add support for disabling relay via environment variable

* [relay] reduce QUIC initial packet size to 1280 (IPv6 min MTU)

* adjust QUIC initial packet size to 1232 based on RFC 9000 §14

client/iface/iface_test.go

@@ -589,6 +589,101 @@ func Test_ConnectPeers(t *testing.T) {
 
 }
 
+func Test_UserSpaceAddAllowedIPs(t *testing.T) {
+	ifaceName := fmt.Sprintf("utun%d", WgIntNumber+5)
+	wgIP := "10.99.99.21/30"
+	wgPort := 33105
+
+	newNet, err := stdnet.NewNet(context.Background(), nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	opts := WGIFaceOpts{
+		IFaceName:    ifaceName,
+		Address:      wgIP,
+		WGPort:       wgPort,
+		WGPrivKey:    key,
+		MTU:          DefaultMTU,
+		TransportNet: newNet,
+	}
+
+	iface, err := NewWGIFace(opts)
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = iface.Create()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		if err := iface.Close(); err != nil {
+			t.Error(err)
+		}
+	}()
+
+	_, err = iface.Up()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	keepAlive := 15 * time.Second
+	initialAllowedIP := netip.MustParsePrefix("10.99.99.22/32")
+	endpoint, err := net.ResolveUDPAddr("udp", "127.0.0.1:9905")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Add peer with initial endpoint and first allowed IP
+	err = iface.UpdatePeer(peerPubKey, []netip.Prefix{initialAllowedIP}, keepAlive, endpoint, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Phase 1: generate 500 allowed IPs into a list
+	const extraIPs = 500
+	addedPrefixes := make([]netip.Prefix, 0, extraIPs)
+	for i := 0; i < extraIPs; i++ {
+		// Use 172.16.x.y/32 range: i encoded as two octets
+		prefix := netip.MustParsePrefix(fmt.Sprintf("172.16.%d.%d/32", i/256, i%256))
+		addedPrefixes = append(addedPrefixes, prefix)
+	}
+
+	// Phase 2: iterate over the list and add each allowed IP to the peer
+	phase2Start := time.Now()
+	for _, prefix := range addedPrefixes {
+		if addErr := iface.AddAllowedIP(peerPubKey, prefix); addErr != nil {
+			t.Fatalf("failed to add allowed IP %s: %v", prefix, addErr)
+		}
+	}
+	t.Logf("Phase 2 (add %d IPs to peer): %s", extraIPs, time.Since(phase2Start))
+
+	// Verify the peer has all 101 allowed IPs (1 initial + 100 added)
+	peer, err := getPeer(ifaceName, peerPubKey)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if peer.Endpoint.String() != endpoint.String() {
+		t.Fatalf("expected endpoint %s, got %s", endpoint, peer.Endpoint)
+	}
+
+	allExpected := append([]netip.Prefix{initialAllowedIP}, addedPrefixes...)
+	if len(peer.AllowedIPs) != len(allExpected) {
+		t.Fatalf("expected %d allowed IPs, got %d", len(allExpected), len(peer.AllowedIPs))
+	}
+
+	allowedIPSet := make(map[string]struct{}, len(peer.AllowedIPs))
+	for _, aip := range peer.AllowedIPs {
+		allowedIPSet[aip.String()] = struct{}{}
+	}
+	for _, expected := range allExpected {
+		if _, found := allowedIPSet[expected.String()]; !found {
+			t.Errorf("expected allowed IP %s not found in peer config", expected)
+		}
+	}
+}
+
 func getPeer(ifaceName, peerPubKey string) (wgtypes.Peer, error) {
 	wg, err := wgctrl.New()
 	if err != nil {

client/internal/connect.go

@@ -290,6 +290,10 @@ func (c *ConnectClient) run(mobileDependency MobileDependency, runningChan chan
 			return wrapErr(err)
 		}
 
+		if relayClient.IsDisableRelay() {
+			relayURLs = []string{}
+		}
+
 		relayManager := relayClient.NewManager(engineCtx, relayURLs, myPrivateKey.PublicKey().String(), engineConfig.MTU)
 		c.statusRecorder.SetRelayMgr(relayManager)
 		if len(relayURLs) > 0 {
@@ -310,6 +314,8 @@ func (c *ConnectClient) run(mobileDependency MobileDependency, runningChan chan
 		c.engineMutex.Lock()
 		engine := NewEngine(engineCtx, cancel, signalClient, mgmClient, relayManager, engineConfig, mobileDependency, c.statusRecorder, checks, stateManager)
 		engine.SetSyncResponsePersistence(c.persistSyncResponse)
+		engine.SetReadyChan(runningChan)
+		runningChan = nil
 		c.engine = engine
 		c.engineMutex.Unlock()
 
@@ -330,11 +336,6 @@ func (c *ConnectClient) run(mobileDependency MobileDependency, runningChan chan
 		log.Infof("Netbird engine started, the IP is: %s", peerConfig.GetAddress())
 		state.Set(StatusConnected)
 
-		if runningChan != nil {
-			close(runningChan)
-			runningChan = nil
-		}
-
 		<-engineCtx.Done()
 
 		c.engineMutex.Lock()

client/internal/engine.go

@@ -28,8 +28,8 @@ import (
 	"github.com/netbirdio/netbird/client/firewall"
 	firewallManager "github.com/netbirdio/netbird/client/firewall/manager"
 	"github.com/netbirdio/netbird/client/iface"
-	nbnetstack "github.com/netbirdio/netbird/client/iface/netstack"
 	"github.com/netbirdio/netbird/client/iface/device"
+	nbnetstack "github.com/netbirdio/netbird/client/iface/netstack"
 	"github.com/netbirdio/netbird/client/iface/udpmux"
 	"github.com/netbirdio/netbird/client/internal/acl"
 	"github.com/netbirdio/netbird/client/internal/debug"
@@ -217,6 +217,10 @@ type Engine struct {
 	// WireGuard interface monitor
 	wgIfaceMonitor *WGIfaceMonitor
 
+	// readyChan is closed when the first sync message is received from management
+	readyChan     chan struct{}
+	readyChanOnce sync.Once
+
 	// shutdownWg tracks all long-running goroutines to ensure clean shutdown
 	shutdownWg sync.WaitGroup
 
@@ -275,6 +279,10 @@ func NewEngine(
 	return engine
 }
 
+func (e *Engine) SetReadyChan(ch chan struct{}) {
+	e.readyChan = ch
+}
+
 func (e *Engine) Stop() error {
 	if e == nil {
 		// this seems to be a very odd case but there was the possibility if the netbird down command comes before the engine is fully started
@@ -834,6 +842,13 @@ func (e *Engine) handleSync(update *mgmProto.SyncResponse) error {
 	defer func() {
 		log.Infof("sync finished in %s", time.Since(started))
 	}()
+
+	e.readyChanOnce.Do(func() {
+		if e.readyChan != nil {
+			close(e.readyChan)
+		}
+	})
+
 	e.syncMsgMux.Lock()
 	defer e.syncMsgMux.Unlock()
 
@@ -880,9 +895,11 @@ func (e *Engine) handleSync(update *mgmProto.SyncResponse) error {
 		// todo update signal
 	}
 
+	uCheckTime := time.Now()
 	if err := e.updateChecksIfNew(update.Checks); err != nil {
 		return err
 	}
+	log.Infof("update check finished in %s", time.Since(uCheckTime))
 
 	nm := update.GetNetworkMap()
 	if nm == nil {
@@ -925,7 +942,9 @@ func (e *Engine) handleRelayUpdate(update *mgmProto.RelayConfig) error {
 			return fmt.Errorf("update relay token: %w", err)
 		}
 
-		e.relayManager.UpdateServerURLs(update.Urls)
+		if !relayClient.IsDisableRelay() {
+			e.relayManager.UpdateServerURLs(update.Urls)
+		}
 
 		// Just in case the agent started with an MGM server where the relay was disabled but was later enabled.
 		// We can ignore all errors because the guard will manage the reconnection retries.

client/internal/peer/conn.go

@@ -434,14 +434,14 @@ func (conn *Conn) onICEStateDisconnected(sessionChanged bool) {
 			conn.resetEndpoint()
 		}
 
+		// todo consider to move after the ConfigureWGEndpoint
 		conn.wgProxyRelay.Work()
 
 		presharedKey := conn.presharedKey(conn.rosenpassRemoteKey)
-		if err := conn.endpointUpdater.ConfigureWGEndpoint(conn.wgProxyRelay.EndpointAddr(), presharedKey); err != nil {
+		if err := conn.endpointUpdater.SwitchWGEndpoint(conn.wgProxyRelay.EndpointAddr(), presharedKey); err != nil {
 			conn.Log.Errorf("failed to switch to relay conn: %v", err)
 		}
 
-		conn.wgProxyRelay.Work()
 		conn.currentConnPriority = conntype.Relay
 	} else {
 		conn.Log.Infof("ICE disconnected, do not switch to Relay. Reset priority to: %s", conntype.None.String())
@@ -503,20 +503,22 @@ func (conn *Conn) onRelayConnectionIsReady(rci RelayConnInfo) {
 		return
 	}
 
-	wgProxy.Work()
-	presharedKey := conn.presharedKey(rci.rosenpassPubKey)
+	controller := isController(conn.config)
 
+	if controller {
+		wgProxy.Work()
+	}
 	conn.enableWgWatcherIfNeeded()
-
-	if err := conn.endpointUpdater.ConfigureWGEndpoint(wgProxy.EndpointAddr(), presharedKey); err != nil {
+	if err := conn.endpointUpdater.ConfigureWGEndpoint(wgProxy.EndpointAddr(), conn.presharedKey(rci.rosenpassPubKey)); err != nil {
 		if err := wgProxy.CloseConn(); err != nil {
 			conn.Log.Warnf("Failed to close relay connection: %v", err)
 		}
 		conn.Log.Errorf("Failed to update WireGuard peer configuration: %v", err)
 		return
 	}
-
-	wgConfigWorkaround()
+	if !controller {
+		wgProxy.Work()
+	}
 	conn.rosenpassRemoteKey = rci.rosenpassPubKey
 	conn.currentConnPriority = conntype.Relay
 	conn.statusRelay.SetConnected()
@@ -877,9 +879,3 @@ func isController(config ConnConfig) bool {
 func isRosenpassEnabled(remoteRosenpassPubKey []byte) bool {
 	return remoteRosenpassPubKey != nil
 }
-
-// wgConfigWorkaround is a workaround for the issue with WireGuard configuration update
-// When update a peer configuration in near to each other time, the second update can be ignored by WireGuard
-func wgConfigWorkaround() {
-	time.Sleep(100 * time.Millisecond)
-}

client/internal/peer/endpoint.go

@@ -34,28 +34,27 @@ func NewEndpointUpdater(log *logrus.Entry, wgConfig WgConfig, initiator bool) *E
 	}
 }
 
-// ConfigureWGEndpoint sets up the WireGuard endpoint configuration.
-// The initiator immediately configures the endpoint, while the non-initiator
-// waits for a fallback period before configuring to avoid handshake congestion.
 func (e *EndpointUpdater) ConfigureWGEndpoint(addr *net.UDPAddr, presharedKey *wgtypes.Key) error {
 	e.mu.Lock()
 	defer e.mu.Unlock()
 
 	if e.initiator {
-		e.log.Debugf("configure up WireGuard as initiatr")
-		return e.updateWireGuardPeer(addr, presharedKey)
+		e.log.Debugf("configure up WireGuard as initiator")
+		return e.configureAsInitiator(addr, presharedKey)
 	}
 
+	e.log.Debugf("configure up WireGuard as responder")
+	return e.configureAsResponder(addr, presharedKey)
+}
+
+func (e *EndpointUpdater) SwitchWGEndpoint(addr *net.UDPAddr, presharedKey *wgtypes.Key) error {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+
 	// prevent to run new update while cancel the previous update
 	e.waitForCloseTheDelayedUpdate()
 
-	var ctx context.Context
-	ctx, e.cancelFunc = context.WithCancel(context.Background())
-	e.updateWg.Add(1)
-	go e.scheduleDelayedUpdate(ctx, addr, presharedKey)
-
-	e.log.Debugf("configure up WireGuard and wait for handshake")
-	return e.updateWireGuardPeer(nil, presharedKey)
+	return e.updateWireGuardPeer(addr, presharedKey)
 }
 
 func (e *EndpointUpdater) RemoveWgPeer() error {
@@ -67,9 +66,37 @@ func (e *EndpointUpdater) RemoveWgPeer() error {
 }
 
 func (e *EndpointUpdater) RemoveEndpointAddress() error {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+
+	e.waitForCloseTheDelayedUpdate()
 	return e.wgConfig.WgInterface.RemoveEndpointAddress(e.wgConfig.RemoteKey)
 }
 
+func (e *EndpointUpdater) configureAsInitiator(addr *net.UDPAddr, presharedKey *wgtypes.Key) error {
+	if err := e.updateWireGuardPeer(addr, presharedKey); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (e *EndpointUpdater) configureAsResponder(addr *net.UDPAddr, presharedKey *wgtypes.Key) error {
+	// prevent to run new update while cancel the previous update
+	e.waitForCloseTheDelayedUpdate()
+
+	e.log.Debugf("configure up WireGuard and wait for handshake")
+	var ctx context.Context
+	ctx, e.cancelFunc = context.WithCancel(context.Background())
+	e.updateWg.Add(1)
+	go e.scheduleDelayedUpdate(ctx, addr, presharedKey)
+
+	if err := e.updateWireGuardPeer(nil, presharedKey); err != nil {
+		e.waitForCloseTheDelayedUpdate()
+		return err
+	}
+	return nil
+}
+
 func (e *EndpointUpdater) waitForCloseTheDelayedUpdate() {
 	if e.cancelFunc == nil {
 		return
@@ -105,3 +132,9 @@ func (e *EndpointUpdater) updateWireGuardPeer(endpoint *net.UDPAddr, presharedKe
 		presharedKey,
 	)
 }
+
+// wgConfigWorkaround is a workaround for the issue with WireGuard configuration update
+// When update a peer configuration in near to each other time, the second update can be ignored by WireGuard
+func wgConfigWorkaround() {
+	time.Sleep(100 * time.Millisecond)
+}

client/internal/peer/ice/agent.go

@@ -12,6 +12,7 @@ import (
 	log "github.com/sirupsen/logrus"
 
 	"github.com/netbirdio/netbird/client/internal/stdnet"
+	relayClient "github.com/netbirdio/netbird/shared/relay/client"
 )
 
 const (
@@ -125,6 +126,10 @@ func GenerateICECredentials() (string, string, error) {
 }
 
 func CandidateTypes() []ice.CandidateType {
+	if relayClient.IsDisableRelay() {
+		return []ice.CandidateType{ice.CandidateTypeHost, ice.CandidateTypeServerReflexive, ice.CandidateTypeRelay}
+	}
+
 	if hasICEForceRelayConn() {
 		return []ice.CandidateType{ice.CandidateTypeRelay}
 	}

go.mod

@@ -40,7 +40,7 @@ require (
 	github.com/c-robinson/iplib v1.0.3
 	github.com/caddyserver/certmagic v0.21.3
 	github.com/cilium/ebpf v0.15.0
-	github.com/coder/websocket v1.8.13
+	github.com/coder/websocket v1.8.14
 	github.com/coreos/go-iptables v0.7.0
 	github.com/coreos/go-oidc/v3 v3.14.1
 	github.com/creack/pty v1.1.24

go.sum

@@ -107,8 +107,8 @@ github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UF
 github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/cilium/ebpf v0.15.0 h1:7NxJhNiBT3NG8pZJ3c+yfrVdHY8ScgKD27sScgjLMMk=
 github.com/cilium/ebpf v0.15.0/go.mod h1:DHp1WyrLeiBh19Cf/tfiSMhqheEiK8fXFZ4No0P1Hso=
-github.com/coder/websocket v1.8.13 h1:f3QZdXy7uGVz+4uCJy2nTZyM0yTBj8yANEHhqlXZ9FE=
-github.com/coder/websocket v1.8.13/go.mod h1:LNVeNrXQZfe5qhS9ALED3uA+l5pPqvwXg3CKoDBB2gs=
+github.com/coder/websocket v1.8.14 h1:9L0p0iKiNOibykf283eHkKUHHrpG7f65OE3BhhO7v9g=
+github.com/coder/websocket v1.8.14/go.mod h1:NX3SzP+inril6yawo5CQXx8+fk145lPDC6pumgx0mVg=
 github.com/containerd/containerd v1.7.29 h1:90fWABQsaN9mJhGkoVnuzEY+o1XDPbg9BTC9QTAHnuE=
 github.com/containerd/containerd v1.7.29/go.mod h1:azUkWcOvHrWvaiUjSQH0fjzuHIwSPg1WL5PshGP4Szs=
 github.com/containerd/log v0.1.0 h1:TCJt7ioM2cr/tfR8GPbGf9/VRAX8D2B4PjzCpfX540I=

infrastructure_files/getting-started.sh

@@ -577,9 +577,6 @@ render_docker_compose_traefik_builtin() {
   proxy:
     image: $NETBIRD_PROXY_IMAGE
     container_name: netbird-proxy
-    # Hairpin NAT fix: route domain back to traefik's static IP within Docker
-    extra_hosts:
-      - \"$NETBIRD_DOMAIN:$TRAEFIK_IP\"
     ports:
     - 51820:51820/udp
     restart: unless-stopped
@@ -822,9 +819,6 @@ NB_PROXY_TOKEN=$PROXY_TOKEN
 NB_PROXY_CERTIFICATE_DIRECTORY=/certs
 NB_PROXY_ACME_CERTIFICATES=true
 NB_PROXY_ACME_CHALLENGE_TYPE=tls-alpn-01
-NB_PROXY_OIDC_CLIENT_ID=netbird-proxy
-NB_PROXY_OIDC_ENDPOINT=$NETBIRD_HTTP_PROTOCOL://$NETBIRD_DOMAIN/oauth2
-NB_PROXY_OIDC_SCOPES=openid,profile,email
 NB_PROXY_FORWARDED_PROTO=https
 # Enable PROXY protocol to preserve client IPs through L4 proxies (Traefik TCP passthrough)
 NB_PROXY_PROXY_PROTOCOL=true

proxy/cmd/proxy/cmd/root.go

@@ -6,14 +6,14 @@ import (
 	"os"
 	"os/signal"
 	"strconv"
-	"strings"
 	"syscall"
 
-	"github.com/netbirdio/netbird/shared/management/domain"
 	log "github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
 	"golang.org/x/crypto/acme"
 
+	"github.com/netbirdio/netbird/shared/management/domain"
+
 	"github.com/netbirdio/netbird/proxy"
 	nbacme "github.com/netbirdio/netbird/proxy/internal/acme"
 	"github.com/netbirdio/netbird/util"
@@ -46,10 +46,6 @@ var (
 	debugEndpoint     bool
 	debugEndpointAddr string
 	healthAddr        string
-	oidcClientID      string
-	oidcClientSecret  string
-	oidcEndpoint      string
-	oidcScopes        string
 	forwardedProto    string
 	trustedProxies    string
 	certFile          string
@@ -81,10 +77,6 @@ func init() {
 	rootCmd.Flags().BoolVar(&debugEndpoint, "debug-endpoint", envBoolOrDefault("NB_PROXY_DEBUG_ENDPOINT", false), "Enable debug HTTP endpoint")
 	rootCmd.Flags().StringVar(&debugEndpointAddr, "debug-endpoint-addr", envStringOrDefault("NB_PROXY_DEBUG_ENDPOINT_ADDRESS", "localhost:8444"), "Address for the debug HTTP endpoint")
 	rootCmd.Flags().StringVar(&healthAddr, "health-addr", envStringOrDefault("NB_PROXY_HEALTH_ADDRESS", "localhost:8080"), "Address for the health probe endpoint (liveness/readiness/startup)")
-	rootCmd.Flags().StringVar(&oidcClientID, "oidc-id", envStringOrDefault("NB_PROXY_OIDC_CLIENT_ID", "netbird-proxy"), "The OAuth2 Client ID for OIDC User Authentication")
-	rootCmd.Flags().StringVar(&oidcClientSecret, "oidc-secret", envStringOrDefault("NB_PROXY_OIDC_CLIENT_SECRET", ""), "The OAuth2 Client Secret for OIDC User Authentication")
-	rootCmd.Flags().StringVar(&oidcEndpoint, "oidc-endpoint", envStringOrDefault("NB_PROXY_OIDC_ENDPOINT", ""), "The OIDC Endpoint for OIDC User Authentication")
-	rootCmd.Flags().StringVar(&oidcScopes, "oidc-scopes", envStringOrDefault("NB_PROXY_OIDC_SCOPES", "openid,profile,email"), "The OAuth2 scopes for OIDC User Authentication, comma separated")
 	rootCmd.Flags().StringVar(&forwardedProto, "forwarded-proto", envStringOrDefault("NB_PROXY_FORWARDED_PROTO", "auto"), "X-Forwarded-Proto value for backends: auto, http, or https")
 	rootCmd.Flags().StringVar(&trustedProxies, "trusted-proxies", envStringOrDefault("NB_PROXY_TRUSTED_PROXIES", ""), "Comma-separated list of trusted upstream proxy CIDR ranges (e.g. '10.0.0.0/8,192.168.1.1')")
 	rootCmd.Flags().StringVar(&certFile, "cert-file", envStringOrDefault("NB_PROXY_CERTIFICATE_FILE", "tls.crt"), "TLS certificate filename within the certificate directory")
@@ -159,10 +151,6 @@ func runServer(cmd *cobra.Command, args []string) error {
 		DebugEndpointEnabled:     debugEndpoint,
 		DebugEndpointAddress:     debugEndpointAddr,
 		HealthAddress:            healthAddr,
-		OIDCClientId:             oidcClientID,
-		OIDCClientSecret:         oidcClientSecret,
-		OIDCEndpoint:             oidcEndpoint,
-		OIDCScopes:               strings.Split(oidcScopes, ","),
 		ForwardedProto:           forwardedProto,
 		TrustedProxies:           parsedTrustedProxies,
 		CertLockMethod:           nbacme.CertLockMethod(certLockMethod),

proxy/server.go

@@ -23,7 +23,7 @@ import (
 	"time"
 
 	"github.com/cenkalti/backoff/v4"
-	proxyproto "github.com/pires/go-proxyproto"
+	"github.com/pires/go-proxyproto"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	log "github.com/sirupsen/logrus"
@@ -89,11 +89,7 @@ type Server struct {
 	ACMEChallengeType string
 	// CertLockMethod controls how ACME certificate locks are coordinated
 	// across replicas. Default: CertLockAuto (detect environment).
-	CertLockMethod   acme.CertLockMethod
-	OIDCClientId     string
-	OIDCClientSecret string
-	OIDCEndpoint     string
-	OIDCScopes       []string
+	CertLockMethod acme.CertLockMethod
 
 	// DebugEndpointEnabled enables the debug HTTP endpoint.
 	DebugEndpointEnabled bool

relay/server/listener/quic/listener.go

@@ -11,6 +11,7 @@ import (
 	log "github.com/sirupsen/logrus"
 
 	"github.com/netbirdio/netbird/relay/protocol"
+	nbRelay "github.com/netbirdio/netbird/shared/relay"
 )
 
 const Proto protocol.Protocol = "quic"
@@ -27,7 +28,7 @@ type Listener struct {
 func (l *Listener) Listen(acceptFn func(conn net.Conn)) error {
 	quicCfg := &quic.Config{
 		EnableDatagrams:   true,
-		InitialPacketSize: 1452,
+		InitialPacketSize: nbRelay.QUICInitialPacketSize,
 	}
 	listener, err := quic.ListenAddr(l.Address, l.TLSConfig, quicCfg)
 	if err != nil {

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

@@ -12,6 +12,7 @@ import (
 	log "github.com/sirupsen/logrus"
 
 	nbnet "github.com/netbirdio/netbird/client/net"
+	nbRelay "github.com/netbirdio/netbird/shared/relay"
 	quictls "github.com/netbirdio/netbird/shared/relay/tls"
 )
 
@@ -42,7 +43,7 @@ func (d Dialer) Dial(ctx context.Context, address string) (net.Conn, error) {
 		KeepAlivePeriod:   30 * time.Second,
 		MaxIdleTimeout:    4 * time.Minute,
 		EnableDatagrams:   true,
-		InitialPacketSize: 1452,
+		InitialPacketSize: nbRelay.QUICInitialPacketSize,
 	}
 
 	udpConn, err := nbnet.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4zero, Port: 0})

shared/relay/client/env.go

@@ -0,0 +1,15 @@
+package client
+
+import (
+	"os"
+	"strconv"
+)
+
+const (
+	envKeyNBDebugDisableRelay = "NB_DEBUG_DISABLE_RELAY"
+)
+
+func IsDisableRelay() bool {
+	v, _ := strconv.ParseBool(os.Getenv(envKeyNBDebugDisableRelay))
+	return v
+}

shared/relay/constants.go

@@ -3,4 +3,9 @@ package relay
 const (
 	// WebSocketURLPath is the path for the websocket relay connection
 	WebSocketURLPath = "/relay"
+
+	// QUICInitialPacketSize is the conservative initial QUIC packet size (bytes)
+	// for unknown-path PMTU, per RFC 9000 §14: 1280 (IPv6 min MTU) − 40 (IPv6
+	// header) − 8 (UDP header) = 1232. DPLPMTUD may probe larger sizes later.
+	QUICInitialPacketSize = 1232
 )