0/0"),
+				NetworkType:   route.IPv4Network,
+				Enabled:       true,
+				SkipAutoApply: skipAutoApply,
+			},
+		},
+	}
+}
+
+func TestUpdateRouteSelectorFromManagement(t *testing.T) {
+	t.Run("management auto-apply selects exit node without user selection", func(t *testing.T) {
+		m := &DefaultManager{routeSelector: routeselector.NewRouteSelector()}
+		routes := exitNodeRoutes("exit1", false)
+
+		m.updateRouteSelectorFromManagement(routes)
+
+		require.True(t, m.routeSelector.IsSelected("exit1"), "auto-apply exit node should be selected")
+		require.Len(t, m.routeSelector.FilterSelectedExitNodes(routes), 1, "selected exit node should pass the filter")
+	})
+
+	t.Run("management SkipAutoApply leaves exit node deselected", func(t *testing.T) {
+		m := &DefaultManager{routeSelector: routeselector.NewRouteSelector()}
+		routes := exitNodeRoutes("exit1", true)
+
+		m.updateRouteSelectorFromManagement(routes)
+
+		require.False(t, m.routeSelector.IsSelected("exit1"), "SkipAutoApply exit node should not be selected")
+		require.Empty(t, m.routeSelector.FilterSelectedExitNodes(routes), "deselected exit node should be filtered out")
+	})
+
+	t.Run("user selection is not overridden by management", func(t *testing.T) {
+		m := &DefaultManager{routeSelector: routeselector.NewRouteSelector()}
+		require.NoError(t, m.routeSelector.SelectRoutes([]route.NetID{"exit1"}, true, []route.NetID{"exit1"}))
+		routes := exitNodeRoutes("exit1", true)
+
+		m.updateRouteSelectorFromManagement(routes)
+
+		require.True(t, m.routeSelector.IsSelected("exit1"), "explicit user selection must survive a management sync that wants to skip auto-apply")
+		require.Len(t, m.routeSelector.FilterSelectedExitNodes(routes), 1, "user-selected exit node should pass the filter")
+	})
+
+	t.Run("deselect-all is preserved across a management sync", func(t *testing.T) {
+		m := &DefaultManager{routeSelector: routeselector.NewRouteSelector()}
+		m.routeSelector.DeselectAllRoutes()
+		routes := exitNodeRoutes("exit1", false)
+
+		m.updateRouteSelectorFromManagement(routes)
+
+		require.True(t, m.routeSelector.IsDeselectAll(), "an explicit deselect-all must not be cleared by management auto-apply")
+		require.Empty(t, m.routeSelector.FilterSelectedExitNodes(routes), "no routes should be selected while deselect-all is set")
+	})
+}

client/internal/routeselector/routeselector.go

@@ -4,7 +4,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"slices"
-	"strings"
 	"sync"
 
 	"github.com/hashicorp/go-multierror"
@@ -116,6 +115,14 @@ func (rs *RouteSelector) DeselectAllRoutes() {
 	clear(rs.selectedRoutes)
 }
 
+// IsDeselectAll reports whether the user has explicitly deselected all routes.
+func (rs *RouteSelector) IsDeselectAll() bool {
+	rs.mu.RLock()
+	defer rs.mu.RUnlock()
+
+	return rs.deselectAll
+}
+
 // IsSelected checks if a specific route is selected.
 func (rs *RouteSelector) IsSelected(routeID route.NetID) bool {
 	rs.mu.RLock()
@@ -124,6 +131,33 @@ func (rs *RouteSelector) IsSelected(routeID route.NetID) bool {
 	return rs.isSelectedLocked(routeID)
 }
 
+// SyncPairedSelection forces pairedID's explicit selection state to match baseID's,
+// so a synthesized "-v6" exit route always follows its v4 base: selecting or
+// deselecting the v4 exit node governs the ::/0 pair, and any stale (orphaned)
+// explicit state on the v6 entry is reset. The v4/v6 exit pair is treated as a single
+// toggle, so the v6 entry carries no independent selection of its own.
+func (rs *RouteSelector) SyncPairedSelection(baseID, pairedID route.NetID) {
+	rs.mu.Lock()
+	defer rs.mu.Unlock()
+
+	if rs.deselectAll {
+		return
+	}
+
+	_, baseSelected := rs.selectedRoutes[baseID]
+	_, baseDeselected := rs.deselectedRoutes[baseID]
+
+	delete(rs.selectedRoutes, pairedID)
+	delete(rs.deselectedRoutes, pairedID)
+
+	switch {
+	case baseSelected:
+		rs.selectedRoutes[pairedID] = struct{}{}
+	case baseDeselected:
+		rs.deselectedRoutes[pairedID] = struct{}{}
+	}
+}
+
 // FilterSelected removes unselected routes from the provided map.
 func (rs *RouteSelector) FilterSelected(routes route.HAMap) route.HAMap {
 	rs.mu.RLock()
@@ -143,14 +177,13 @@ func (rs *RouteSelector) FilterSelected(routes route.HAMap) route.HAMap {
 }
 
 // HasUserSelectionForRoute returns true if the user has explicitly selected or deselected this route.
-// Intended for exit-node code paths: a v6 exit-node pair (e.g. "MyExit-v6") with no explicit state of
-// its own inherits its v4 base's state, so legacy persisted selections that predate v6 pairing
-// transparently apply to the synthesized v6 entry.
+// The lookup is literal; v4/v6 exit pairs are kept consistent at write time via SyncPairedSelection,
+// so a synthesized "-v6" entry carries the same explicit state as its v4 base.
 func (rs *RouteSelector) HasUserSelectionForRoute(routeID route.NetID) bool {
 	rs.mu.RLock()
 	defer rs.mu.RUnlock()
 
-	return rs.hasUserSelectionForRouteLocked(rs.effectiveNetID(routeID))
+	return rs.hasUserSelectionForRouteLocked(routeID)
 }
 
 func (rs *RouteSelector) FilterSelectedExitNodes(routes route.HAMap) route.HAMap {
@@ -179,83 +212,6 @@ func (rs *RouteSelector) FilterSelectedExitNodes(routes route.HAMap) route.HAMap
 	return filtered
 }
 
-// effectiveNetID returns the v4 base for a "-v6" exit pair entry that has no explicit
-// state of its own, so selections made on the v4 entry govern the v6 entry automatically.
-// Only call this from exit-node-specific code paths: applying it to a non-exit "-v6" route
-// would make it inherit unrelated v4 state. Must be called with rs.mu held.
-func (rs *RouteSelector) effectiveNetID(id route.NetID) route.NetID {
-	name := string(id)
-	if !strings.HasSuffix(name, route.V6ExitSuffix) {
-		return id
-	}
-	if _, ok := rs.selectedRoutes[id]; ok {
-		return id
-	}
-	if _, ok := rs.deselectedRoutes[id]; ok {
-		return id
-	}
-	return route.NetID(strings.TrimSuffix(name, route.V6ExitSuffix))
-}
-
-func (rs *RouteSelector) isSelectedLocked(routeID route.NetID) bool {
-	if rs.deselectAll {
-		return false
-	}
-	_, deselected := rs.deselectedRoutes[routeID]
-	return !deselected
-}
-
-func (rs *RouteSelector) isDeselectedLocked(netID route.NetID) bool {
-	if rs.deselectAll {
-		return true
-	}
-	_, deselected := rs.deselectedRoutes[netID]
-	return deselected
-}
-
-func (rs *RouteSelector) hasUserSelectionForRouteLocked(routeID route.NetID) bool {
-	_, selected := rs.selectedRoutes[routeID]
-	_, deselected := rs.deselectedRoutes[routeID]
-	return selected || deselected
-}
-
-func isExitNode(rt []*route.Route) bool {
-	return len(rt) > 0 && (route.IsV4DefaultRoute(rt[0].Network) || route.IsV6DefaultRoute(rt[0].Network))
-}
-
-func (rs *RouteSelector) applyExitNodeFilter(
-	id route.HAUniqueID,
-	netID route.NetID,
-	rt []*route.Route,
-	out route.HAMap,
-) {
-	// Exit-node path: apply the v4/v6 pair mirror so a deselect on the v4 base also
-	// drops the synthesized v6 entry that lacks its own explicit state.
-	effective := rs.effectiveNetID(netID)
-	if rs.hasUserSelectionForRouteLocked(effective) {
-		if rs.isSelectedLocked(effective) {
-			out[id] = rt
-		}
-		return
-	}
-
-	// no explicit selection for this route: defer to management's SkipAutoApply flag
-	sel := collectSelected(rt)
-	if len(sel) > 0 {
-		out[id] = sel
-	}
-}
-
-func collectSelected(rt []*route.Route) []*route.Route {
-	var sel []*route.Route
-	for _, r := range rt {
-		if !r.SkipAutoApply {
-			sel = append(sel, r)
-		}
-	}
-	return sel
-}
-
 // MarshalJSON implements the json.Marshaler interface
 func (rs *RouteSelector) MarshalJSON() ([]byte, error) {
 	rs.mu.RLock()
@@ -309,3 +265,59 @@ func (rs *RouteSelector) UnmarshalJSON(data []byte) error {
 
 	return nil
 }
+
+func (rs *RouteSelector) isSelectedLocked(routeID route.NetID) bool {
+	if rs.deselectAll {
+		return false
+	}
+	_, deselected := rs.deselectedRoutes[routeID]
+	return !deselected
+}
+
+func (rs *RouteSelector) isDeselectedLocked(netID route.NetID) bool {
+	if rs.deselectAll {
+		return true
+	}
+	_, deselected := rs.deselectedRoutes[netID]
+	return deselected
+}
+
+func (rs *RouteSelector) hasUserSelectionForRouteLocked(routeID route.NetID) bool {
+	_, selected := rs.selectedRoutes[routeID]
+	_, deselected := rs.deselectedRoutes[routeID]
+	return selected || deselected
+}
+
+func (rs *RouteSelector) applyExitNodeFilter(
+	id route.HAUniqueID,
+	netID route.NetID,
+	rt []*route.Route,
+	out route.HAMap,
+) {
+	if rs.hasUserSelectionForRouteLocked(netID) {
+		if rs.isSelectedLocked(netID) {
+			out[id] = rt
+		}
+		return
+	}
+
+	// no explicit selection for this route: defer to management's SkipAutoApply flag
+	sel := collectSelected(rt)
+	if len(sel) > 0 {
+		out[id] = sel
+	}
+}
+
+func isExitNode(rt []*route.Route) bool {
+	return len(rt) > 0 && (route.IsV4DefaultRoute(rt[0].Network) || route.IsV6DefaultRoute(rt[0].Network))
+}
+
+func collectSelected(rt []*route.Route) []*route.Route {
+	var sel []*route.Route
+	for _, r := range rt {
+		if !r.SkipAutoApply {
+			sel = append(sel, r)
+		}
+	}
+	return sel
+}

client/internal/routeselector/routeselector_test.go

@@ -330,39 +330,73 @@ func TestRouteSelector_FilterSelectedExitNodes(t *testing.T) {
 	assert.Len(t, filtered, 0) // No routes should be selected
 }
 
-// TestRouteSelector_V6ExitPairInherits covers the v4/v6 exit-node pair selection
-// mirror. The mirror is scoped to exit-node code paths: HasUserSelectionForRoute
-// and FilterSelectedExitNodes resolve a "-v6" entry without explicit state to its
-// v4 base, so legacy persisted selections that predate v6 pairing transparently
-// apply to the synthesized v6 entry. General lookups (IsSelected, FilterSelected)
-// stay literal so unrelated routes named "*-v6" don't inherit unrelated state.
-func TestRouteSelector_V6ExitPairInherits(t *testing.T) {
+// TestRouteSelector_V6ExitPairSync covers SyncPairedSelection, which keeps a v4
+// exit node and its synthesized "-v6" counterpart consistent. The selector itself
+// is literal and never infers a v6 entry's state from its v4 base; callers that know
+// the pairing (exit-node code paths) call SyncPairedSelection to force the v6 entry
+// to follow the base, treating the pair as a single toggle.
+func TestRouteSelector_V6ExitPairSync(t *testing.T) {
 	all := []route.NetID{"exit1", "exit1-v6", "exit2", "exit2-v6", "corp", "corp-v6"}
 
-	t.Run("HasUserSelectionForRoute mirrors deselected v4 base", func(t *testing.T) {
+	t.Run("selector lookups stay literal without sync", func(t *testing.T) {
 		rs := routeselector.NewRouteSelector()
 		require.NoError(t, rs.DeselectRoutes([]route.NetID{"exit1"}, all))
 
-		assert.True(t, rs.HasUserSelectionForRoute("exit1-v6"), "v6 pair sees v4 base's user selection")
+		// The selector does not pair-resolve: the v6 entry is independent until synced.
+		assert.False(t, rs.HasUserSelectionForRoute("exit1-v6"), "v6 entry has no state of its own")
+		assert.True(t, rs.IsSelected("exit1-v6"), "unsynced v6 entry stays selected by default")
 
-		// unrelated v6 with no v4 base touched is unaffected
-		assert.False(t, rs.HasUserSelectionForRoute("exit2-v6"))
+		// A route literally named "exit1-something" must never pair-resolve either.
+		assert.False(t, rs.HasUserSelectionForRoute("exit1-something"))
 	})
 
-	t.Run("IsSelected stays literal for non-exit lookups", func(t *testing.T) {
-		rs := routeselector.NewRouteSelector()
-		require.NoError(t, rs.DeselectRoutes([]route.NetID{"corp"}, all))
-
-		// A non-exit route literally named "corp-v6" must not inherit "corp"'s state
-		// via the mirror; the mirror only applies in exit-node code paths.
-		assert.False(t, rs.IsSelected("corp"))
-		assert.True(t, rs.IsSelected("corp-v6"), "non-exit *-v6 routes must not inherit unrelated v4 state")
-	})
-
-	t.Run("explicit v6 state overrides v4 base in filter", func(t *testing.T) {
+	t.Run("sync mirrors deselected v4 base onto v6", func(t *testing.T) {
 		rs := routeselector.NewRouteSelector()
 		require.NoError(t, rs.DeselectRoutes([]route.NetID{"exit1"}, all))
+
+		rs.SyncPairedSelection("exit1", "exit1-v6")
+
+		assert.False(t, rs.IsSelected("exit1"))
+		assert.False(t, rs.IsSelected("exit1-v6"), "v6 pair follows v4 base deselect")
+		assert.True(t, rs.HasUserSelectionForRoute("exit1-v6"), "v6 carries explicit deselect after sync")
+	})
+
+	t.Run("sync mirrors selected v4 base onto v6", func(t *testing.T) {
+		rs := routeselector.NewRouteSelector()
+		require.NoError(t, rs.SelectRoutes([]route.NetID{"exit1"}, false, all))
+
+		rs.SyncPairedSelection("exit1", "exit1-v6")
+
+		assert.True(t, rs.IsSelected("exit1"))
+		assert.True(t, rs.IsSelected("exit1-v6"), "v6 pair follows v4 base select")
+	})
+
+	t.Run("sync clears v6 state when base has no explicit selection", func(t *testing.T) {
+		rs := routeselector.NewRouteSelector()
 		require.NoError(t, rs.SelectRoutes([]route.NetID{"exit1-v6"}, true, all))
+		require.True(t, rs.HasUserSelectionForRoute("exit1-v6"))
+
+		rs.SyncPairedSelection("exit1", "exit1-v6")
+
+		assert.False(t, rs.HasUserSelectionForRoute("exit1-v6"),
+			"v6 explicit state is cleared so it follows management like its base")
+	})
+
+	// Regression for the observed bug (see netbird-engine.log): persisted state has
+	// the v4 base deselected but the v6 sibling explicitly selected (orphaned). The
+	// sync must reset the orphan so the ::/0 route does not leak onto the tunnel.
+	t.Run("sync clears orphaned explicit v6 selection on deselected base", func(t *testing.T) {
+		rs := routeselector.NewRouteSelector()
+
+		// Prior state: both explicitly selected, then only the v4 base deselected,
+		// leaving the v6 entry as a stale explicit selection.
+		require.NoError(t, rs.SelectRoutes([]route.NetID{"exit1", "exit1-v6"}, true, all))
+		require.NoError(t, rs.DeselectRoutes([]route.NetID{"exit1"}, all))
+		require.True(t, rs.IsSelected("exit1-v6"), "precondition: orphaned v6 selection")
+
+		rs.SyncPairedSelection("exit1", "exit1-v6")
+
+		assert.False(t, rs.IsSelected("exit1-v6"), "orphaned v6 selection reset to follow v4 deselect")
 
 		v4Route := &route.Route{NetID: "exit1", Network: netip.MustParsePrefix("0.0.0.0/0")}
 		v6Route := &route.Route{NetID: "exit1-v6", Network: netip.MustParsePrefix("::/0")}
@@ -370,23 +404,14 @@ func TestRouteSelector_V6ExitPairInherits(t *testing.T) {
 			"exit1|0.0.0.0/0": {v4Route},
 			"exit1-v6|::/0":   {v6Route},
 		}
-
 		filtered := rs.FilterSelectedExitNodes(routes)
-		assert.NotContains(t, filtered, route.HAUniqueID("exit1|0.0.0.0/0"))
-		assert.Contains(t, filtered, route.HAUniqueID("exit1-v6|::/0"), "explicit v6 select wins over v4 base")
+		assert.Empty(t, filtered, "deselecting v4 base must drop the v6 pair even if it was explicitly selected before")
 	})
 
-	t.Run("non-v6-suffix routes unaffected", func(t *testing.T) {
-		rs := routeselector.NewRouteSelector()
-		require.NoError(t, rs.DeselectRoutes([]route.NetID{"exit1"}, all))
-
-		// A route literally named "exit1-something" must not pair-resolve.
-		assert.False(t, rs.HasUserSelectionForRoute("exit1-something"))
-	})
-
-	t.Run("filter v6 paired with deselected v4 base", func(t *testing.T) {
+	t.Run("filter drops synced v6 pair of deselected v4 base", func(t *testing.T) {
 		rs := routeselector.NewRouteSelector()
 		require.NoError(t, rs.DeselectRoutes([]route.NetID{"exit1"}, all))
+		rs.SyncPairedSelection("exit1", "exit1-v6")
 
 		v4Route := &route.Route{NetID: "exit1", Network: netip.MustParsePrefix("0.0.0.0/0")}
 		v6Route := &route.Route{NetID: "exit1-v6", Network: netip.MustParsePrefix("::/0")}
@@ -399,6 +424,15 @@ func TestRouteSelector_V6ExitPairInherits(t *testing.T) {
 		assert.Empty(t, filtered, "deselecting v4 base must also drop the v6 pair")
 	})
 
+	t.Run("deselectAll makes sync a no-op", func(t *testing.T) {
+		rs := routeselector.NewRouteSelector()
+		rs.DeselectAllRoutes()
+
+		rs.SyncPairedSelection("exit1", "exit1-v6")
+
+		assert.False(t, rs.HasUserSelectionForRoute("exit1-v6"), "sync must not write explicit state under deselectAll")
+	})
+
 	t.Run("non-exit *-v6 routes pass through FilterSelectedExitNodes", func(t *testing.T) {
 		rs := routeselector.NewRouteSelector()
 		require.NoError(t, rs.DeselectRoutes([]route.NetID{"corp"}, all))

client/ios/NetBirdSDK/client.go

@@ -54,6 +54,7 @@ type selectRoute struct {
 	Network       netip.Prefix
 	Domains       domain.List
 	Selected      bool
+	Status        string
 	extraNetworks []netip.Prefix
 }
 
@@ -377,9 +378,57 @@ func (c *Client) GetRoutesSelectionDetails() (*RoutesSelectionDetails, error) {
 	routes := buildSelectRoutes(routesMap, routeSelector.IsSelected, v6ExitMerged)
 	resolvedDomains := c.recorder.GetResolvedDomainsStates()
 
+	// Compute each route's connection status in the core (mirroring the Android
+	// bridge), so the UI doesn't have to infer it by string-matching the joined
+	// Network value against peer routes. For a merged exit node the status reflects
+	// whichever of the v4/v6 prefixes is served by a connected peer; for dynamic
+	// (DNS) routes the peer route key is the domain pattern (see dynamic.Route.String).
+	connectedRoutes := c.connectedRouteSet()
+	for _, r := range routes {
+		r.Status = routeStatus(r, connectedRoutes)
+	}
+
 	return prepareRouteSelectionDetails(routes, resolvedDomains), nil
 }
 
+// connectedRouteSet returns the set of route keys (as strings) currently served by a
+// connected peer, gathered across all connected peers' route tables. The keys match
+// what the route manager records: a prefix string for static routes (e.g. "0.0.0.0/0")
+// and the domain pattern for dynamic routes (e.g. "*.example.com").
+func (c *Client) connectedRouteSet() map[string]struct{} {
+	connected := map[string]struct{}{}
+	for _, p := range c.recorder.GetFullStatus().Peers {
+		if p.ConnStatus != peer.StatusConnected {
+			continue
+		}
+		for r := range p.GetRoutes() {
+			connected[r] = struct{}{}
+		}
+	}
+	return connected
+}
+
+// routeStatus reports "Connected" if any of the route's keys is served by a connected
+// peer: the primary Network prefix, an extra v6 network of a merged exit node, or the
+// domain pattern for a dynamic DNS route. Otherwise "Idle".
+func routeStatus(r *selectRoute, connectedRoutes map[string]struct{}) string {
+	keys := make([]string, 0, 1+len(r.extraNetworks))
+	if len(r.Domains) > 0 {
+		keys = append(keys, r.Domains.SafeString())
+	} else {
+		keys = append(keys, r.Network.String())
+	}
+	for _, extra := range r.extraNetworks {
+		keys = append(keys, extra.String())
+	}
+	for _, k := range keys {
+		if _, ok := connectedRoutes[k]; ok {
+			return peer.StatusConnected.String()
+		}
+	}
+	return peer.StatusIdle.String()
+}
+
 func buildSelectRoutes(routesMap map[route.NetID][]*route.Route, isSelected func(route.NetID) bool, v6Merged map[route.NetID]struct{}) []*selectRoute {
 	var routes []*selectRoute
 	for id, rt := range routesMap {
@@ -462,6 +511,7 @@ func prepareRouteSelectionDetails(routes []*selectRoute, resolvedDomains map[dom
 			Network:  netStr,
 			Domains:  &domainDetails,
 			Selected: r.Selected,
+			Status:   r.Status,
 		})
 	}
 

client/ios/NetBirdSDK/routes.go

@@ -20,6 +20,7 @@ type RoutesSelectionInfo struct {
 	Network  string
 	Domains  *DomainDetails
 	Selected bool
+	Status   string
 }
 
 type DomainCollection interface {

formatter/hook/hook.go

@@ -99,6 +99,9 @@ func addFields(entry *logrus.Entry) {
 	if ctxAccountID, ok := entry.Context.Value(context.AccountIDKey).(string); ok {
 		entry.Data[context.AccountIDKey] = ctxAccountID
 	}
+	if ctxUserAgent, ok := entry.Context.Value(context.UserAgentKey).(string); ok {
+		entry.Data[context.UserAgentKey] = ctxUserAgent
+	}
 	if ctxInitiatorID, ok := entry.Context.Value(context.UserIDKey).(string); ok {
 		entry.Data[context.UserIDKey] = ctxInitiatorID
 	}

go.mod

@@ -2,6 +2,8 @@ module github.com/netbirdio/netbird
 
 go 1.25.5
 
+toolchain go1.25.11
+
 require (
 	cunicu.li/go-rosenpass v0.5.42
 	github.com/cenkalti/backoff/v4 v4.3.0
@@ -54,6 +56,7 @@ require (
 	github.com/fsnotify/fsnotify v1.9.0
 	github.com/gliderlabs/ssh v0.3.8
 	github.com/go-jose/go-jose/v4 v4.1.4
+	github.com/goccy/go-yaml v1.18.0
 	github.com/godbus/dbus/v5 v5.1.0
 	github.com/golang-jwt/jwt/v5 v5.3.1
 	github.com/golang/mock v1.6.0
@@ -211,10 +214,9 @@ require (
 	github.com/go-viper/mapstructure/v2 v2.5.0 // indirect
 	github.com/go-webauthn/webauthn v0.16.4 // indirect
 	github.com/go-webauthn/x v0.2.3 // indirect
-	github.com/goccy/go-yaml v1.18.0 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/golang-jwt/jwt/v4 v4.5.2 // indirect
-	github.com/google/btree v1.1.2 // indirect
+	github.com/google/btree v1.1.3 // indirect
 	github.com/google/go-querystring v1.1.0 // indirect
 	github.com/google/go-tpm v0.9.8 // indirect
 	github.com/google/s2a-go v0.1.9 // indirect

go.sum

@@ -275,8 +275,8 @@ github.com/golang/protobuf v1.5.2/go.mod h1:XVQd3VNwM+JqD3oG2Ue2ip4fOMUkwXdXDdiu
 github.com/golang/protobuf v1.5.3/go.mod h1:XVQd3VNwM+JqD3oG2Ue2ip4fOMUkwXdXDdiuN0vRsmY=
 github.com/golang/protobuf v1.5.4 h1:i7eJL8qZTpSEXOPTxNKhASYpMn+8e5Q6AdndVa1dWek=
 github.com/golang/protobuf v1.5.4/go.mod h1:lnTiLA8Wa4RWRcIUkrtSVa5nRhsEGBg48fD6rSs7xps=
-github.com/google/btree v1.1.2 h1:xf4v41cLI2Z6FxbKm+8Bu+m8ifhj15JuZ9sa0jZCMUU=
-github.com/google/btree v1.1.2/go.mod h1:qOPhT0dTNdNzV6Z/lhRX0YXUafgPLFUh+gZMl761Gm4=
+github.com/google/btree v1.1.3 h1:CVpQJjYgC4VbzxeGVHfvZrv1ctoYCAI8vbl07Fcxlyg=
+github.com/google/btree v1.1.3/go.mod h1:qOPhT0dTNdNzV6Z/lhRX0YXUafgPLFUh+gZMl761Gm4=
 github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/google/go-cmp v0.3.1/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/google/go-cmp v0.4.0/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=

management/internals/modules/reverseproxy/service/manager/l4_port_test.go

@@ -488,6 +488,195 @@ func TestUpdate_AllowsPortChange(t *testing.T) {
 	assert.Equal(t, uint16(54321), updated.ListenPort, "explicit port change should be applied")
 }
 
+func TestUpdate_PreservesPortWhenCustomPortsNotSupported(t *testing.T) {
+	mgr, testStore, _ := setupL4Test(t, boolPtr(false))
+	ctx := context.Background()
+
+	existing := seedService(t, testStore, "tcp-svc", "tcp", testCluster, testCluster, 12345)
+
+	updated := &rpservice.Service{
+		ID:           existing.ID,
+		AccountID:    testAccountID,
+		Name:         "tcp-svc-renamed",
+		Mode:         "tcp",
+		Domain:       testCluster,
+		ProxyCluster: testCluster,
+		ListenPort:   0,
+		Enabled:      true,
+		Targets: []*rpservice.Target{
+			{AccountID: testAccountID, TargetId: testPeerID, TargetType: rpservice.TargetTypePeer, Protocol: "tcp", Port: 9090, Enabled: true},
+		},
+	}
+
+	_, err := mgr.persistServiceUpdate(ctx, testAccountID, updated)
+	require.NoError(t, err, "update must not be rejected by the custom-port capability check")
+	assert.Equal(t, uint16(12345), updated.ListenPort, "existing listen port should be preserved on unsupported cluster")
+}
+
+func TestUpdate_PreservesPortWhenCustomPortsUnknown(t *testing.T) {
+	mgr, testStore, _ := setupL4Test(t, nil)
+	ctx := context.Background()
+
+	existing := seedService(t, testStore, "tcp-svc", "tcp", testCluster, testCluster, 12345)
+
+	updated := &rpservice.Service{
+		ID:           existing.ID,
+		AccountID:    testAccountID,
+		Name:         "tcp-svc-renamed",
+		Mode:         "tcp",
+		Domain:       testCluster,
+		ProxyCluster: testCluster,
+		ListenPort:   0,
+		Enabled:      true,
+		Targets: []*rpservice.Target{
+			{AccountID: testAccountID, TargetId: testPeerID, TargetType: rpservice.TargetTypePeer, Protocol: "tcp", Port: 9090, Enabled: true},
+		},
+	}
+
+	_, err := mgr.persistServiceUpdate(ctx, testAccountID, updated)
+	require.NoError(t, err, "update must not be rejected when cluster capability is unknown")
+	assert.Equal(t, uint16(12345), updated.ListenPort, "existing listen port should be preserved when capability is unknown")
+}
+
+func TestUpdate_RejectsPortChangeWhenCustomPortsNotSupported(t *testing.T) {
+	mgr, testStore, _ := setupL4Test(t, boolPtr(false))
+	ctx := context.Background()
+
+	existing := seedService(t, testStore, "tcp-svc", "tcp", testCluster, testCluster, 12345)
+
+	updated := &rpservice.Service{
+		ID:           existing.ID,
+		AccountID:    testAccountID,
+		Name:         "tcp-svc",
+		Mode:         "tcp",
+		Domain:       testCluster,
+		ProxyCluster: testCluster,
+		ListenPort:   54321,
+		Enabled:      true,
+		Targets: []*rpservice.Target{
+			{AccountID: testAccountID, TargetId: testPeerID, TargetType: rpservice.TargetTypePeer, Protocol: "tcp", Port: 9090, Enabled: true},
+		},
+	}
+
+	_, err := mgr.persistServiceUpdate(ctx, testAccountID, updated)
+	require.Error(t, err, "explicit port change on update must be rejected on unsupported clusters")
+	assert.Contains(t, err.Error(), "custom ports not supported on target cluster")
+}
+
+func TestUpdate_TLSPortChangeAllowedWhenNotSupported(t *testing.T) {
+	mgr, testStore, _ := setupL4Test(t, boolPtr(false))
+	ctx := context.Background()
+
+	existing := seedService(t, testStore, "tls-svc", "tls", "app.example.com", testCluster, 443)
+
+	updated := &rpservice.Service{
+		ID:           existing.ID,
+		AccountID:    testAccountID,
+		Name:         "tls-svc",
+		Mode:         "tls",
+		Domain:       "app.example.com",
+		ProxyCluster: testCluster,
+		ListenPort:   9999,
+		Enabled:      true,
+		Targets: []*rpservice.Target{
+			{AccountID: testAccountID, TargetId: testPeerID, TargetType: rpservice.TargetTypePeer, Protocol: "tcp", Port: 8443, Enabled: true},
+		},
+	}
+
+	_, err := mgr.persistServiceUpdate(ctx, testAccountID, updated)
+	require.NoError(t, err, "TLS port change uses SNI routing and is exempt from the custom-port check")
+	assert.Equal(t, uint16(9999), updated.ListenPort, "TLS port change should be applied")
+}
+
+func TestValidateL4PortDiffOnClusterDiff(t *testing.T) {
+	tests := []struct {
+		name        string
+		mode        string
+		customPorts *bool
+		newPort     uint16
+		oldPort     uint16
+		wantErr     bool
+	}{
+		{"tcp port change unsupported", "tcp", boolPtr(false), 54321, 12345, true},
+		{"tcp port change unknown capability", "tcp", nil, 54321, 12345, true},
+		{"udp port change unsupported", "udp", boolPtr(false), 54321, 12345, true},
+		{"tcp first port assignment unsupported", "tcp", boolPtr(false), 54321, 0, true},
+		{"tcp port change supported", "tcp", boolPtr(true), 54321, 12345, false},
+		{"tcp port unchanged unsupported", "tcp", boolPtr(false), 12345, 12345, false},
+		{"tcp zero port unsupported", "tcp", boolPtr(false), 0, 12345, false},
+		{"tls port change unsupported", "tls", boolPtr(false), 9999, 443, false},
+		{"http mode ignored", "http", boolPtr(false), 54321, 12345, false},
+		{"empty mode ignored", "", boolPtr(false), 54321, 12345, false},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			newSvc := &rpservice.Service{Mode: tc.mode, ListenPort: tc.newPort, ProxyCluster: testCluster}
+			oldSvc := &rpservice.Service{Mode: tc.mode, ListenPort: tc.oldPort, ProxyCluster: testCluster}
+
+			err := validateL4PortDiffOnClusterDiff(tc.customPorts, newSvc, oldSvc)
+			if tc.wantErr {
+				assert.Error(t, err, "port diff should be rejected for %s", tc.name)
+			} else {
+				assert.NoError(t, err, "port diff should be allowed for %s", tc.name)
+			}
+		})
+	}
+}
+
+func TestUpdate_PortConflictRejected(t *testing.T) {
+	mgr, testStore, _ := setupL4Test(t, boolPtr(true))
+	ctx := context.Background()
+
+	seedService(t, testStore, "tcp-a", "tcp", "tcp-a."+testCluster, testCluster, 5432)
+	svcB := seedService(t, testStore, "tcp-b", "tcp", "tcp-b."+testCluster, testCluster, 6543)
+
+	updated := &rpservice.Service{
+		ID:           svcB.ID,
+		AccountID:    testAccountID,
+		Name:         "tcp-b",
+		Mode:         "tcp",
+		Domain:       "tcp-b." + testCluster,
+		ProxyCluster: testCluster,
+		ListenPort:   5432,
+		Enabled:      true,
+		Targets: []*rpservice.Target{
+			{AccountID: testAccountID, TargetId: testPeerID, TargetType: rpservice.TargetTypePeer, Protocol: "tcp", Port: 9090, Enabled: true},
+		},
+	}
+
+	_, err := mgr.persistServiceUpdate(ctx, testAccountID, updated)
+	require.Error(t, err, "updating to a port held by another service should be rejected")
+	assert.Contains(t, err.Error(), "already in use")
+}
+
+func TestUpdate_AutoAssignsWhenNoPort(t *testing.T) {
+	mgr, testStore, _ := setupL4Test(t, boolPtr(false))
+	ctx := context.Background()
+
+	existing := seedService(t, testStore, "tcp-svc", "tcp", testCluster, testCluster, 0)
+
+	updated := &rpservice.Service{
+		ID:           existing.ID,
+		AccountID:    testAccountID,
+		Name:         "tcp-svc",
+		Mode:         "tcp",
+		Domain:       testCluster,
+		ProxyCluster: testCluster,
+		ListenPort:   0,
+		Enabled:      true,
+		Targets: []*rpservice.Target{
+			{AccountID: testAccountID, TargetId: testPeerID, TargetType: rpservice.TargetTypePeer, Protocol: "tcp", Port: 9090, Enabled: true},
+		},
+	}
+
+	_, err := mgr.persistServiceUpdate(ctx, testAccountID, updated)
+	require.NoError(t, err)
+	assert.True(t, updated.ListenPort >= autoAssignPortMin && updated.ListenPort <= autoAssignPortMax,
+		"auto-assigned port %d should be in range [%d, %d]", updated.ListenPort, autoAssignPortMin, autoAssignPortMax)
+	assert.True(t, updated.PortAutoAssigned, "PortAutoAssigned should be set when update triggers auto-assignment")
+}
+
 func TestCreateServiceFromPeer_TCP(t *testing.T) {
 	mgr, _, _ := setupL4Test(t, boolPtr(false))
 	ctx := context.Background()

management/internals/modules/reverseproxy/service/manager/manager.go

@@ -338,7 +338,7 @@ func (m *Manager) persistNewService(ctx context.Context, accountID string, svc *
 			}
 		}
 
-		if err := m.ensureL4Port(ctx, transaction, svc, customPorts); err != nil {
+		if err := m.ensureL4Port(ctx, transaction, svc, customPorts, false); err != nil {
 			return err
 		}
 
@@ -367,11 +367,11 @@ func (m *Manager) clusterCustomPorts(ctx context.Context, svc *service.Service)
 
 // ensureL4Port auto-assigns a listen port when needed and validates cluster support.
 // customPorts must be pre-computed via clusterCustomPorts before entering a transaction.
-func (m *Manager) ensureL4Port(ctx context.Context, tx store.Store, svc *service.Service, customPorts *bool) error {
+func (m *Manager) ensureL4Port(ctx context.Context, tx store.Store, svc *service.Service, customPorts *bool, serviceUpdate bool) error {
 	if !service.IsL4Protocol(svc.Mode) {
 		return nil
 	}
-	if service.IsPortBasedProtocol(svc.Mode) && svc.ListenPort > 0 && (customPorts == nil || !*customPorts) {
+	if service.IsPortBasedProtocol(svc.Mode) && svc.ListenPort > 0 && !serviceUpdate && (customPorts == nil || !*customPorts) {
 		if svc.Source != service.SourceEphemeral {
 			return status.Errorf(status.InvalidArgument, "custom ports not supported on cluster %s", svc.ProxyCluster)
 		}
@@ -465,7 +465,7 @@ func (m *Manager) persistNewEphemeralService(ctx context.Context, accountID, pee
 			return err
 		}
 
-		if err := m.ensureL4Port(ctx, transaction, svc, customPorts); err != nil {
+		if err := m.ensureL4Port(ctx, transaction, svc, customPorts, false); err != nil {
 			return err
 		}
 
@@ -651,12 +651,22 @@ func (m *Manager) executeServiceUpdate(ctx context.Context, transaction store.St
 	m.preserveListenPort(service, existingService)
 	updateInfo.serviceEnabledChanged = existingService.Enabled != service.Enabled
 
-	if err := m.ensureL4Port(ctx, transaction, service, customPorts); err != nil {
+	// if the service is being updated, and we decide in the future to allow mode update,
+	// we should reconsider the currently assigned port if not 0 for clusters that don't support custom ports
+	if err := validateL4PortDiffOnClusterDiff(customPorts, service, existingService); err != nil {
 		return err
 	}
+
+	if err := m.ensureL4Port(ctx, transaction, service, customPorts, true); err != nil {
+		return err
+	}
+
+	// we can try carrying the previous service port into a new cluster, if this becomes a problem for multiple users,
+	// we should reconsider adding another check
 	if err := m.checkPortConflict(ctx, transaction, service); err != nil {
 		return err
 	}
+
 	if err := transaction.UpdateService(ctx, service); err != nil {
 		return fmt.Errorf("update service: %w", err)
 	}
@@ -664,6 +674,21 @@ func (m *Manager) executeServiceUpdate(ctx context.Context, transaction store.St
 	return nil
 }
 
+// validateL4PortDiffOnClusterDiff checks if custom L4 ports are configured and validates port changes across clusters.
+// It ensures no port changes if custom ports are unsupported for a given cluster and protocol mode.
+// Returns an error if validation fails, otherwise returns nil.
+func validateL4PortDiffOnClusterDiff(customPorts *bool, newSVC, oldSVC *service.Service) error {
+	if !service.IsPortBasedProtocol(newSVC.Mode) || (customPorts != nil && *customPorts) {
+		return nil
+	}
+
+	if newSVC.ListenPort != 0 && newSVC.ListenPort != oldSVC.ListenPort {
+		return status.Errorf(status.InvalidArgument, "custom ports not supported on target cluster %s", newSVC.ProxyCluster)
+	}
+
+	return nil
+}
+
 // handleDomainChange validates the new domain is free inside the transaction
 // and applies the pre-resolved cluster (computed outside the tx by
 // resolveEffectiveCluster). It must NOT call clusterDeriver here: that talks

management/internals/shared/grpc/conversion.go

@@ -8,6 +8,8 @@ import (
 	"strings"
 	"time"
 
+	"github.com/hashicorp/go-version"
+	nbversion "github.com/netbirdio/netbird/version"
 	log "github.com/sirupsen/logrus"
 	goproto "google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/types/known/timestamppb"
@@ -28,6 +30,23 @@ import (
 	"github.com/netbirdio/netbird/shared/sshauth"
 )
 
+const (
+	// deprecatedRemotePeersVersion is the version of Netbird that introduced the NetworkMap.RemotePeers field, deprecated in favor of RemotePeers.
+	deprecatedRemotePeersVersion = "0.29.3"
+)
+
+// precomputedDeprecatedRemotePeersConstraint is the parsed ">= 0.29.3" constraint,
+// built once at init since the bound is a compile-time constant.
+var precomputedDeprecatedRemotePeersConstraint version.Constraints
+
+func init() {
+	constraint, err := version.NewConstraint(">= " + deprecatedRemotePeersVersion)
+	if err != nil {
+		panic("parse deprecated remote peers version constraint: " + err.Error())
+	}
+	precomputedDeprecatedRemotePeersConstraint = constraint
+}
+
 func toNetbirdConfig(config *nbconfig.Config, turnCredentials *Token, relayToken *Token, extraSettings *types.ExtraSettings) *proto.NetbirdConfig {
 	if config == nil {
 		return nil
@@ -155,7 +174,11 @@ func ToSyncResponse(ctx context.Context, config *nbconfig.Config, httpConfig *nb
 
 	remotePeers := make([]*proto.RemotePeerConfig, 0, len(networkMap.Peers)+len(networkMap.OfflinePeers))
 	remotePeers = appendRemotePeerConfig(remotePeers, networkMap.Peers, dnsName, includeIPv6)
-	response.RemotePeers = remotePeers
+
+	if !shouldSkipSendingDeprecatedRemotePeers(peer.Meta.WtVersion) {
+		response.RemotePeers = remotePeers
+	}
+
 	response.NetworkMap.RemotePeers = remotePeers
 	response.RemotePeersIsEmpty = len(remotePeers) == 0
 	response.NetworkMap.RemotePeersIsEmpty = response.RemotePeersIsEmpty
@@ -246,6 +269,19 @@ func buildAuthorizedUsersProto(ctx context.Context, authorizedUsers map[string]m
 	return hashedUsers, machineUsers
 }
 
+func shouldSkipSendingDeprecatedRemotePeers(peerVersion string) bool {
+	if nbversion.IsDevelopmentVersion(peerVersion) {
+		return true
+	}
+
+	peerNBVersion, err := version.NewVersion(peerVersion)
+	if err != nil {
+		return false
+	}
+
+	return precomputedDeprecatedRemotePeersConstraint.Check(peerNBVersion)
+}
+
 func appendRemotePeerConfig(dst []*proto.RemotePeerConfig, peers []*nbpeer.Peer, dnsName string, includeIPv6 bool) []*proto.RemotePeerConfig {
 	for _, rPeer := range peers {
 		allowedIPs := []string{rPeer.IP.String() + "/32"}
@@ -363,7 +399,6 @@ func toProtocolFirewallRules(rules []*types.FirewallRule, includeIPv6, useSource
 	return result
 }
 
-
 // populateSourcePrefixes sets SourcePrefixes on fwRule and returns any
 // additional rules needed (e.g. a v6 wildcard clone when the peer IP is unspecified).
 func populateSourcePrefixes(fwRule *proto.FirewallRule, rule *types.FirewallRule, includeIPv6 bool) []*proto.FirewallRule {

management/internals/shared/grpc/conversion_test.go

@@ -202,6 +202,42 @@ func TestBuildJWTConfig_Audiences(t *testing.T) {
 	}
 }
 
+// TestShouldSkipSendingDeprecatedRemotePeers covers the version gate that
+// stops populating the deprecated top-level SyncResponse.RemotePeers field for
+// peers new enough to read RemotePeers off the NetworkMap. Development builds
+// are treated as latest and skip the field. The gate otherwise fails safe: a
+// release version older than the boundary, or one that can't be parsed (empty,
+// garbage, prereleases of the boundary) still receives the deprecated field so
+// older/unknown clients keep working.
+func TestShouldSkipSendingDeprecatedRemotePeers(t *testing.T) {
+	tests := []struct {
+		name        string
+		peerVersion string
+		wantSkip    bool
+	}{
+		{"exact boundary skips", "0.29.3", true},
+		{"newer patch skips", "0.29.4", true},
+		{"newer minor skips", "0.30.0", true},
+		{"newer major skips", "1.0.0", true},
+		{"v-prefixed newer skips", "v0.30.0", true},
+		{"development build skips", "development", true},
+		{"development build with commit skips", "development-abc123def456-dirty", true},
+		{"older patch keeps field", "0.29.2", false},
+		{"older minor keeps field", "0.28.0", false},
+		{"prerelease of boundary keeps field", "0.29.3-SNAPSHOT", false},
+		{"tagged dev prerelease keeps field", "v0.31.1-dev", false},
+		{"empty version keeps field", "", false},
+		{"garbage version keeps field", "not-a-version", false},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got := shouldSkipSendingDeprecatedRemotePeers(tc.peerVersion)
+			assert.Equal(t, tc.wantSkip, got, "skip decision for peer version %q", tc.peerVersion)
+		})
+	}
+}
+
 // TestEncodeSessionExpiresAt pins the wire encoding the client's
 // applySessionDeadline depends on:
 //

management/internals/shared/grpc/proxy.go

@@ -666,8 +666,10 @@ func (s *ProxyServiceServer) sender(conn *proxyConnection, errChan chan<- error)
 		case resp := <-conn.sendChan:
 			if err := conn.sendResponse(resp); err != nil {
 				errChan <- err
+				log.WithContext(conn.ctx).Tracef("Failed to send response to proxy %s: %v", conn.proxyID, err)
 				return
 			}
+			log.WithContext(conn.ctx).Tracef("Send response to proxy %s", conn.proxyID)
 		case <-conn.ctx.Done():
 			return
 		}

management/server/context/keys.go

@@ -12,6 +12,7 @@ const (
 	RoleKey      = nbcontext.RoleKey
 	UserIDKey    = nbcontext.UserIDKey
 	PeerIDKey    = nbcontext.PeerIDKey
+	UserAgentKey = nbcontext.UserAgentKey
 )
 
 // RoleFromContext returns the role stored in ctx, or empty string and false if absent.

management/server/telemetry/http_api_metrics.go

@@ -21,6 +21,8 @@ const (
 	httpRequestCounterPrefix  = "management.http.request.counter"
 	httpResponseCounterPrefix = "management.http.response.counter"
 	httpRequestDurationPrefix = "management.http.request.duration.ms"
+
+	RequestIDHeader = "X-Request-Id"
 )
 
 // WrappedResponseWriter is a wrapper for http.ResponseWriter that allows the
@@ -172,6 +174,10 @@ func (m *HTTPMiddleware) Handler(h http.Handler) http.Handler {
 		reqID := xid.New().String()
 		//nolint
 		ctx = context.WithValue(ctx, nbContext.RequestIDKey, reqID)
+		//nolint
+		ctx = context.WithValue(ctx, nbContext.UserAgentKey, r.UserAgent())
+
+		rw.Header().Set(RequestIDHeader, reqID)
 
 		log.WithContext(ctx).Tracef("HTTP request %v: %v %v", reqID, r.Method, r.URL)
 

management/server/types/networkmap_components.go

@@ -557,7 +557,6 @@ func (c *NetworkMapComponents) getRoutingPeerRoutes(peerID string) (enabledRoute
 	return enabledRoutes, disabledRoutes
 }
 
-
 func (c *NetworkMapComponents) filterRoutesByGroups(routes []*route.Route, groupListMap LookupMap) []*route.Route {
 	var filteredRoutes []*route.Route
 	for _, r := range routes {
@@ -628,9 +627,14 @@ func (c *NetworkMapComponents) getDefaultPermit(r *route.Route, includeIPv6 bool
 
 	rules := []*RouteFirewallRule{&rule}
 
-	if includeIPv6 && r.IsDynamic() {
+	isDefaultV4 := r.Network.Addr().Is4() && r.Network.Bits() == 0
+	if includeIPv6 && (r.IsDynamic() || isDefaultV4) {
 		ruleV6 := rule
 		ruleV6.SourceRanges = []string{"::/0"}
+		if isDefaultV4 {
+			ruleV6.Destination = "::/0"
+			ruleV6.RouteID = r.ID + "-v6-default"
+		}
 		rules = append(rules, &ruleV6)
 	}
 

management/server/types/networkmap_components_correctness_test.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net"
 	"net/netip"
+	"slices"
 	"testing"
 	"time"
 
@@ -1029,6 +1030,48 @@ func TestComponents_RouteDefaultPermit(t *testing.T) {
 	assert.True(t, hasDefaultPermit, "route without ACG should have default permit rule with 0.0.0.0/0 source")
 }
 
+// TestComponents_ExitNodeDefaultPermitIPv6 verifies that a default exit node route
+// (0.0.0.0/0) without AccessControlGroups also emits an IPv6 default permit rule
+// (::/0 source and destination) for peers that support IPv6, mirroring the route
+// the client installs. Without it, IPv6 traffic is routed to the exit node but
+// dropped at the forward chain.
+func TestComponents_ExitNodeDefaultPermitIPv6(t *testing.T) {
+	account, validatedPeers := scalableTestAccount(20, 2)
+
+	routingPeerID := "peer-5"
+	routingPeer := account.Peers[routingPeerID]
+	routingPeer.IPv6 = netip.MustParseAddr("fd00::5")
+	routingPeer.Meta.Capabilities = append(routingPeer.Meta.Capabilities, nbpeer.PeerCapabilityIPv6Overlay)
+
+	account.Routes["route-exit"] = &route.Route{
+		ID: "route-exit", Network: netip.MustParsePrefix("0.0.0.0/0"),
+		PeerID: routingPeerID, Peer: routingPeer.Key,
+		Enabled: true, Groups: []string{"group-all"}, PeerGroups: []string{"group-0"},
+		AccessControlGroups: []string{},
+		AccountID:           "test-account",
+	}
+
+	nm := componentsNetworkMap(account, routingPeerID, validatedPeers)
+	require.NotNil(t, nm)
+
+	hasV4 := false
+	hasV6 := false
+	for _, rfr := range nm.RoutesFirewallRules {
+		switch rfr.Destination {
+		case "0.0.0.0/0":
+			if slices.Contains(rfr.SourceRanges, "0.0.0.0/0") {
+				hasV4 = true
+			}
+		case "::/0":
+			if slices.Contains(rfr.SourceRanges, "::/0") {
+				hasV6 = true
+			}
+		}
+	}
+	assert.True(t, hasV4, "exit node route should have an IPv4 default permit rule (0.0.0.0/0)")
+	assert.True(t, hasV6, "exit node route should have an IPv6 default permit rule (::/0)")
+}
+
 // ──────────────────────────────────────────────────────────────────────────────
 // 15. MULTIPLE ROUTERS PER NETWORK
 // ──────────────────────────────────────────────────────────────────────────────

proxy/cmd/proxy/cmd/root.go

@@ -249,6 +249,7 @@ func runServer(cmd *cobra.Command, args []string) error {
 		Private:                  private,
 		MaxDialTimeout:           maxDialTimeout,
 		MaxSessionIdleTimeout:    maxSessionIdleTimeout,
+		MappingBatchWatchdog:     envDurationOrDefault("NB_PROXY_MAPPING_BATCH_WATCHDOG", 0),
 		GeoDataDir:               geoDataDir,
 		CrowdSecAPIURL:           crowdsecAPIURL,
 		CrowdSecAPIKey:           crowdsecAPIKey,

proxy/internal/roundtrip/netbird.go

@@ -28,6 +28,10 @@ import (
 
 const deviceNamePrefix = "ingress-proxy-"
 
+const clientStopTimeout = 30 * time.Second
+
+const createProxyPeerTimeout = 30 * time.Second
+
 // backendKey identifies a backend by its host:port from the target URL.
 type backendKey string
 
@@ -162,6 +166,7 @@ type NetBird struct {
 
 	clientsMux     sync.RWMutex
 	clients        map[types.AccountID]*clientEntry
+	lifecycleMu    sync.Map
 	initLogOnce    sync.Once
 	statusNotifier statusNotifier
 	// readyHandler runs after the embedded client for an account reports
@@ -177,6 +182,10 @@ type NetBird struct {
 	// (i.e. when a new client was actually created, not when an existing one
 	// was reused). The duration covers keygen + gRPC CreateProxyPeer + embed.New.
 	OnAddPeer func(d time.Duration, err error)
+
+	// startClient runs the post-create client startup. Nil uses runClientStartup;
+	// tests override it to avoid a real embed client.Start.
+	startClient func(accountID types.AccountID, client *embed.Client)
 }
 
 // ClientDebugInfo contains debug information about a client.
@@ -200,31 +209,20 @@ type skipTLSVerifyContextKey struct{}
 func (n *NetBird) AddPeer(ctx context.Context, accountID types.AccountID, key ServiceKey, authToken string, serviceID types.ServiceID) error {
 	si := serviceInfo{serviceID: serviceID}
 
-	n.clientsMux.Lock()
+	if n.registerExistingClient(accountID, key, si) {
+		return nil
+	}
 
-	entry, exists := n.clients[accountID]
-	if exists {
-		entry.services[key] = si
-		started := entry.started
-		n.clientsMux.Unlock()
-
-		n.logger.WithFields(log.Fields{
-			"account_id":  accountID,
-			"service_key": key,
-		}).Debug("registered service with existing client")
-
-		if started && n.statusNotifier != nil {
-			// Use a background context, not the caller's: the management
-			// connection notification must land even if the request /
-			// stream that triggered this registration is cancelled.
-			// Mirrors the async runClientStartup path.
-			if err := n.statusNotifier.NotifyStatus(context.Background(), accountID, serviceID, true); err != nil {
-				n.logger.WithFields(log.Fields{
-					"account_id":  accountID,
-					"service_key": key,
-				}).WithError(err).Warn("failed to notify status for existing client")
-			}
+	lifecycle := n.accountLifecycle(accountID)
+	lifecycle.Lock()
+	transferred := false
+	defer func() {
+		if !transferred {
+			lifecycle.Unlock()
 		}
+	}()
+
+	if n.registerExistingClient(accountID, key, si) {
 		return nil
 	}
 
@@ -234,10 +232,10 @@ func (n *NetBird) AddPeer(ctx context.Context, accountID types.AccountID, key Se
 		n.OnAddPeer(time.Since(createStart), err)
 	}
 	if err != nil {
-		n.clientsMux.Unlock()
 		return err
 	}
 
+	n.clientsMux.Lock()
 	n.clients[accountID] = entry
 	n.clientsMux.Unlock()
 
@@ -246,17 +244,64 @@ func (n *NetBird) AddPeer(ctx context.Context, accountID types.AccountID, key Se
 		"service_key": key,
 	}).Info("created new client for account")
 
-	// Attempt to start the client in the background; if this fails we will
-	// retry on the first request via RoundTrip. runClientStartup uses its
-	// own background context so the caller's request-scoped ctx can't
-	// cancel the inbound bring-up.
-	go n.runClientStartup(accountID, entry.client)
+	transferred = true
+	go func() {
+		defer lifecycle.Unlock()
+		n.startClientStartup(accountID, entry.client)
+	}()
 
 	return nil
 }
 
+func (n *NetBird) startClientStartup(accountID types.AccountID, client *embed.Client) {
+	if n.startClient != nil {
+		n.startClient(accountID, client)
+		return
+	}
+	n.runClientStartup(accountID, client)
+}
+
+// registerExistingClient registers the service against an already-present
+// client for the account and returns true when it did. It notifies management
+// of the new service when the client is already started.
+func (n *NetBird) registerExistingClient(accountID types.AccountID, key ServiceKey, si serviceInfo) bool {
+	n.clientsMux.Lock()
+	entry, exists := n.clients[accountID]
+	if !exists {
+		n.clientsMux.Unlock()
+		return false
+	}
+	entry.services[key] = si
+	started := entry.started
+	n.clientsMux.Unlock()
+
+	n.logger.WithFields(log.Fields{
+		"account_id":  accountID,
+		"service_key": key,
+	}).Debug("registered service with existing client")
+
+	if started && n.statusNotifier != nil {
+		if err := n.statusNotifier.NotifyStatus(context.Background(), accountID, si.serviceID, true); err != nil {
+			n.logger.WithFields(log.Fields{
+				"account_id":  accountID,
+				"service_key": key,
+			}).WithError(err).Warn("failed to notify status for existing client")
+		}
+	}
+	return true
+}
+
+// accountLifecycle returns the per-account lifecycle mutex, serialising client
+// creation against teardown so a slow client.Stop cannot race a new
+// client.Start for the same account, without blocking clientsMux.
+func (n *NetBird) accountLifecycle(accountID types.AccountID) *sync.Mutex {
+	mu, _ := n.lifecycleMu.LoadOrStore(accountID, &sync.Mutex{})
+	return mu.(*sync.Mutex)
+}
+
 // createClientEntry generates a WireGuard keypair, authenticates with management,
-// and creates an embedded NetBird client. Must be called with clientsMux held.
+// and creates an embedded NetBird client. Must be called with the account's
+// lifecycle mutex held.
 func (n *NetBird) createClientEntry(ctx context.Context, accountID types.AccountID, key ServiceKey, authToken string, si serviceInfo) (*clientEntry, error) {
 	serviceID := si.serviceID
 	n.logger.WithFields(log.Fields{
@@ -276,7 +321,9 @@ func (n *NetBird) createClientEntry(ctx context.Context, accountID types.Account
 		"public_key": publicKey.String(),
 	}).Debug("authenticating new proxy peer with management")
 
-	resp, err := n.mgmtClient.CreateProxyPeer(ctx, &proto.CreateProxyPeerRequest{
+	createCtx, cancel := context.WithTimeout(ctx, createProxyPeerTimeout)
+	defer cancel()
+	resp, err := n.mgmtClient.CreateProxyPeer(createCtx, &proto.CreateProxyPeerRequest{
 		ServiceId:          string(serviceID),
 		AccountId:          string(accountID),
 		Token:              authToken,
@@ -444,6 +491,15 @@ func (n *NetBird) notifyClientReady(accountID types.AccountID, client *embed.Cli
 // RemovePeer unregisters a service from an account. The client is only stopped
 // when no services are using it anymore.
 func (n *NetBird) RemovePeer(ctx context.Context, accountID types.AccountID, key ServiceKey) error {
+	lifecycle := n.accountLifecycle(accountID)
+	lifecycle.Lock()
+	transferred := false
+	defer func() {
+		if !transferred {
+			lifecycle.Unlock()
+		}
+	}()
+
 	n.clientsMux.Lock()
 
 	entry, exists := n.clients[accountID]
@@ -466,17 +522,8 @@ func (n *NetBird) RemovePeer(ctx context.Context, accountID types.AccountID, key
 	delete(entry.services, key)
 
 	stopClient := len(entry.services) == 0
-	var client *embed.Client
-	var transport, insecureTransport *http.Transport
-	var inbound any
-	var stopHandler func(types.AccountID, any)
 	if stopClient {
 		n.logger.WithField("account_id", accountID).Info("stopping client, no more services")
-		client = entry.client
-		transport = entry.transport
-		insecureTransport = entry.insecureTransport
-		inbound = entry.inbound
-		stopHandler = n.stopHandler
 		delete(n.clients, accountID)
 	} else {
 		n.logger.WithFields(log.Fields{
@@ -490,19 +537,40 @@ func (n *NetBird) RemovePeer(ctx context.Context, accountID types.AccountID, key
 	n.notifyDisconnect(ctx, accountID, key, si.serviceID)
 
 	if stopClient {
-		if inbound != nil && stopHandler != nil {
-			stopHandler(accountID, inbound)
-		}
-		transport.CloseIdleConnections()
-		insecureTransport.CloseIdleConnections()
-		if err := client.Stop(ctx); err != nil {
-			n.logger.WithField("account_id", accountID).WithError(err).Warn("failed to stop netbird client")
-		}
+		transferred = true
+		go n.stopClientLocked(accountID, lifecycle, entry)
 	}
 
 	return nil
 }
 
+// stopClientLocked releases a client's resources off the caller's goroutine so a
+// slow client.Stop cannot wedge the mapping receive loop (which calls RemovePeer
+// synchronously). It unlocks lifecycle when done so a new client.Start for the
+// same account waits for this teardown.
+func (n *NetBird) stopClientLocked(accountID types.AccountID, lifecycle *sync.Mutex, entry *clientEntry) {
+	defer lifecycle.Unlock()
+
+	if entry.inbound != nil && n.stopHandler != nil {
+		n.stopHandler(accountID, entry.inbound)
+	}
+	if entry.transport != nil {
+		entry.transport.CloseIdleConnections()
+	}
+	if entry.insecureTransport != nil {
+		entry.insecureTransport.CloseIdleConnections()
+	}
+	if entry.client == nil {
+		return
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), clientStopTimeout)
+	defer cancel()
+	if err := entry.client.Stop(ctx); err != nil {
+		n.logger.WithField("account_id", accountID).WithError(err).Warn("failed to stop netbird client")
+	}
+}
+
 func (n *NetBird) notifyDisconnect(ctx context.Context, accountID types.AccountID, key ServiceKey, serviceID types.ServiceID) {
 	if n.statusNotifier == nil {
 		return

proxy/internal/roundtrip/netbird_test.go

@@ -6,6 +6,7 @@ import (
 	"net/netip"
 	"sync"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -22,6 +23,18 @@ func (m *mockMgmtClient) CreateProxyPeer(_ context.Context, _ *proto.CreateProxy
 	return &proto.CreateProxyPeerResponse{Success: true}, nil
 }
 
+// signalMgmtClient closes entered the first time CreateProxyPeer is called, so
+// tests can detect AddPeer reaching client creation.
+type signalMgmtClient struct {
+	entered chan struct{}
+	once    sync.Once
+}
+
+func (m *signalMgmtClient) CreateProxyPeer(_ context.Context, _ *proto.CreateProxyPeerRequest, _ ...grpc.CallOption) (*proto.CreateProxyPeerResponse, error) {
+	m.once.Do(func() { close(m.entered) })
+	return &proto.CreateProxyPeerResponse{Success: true}, nil
+}
+
 type mockStatusNotifier struct {
 	mu       sync.Mutex
 	statuses []statusCall
@@ -52,11 +65,15 @@ func (m *mockStatusNotifier) calls() []statusCall {
 // mockNetBird creates a NetBird instance for testing without actually connecting.
 // It uses an invalid management URL to prevent real connections.
 func mockNetBird() *NetBird {
-	return NewNetBird(context.Background(), "test-proxy", "invalid.test", ClientConfig{
+	nb := NewNetBird(context.Background(), "test-proxy", "invalid.test", ClientConfig{
 		MgmtAddr:     "http://invalid.test:9999",
 		WGPort:       0,
 		PreSharedKey: "",
 	}, nil, nil, &mockMgmtClient{})
+	// Skip the real embed client.Start, which would hang against the unreachable
+	// mgmt URL and (now that the lifecycle lock spans startup) serialise removes.
+	nb.startClient = func(types.AccountID, *embed.Client) {}
+	return nb
 }
 
 func TestNetBird_AddPeer_CreatesClientForNewAccount(t *testing.T) {
@@ -288,6 +305,7 @@ func TestNetBird_AddPeer_ExistingStartedClient_NotifiesStatus(t *testing.T) {
 		WGPort:       0,
 		PreSharedKey: "",
 	}, nil, notifier, &mockMgmtClient{})
+	nb.startClient = func(types.AccountID, *embed.Client) {}
 	accountID := types.AccountID("account-1")
 
 	// Add first service — creates a new client entry.
@@ -372,6 +390,117 @@ func TestNetBird_RemovePeer_NotifiesDisconnection(t *testing.T) {
 	assert.False(t, calls[0].connected)
 }
 
+// TestNetBird_RemovePeer_TeardownIsAsync proves the fix for the receive-loop
+// stall: RemovePeer must return promptly even when the client teardown blocks,
+// because teardown runs off the caller's goroutine. The receive loop calls
+// RemovePeer synchronously, so a blocking teardown inline would wedge it.
+func TestNetBird_RemovePeer_TeardownIsAsync(t *testing.T) {
+	nb := NewNetBird(context.Background(), "test-proxy", "invalid.test", ClientConfig{
+		MgmtAddr: "http://invalid.test:9999",
+	}, nil, &mockStatusNotifier{}, &mockMgmtClient{})
+
+	accountID := types.AccountID("acct-async-teardown")
+	key := DomainServiceKey("svc.example")
+
+	teardownEntered := make(chan struct{})
+	releaseTeardown := make(chan struct{})
+	nb.SetClientLifecycle(nil, func(types.AccountID, any) {
+		close(teardownEntered)
+		<-releaseTeardown
+	})
+
+	nb.clientsMux.Lock()
+	nb.clients[accountID] = &clientEntry{
+		services: map[ServiceKey]serviceInfo{key: {serviceID: types.ServiceID("svc-1")}},
+		started:  true,
+		inbound:  struct{}{},
+	}
+	nb.clientsMux.Unlock()
+
+	done := make(chan error, 1)
+	go func() { done <- nb.RemovePeer(context.Background(), accountID, key) }()
+
+	select {
+	case err := <-done:
+		require.NoError(t, err)
+	case <-time.After(2 * time.Second):
+		t.Fatal("RemovePeer did not return while teardown was blocked — teardown is not async")
+	}
+
+	select {
+	case <-teardownEntered:
+	case <-time.After(2 * time.Second):
+		t.Fatal("teardown never ran")
+	}
+
+	close(releaseTeardown)
+}
+
+// TestNetBird_AddPeer_WaitsForTeardown proves the lifecycle lock serialises a
+// new client bringup behind an in-flight teardown for the same account, so a
+// slow client.Stop can never race a new client.Start for that account.
+//
+// It targets the handoff race specifically: AddPeer is launched immediately
+// after RemovePeer returns, WITHOUT waiting for the teardown goroutine to start.
+// This only passes if RemovePeer acquires the lifecycle lock synchronously
+// (before returning) and hands it to the teardown goroutine — if the goroutine
+// acquired the lock itself, AddPeer could win the lock in this window and start
+// a replacement client while the old teardown is still pending.
+func TestNetBird_AddPeer_WaitsForTeardown(t *testing.T) {
+	nb := NewNetBird(context.Background(), "test-proxy", "invalid.test", ClientConfig{
+		MgmtAddr: "http://invalid.test:9999",
+	}, nil, &mockStatusNotifier{}, &mockMgmtClient{})
+	nb.startClient = func(types.AccountID, *embed.Client) {}
+
+	accountID := types.AccountID("acct-serialize")
+	key := DomainServiceKey("svc.example")
+
+	addEntered := make(chan struct{})
+	releaseTeardown := make(chan struct{})
+	nb.SetClientLifecycle(nil, func(types.AccountID, any) {
+		// Block teardown until released. If AddPeer ever reaches createClientEntry
+		// (signalled via the mgmt client below) while we hold the lock, the lock
+		// failed to serialise and the test fails before we release.
+		<-releaseTeardown
+	})
+
+	nb.clientsMux.Lock()
+	nb.clients[accountID] = &clientEntry{
+		services: map[ServiceKey]serviceInfo{key: {serviceID: types.ServiceID("svc-1")}},
+		started:  true,
+		inbound:  struct{}{},
+	}
+	nb.clientsMux.Unlock()
+
+	// createClientEntry calls CreateProxyPeer; closing addEntered there tells us
+	// AddPeer got past the lifecycle lock and into client creation.
+	nb.mgmtClient = &signalMgmtClient{entered: addEntered}
+
+	require.NoError(t, nb.RemovePeer(context.Background(), accountID, key))
+
+	// Launch AddPeer with NO synchronisation against the teardown goroutine.
+	addReturned := make(chan struct{})
+	go func() {
+		_ = nb.AddPeer(context.Background(), accountID, DomainServiceKey("svc2.example"), "key-2", types.ServiceID("svc-2"))
+		close(addReturned)
+	}()
+
+	select {
+	case <-addEntered:
+		t.Fatal("AddPeer entered client creation while teardown held the lifecycle lock — handoff race not closed")
+	case <-addReturned:
+		t.Fatal("AddPeer completed while teardown held the lifecycle lock — not serialised")
+	case <-time.After(300 * time.Millisecond):
+	}
+
+	close(releaseTeardown)
+	select {
+	case <-addReturned:
+	case <-time.After(2 * time.Second):
+		t.Fatal("AddPeer never completed after teardown released the lifecycle lock")
+	}
+}
+
 // TestNotifyClientReady_UsesBackgroundCtx pins the contract that the
 // post-Start hooks (readyHandler + statusNotifier.NotifyStatus) run on
 // a fresh context.Background() rather than inheriting the AddPeer

proxy/lifecycle.go

@@ -114,6 +114,10 @@ type Config struct {
 	MaxDialTimeout time.Duration
 	// MaxSessionIdleTimeout caps the per-service session idle timeout.
 	MaxSessionIdleTimeout time.Duration
+	// MappingBatchWatchdog bounds how long a single mapping batch may spend
+	// being applied before the receive loop reconnects to resync. Zero falls
+	// back to the internal default.
+	MappingBatchWatchdog time.Duration
 
 	// GeoDataDir is the directory containing GeoLite2 MMDB files.
 	GeoDataDir string
@@ -164,6 +168,7 @@ func New(ctx context.Context, cfg Config) *Server {
 		Private:                  cfg.Private,
 		MaxDialTimeout:           cfg.MaxDialTimeout,
 		MaxSessionIdleTimeout:    cfg.MaxSessionIdleTimeout,
+		MappingBatchWatchdog:     cfg.MappingBatchWatchdog,
 		GeoDataDir:               cfg.GeoDataDir,
 		CrowdSecAPIURL:           cfg.CrowdSecAPIURL,
 		CrowdSecAPIKey:           cfg.CrowdSecAPIKey,

proxy/mapping_stall_test.go

@@ -0,0 +1,282 @@
+package proxy
+
+import (
+	"context"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/metadata"
+
+	"github.com/netbirdio/netbird/proxy/internal/roundtrip"
+	"github.com/netbirdio/netbird/proxy/internal/types"
+	"github.com/netbirdio/netbird/shared/management/proto"
+)
+
+// blockingMgmtClient implements roundtrip's managementClient interface.
+// CreateProxyPeer parks until release is closed, signalling entry on entered.
+// This reproduces the confirmed real-world stall: createClientEntry calls
+// CreateProxyPeer synchronously while holding clientsMux, and the proxy's
+// receive loop calls that path synchronously inside processMappings.
+type blockingMgmtClient struct {
+	entered chan struct{}
+	once    sync.Once
+}
+
+func (b *blockingMgmtClient) CreateProxyPeer(ctx context.Context, _ *proto.CreateProxyPeerRequest, _ ...grpc.CallOption) (*proto.CreateProxyPeerResponse, error) {
+	b.once.Do(func() { close(b.entered) })
+	// Park until the caller's context is cancelled. In production this ctx is
+	// the gRPC mapping-stream context with no per-call timeout, so a slow or
+	// unresponsive CreateProxyPeer parks the receive loop here indefinitely.
+	<-ctx.Done()
+	return nil, ctx.Err()
+}
+
+// gatedMappingStream is a mock GetMappingUpdate client stream that hands out a
+// pre-seeded list of messages, then records how many times Recv advanced. It
+// lets the test observe whether the single-threaded receive loop ever gets
+// past the first (blocking) batch to pull the second message.
+type gatedMappingStream struct {
+	grpc.ClientStream
+	messages []*proto.GetMappingUpdateResponse
+	idx      int32
+}
+
+func (g *gatedMappingStream) Recv() (*proto.GetMappingUpdateResponse, error) {
+	i := int(atomic.LoadInt32(&g.idx))
+	if i >= len(g.messages) {
+		// Block instead of returning EOF so the loop doesn't exit; we only
+		// care whether the loop ever reaches this second Recv at all.
+		select {}
+	}
+	msg := g.messages[i]
+	atomic.AddInt32(&g.idx, 1)
+	return msg, nil
+}
+
+func (g *gatedMappingStream) deliveredCount() int32 { return atomic.LoadInt32(&g.idx) }
+
+func (g *gatedMappingStream) Header() (metadata.MD, error) { return nil, nil } //nolint:nilnil
+func (g *gatedMappingStream) Trailer() metadata.MD         { return nil }
+func (g *gatedMappingStream) CloseSend() error             { return nil }
+func (g *gatedMappingStream) Context() context.Context     { return context.Background() }
+func (g *gatedMappingStream) SendMsg(any) error            { return nil }
+func (g *gatedMappingStream) RecvMsg(any) error            { return nil }
+
+// noopNotifier satisfies roundtrip's statusNotifier interface.
+type noopNotifier struct{}
+
+func (noopNotifier) NotifyStatus(context.Context, types.AccountID, types.ServiceID, bool) error {
+	return nil
+}
+
+// noopProxyClient is a proto.ProxyServiceClient that no-ops the one method the
+// teardown unwind reaches (SendStatusUpdate, via notifyError when the parked
+// AddPeer is cancelled). The embedded nil interface satisfies the rest at
+// compile time; none of those methods are called by this test.
+type noopProxyClient struct {
+	proto.ProxyServiceClient
+}
+
+func (noopProxyClient) SendStatusUpdate(context.Context, *proto.SendStatusUpdateRequest, ...grpc.CallOption) (*proto.SendStatusUpdateResponse, error) {
+	return &proto.SendStatusUpdateResponse{}, nil
+}
+
+// TestMappingStream_StallsWhenApplyBlocks proves the deadlock: the proxy's
+// mapping receive loop processes batches strictly serially, so when applying
+// one batch blocks (here: createClientEntry parked on a synchronous
+// CreateProxyPeer call, exactly as observed in production), the loop never
+// advances to Recv the next batch. Management can keep sending updates onto
+// the stream with no error and no channel overflow, yet the proxy applies
+// nothing further — it is stuck.
+func TestMappingStream_StallsWhenApplyBlocks(t *testing.T) {
+	logger := log.New()
+	logger.SetLevel(log.PanicLevel)
+
+	mgmt := &blockingMgmtClient{
+		entered: make(chan struct{}),
+	}
+
+	nb := roundtrip.NewNetBird(
+		context.Background(),
+		"proxy-test",
+		"proxy.example.com",
+		roundtrip.ClientConfig{},
+		logger,
+		noopNotifier{},
+		mgmt,
+	)
+
+	s := &Server{
+		Logger:       logger,
+		netbird:      nb,
+		mgmtClient:   noopProxyClient{},
+		routerReady:  closedChan(),
+		lastMappings: make(map[types.ServiceID]*proto.ProxyMapping),
+	}
+
+	// First batch: a CREATED mapping for a brand-new account. addMapping ->
+	// netbird.AddPeer -> createClientEntry -> CreateProxyPeer, which blocks.
+	// Empty Path keeps setupHTTPMapping a no-op (it returns early), so the
+	// ONLY blocking point is the synchronous CreateProxyPeer in AddPeer —
+	// no routers/auth need wiring. The second batch exists only to detect
+	// whether the loop ever advances past the blocked first batch.
+	stream := &gatedMappingStream{
+		messages: []*proto.GetMappingUpdateResponse{
+			{
+				Mapping: []*proto.ProxyMapping{
+					{
+						Type:      proto.ProxyMappingUpdateType_UPDATE_TYPE_CREATED,
+						Id:        "svc-1",
+						AccountId: "acct-1",
+						AuthToken: "token-1",
+					},
+				},
+			},
+			{
+				Mapping: []*proto.ProxyMapping{
+					{
+						Type:      proto.ProxyMappingUpdateType_UPDATE_TYPE_CREATED,
+						Id:        "svc-2",
+						AccountId: "acct-2",
+						AuthToken: "token-2",
+					},
+				},
+			},
+		},
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	// Unblock the parked apply on teardown via ctx (CreateProxyPeer returns
+	// ctx.Err()), so the wedged loop goroutine unwinds before embed.New —
+	// avoiding any dependency on collaborators this test deliberately leaves
+	// nil. The deadlock is fully proven before this fires.
+	t.Cleanup(cancel)
+
+	loopDone := make(chan struct{})
+	syncDone := false
+	go func() {
+		defer close(loopDone)
+		_ = s.handleMappingStream(ctx, stream, &syncDone, time.Time{})
+	}()
+
+	// The loop must reach the blocking apply for the first batch.
+	select {
+	case <-mgmt.entered:
+	case <-time.After(2 * time.Second):
+		t.Fatal("receive loop never reached CreateProxyPeer for the first batch")
+	}
+
+	// THE DEADLOCK: while the first batch is parked in CreateProxyPeer, the
+	// single-threaded loop cannot advance. The second batch is never pulled,
+	// even though it is already available on the stream. Give it ample time.
+	// deliveredCount is atomic; syncDone is intentionally not read here because
+	// the loop goroutine owns it (reading it from the test would race).
+	time.Sleep(500 * time.Millisecond)
+	assert.Equal(t, int32(1), stream.deliveredCount(),
+		"loop must NOT consume the second batch while the first is blocked in apply — proxy is stuck")
+
+	select {
+	case <-loopDone:
+		t.Fatal("receive loop returned while it should be wedged in apply")
+	default:
+		// Still wedged, as expected.
+	}
+}
+
+// TestMappingStream_StallsWhenRemoveBlocks proves the deadlock for the REMOVE
+// path observed in production: a mapping remove tears down the account's last
+// embedded client via netbird.RemovePeer -> client.Stop -> Engine.Stop, whose
+// jobExecutorWG.Wait() is unbounded. Because the receive loop is single-
+// threaded, a blocked remove wedges the loop: no further mapping updates of any
+// kind (create/modify/remove) are applied, while management keeps sending them
+// successfully (no send error, no channel-full). Matches the reported symptom:
+// the last log line is a remove that stops a client, then silence.
+func TestMappingStream_StallsWhenRemoveBlocks(t *testing.T) {
+	logger := log.New()
+	logger.SetLevel(log.PanicLevel)
+
+	enteredRemove := make(chan struct{})
+	blockRemove := make(chan struct{})
+	var once sync.Once
+
+	s := &Server{
+		Logger:       logger,
+		mgmtClient:   noopProxyClient{},
+		routerReady:  closedChan(),
+		lastMappings: make(map[types.ServiceID]*proto.ProxyMapping),
+		// Stand in for netbird.RemovePeer -> client.Stop hanging on
+		// Engine.Stop's unbounded jobExecutorWG.Wait(). Only the first remove
+		// blocks; later removes return immediately so the recovery assertion
+		// can observe the loop advancing.
+		removePeer: func(ctx context.Context, _ types.AccountID, _ roundtrip.ServiceKey) error {
+			first := false
+			once.Do(func() {
+				first = true
+				close(enteredRemove)
+			})
+			if !first {
+				return nil
+			}
+			select {
+			case <-blockRemove:
+			case <-ctx.Done():
+			}
+			return nil
+		},
+	}
+
+	// Batch 1 removes a service (blocks in teardown). Batch 2 is a later update
+	// that must never be applied while the remove is wedged.
+	stream := &gatedMappingStream{
+		messages: []*proto.GetMappingUpdateResponse{
+			{
+				Mapping: []*proto.ProxyMapping{
+					{Type: proto.ProxyMappingUpdateType_UPDATE_TYPE_REMOVED, Id: "svc-1", AccountId: "acct-1"},
+				},
+			},
+			{
+				Mapping: []*proto.ProxyMapping{
+					{Type: proto.ProxyMappingUpdateType_UPDATE_TYPE_REMOVED, Id: "svc-2", AccountId: "acct-1"},
+				},
+			},
+		},
+	}
+
+	loopDone := make(chan struct{})
+	syncDone := false
+	go func() {
+		defer close(loopDone)
+		_ = s.handleMappingStream(context.Background(), stream, &syncDone, time.Time{})
+	}()
+
+	select {
+	case <-enteredRemove:
+	case <-time.After(2 * time.Second):
+		t.Fatal("receive loop never reached the blocking remove for the first batch")
+	}
+
+	// THE DEADLOCK: the loop is parked in the blocked remove and cannot advance.
+	// syncDone is owned by the loop goroutine, so it is not read here.
+	time.Sleep(500 * time.Millisecond)
+	assert.Equal(t, int32(1), stream.deliveredCount(),
+		"loop must NOT consume the second batch while the first remove is blocked — proxy is stuck")
+
+	select {
+	case <-loopDone:
+		t.Fatal("receive loop returned while it should be wedged on the remove")
+	default:
+	}
+
+	// Unblock and confirm the wedge was solely the blocked remove: the loop
+	// then advances and consumes the next batch.
+	close(blockRemove)
+	assert.Eventually(t, func() bool {
+		return stream.deliveredCount() >= 2
+	}, 2*time.Second, 5*time.Millisecond,
+		"once the remove unblocks, the loop must advance and consume the next batch")
+}

proxy/server.go

@@ -24,6 +24,7 @@ import (
 	"time"
 
 	"github.com/cenkalti/backoff/v4"
+	"github.com/google/uuid"
 	"github.com/pires/go-proxyproto"
 	prometheus2 "github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
@@ -75,29 +76,30 @@ type portRouter struct {
 }
 
 type Server struct {
-	ctx           context.Context
-	mgmtClient    proto.ProxyServiceClient
-	proxy         *proxy.ReverseProxy
-	netbird       *roundtrip.NetBird
-	acme          *acme.Manager
-	auth          *auth.Middleware
-	http          *http.Server
-	https         *http.Server
-	debug         *http.Server
-	healthServer  *health.Server
-	healthChecker *health.Checker
-	meter         *proxymetrics.Metrics
-	accessLog     *accesslog.Logger
-	mainRouter    *nbtcp.Router
-	mainPort      uint16
-	udpMu         sync.Mutex
-	udpRelays     map[types.ServiceID]*udprelay.Relay
-	udpRelayWg    sync.WaitGroup
-	portMu        sync.RWMutex
-	portRouters   map[uint16]*portRouter
-	svcPorts      map[types.ServiceID][]uint16
-	lastMappings  map[types.ServiceID]*proto.ProxyMapping
-	portRouterWg  sync.WaitGroup
+	ctx               context.Context
+	mgmtClient        proto.ProxyServiceClient
+	proxy             *proxy.ReverseProxy
+	netbird           *roundtrip.NetBird
+	acme              *acme.Manager
+	staticCertWatcher *certwatch.Watcher
+	auth              *auth.Middleware
+	http              *http.Server
+	https             *http.Server
+	debug             *http.Server
+	healthServer      *health.Server
+	healthChecker     *health.Checker
+	meter             *proxymetrics.Metrics
+	accessLog         *accesslog.Logger
+	mainRouter        *nbtcp.Router
+	mainPort          uint16
+	udpMu             sync.Mutex
+	udpRelays         map[types.ServiceID]*udprelay.Relay
+	udpRelayWg        sync.WaitGroup
+	portMu            sync.RWMutex
+	portRouters       map[uint16]*portRouter
+	svcPorts          map[types.ServiceID][]uint16
+	lastMappings      map[types.ServiceID]*proto.ProxyMapping
+	portRouterWg      sync.WaitGroup
 
 	// hijackTracker tracks hijacked connections (e.g. WebSocket upgrades)
 	// so they can be closed during graceful shutdown, since http.Server.Shutdown
@@ -118,6 +120,9 @@ type Server struct {
 	// The mapping worker waits on this before processing updates.
 	routerReady chan struct{}
 
+	// removePeer defaults to netbird.RemovePeer; overridable in tests.
+	removePeer func(ctx context.Context, accountID types.AccountID, key roundtrip.ServiceKey) error
+
 	// inbound, when non-nil, manages per-account inbound listeners. Set by
 	// initPrivateInbound only when Private is true so the standalone
 	// proxy keeps its zero-overhead default path.
@@ -227,6 +232,10 @@ type Server struct {
 	// Zero means no cap (the proxy honors whatever management sends).
 	// Set via NB_PROXY_MAX_SESSION_IDLE_TIMEOUT for shared deployments.
 	MaxSessionIdleTimeout time.Duration
+	// MappingBatchWatchdog bounds how long a single mapping batch may spend
+	// in processMappings before the receive loop reconnects to resync.
+	// Zero uses defaultMappingBatchWatchdog.
+	MappingBatchWatchdog time.Duration
 }
 
 // clampIdleTimeout returns d capped to MaxSessionIdleTimeout when configured.
@@ -607,7 +616,7 @@ func (s *Server) initDefaults() {
 
 	// If no ID is set then one can be generated.
 	if s.ID == "" {
-		s.ID = "netbird-proxy-" + s.startTime.Format("20060102150405")
+		s.ID = fmt.Sprintf("netbird-proxy-%s", uuid.NewString())
 	}
 	// Fallback version option in case it is not set.
 	if s.Version == "" {
@@ -785,6 +794,7 @@ func (s *Server) configureTLS(ctx context.Context) (*tls.Config, error) {
 			return nil, fmt.Errorf("initialize certificate watcher: %w", err)
 		}
 		go certWatcher.Watch(ctx)
+		s.staticCertWatcher = certWatcher
 		tlsConfig.GetCertificate = certWatcher.GetCertificate
 		return tlsConfig, nil
 	}
@@ -1172,24 +1182,30 @@ func (s *Server) newManagementMappingWorker(ctx context.Context, client proto.Pr
 			s.healthChecker.SetManagementConnected(false)
 		}
 
+		connected := false
+		onConnected := func() { connected = true }
+
 		var streamErr error
 		if syncSupported {
-			streamErr = s.trySyncMappings(ctx, client, &initialSyncDone)
+			streamErr = s.trySyncMappings(ctx, client, &initialSyncDone, onConnected)
 			if isSyncUnimplemented(streamErr) {
 				syncSupported = false
 				s.Logger.Info("management does not support SyncMappings, falling back to GetMappingUpdate")
-				streamErr = s.tryGetMappingUpdate(ctx, client, &initialSyncDone)
+				streamErr = s.tryGetMappingUpdate(ctx, client, &initialSyncDone, onConnected)
 			}
 		} else {
-			streamErr = s.tryGetMappingUpdate(ctx, client, &initialSyncDone)
+			streamErr = s.tryGetMappingUpdate(ctx, client, &initialSyncDone, onConnected)
 		}
 
 		if s.healthChecker != nil {
 			s.healthChecker.SetManagementConnected(false)
 		}
 
-		// Stream established — reset backoff so the next failure retries quickly.
-		bo.Reset()
+		// Reset backoff only when a stream actually connected, so immediate
+		// connect failures still back off instead of spinning.
+		if connected {
+			bo.Reset()
+		}
 
 		if streamErr == nil {
 			return fmt.Errorf("stream closed by server")
@@ -1221,7 +1237,7 @@ func (s *Server) proxyCapabilities() *proto.ProxyCapabilities {
 	}
 }
 
-func (s *Server) tryGetMappingUpdate(ctx context.Context, client proto.ProxyServiceClient, initialSyncDone *bool) error {
+func (s *Server) tryGetMappingUpdate(ctx context.Context, client proto.ProxyServiceClient, initialSyncDone *bool, onConnected func()) error {
 	connectTime := time.Now()
 	mappingClient, err := client.GetMappingUpdate(ctx, &proto.GetMappingUpdateRequest{
 		ProxyId:      s.ID,
@@ -1234,6 +1250,7 @@ func (s *Server) tryGetMappingUpdate(ctx context.Context, client proto.ProxyServ
 		return fmt.Errorf("create mapping stream: %w", err)
 	}
 
+	onConnected()
 	if s.healthChecker != nil {
 		s.healthChecker.SetManagementConnected(true)
 	}
@@ -1242,7 +1259,7 @@ func (s *Server) tryGetMappingUpdate(ctx context.Context, client proto.ProxyServ
 	return s.handleMappingStream(ctx, mappingClient, initialSyncDone, connectTime)
 }
 
-func (s *Server) trySyncMappings(ctx context.Context, client proto.ProxyServiceClient, initialSyncDone *bool) error {
+func (s *Server) trySyncMappings(ctx context.Context, client proto.ProxyServiceClient, initialSyncDone *bool, onConnected func()) error {
 	connectTime := time.Now()
 	stream, err := client.SyncMappings(ctx)
 	if err != nil {
@@ -1263,6 +1280,7 @@ func (s *Server) trySyncMappings(ctx context.Context, client proto.ProxyServiceC
 		return fmt.Errorf("send sync init: %w", err)
 	}
 
+	onConnected()
 	if s.healthChecker != nil {
 		s.healthChecker.SetManagementConnected(true)
 	}
@@ -1307,7 +1325,9 @@ func (s *Server) handleSyncMappingsStream(ctx context.Context, stream proto.Prox
 
 			batchStart := time.Now()
 			s.Logger.Debug("Received mapping update, starting processing")
-			s.processMappings(ctx, msg.GetMapping())
+			if err := s.processMappingsGuarded(ctx, msg.GetMapping()); err != nil {
+				return err
+			}
 			s.Logger.Debug("Processing mapping update completed")
 			tracker.recordBatch(ctx, s, msg.GetMapping(), msg.GetInitialSyncComplete(), batchStart)
 
@@ -1391,7 +1411,9 @@ func (s *Server) handleMappingStream(ctx context.Context, mappingClient proto.Pr
 
 			batchStart := time.Now()
 			s.Logger.Debug("Received mapping update, starting processing")
-			s.processMappings(ctx, msg.GetMapping())
+			if err := s.processMappingsGuarded(ctx, msg.GetMapping()); err != nil {
+				return err
+			}
 			s.Logger.Debug("Processing mapping update completed")
 			tracker.recordBatch(ctx, s, msg.GetMapping(), msg.GetInitialSyncComplete(), batchStart)
 		}
@@ -1456,6 +1478,44 @@ func redactMappingForLog(m *proto.ProxyMapping) *proto.ProxyMapping {
 	return c
 }
 
+const defaultMappingBatchWatchdog = 2 * time.Minute
+
+// mappingBatchWatchdog returns the configured batch watchdog or the default.
+func (s *Server) mappingBatchWatchdog() time.Duration {
+	if s.MappingBatchWatchdog > 0 {
+		return s.MappingBatchWatchdog
+	}
+	return defaultMappingBatchWatchdog
+}
+
+// processMappingsGuarded applies a batch under a watchdog, returning an error
+// if processing exceeds the watchdog so the caller reconnects and resyncs
+// instead of wedging silently.
+func (s *Server) processMappingsGuarded(ctx context.Context, mappings []*proto.ProxyMapping) error {
+	batchCtx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	done := make(chan struct{})
+	go func() {
+		defer close(done)
+		s.processMappings(batchCtx, mappings)
+	}()
+
+	watchdog := s.mappingBatchWatchdog()
+	timer := time.NewTimer(watchdog)
+	defer timer.Stop()
+
+	select {
+	case <-done:
+		return nil
+	case <-ctx.Done():
+		return ctx.Err()
+	case <-timer.C:
+		s.Logger.Errorf("processing mapping batch exceeded %s, cancelling and reconnecting to resync", watchdog)
+		return fmt.Errorf("mapping batch processing stalled after %s", watchdog)
+	}
+}
+
 func (s *Server) processMappings(ctx context.Context, mappings []*proto.ProxyMapping) {
 	debug := s.Logger != nil && s.Logger.IsLevelEnabled(log.DebugLevel)
 	for _, mapping := range mappings {
@@ -1566,6 +1626,8 @@ func (s *Server) setupHTTPMapping(ctx context.Context, mapping *proto.ProxyMappi
 	var wildcardHit bool
 	if s.acme != nil {
 		wildcardHit = s.acme.AddDomain(d, accountID, svcID)
+	} else {
+		wildcardHit = s.staticCertCovers(d)
 	}
 	httpRoute := nbtcp.Route{
 		Type:      nbtcp.RouteHTTP,
@@ -1590,6 +1652,26 @@ func (s *Server) setupHTTPMapping(ctx context.Context, mapping *proto.ProxyMappi
 	return nil
 }
 
+// staticCertCovers reports whether the static certificate loaded when ACME is
+// disabled covers the given domain, making it certificate-ready immediately —
+// the equivalent of a wildcard hit in the ACME path. Domains the certificate
+// does not cover are logged: clients connecting to them will get TLS errors.
+func (s *Server) staticCertCovers(d domain.Domain) bool {
+	if s.staticCertWatcher == nil {
+		return false
+	}
+	leaf := s.staticCertWatcher.Leaf()
+	if leaf == nil {
+		return false
+	}
+	name := d.PunycodeString()
+	if err := leaf.VerifyHostname(name); err != nil {
+		s.Logger.Warnf("static certificate (SANs %v) does not cover domain %q: %v", leaf.DNSNames, name, err)
+		return false
+	}
+	return true
+}
+
 // setupTCPMapping sets up a TCP port-forwarding fallback route on the listen port.
 func (s *Server) setupTCPMapping(ctx context.Context, mapping *proto.ProxyMapping) error {
 	svcID := types.ServiceID(mapping.GetId())
@@ -1951,7 +2033,11 @@ func (s *Server) updateMapping(ctx context.Context, mapping *proto.ProxyMapping)
 func (s *Server) removeMapping(ctx context.Context, mapping *proto.ProxyMapping) {
 	accountID := types.AccountID(mapping.GetAccountId())
 	svcKey := s.serviceKeyForMapping(mapping)
-	if err := s.netbird.RemovePeer(ctx, accountID, svcKey); err != nil {
+	removePeer := s.removePeer
+	if removePeer == nil {
+		removePeer = s.netbird.RemovePeer
+	}
+	if err := removePeer(ctx, accountID, svcKey); err != nil {
 		s.Logger.WithFields(log.Fields{
 			"account_id": accountID,
 			"service_id": mapping.GetId(),

proxy/static_cert_test.go

@@ -0,0 +1,89 @@
+package proxy
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"math/big"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/netbirdio/netbird/proxy/internal/certwatch"
+	"github.com/netbirdio/netbird/shared/management/domain"
+)
+
+func generateCertWithSANs(t *testing.T, dnsNames []string) (certPEM, keyPEM []byte) {
+	t.Helper()
+
+	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	require.NoError(t, err)
+
+	template := &x509.Certificate{
+		SerialNumber: big.NewInt(1),
+		Subject:      pkix.Name{CommonName: dnsNames[0]},
+		DNSNames:     dnsNames,
+		NotBefore:    time.Now().Add(-time.Hour),
+		NotAfter:     time.Now().Add(24 * time.Hour),
+	}
+
+	certDER, err := x509.CreateCertificate(rand.Reader, template, template, &key.PublicKey, key)
+	require.NoError(t, err)
+	certPEM = pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certDER})
+
+	keyDER, err := x509.MarshalECPrivateKey(key)
+	require.NoError(t, err)
+	keyPEM = pem.EncodeToMemory(&pem.Block{Type: "EC PRIVATE KEY", Bytes: keyDER})
+
+	return certPEM, keyPEM
+}
+
+func newStaticWatcher(t *testing.T, dnsNames []string) *certwatch.Watcher {
+	t.Helper()
+
+	dir := t.TempDir()
+	certPEM, keyPEM := generateCertWithSANs(t, dnsNames)
+	certPath := filepath.Join(dir, "tls.crt")
+	keyPath := filepath.Join(dir, "tls.key")
+	require.NoError(t, os.WriteFile(certPath, certPEM, 0o600))
+	require.NoError(t, os.WriteFile(keyPath, keyPEM, 0o600))
+
+	w, err := certwatch.NewWatcher(certPath, keyPath, quietLifecycleLogger())
+	require.NoError(t, err)
+	return w
+}
+
+func TestStaticCertCovers(t *testing.T) {
+	s := &Server{
+		Logger:            quietLifecycleLogger(),
+		staticCertWatcher: newStaticWatcher(t, []string{"*.p.example.com", "exact.example.com"}),
+	}
+
+	cases := []struct {
+		domain  string
+		covered bool
+	}{
+		{"svc.p.example.com", true},
+		{"exact.example.com", true},
+		{"a.b.p.example.com", false}, // wildcard does not span labels
+		{"p.example.com", false},
+		{"other.example.com", false},
+	}
+	for _, tc := range cases {
+		t.Run(tc.domain, func(t *testing.T) {
+			assert.Equal(t, tc.covered, s.staticCertCovers(domain.Domain(tc.domain)))
+		})
+	}
+}
+
+func TestStaticCertCoversNoWatcher(t *testing.T) {
+	s := &Server{Logger: quietLifecycleLogger()}
+	assert.False(t, s.staticCertCovers(domain.Domain("svc.p.example.com")))
+}

shared/context/keys.go

@@ -6,4 +6,5 @@ const (
 	RoleKey      = "role"
 	UserIDKey    = "userID"
 	PeerIDKey    = "peerID"
+	UserAgentKey = "userAgent"
 )

shared/management/client/client_test.go

@@ -322,15 +322,21 @@ func TestClient_Sync(t *testing.T) {
 		if resp.GetNetbirdConfig() == nil {
 			t.Error("expecting non nil NetbirdConfig got nil")
 		}
-		if len(resp.GetRemotePeers()) != 1 {
-			t.Errorf("expecting RemotePeers size %d got %d", 1, len(resp.GetRemotePeers()))
+		// we test network map peers from 0.29.3 and dev builds
+		if len(resp.GetRemotePeers()) != 0 {
+			t.Error("expecting top-level RemotePeers to be empty for v0.29.3+ clients")
+		}
+		networkMap := resp.GetNetworkMap()
+		if len(networkMap.GetRemotePeers()) != 1 {
+			t.Errorf("expecting RemotePeers size %d got %d", 1, len(networkMap.GetRemotePeers()))
 			return
 		}
-		if resp.GetRemotePeersIsEmpty() == true {
+
+		if networkMap.GetRemotePeersIsEmpty() {
 			t.Error("expecting RemotePeers property to be false, got true")
 		}
-		if resp.GetRemotePeers()[0].GetWgPubKey() != remoteKey.PublicKey().String() {
-			t.Errorf("expecting RemotePeer public key %s got %s", remoteKey.PublicKey().String(), resp.GetRemotePeers()[0].GetWgPubKey())
+		if networkMap.GetRemotePeers()[0].GetWgPubKey() != remoteKey.PublicKey().String() {
+			t.Errorf("expecting RemotePeer public key %s got %s", remoteKey.PublicKey().String(), networkMap.GetRemotePeers()[0].GetWgPubKey())
 		}
 	case <-time.After(3 * time.Second):
 		t.Error("timeout waiting for test to finish")

shared/management/http/api/openapi.yml

@@ -5107,31 +5107,63 @@ components:
   responses:
     not_found:
       description: Resource not found
+      headers:
+        X-Request-Id:
+          $ref: '#/components/headers/X-Request-Id'
       content: { }
     validation_failed_simple:
       description: Validation failed
+      headers:
+        X-Request-Id:
+          $ref: '#/components/headers/X-Request-Id'
       content: { }
     bad_request:
       description: Bad Request
+      headers:
+        X-Request-Id:
+          $ref: '#/components/headers/X-Request-Id'
       content: { }
     internal_error:
       description: Internal Server Error
+      headers:
+        X-Request-Id:
+          $ref: '#/components/headers/X-Request-Id'
       content: { }
     validation_failed:
       description: Validation failed
+      headers:
+        X-Request-Id:
+          $ref: '#/components/headers/X-Request-Id'
       content: { }
     forbidden:
       description: Forbidden
+      headers:
+        X-Request-Id:
+          $ref: '#/components/headers/X-Request-Id'
       content: { }
     requires_authentication:
       description: Requires authentication
+      headers:
+        X-Request-Id:
+          $ref: '#/components/headers/X-Request-Id'
       content: { }
     conflict:
       description: Conflict
+      headers:
+        X-Request-Id:
+          $ref: '#/components/headers/X-Request-Id'
       content:
         application/json:
           schema:
             $ref: '#/components/schemas/ErrorResponse'
+  headers:
+    X-Request-Id:
+      description: |
+        Unique identifier assigned to the request by the server and set on every
+        response. Useful for correlating client requests with server-side logs.
+      schema:
+        type: string
+        example: cot7r4n3l3vh3qj4qveg
   securitySchemes:
     BearerAuth:
       type: http

shared/relay/client/client.go

@@ -9,12 +9,14 @@ import (
 	"net/url"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	log "github.com/sirupsen/logrus"
 
 	auth "github.com/netbirdio/netbird/shared/relay/auth/hmac"
 	"github.com/netbirdio/netbird/shared/relay/client/dialer"
+	netErr "github.com/netbirdio/netbird/shared/relay/client/dialer/net"
 	"github.com/netbirdio/netbird/shared/relay/healthcheck"
 	"github.com/netbirdio/netbird/shared/relay/messages"
 )
@@ -172,6 +174,19 @@ type Client struct {
 	stateSubscription *PeersStateSubscription
 
 	mtu uint16
+
+	// transportFallback, when set, records datagram-too-large failures so a
+	// datagram-sized transport is avoided on subsequent connects. Shared via
+	// the manager.
+	transportFallback *transportFallback
+	// datagramFallbackTriggered guards a single fallback per connection so a
+	// burst of oversized datagrams triggers one reconnect, not many.
+	datagramFallbackTriggered atomic.Bool
+}
+
+// SetTransportFallback wires the shared datagram-transport fallback tracker.
+func (c *Client) SetTransportFallback(tf *transportFallback) {
+	c.transportFallback = tf
 }
 
 // NewClient creates a new client for the relay server. The client is not connected to the server until the Connect
@@ -361,12 +376,13 @@ func (c *Client) Close() error {
 }
 
 func (c *Client) connect(ctx context.Context) (*RelayAddr, error) {
-	dialers := c.getDialers()
+	mode := transportModeFromEnv()
+	dialers := c.getDialers(mode)
 
 	var conn net.Conn
 	if c.serverIP.IsValid() {
 		var err error
-		conn, err = c.dialRaceDirect(ctx, dialers)
+		conn, err = c.dialRaceDirect(ctx, mode, dialers)
 		if err != nil {
 			c.log.Infof("dial via server IP %s failed, falling back to FQDN: %v", c.serverIP, err)
 			conn = nil
@@ -375,6 +391,9 @@ func (c *Client) connect(ctx context.Context) (*RelayAddr, error) {
 
 	if conn == nil {
 		rd := dialer.NewRaceDial(c.log, dialer.DefaultConnectionTimeout, c.connectionURL, dialers...)
+		if mode.sequential() {
+			rd.WithSequential()
+		}
 		var err error
 		conn, err = rd.Dial(ctx)
 		if err != nil {
@@ -382,6 +401,7 @@ func (c *Client) connect(ctx context.Context) (*RelayAddr, error) {
 		}
 	}
 	c.relayConn = conn
+	c.datagramFallbackTriggered.Store(false)
 
 	instanceURL, err := c.handShake(ctx)
 	if err != nil {
@@ -396,7 +416,7 @@ func (c *Client) connect(ctx context.Context) (*RelayAddr, error) {
 }
 
 // dialRaceDirect dials c.serverIP, preserving the original FQDN as the TLS ServerName for SNI.
-func (c *Client) dialRaceDirect(ctx context.Context, dialers []dialer.DialeFn) (net.Conn, error) {
+func (c *Client) dialRaceDirect(ctx context.Context, mode TransportMode, dialers []dialer.DialeFn) (net.Conn, error) {
 	directURL, serverName, err := substituteHost(c.connectionURL, c.serverIP)
 	if err != nil {
 		return nil, fmt.Errorf("substitute host: %w", err)
@@ -406,6 +426,9 @@ func (c *Client) dialRaceDirect(ctx context.Context, dialers []dialer.DialeFn) (
 
 	rd := dialer.NewRaceDial(c.log, dialer.DefaultConnectionTimeout, directURL, dialers...).
 		WithServerName(serverName)
+	if mode.sequential() {
+		rd.WithSequential()
+	}
 	return rd.Dial(ctx)
 }
 
@@ -631,13 +654,53 @@ func (c *Client) writeTo(containerRef *connContainer, dstID messages.PeerID, pay
 	}
 
 	// the write always return with 0 length because the underling does not support the size feedback.
-	_, err = c.relayConn.Write(msg)
+	conn := c.relayConn
+	_, err = conn.Write(msg)
 	if err != nil {
-		c.log.Errorf("failed to write transport message: %s", err)
+		if errors.Is(err, netErr.ErrDatagramTooLarge) {
+			c.onDatagramTooLarge(conn, err)
+		} else {
+			c.log.Errorf("failed to write transport message: %s", err)
+		}
 	}
 	return len(payload), err
 }
 
+// onDatagramTooLarge reacts to a datagram rejected as too large for the path.
+// When a non-datagram transport is available, it records a fallback for this
+// server and closes the connection so the reconnect avoids datagram-sized
+// transports. A single fallback is triggered per connection regardless of how
+// many oversized datagrams arrive. cause carries the datagram size and budget.
+func (c *Client) onDatagramTooLarge(conn net.Conn, cause error) {
+	// Handle one oversized datagram per connection; a burst triggers a single
+	// fallback (and a single log line), not many.
+	if !c.datagramFallbackTriggered.CompareAndSwap(false, true) {
+		return
+	}
+
+	// If the selected mode offers no non-datagram transport (e.g. pinned to a
+	// datagram-sized transport), reconnecting would just re-fail, so leave the
+	// connection up rather than loop.
+	if len(nonDatagramSized(c.baseDialers(transportModeFromEnv()))) == 0 {
+		c.log.Warnf("%s, but no non-datagram transport is available, not falling back", cause)
+		return
+	}
+
+	// Without the shared tracker a reconnect would just select the same
+	// transport again and re-fail, so leave the connection up rather than loop.
+	if c.transportFallback == nil {
+		c.log.Debugf("%s, but no transport fallback configured, leaving connection up", cause)
+		return
+	}
+
+	window := c.transportFallback.recordFailure(c.connectionURL)
+	c.log.Warnf("%s, avoiding datagram-sized transport for %s", cause, window)
+
+	if err := conn.Close(); err != nil {
+		c.log.Debugf("close relay connection for transport fallback: %s", err)
+	}
+}
+
 func (c *Client) listenForStopEvents(ctx context.Context, hc *healthcheck.Receiver, conn net.Conn, internalStopFlag *internalStopFlag) {
 	for {
 		select {

shared/relay/client/dialer/capability.go

@@ -0,0 +1,18 @@
+package dialer
+
+// DatagramSized is implemented by dialers whose connections carry each write in
+// a single datagram, so a write can be rejected when it exceeds the path's
+// datagram budget (e.g. QUIC). Transports without this capability (e.g.
+// WebSocket over TCP) impose no per-write size limit, so the relay client can
+// fall back to them when a datagram-sized transport rejects a write as too
+// large. The capability is advertised per dialer rather than hardcoded, so a
+// new transport only needs to declare whether it is datagram-sized.
+type DatagramSized interface {
+	DatagramSized()
+}
+
+// IsDatagramSized reports whether d produces datagram-sized connections.
+func IsDatagramSized(d DialeFn) bool {
+	_, ok := d.(DatagramSized)
+	return ok
+}

shared/relay/client/dialer/net/err.go

@@ -4,4 +4,9 @@ import "errors"
 
 var (
 	ErrClosedByServer = errors.New("closed by server")
+
+	// ErrDatagramTooLarge is returned when a transport message exceeds the
+	// QUIC datagram size the path to the relay can carry. The relay client
+	// treats it as a signal to fall back to a non-datagram transport.
+	ErrDatagramTooLarge = errors.New("datagram frame too large")
 )

shared/relay/client/dialer/quic/conn.go

@@ -8,7 +8,6 @@ import (
 	"time"
 
 	"github.com/quic-go/quic-go"
-	log "github.com/sirupsen/logrus"
 
 	netErr "github.com/netbirdio/netbird/shared/relay/client/dialer/net"
 )
@@ -52,11 +51,8 @@ func (c *Conn) Read(b []byte) (n int, err error) {
 }
 
 func (c *Conn) Write(b []byte) (int, error) {
-	err := c.session.SendDatagram(b)
-	if err != nil {
-		err = c.remoteCloseErrHandling(err)
-		log.Errorf("failed to write to QUIC stream: %v", err)
-		return 0, err
+	if err := c.session.SendDatagram(b); err != nil {
+		return 0, c.writeErrHandling(err, len(b))
 	}
 	return len(b), nil
 }
@@ -95,3 +91,15 @@ func (c *Conn) remoteCloseErrHandling(err error) error {
 	}
 	return err
 }
+
+// writeErrHandling normalizes SendDatagram errors. A datagram that exceeds the
+// path's QUIC packet budget is mapped to ErrDatagramTooLarge (annotated with the
+// datagram size and path budget) so the relay client can fall back to a
+// non-datagram transport.
+func (c *Conn) writeErrHandling(err error, size int) error {
+	var tooLarge *quic.DatagramTooLargeError
+	if errors.As(err, &tooLarge) {
+		return fmt.Errorf("%w: %d byte datagram over path budget %d", netErr.ErrDatagramTooLarge, size, tooLarge.MaxDatagramPayloadSize)
+	}
+	return c.remoteCloseErrHandling(err)
+}

shared/relay/client/dialer/quic/quic.go

@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/quic-go/quic-go"
+	"github.com/quic-go/quic-go/logging"
 	log "github.com/sirupsen/logrus"
 
 	nbnet "github.com/netbirdio/netbird/client/net"
@@ -23,6 +24,12 @@ func (d Dialer) Protocol() string {
 	return Network
 }
 
+// DatagramSized marks QUIC as a datagram-sized transport: relay traffic is
+// carried in QUIC DATAGRAM frames, which must fit a single packet.
+func (d Dialer) DatagramSized() {
+	// Intentional marker method; presence is the capability signal.
+}
+
 func (d Dialer) Dial(ctx context.Context, address, serverName string) (net.Conn, error) {
 	quicURL, err := prepareURL(address)
 	if err != nil {
@@ -47,6 +54,7 @@ func (d Dialer) Dial(ctx context.Context, address, serverName string) (net.Conn,
 		MaxIdleTimeout:    4 * time.Minute,
 		EnableDatagrams:   true,
 		InitialPacketSize: nbRelay.QUICInitialPacketSize,
+		Tracer:            connectionTracer(quicURL),
 	}
 
 	udpConn, err := nbnet.ListenUDP("udp", &net.UDPAddr{Port: 0})
@@ -74,6 +82,28 @@ func (d Dialer) Dial(ctx context.Context, address, serverName string) (net.Conn,
 	return conn, nil
 }
 
+// connectionTracer returns a QUIC tracer that logs the DPLPMTUD result and the
+// reason a relay connection closed, so the path MTU settled on and teardown
+// cause are visible in logs. Lines carry the relay address as a structured
+// field, matching the rest of the relay client logging.
+func connectionTracer(addr string) func(context.Context, logging.Perspective, quic.ConnectionID) *logging.ConnectionTracer {
+	relayLog := log.WithField("relay", addr)
+	return func(context.Context, logging.Perspective, quic.ConnectionID) *logging.ConnectionTracer {
+		return &logging.ConnectionTracer{
+			UpdatedMTU: func(mtu logging.ByteCount, done bool) {
+				if done {
+					relayLog.Infof("QUIC path MTU settled at %d", mtu)
+					return
+				}
+				relayLog.Debugf("QUIC path MTU probing at %d", mtu)
+			},
+			ClosedConnection: func(err error) {
+				relayLog.Debugf("QUIC connection closed: %v", err)
+			},
+		}
+	}
+}
+
 func prepareURL(address string) (string, error) {
 	var host string
 	var defaultPort string

shared/relay/client/dialer/race_dialer.go

@@ -32,6 +32,7 @@ type RaceDial struct {
 	serverName        string
 	dialerFns         []DialeFn
 	connectionTimeout time.Duration
+	sequential        bool
 }
 
 func NewRaceDial(log *log.Entry, connectionTimeout time.Duration, serverURL string, dialerFns ...DialeFn) *RaceDial {
@@ -53,7 +54,21 @@ func (r *RaceDial) WithServerName(serverName string) *RaceDial {
 	return r
 }
 
+// WithSequential makes Dial try the dialers in order, falling back to the next
+// only when one fails to connect, instead of racing them concurrently.
+//
+// Mutates the receiver and is not safe for concurrent reconfiguration; a
+// RaceDial is intended to be constructed per dial and discarded.
+func (r *RaceDial) WithSequential() *RaceDial {
+	r.sequential = true
+	return r
+}
+
 func (r *RaceDial) Dial(ctx context.Context) (net.Conn, error) {
+	if r.sequential {
+		return r.dialSequential(ctx)
+	}
+
 	connChan := make(chan dialResult, len(r.dialerFns))
 	winnerConn := make(chan net.Conn, 1)
 	abortCtx, abort := context.WithCancel(ctx)
@@ -72,6 +87,30 @@ func (r *RaceDial) Dial(ctx context.Context) (net.Conn, error) {
 	return conn, nil
 }
 
+// dialSequential tries each dialer in order, returning the first connection and
+// falling back to the next on failure.
+func (r *RaceDial) dialSequential(ctx context.Context) (net.Conn, error) {
+	for _, dfn := range r.dialerFns {
+		if err := ctx.Err(); err != nil {
+			return nil, err
+		}
+		attemptCtx, cancel := context.WithTimeout(ctx, r.connectionTimeout)
+		r.log.Infof("dialing Relay server via %s", dfn.Protocol())
+		conn, err := dfn.Dial(attemptCtx, r.serverURL, r.serverName)
+		cancel()
+		if err != nil {
+			if errors.Is(err, context.Canceled) {
+				return nil, err
+			}
+			r.log.Errorf("failed to dial via %s: %s", dfn.Protocol(), err)
+			continue
+		}
+		r.log.Infof("successfully dialed via: %s", dfn.Protocol())
+		return conn, nil
+	}
+	return nil, errors.New("failed to dial to Relay server on any protocol")
+}
+
 func (r *RaceDial) dial(dfn DialeFn, abortCtx context.Context, connChan chan dialResult) {
 	ctx, cancel := context.WithTimeout(abortCtx, r.connectionTimeout)
 	defer cancel()

shared/relay/client/dialer/race_dialer_test.go

@@ -250,3 +250,66 @@ func TestRaceDialFirstSuccessfulDialerWins(t *testing.T) {
 		}
 	}
 }
+
+func TestRaceDialSequentialFallback(t *testing.T) {
+	logger := logrus.NewEntry(logrus.New())
+	serverURL := "test.server.com"
+
+	var firstDialed, secondDialed bool
+	preferred := &MockDialer{
+		protocolStr: "quic",
+		dialFunc: func(ctx context.Context, address string) (net.Conn, error) {
+			firstDialed = true
+			return nil, errors.New("quic unreachable")
+		},
+	}
+	fallbackConn := &MockConn{remoteAddr: &MockAddr{network: "ws"}}
+	fallback := &MockDialer{
+		protocolStr: "ws",
+		dialFunc: func(ctx context.Context, address string) (net.Conn, error) {
+			secondDialed = true
+			return fallbackConn, nil
+		},
+	}
+
+	rd := NewRaceDial(logger, DefaultConnectionTimeout, serverURL, preferred, fallback).WithSequential()
+	conn, err := rd.Dial(context.Background())
+	if err != nil {
+		t.Fatalf("expected fallback to succeed, got %v", err)
+	}
+	if conn != fallbackConn {
+		t.Errorf("expected fallback connection, got %v", conn)
+	}
+	if !firstDialed || !secondDialed {
+		t.Errorf("expected both dialers attempted in order, first=%v second=%v", firstDialed, secondDialed)
+	}
+}
+
+func TestRaceDialSequentialPreferredWins(t *testing.T) {
+	logger := logrus.NewEntry(logrus.New())
+	serverURL := "test.server.com"
+
+	preferredConn := &MockConn{remoteAddr: &MockAddr{network: "quic"}}
+	preferred := &MockDialer{
+		protocolStr: "quic",
+		dialFunc: func(ctx context.Context, address string) (net.Conn, error) {
+			return preferredConn, nil
+		},
+	}
+	fallback := &MockDialer{
+		protocolStr: "ws",
+		dialFunc: func(ctx context.Context, address string) (net.Conn, error) {
+			t.Errorf("fallback dialer must not be tried when preferred succeeds")
+			return nil, errors.New("should not happen")
+		},
+	}
+
+	rd := NewRaceDial(logger, DefaultConnectionTimeout, serverURL, preferred, fallback).WithSequential()
+	conn, err := rd.Dial(context.Background())
+	if err != nil {
+		t.Fatalf("expected preferred to succeed, got %v", err)
+	}
+	if conn != preferredConn {
+		t.Errorf("expected preferred connection, got %v", conn)
+	}
+}

shared/relay/client/dialers_generic.go

@@ -9,11 +9,42 @@ import (
 	"github.com/netbirdio/netbird/shared/relay/client/dialer/ws"
 )
 
-// getDialers returns the list of dialers to use for connecting to the relay server.
-func (c *Client) getDialers() []dialer.DialeFn {
-	if c.mtu > 0 && c.mtu > iface.DefaultMTU {
-		c.log.Infof("MTU %d exceeds default (%d), forcing WebSocket transport to avoid DATAGRAM frame size issues", c.mtu, iface.DefaultMTU)
-		return []dialer.DialeFn{ws.Dialer{}}
+// getDialers returns the ordered dialers for connecting to the relay server. It
+// applies the datagram fallback generically: if this server recently rejected a
+// datagram-sized transport, those dialers are dropped, leaving the rest.
+func (c *Client) getDialers(mode TransportMode) []dialer.DialeFn {
+	dialers := c.baseDialers(mode)
+
+	if c.transportFallback != nil && c.transportFallback.avoidDatagramSized(c.connectionURL) {
+		if filtered := nonDatagramSized(dialers); len(filtered) > 0 {
+			c.log.Infof("relay recently rejected a datagram-sized transport, avoiding it")
+			return filtered
+		}
 	}
-	return []dialer.DialeFn{quic.Dialer{}, ws.Dialer{}}
+	return dialers
+}
+
+// baseDialers returns the ordered dialers for the mode, before any datagram
+// fallback filtering. For racing modes (auto) the order is irrelevant; for
+// prefer modes the first entry is tried before falling back to the second.
+func (c *Client) baseDialers(mode TransportMode) []dialer.DialeFn {
+	switch mode {
+	case TransportModeWS:
+		c.log.Infof("%s=ws, using WebSocket transport", EnvRelayTransport)
+		return []dialer.DialeFn{ws.Dialer{}}
+	case TransportModeQUIC:
+		c.log.Infof("%s=quic, using QUIC transport", EnvRelayTransport)
+		return []dialer.DialeFn{quic.Dialer{}}
+	}
+
+	all := []dialer.DialeFn{quic.Dialer{}, ws.Dialer{}}
+	if mode == TransportModePreferWS {
+		all = []dialer.DialeFn{ws.Dialer{}, quic.Dialer{}}
+	}
+
+	if c.mtu > 0 && c.mtu > iface.DefaultMTU {
+		c.log.Infof("MTU %d exceeds default (%d), avoiding datagram-sized transports", c.mtu, iface.DefaultMTU)
+		return nonDatagramSized(all)
+	}
+	return all
 }

shared/relay/client/dialers_generic_test.go

@@ -0,0 +1,101 @@
+//go:build !js
+
+package client
+
+import (
+	"os"
+	"testing"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+
+	"github.com/netbirdio/netbird/client/iface"
+	"github.com/netbirdio/netbird/shared/relay/client/dialer"
+	netErr "github.com/netbirdio/netbird/shared/relay/client/dialer/net"
+	"github.com/netbirdio/netbird/shared/relay/client/dialer/quic"
+	"github.com/netbirdio/netbird/shared/relay/client/dialer/ws"
+)
+
+// TestDatagramSizedCapability locks the capability the generic fallback relies
+// on: QUIC is datagram-sized, WebSocket is not.
+func TestDatagramSizedCapability(t *testing.T) {
+	assert.True(t, dialer.IsDatagramSized(quic.Dialer{}), "QUIC must advertise datagram-sized")
+	assert.False(t, dialer.IsDatagramSized(ws.Dialer{}), "WebSocket must not advertise datagram-sized")
+}
+
+func protocols(dialers []dialer.DialeFn) []string {
+	out := make([]string, len(dialers))
+	for i, d := range dialers {
+		out[i] = d.Protocol()
+	}
+	return out
+}
+
+func TestGetDialers(t *testing.T) {
+	const url = "rels://relay.example:443"
+
+	tests := []struct {
+		name     string
+		mode     string
+		mtu      uint16
+		preferWS bool
+		want     []string
+	}{
+		{name: "auto races quic and ws", mode: "auto", mtu: iface.DefaultMTU, want: []string{"quic", "WS"}},
+		{name: "ws pinned", mode: "ws", mtu: iface.DefaultMTU, want: []string{"WS"}},
+		{name: "quic pinned", mode: "quic", mtu: iface.DefaultMTU, want: []string{"quic"}},
+		{name: "prefer-quic orders quic first", mode: "prefer-quic", mtu: iface.DefaultMTU, want: []string{"quic", "WS"}},
+		{name: "prefer-ws orders ws first", mode: "prefer-ws", mtu: iface.DefaultMTU, want: []string{"WS", "quic"}},
+		{name: "mtu above default forces ws", mode: "auto", mtu: iface.DefaultMTU + 100, want: []string{"WS"}},
+		{name: "sticky fallback forces ws in auto", mode: "auto", mtu: iface.DefaultMTU, preferWS: true, want: []string{"WS"}},
+		{name: "sticky fallback forces ws in prefer-quic", mode: "prefer-quic", mtu: iface.DefaultMTU, preferWS: true, want: []string{"WS"}},
+		{name: "quic pin overrides sticky fallback", mode: "quic", mtu: iface.DefaultMTU, preferWS: true, want: []string{"quic"}},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Setenv(EnvRelayTransport, tc.mode)
+			if tc.mode == "" {
+				os.Unsetenv(EnvRelayTransport)
+			}
+
+			tf := newTransportFallback()
+			if tc.preferWS {
+				tf.recordFailure(url)
+			}
+
+			c := &Client{
+				log:               log.WithField("test", t.Name()),
+				connectionURL:     url,
+				mtu:               tc.mtu,
+				transportFallback: tf,
+			}
+
+			assert.Equal(t, tc.want, protocols(c.getDialers(transportModeFromEnv())))
+		})
+	}
+}
+
+// TestStickyFallbackAfterDatagramTooLarge verifies the full chain: an oversized
+// datagram records a fallback that makes the next dial pick WebSocket, the way a
+// reconnect would after the connection is closed.
+func TestStickyFallbackAfterDatagramTooLarge(t *testing.T) {
+	const url = "rels://relay.example:443"
+	t.Setenv(EnvRelayTransport, string(TransportModeAuto))
+
+	c := &Client{
+		log:               log.WithField("test", t.Name()),
+		connectionURL:     url,
+		mtu:               iface.DefaultMTU,
+		transportFallback: newTransportFallback(),
+	}
+
+	// First dial races both transports.
+	assert.Equal(t, []string{"quic", "WS"}, protocols(c.getDialers(transportModeFromEnv())))
+
+	// An oversized datagram records the fallback for this server.
+	c.onDatagramTooLarge(&closeTrackingConn{}, netErr.ErrDatagramTooLarge)
+
+	// The reconnect now sticks to WebSocket.
+	assert.Equal(t, []string{"WS"}, protocols(c.getDialers(transportModeFromEnv())))
+}

shared/relay/client/dialers_js.go

@@ -7,7 +7,11 @@ import (
 	"github.com/netbirdio/netbird/shared/relay/client/dialer/ws"
 )
 
-func (c *Client) getDialers() []dialer.DialeFn {
+func (c *Client) getDialers(_ TransportMode) []dialer.DialeFn {
 	// JS/WASM build only uses WebSocket transport
 	return []dialer.DialeFn{ws.Dialer{}}
 }
+
+func (c *Client) baseDialers(_ TransportMode) []dialer.DialeFn {
+	return []dialer.DialeFn{ws.Dialer{}}
+}

shared/relay/client/manager.go

@@ -79,23 +79,30 @@ type Manager struct {
 
 	cleanupInterval      time.Duration
 	keepUnusedServerTime time.Duration
+
+	// transportFallback is shared across home and foreign relay clients so a
+	// datagram-too-large failure makes that server avoid datagram-sized transports across reconnects.
+	transportFallback *transportFallback
 }
 
 // NewManager creates a new manager instance.
 // The serverURL address can be empty. In this case, the manager will not serve.
 func NewManager(ctx context.Context, serverURLs []string, peerID string, mtu uint16, opts ...ManagerOption) *Manager {
 	tokenStore := &relayAuth.TokenStore{}
+	tf := newTransportFallback()
 
 	m := &Manager{
-		ctx:        ctx,
-		peerID:     peerID,
-		tokenStore: tokenStore,
-		mtu:        mtu,
+		ctx:               ctx,
+		peerID:            peerID,
+		tokenStore:        tokenStore,
+		mtu:               mtu,
+		transportFallback: tf,
 		serverPicker: &ServerPicker{
 			TokenStore:        tokenStore,
 			PeerID:            peerID,
 			MTU:               mtu,
 			ConnectionTimeout: defaultConnectionTimeout,
+			TransportFallback: tf,
 		},
 		relayClients:            make(map[string]*RelayTrack),
 		onDisconnectedListeners: make(map[string]*list.List),
@@ -287,6 +294,7 @@ func (m *Manager) openConnVia(ctx context.Context, serverAddress, peerKey string
 	m.relayClientsMutex.Unlock()
 
 	relayClient := NewClientWithServerIP(serverAddress, serverIP, m.tokenStore, m.peerID, m.mtu)
+	relayClient.SetTransportFallback(m.transportFallback)
 	err := relayClient.Connect(m.ctx)
 	if err != nil {
 		rt.err = err

shared/relay/client/picker.go

@@ -29,6 +29,7 @@ type ServerPicker struct {
 	PeerID            string
 	MTU               uint16
 	ConnectionTimeout time.Duration
+	TransportFallback *transportFallback
 }
 
 func (sp *ServerPicker) PickServer(parentCtx context.Context) (*Client, error) {
@@ -70,6 +71,7 @@ func (sp *ServerPicker) PickServer(parentCtx context.Context) (*Client, error) {
 func (sp *ServerPicker) startConnection(ctx context.Context, resultChan chan connResult, url string) {
 	log.Infof("try to connecting to relay server: %s", url)
 	relayClient := NewClient(url, sp.TokenStore, sp.PeerID, sp.MTU)
+	relayClient.SetTransportFallback(sp.TransportFallback)
 	err := relayClient.Connect(ctx)
 	resultChan <- connResult{
 		RelayClient: relayClient,

shared/relay/client/transport.go

@@ -0,0 +1,129 @@
+package client
+
+import (
+	"os"
+	"strings"
+	"sync"
+	"time"
+
+	log "github.com/sirupsen/logrus"
+
+	"github.com/netbirdio/netbird/shared/relay/client/dialer"
+)
+
+// EnvRelayTransport pins the relay transport. Valid values: "auto" (default,
+// race QUIC and WebSocket), "quic" (QUIC only), "ws" (WebSocket only),
+// "prefer-quic" / "prefer-ws" (try the preferred transport first, fall back to
+// the other only if it fails to connect; no race). The prefer modes trade a
+// slower connect when the preferred transport is blackholed for deterministic
+// transport selection.
+const EnvRelayTransport = "NB_RELAY_TRANSPORT"
+
+const (
+	// transportFallbackBase is the initial window a relay server avoids
+	// datagram-sized transports after a datagram is rejected as too large.
+	transportFallbackBase = 10 * time.Minute
+	// transportFallbackMax caps the pinned window when failures repeat.
+	transportFallbackMax = 60 * time.Minute
+)
+
+// TransportMode selects which relay dialers are used.
+type TransportMode string
+
+const (
+	TransportModeAuto       TransportMode = "auto"
+	TransportModeQUIC       TransportMode = "quic"
+	TransportModeWS         TransportMode = "ws"
+	TransportModePreferQUIC TransportMode = "prefer-quic"
+	TransportModePreferWS   TransportMode = "prefer-ws"
+)
+
+// transportModeFromEnv reads EnvRelayTransport, defaulting to auto for an empty
+// or unrecognized value.
+func transportModeFromEnv() TransportMode {
+	switch TransportMode(strings.ToLower(strings.TrimSpace(os.Getenv(EnvRelayTransport)))) {
+	case "", TransportModeAuto:
+		return TransportModeAuto
+	case TransportModeQUIC:
+		return TransportModeQUIC
+	case TransportModeWS:
+		return TransportModeWS
+	case TransportModePreferQUIC:
+		return TransportModePreferQUIC
+	case TransportModePreferWS:
+		return TransportModePreferWS
+	default:
+		log.Warnf("invalid %s value %q, using %q", EnvRelayTransport, os.Getenv(EnvRelayTransport), TransportModeAuto)
+		return TransportModeAuto
+	}
+}
+
+// sequential reports whether the mode tries dialers in order with fallback
+// instead of racing them concurrently.
+func (m TransportMode) sequential() bool {
+	return m == TransportModePreferQUIC || m == TransportModePreferWS
+}
+
+// transportFallback tracks relay servers that have rejected a datagram-sized
+// transport (a write too large for the path) and should temporarily avoid such
+// transports. It is shared across the relay manager so the preference survives
+// client recreation (foreign relay clients are evicted and rebuilt on
+// disconnect). Entries are keyed by server URL and expire after a window that
+// grows on repeated failures.
+type transportFallback struct {
+	mu      sync.Mutex
+	entries map[string]*fallbackEntry
+}
+
+type fallbackEntry struct {
+	until    time.Time
+	duration time.Duration
+}
+
+func newTransportFallback() *transportFallback {
+	return &transportFallback{entries: make(map[string]*fallbackEntry)}
+}
+
+// avoidDatagramSized reports whether serverURL is currently within a window
+// where datagram-sized transports should be avoided.
+func (f *transportFallback) avoidDatagramSized(serverURL string) bool {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	e := f.entries[serverURL]
+	return e != nil && time.Now().Before(e.until)
+}
+
+// recordFailure makes serverURL avoid datagram-sized transports for a window:
+// transportFallbackBase on the first failure, doubling up to transportFallbackMax
+// when a datagram transport fails again after a previous window expired. It
+// returns the active window duration.
+func (f *transportFallback) recordFailure(serverURL string) time.Duration {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+
+	now := time.Now()
+	e := f.entries[serverURL]
+	switch {
+	case e == nil:
+		e = &fallbackEntry{duration: transportFallbackBase}
+		f.entries[serverURL] = e
+	case now.Before(e.until):
+		return time.Until(e.until)
+	default:
+		e.duration = min(e.duration*2, transportFallbackMax)
+	}
+	e.until = now.Add(e.duration)
+	return e.duration
+}
+
+// nonDatagramSized returns the dialers from in that are not datagram-sized,
+// preserving order.
+func nonDatagramSized(in []dialer.DialeFn) []dialer.DialeFn {
+	out := make([]dialer.DialeFn, 0, len(in))
+	for _, d := range in {
+		if !dialer.IsDatagramSized(d) {
+			out = append(out, d)
+		}
+	}
+	return out
+}

shared/relay/client/transport_test.go

@@ -0,0 +1,140 @@
+package client
+
+import (
+	"net"
+	"os"
+	"testing"
+	"time"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	netErr "github.com/netbirdio/netbird/shared/relay/client/dialer/net"
+)
+
+// closeTrackingConn records whether Close was called; only Close is exercised.
+type closeTrackingConn struct {
+	net.Conn
+	closed bool
+}
+
+func (c *closeTrackingConn) Close() error {
+	c.closed = true
+	return nil
+}
+
+func TestTransportModeFromEnv(t *testing.T) {
+	tests := []struct {
+		value string
+		want  TransportMode
+	}{
+		{"", TransportModeAuto},
+		{"auto", TransportModeAuto},
+		{"quic", TransportModeQUIC},
+		{"QUIC", TransportModeQUIC},
+		{"ws", TransportModeWS},
+		{" Ws ", TransportModeWS},
+		{"prefer-quic", TransportModePreferQUIC},
+		{"prefer-ws", TransportModePreferWS},
+		{"garbage", TransportModeAuto},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.value, func(t *testing.T) {
+			t.Setenv(EnvRelayTransport, tc.value)
+			if tc.value == "" {
+				os.Unsetenv(EnvRelayTransport)
+			}
+			assert.Equal(t, tc.want, transportModeFromEnv())
+		})
+	}
+}
+
+func TestTransportFallbackRecordAndExpiry(t *testing.T) {
+	const url = "rels://relay.example:443"
+	f := newTransportFallback()
+
+	assert.False(t, f.avoidDatagramSized(url), "no fallback recorded yet")
+
+	d := f.recordFailure(url)
+	assert.Equal(t, transportFallbackBase, d, "first failure pins for the base window")
+	assert.True(t, f.avoidDatagramSized(url), "datagram-sized transport avoided within the window")
+
+	// A second failure while still inside the window must not grow the window.
+	d = f.recordFailure(url)
+	assert.LessOrEqual(t, d, transportFallbackBase, "still within the active window")
+	require.NotNil(t, f.entries[url])
+	assert.Equal(t, transportFallbackBase, f.entries[url].duration, "duration unchanged inside window")
+
+	// Expire the window: datagram-sized transport allowed again.
+	f.entries[url].until = time.Now().Add(-time.Second)
+	assert.False(t, f.avoidDatagramSized(url), "window expired, datagram-sized transport allowed")
+}
+
+func TestTransportFallbackGrowsOnRepeat(t *testing.T) {
+	const url = "rels://relay.example:443"
+	f := newTransportFallback()
+
+	want := transportFallbackBase
+	for i := range 6 {
+		d := f.recordFailure(url)
+		assert.Equal(t, want, d, "window after %d expiries", i)
+
+		// expire the window so the next failure is treated as a repeat
+		f.entries[url].until = time.Now().Add(-time.Second)
+
+		want = min(want*2, transportFallbackMax)
+	}
+
+	assert.Equal(t, transportFallbackMax, f.entries[url].duration, "window caps at the max")
+}
+
+func TestOnDatagramTooLargeAuto(t *testing.T) {
+	const url = "rels://relay.example:443"
+	t.Setenv(EnvRelayTransport, string(TransportModeAuto))
+
+	tf := newTransportFallback()
+	c := &Client{
+		log:               log.WithField("test", t.Name()),
+		connectionURL:     url,
+		transportFallback: tf,
+	}
+	conn := &closeTrackingConn{}
+
+	c.onDatagramTooLarge(conn, netErr.ErrDatagramTooLarge)
+
+	assert.True(t, conn.closed, "connection closed to force reconnect")
+	assert.True(t, tf.avoidDatagramSized(url), "fallback recorded for the server")
+
+	// A second oversized datagram on the same connection must not re-close.
+	conn.closed = false
+	c.onDatagramTooLarge(conn, netErr.ErrDatagramTooLarge)
+	assert.False(t, conn.closed, "single fallback per connection")
+}
+
+func TestOnDatagramTooLargeQUICPinned(t *testing.T) {
+	const url = "rels://relay.example:443"
+	t.Setenv(EnvRelayTransport, string(TransportModeQUIC))
+
+	tf := newTransportFallback()
+	c := &Client{
+		log:               log.WithField("test", t.Name()),
+		connectionURL:     url,
+		transportFallback: tf,
+	}
+	conn := &closeTrackingConn{}
+
+	c.onDatagramTooLarge(conn, netErr.ErrDatagramTooLarge)
+
+	assert.False(t, conn.closed, "QUIC pin keeps the connection, no fallback redial")
+	assert.False(t, tf.avoidDatagramSized(url), "QUIC pin records no fallback")
+}
+
+func TestTransportFallbackPerServer(t *testing.T) {
+	f := newTransportFallback()
+	f.recordFailure("rels://a.example:443")
+
+	assert.True(t, f.avoidDatagramSized("rels://a.example:443"))
+	assert.False(t, f.avoidDatagramSized("rels://b.example:443"), "fallback is scoped to one server")
+}