From 719283c792a46311daa334254c5f90a39e0afa00 Mon Sep 17 00:00:00 2001
From: Pascal Fischer <32096965+pascal-fischer@users.noreply.github.com>
Date: Mon, 3 Nov 2025 17:40:12 +0100
Subject: [PATCH 1/5] [management] update db connection lifecycle configuration
 (#4740)

---
 management/server/activity/store/sql_store.go | 23 ++++++++++++-------
 management/server/store/sql_store.go          |  6 ++++-
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/management/server/activity/store/sql_store.go b/management/server/activity/store/sql_store.go
index 80b165938..ffecb6b8f 100644
--- a/management/server/activity/store/sql_store.go
+++ b/management/server/activity/store/sql_store.go
@@ -7,6 +7,7 @@ import (
 	"path/filepath"
 	"runtime"
 	"strconv"
+	"time"
 
 	log "github.com/sirupsen/logrus"
 	"gorm.io/driver/postgres"
@@ -273,15 +274,21 @@ func configureConnectionPool(db *gorm.DB, storeEngine types.Engine) (*gorm.DB, e
 		return nil, err
 	}
 
-	if storeEngine == types.SqliteStoreEngine {
-		sqlDB.SetMaxOpenConns(1)
-	} else {
-		conns, err := strconv.Atoi(os.Getenv(sqlMaxOpenConnsEnv))
-		if err != nil {
-			conns = runtime.NumCPU()
-		}
-		sqlDB.SetMaxOpenConns(conns)
+	conns, err := strconv.Atoi(os.Getenv(sqlMaxOpenConnsEnv))
+	if err != nil {
+		conns = runtime.NumCPU()
 	}
+	if storeEngine == types.SqliteStoreEngine {
+		conns = 1
+	}
+
+	sqlDB.SetMaxOpenConns(conns)
+	sqlDB.SetMaxIdleConns(conns)
+	sqlDB.SetConnMaxLifetime(time.Hour)
+	sqlDB.SetConnMaxIdleTime(3 * time.Minute)
+
+	log.Infof("Set max open db connections to %d, max idle to %d, max lifetime to %v, max idle time to %v",
+		conns, conns, time.Hour, 3*time.Minute)
 
 	return db, nil
 }
diff --git a/management/server/store/sql_store.go b/management/server/store/sql_store.go
index 382d026c8..4201b68f6 100644
--- a/management/server/store/sql_store.go
+++ b/management/server/store/sql_store.go
@@ -89,8 +89,12 @@ func NewSqlStore(ctx context.Context, db *gorm.DB, storeEngine types.Engine, met
 	}
 
 	sql.SetMaxOpenConns(conns)
+	sql.SetMaxIdleConns(conns)
+	sql.SetConnMaxLifetime(time.Hour)
+	sql.SetConnMaxIdleTime(3 * time.Minute)
 
-	log.WithContext(ctx).Infof("Set max open db connections to %d", conns)
+	log.WithContext(ctx).Infof("Set max open db connections to %d, max idle to %d, max lifetime to %v, max idle time to %v",
+		conns, conns, time.Hour, 3*time.Minute)
 
 	if skipMigration {
 		log.WithContext(ctx).Infof("skipping migration")

From 679c58ce472d8763d8bea987662104fa6a381dc2 Mon Sep 17 00:00:00 2001
From: Viktor Liu <17948409+lixmal@users.noreply.github.com>
Date: Tue, 4 Nov 2025 17:06:35 +0100
Subject: [PATCH 2/5] [client] Set up networkd to ignore ip rules (#4730)

---
 client/cmd/service_installer.go | 54 +++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/client/cmd/service_installer.go b/client/cmd/service_installer.go
index 075ead44e..2a87e538d 100644
--- a/client/cmd/service_installer.go
+++ b/client/cmd/service_installer.go
@@ -10,6 +10,8 @@ import (
 	"path/filepath"
 	"runtime"
 
+	log "github.com/sirupsen/logrus"
+
 	"github.com/kardianos/service"
 	"github.com/spf13/cobra"
 
@@ -81,6 +83,10 @@ func configurePlatformSpecificSettings(svcConfig *service.Config) error {
 				svcConfig.Option["LogDirectory"] = dir
 			}
 		}
+
+		if err := configureSystemdNetworkd(); err != nil {
+			log.Warnf("failed to configure systemd-networkd: %v", err)
+		}
 	}
 
 	if runtime.GOOS == "windows" {
@@ -160,6 +166,12 @@ var uninstallCmd = &cobra.Command{
 			return fmt.Errorf("uninstall service: %w", err)
 		}
 
+		if runtime.GOOS == "linux" {
+			if err := cleanupSystemdNetworkd(); err != nil {
+				log.Warnf("failed to cleanup systemd-networkd configuration: %v", err)
+			}
+		}
+
 		cmd.Println("NetBird service has been uninstalled")
 		return nil
 	},
@@ -245,3 +257,45 @@ func isServiceRunning() (bool, error) {
 
 	return status == service.StatusRunning, nil
 }
+
+const (
+	networkdConfDir     = "/etc/systemd/networkd.conf.d"
+	networkdConfFile    = "/etc/systemd/networkd.conf.d/99-netbird.conf"
+	networkdConfContent = `# Created by NetBird to prevent systemd-networkd from removing
+# routes and policy rules managed by NetBird.
+
+[Network]
+ManageForeignRoutes=no
+ManageForeignRoutingPolicyRules=no
+`
+)
+
+// configureSystemdNetworkd creates a drop-in configuration file to prevent
+// systemd-networkd from removing NetBird's routes and policy rules.
+func configureSystemdNetworkd() error {
+	parentDir := filepath.Dir(networkdConfDir)
+	if _, err := os.Stat(parentDir); os.IsNotExist(err) {
+		log.Debug("systemd networkd.conf.d parent directory does not exist, skipping configuration")
+		return nil
+	}
+
+	// nolint:gosec // standard networkd permissions
+	if err := os.WriteFile(networkdConfFile, []byte(networkdConfContent), 0644); err != nil {
+		return fmt.Errorf("write networkd configuration: %w", err)
+	}
+
+	return nil
+}
+
+// cleanupSystemdNetworkd removes the NetBird systemd-networkd configuration file.
+func cleanupSystemdNetworkd() error {
+	if _, err := os.Stat(networkdConfFile); os.IsNotExist(err) {
+		return nil
+	}
+
+	if err := os.Remove(networkdConfFile); err != nil {
+		return fmt.Errorf("remove networkd configuration: %w", err)
+	}
+
+	return nil
+}

From 45c25dca84150c0da85b06875facb01f0bcd119a Mon Sep 17 00:00:00 2001
From: Viktor Liu <17948409+lixmal@users.noreply.github.com>
Date: Tue, 4 Nov 2025 17:18:51 +0100
Subject: [PATCH 3/5] [client] Clamp MSS on outbound traffic (#4735)

---
 client/firewall/create.go                     |   4 +-
 client/firewall/create_linux.go               |  22 +-
 client/firewall/iptables/manager_linux.go     |   5 +-
 .../firewall/iptables/manager_linux_test.go   |   9 +-
 client/firewall/iptables/router_linux.go      |  50 +++-
 client/firewall/iptables/router_linux_test.go |  14 +-
 client/firewall/iptables/state_linux.go       |   8 +-
 client/firewall/nftables/manager_linux.go     |   5 +-
 .../firewall/nftables/manager_linux_test.go   |   9 +-
 client/firewall/nftables/router_linux.go      |  98 ++++++-
 client/firewall/nftables/router_linux_test.go |   9 +-
 client/firewall/nftables/state_linux.go       |   8 +-
 client/firewall/uspfilter/filter.go           | 154 ++++++++--
 .../firewall/uspfilter/filter_bench_test.go   | 277 +++++++++++++++---
 .../firewall/uspfilter/filter_filter_test.go  |   7 +-
 client/firewall/uspfilter/filter_test.go      | 215 +++++++++++++-
 .../firewall/uspfilter/forwarder/forwarder.go |   8 +-
 client/firewall/uspfilter/forwarder/udp.go    |   2 +-
 client/firewall/uspfilter/nat_bench_test.go   |  11 +-
 client/firewall/uspfilter/nat_test.go         |   9 +-
 client/firewall/uspfilter/tracer_test.go      |   3 +-
 client/internal/acl/manager_test.go           |   7 +-
 client/internal/dns/server_test.go            |   2 +-
 client/internal/engine.go                     |   2 +-
 24 files changed, 804 insertions(+), 134 deletions(-)

diff --git a/client/firewall/create.go b/client/firewall/create.go
index 7b265e1d1..24f12bc6d 100644
--- a/client/firewall/create.go
+++ b/client/firewall/create.go
@@ -15,13 +15,13 @@ import (
 )
 
 // NewFirewall creates a firewall manager instance
-func NewFirewall(iface IFaceMapper, _ *statemanager.Manager, flowLogger nftypes.FlowLogger, disableServerRoutes bool) (firewall.Manager, error) {
+func NewFirewall(iface IFaceMapper, _ *statemanager.Manager, flowLogger nftypes.FlowLogger, disableServerRoutes bool, mtu uint16) (firewall.Manager, error) {
 	if !iface.IsUserspaceBind() {
 		return nil, fmt.Errorf("not implemented for this OS: %s", runtime.GOOS)
 	}
 
 	// use userspace packet filtering firewall
-	fm, err := uspfilter.Create(iface, disableServerRoutes, flowLogger)
+	fm, err := uspfilter.Create(iface, disableServerRoutes, flowLogger, mtu)
 	if err != nil {
 		return nil, err
 	}
diff --git a/client/firewall/create_linux.go b/client/firewall/create_linux.go
index aa2f0d4d1..12dcaee8a 100644
--- a/client/firewall/create_linux.go
+++ b/client/firewall/create_linux.go
@@ -34,12 +34,12 @@ const SKIP_NFTABLES_ENV = "NB_SKIP_NFTABLES_CHECK"
 // FWType is the type for the firewall type
 type FWType int
 
-func NewFirewall(iface IFaceMapper, stateManager *statemanager.Manager, flowLogger nftypes.FlowLogger, disableServerRoutes bool) (firewall.Manager, error) {
+func NewFirewall(iface IFaceMapper, stateManager *statemanager.Manager, flowLogger nftypes.FlowLogger, disableServerRoutes bool, mtu uint16) (firewall.Manager, error) {
 	// on the linux system we try to user nftables or iptables
 	// in any case, because we need to allow netbird interface traffic
 	// so we use AllowNetbird traffic from these firewall managers
 	// for the userspace packet filtering firewall
-	fm, err := createNativeFirewall(iface, stateManager, disableServerRoutes)
+	fm, err := createNativeFirewall(iface, stateManager, disableServerRoutes, mtu)
 
 	if !iface.IsUserspaceBind() {
 		return fm, err
@@ -48,11 +48,11 @@ func NewFirewall(iface IFaceMapper, stateManager *statemanager.Manager, flowLogg
 	if err != nil {
 		log.Warnf("failed to create native firewall: %v. Proceeding with userspace", err)
 	}
-	return createUserspaceFirewall(iface, fm, disableServerRoutes, flowLogger)
+	return createUserspaceFirewall(iface, fm, disableServerRoutes, flowLogger, mtu)
 }
 
-func createNativeFirewall(iface IFaceMapper, stateManager *statemanager.Manager, routes bool) (firewall.Manager, error) {
-	fm, err := createFW(iface)
+func createNativeFirewall(iface IFaceMapper, stateManager *statemanager.Manager, routes bool, mtu uint16) (firewall.Manager, error) {
+	fm, err := createFW(iface, mtu)
 	if err != nil {
 		return nil, fmt.Errorf("create firewall: %s", err)
 	}
@@ -64,26 +64,26 @@ func createNativeFirewall(iface IFaceMapper, stateManager *statemanager.Manager,
 	return fm, nil
 }
 
-func createFW(iface IFaceMapper) (firewall.Manager, error) {
+func createFW(iface IFaceMapper, mtu uint16) (firewall.Manager, error) {
 	switch check() {
 	case IPTABLES:
 		log.Info("creating an iptables firewall manager")
-		return nbiptables.Create(iface)
+		return nbiptables.Create(iface, mtu)
 	case NFTABLES:
 		log.Info("creating an nftables firewall manager")
-		return nbnftables.Create(iface)
+		return nbnftables.Create(iface, mtu)
 	default:
 		log.Info("no firewall manager found, trying to use userspace packet filtering firewall")
 		return nil, errors.New("no firewall manager found")
 	}
 }
 
-func createUserspaceFirewall(iface IFaceMapper, fm firewall.Manager, disableServerRoutes bool, flowLogger nftypes.FlowLogger) (firewall.Manager, error) {
+func createUserspaceFirewall(iface IFaceMapper, fm firewall.Manager, disableServerRoutes bool, flowLogger nftypes.FlowLogger, mtu uint16) (firewall.Manager, error) {
 	var errUsp error
 	if fm != nil {
-		fm, errUsp = uspfilter.CreateWithNativeFirewall(iface, fm, disableServerRoutes, flowLogger)
+		fm, errUsp = uspfilter.CreateWithNativeFirewall(iface, fm, disableServerRoutes, flowLogger, mtu)
 	} else {
-		fm, errUsp = uspfilter.Create(iface, disableServerRoutes, flowLogger)
+		fm, errUsp = uspfilter.Create(iface, disableServerRoutes, flowLogger, mtu)
 	}
 
 	if errUsp != nil {
diff --git a/client/firewall/iptables/manager_linux.go b/client/firewall/iptables/manager_linux.go
index 16b50211e..2563a9052 100644
--- a/client/firewall/iptables/manager_linux.go
+++ b/client/firewall/iptables/manager_linux.go
@@ -36,7 +36,7 @@ type iFaceMapper interface {
 }
 
 // Create iptables firewall manager
-func Create(wgIface iFaceMapper) (*Manager, error) {
+func Create(wgIface iFaceMapper, mtu uint16) (*Manager, error) {
 	iptablesClient, err := iptables.NewWithProtocol(iptables.ProtocolIPv4)
 	if err != nil {
 		return nil, fmt.Errorf("init iptables: %w", err)
@@ -47,7 +47,7 @@ func Create(wgIface iFaceMapper) (*Manager, error) {
 		ipv4Client: iptablesClient,
 	}
 
-	m.router, err = newRouter(iptablesClient, wgIface)
+	m.router, err = newRouter(iptablesClient, wgIface, mtu)
 	if err != nil {
 		return nil, fmt.Errorf("create router: %w", err)
 	}
@@ -66,6 +66,7 @@ func (m *Manager) Init(stateManager *statemanager.Manager) error {
 			NameStr:       m.wgIface.Name(),
 			WGAddress:     m.wgIface.Address(),
 			UserspaceBind: m.wgIface.IsUserspaceBind(),
+			MTU:           m.router.mtu,
 		},
 	}
 	stateManager.RegisterState(state)
diff --git a/client/firewall/iptables/manager_linux_test.go b/client/firewall/iptables/manager_linux_test.go
index a5cc62feb..6b5401e2b 100644
--- a/client/firewall/iptables/manager_linux_test.go
+++ b/client/firewall/iptables/manager_linux_test.go
@@ -11,6 +11,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	fw "github.com/netbirdio/netbird/client/firewall/manager"
+	"github.com/netbirdio/netbird/client/iface"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 )
 
@@ -53,7 +54,7 @@ func TestIptablesManager(t *testing.T) {
 	require.NoError(t, err)
 
 	// just check on the local interface
-	manager, err := Create(ifaceMock)
+	manager, err := Create(ifaceMock, iface.DefaultMTU)
 	require.NoError(t, err)
 	require.NoError(t, manager.Init(nil))
 
@@ -114,7 +115,7 @@ func TestIptablesManagerDenyRules(t *testing.T) {
 	ipv4Client, err := iptables.NewWithProtocol(iptables.ProtocolIPv4)
 	require.NoError(t, err)
 
-	manager, err := Create(ifaceMock)
+	manager, err := Create(ifaceMock, iface.DefaultMTU)
 	require.NoError(t, err)
 	require.NoError(t, manager.Init(nil))
 
@@ -198,7 +199,7 @@ func TestIptablesManagerIPSet(t *testing.T) {
 	}
 
 	// just check on the local interface
-	manager, err := Create(mock)
+	manager, err := Create(mock, iface.DefaultMTU)
 	require.NoError(t, err)
 	require.NoError(t, manager.Init(nil))
 
@@ -264,7 +265,7 @@ func TestIptablesCreatePerformance(t *testing.T) {
 	for _, testMax := range []int{10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000} {
 		t.Run(fmt.Sprintf("Testing %d rules", testMax), func(t *testing.T) {
 			// just check on the local interface
-			manager, err := Create(mock)
+			manager, err := Create(mock, iface.DefaultMTU)
 			require.NoError(t, err)
 			require.NoError(t, manager.Init(nil))
 			time.Sleep(time.Second)
diff --git a/client/firewall/iptables/router_linux.go b/client/firewall/iptables/router_linux.go
index 80aea7cf8..305b0bf28 100644
--- a/client/firewall/iptables/router_linux.go
+++ b/client/firewall/iptables/router_linux.go
@@ -30,17 +30,20 @@ const (
 
 	chainPOSTROUTING        = "POSTROUTING"
 	chainPREROUTING         = "PREROUTING"
+	chainFORWARD            = "FORWARD"
 	chainRTNAT              = "NETBIRD-RT-NAT"
 	chainRTFWDIN            = "NETBIRD-RT-FWD-IN"
 	chainRTFWDOUT           = "NETBIRD-RT-FWD-OUT"
 	chainRTPRE              = "NETBIRD-RT-PRE"
 	chainRTRDR              = "NETBIRD-RT-RDR"
+	chainRTMSSCLAMP         = "NETBIRD-RT-MSSCLAMP"
 	routingFinalForwardJump = "ACCEPT"
 	routingFinalNatJump     = "MASQUERADE"
 
 	jumpManglePre  = "jump-mangle-pre"
 	jumpNatPre     = "jump-nat-pre"
 	jumpNatPost    = "jump-nat-post"
+	jumpMSSClamp   = "jump-mss-clamp"
 	markManglePre  = "mark-mangle-pre"
 	markManglePost = "mark-mangle-post"
 	matchSet       = "--match-set"
@@ -48,6 +51,9 @@ const (
 	dnatSuffix = "_dnat"
 	snatSuffix = "_snat"
 	fwdSuffix  = "_fwd"
+
+	// ipTCPHeaderMinSize represents minimum IP (20) + TCP (20) header size for MSS calculation
+	ipTCPHeaderMinSize = 40
 )
 
 type ruleInfo struct {
@@ -77,16 +83,18 @@ type router struct {
 	ipsetCounter     *ipsetCounter
 	wgIface          iFaceMapper
 	legacyManagement bool
+	mtu              uint16
 
 	stateManager *statemanager.Manager
 	ipFwdState   *ipfwdstate.IPForwardingState
 }
 
-func newRouter(iptablesClient *iptables.IPTables, wgIface iFaceMapper) (*router, error) {
+func newRouter(iptablesClient *iptables.IPTables, wgIface iFaceMapper, mtu uint16) (*router, error) {
 	r := &router{
 		iptablesClient: iptablesClient,
 		rules:          make(map[string][]string),
 		wgIface:        wgIface,
+		mtu:            mtu,
 		ipFwdState:     ipfwdstate.NewIPForwardingState(),
 	}
 
@@ -392,6 +400,7 @@ func (r *router) cleanUpDefaultForwardRules() error {
 		{chainRTPRE, tableMangle},
 		{chainRTNAT, tableNat},
 		{chainRTRDR, tableNat},
+		{chainRTMSSCLAMP, tableMangle},
 	} {
 		ok, err := r.iptablesClient.ChainExists(chainInfo.table, chainInfo.chain)
 		if err != nil {
@@ -416,6 +425,7 @@ func (r *router) createContainers() error {
 		{chainRTPRE, tableMangle},
 		{chainRTNAT, tableNat},
 		{chainRTRDR, tableNat},
+		{chainRTMSSCLAMP, tableMangle},
 	} {
 		if err := r.iptablesClient.NewChain(chainInfo.table, chainInfo.chain); err != nil {
 			return fmt.Errorf("create chain %s in table %s: %w", chainInfo.chain, chainInfo.table, err)
@@ -438,6 +448,10 @@ func (r *router) createContainers() error {
 		return fmt.Errorf("add jump rules: %w", err)
 	}
 
+	if err := r.addMSSClampingRules(); err != nil {
+		log.Errorf("failed to add MSS clamping rules: %s", err)
+	}
+
 	return nil
 }
 
@@ -518,6 +532,35 @@ func (r *router) addPostroutingRules() error {
 	return nil
 }
 
+// addMSSClampingRules adds MSS clamping rules to prevent fragmentation for forwarded traffic.
+// TODO: Add IPv6 support
+func (r *router) addMSSClampingRules() error {
+	mss := r.mtu - ipTCPHeaderMinSize
+
+	// Add jump rule from FORWARD chain in mangle table to our custom chain
+	jumpRule := []string{
+		"-j", chainRTMSSCLAMP,
+	}
+	if err := r.iptablesClient.Insert(tableMangle, chainFORWARD, 1, jumpRule...); err != nil {
+		return fmt.Errorf("add jump to MSS clamp chain: %w", err)
+	}
+	r.rules[jumpMSSClamp] = jumpRule
+
+	ruleOut := []string{
+		"-o", r.wgIface.Name(),
+		"-p", "tcp",
+		"--tcp-flags", "SYN,RST", "SYN",
+		"-j", "TCPMSS",
+		"--set-mss", fmt.Sprintf("%d", mss),
+	}
+	if err := r.iptablesClient.Append(tableMangle, chainRTMSSCLAMP, ruleOut...); err != nil {
+		return fmt.Errorf("add outbound MSS clamp rule: %w", err)
+	}
+	r.rules["mss-clamp-out"] = ruleOut
+
+	return nil
+}
+
 func (r *router) insertEstablishedRule(chain string) error {
 	establishedRule := getConntrackEstablished()
 
@@ -558,7 +601,7 @@ func (r *router) addJumpRules() error {
 }
 
 func (r *router) cleanJumpRules() error {
-	for _, ruleKey := range []string{jumpNatPost, jumpManglePre, jumpNatPre} {
+	for _, ruleKey := range []string{jumpNatPost, jumpManglePre, jumpNatPre, jumpMSSClamp} {
 		if rule, exists := r.rules[ruleKey]; exists {
 			var table, chain string
 			switch ruleKey {
@@ -571,6 +614,9 @@ func (r *router) cleanJumpRules() error {
 			case jumpNatPre:
 				table = tableNat
 				chain = chainPREROUTING
+			case jumpMSSClamp:
+				table = tableMangle
+				chain = chainFORWARD
 			default:
 				return fmt.Errorf("unknown jump rule: %s", ruleKey)
 			}
diff --git a/client/firewall/iptables/router_linux_test.go b/client/firewall/iptables/router_linux_test.go
index 3490c5dad..6707573be 100644
--- a/client/firewall/iptables/router_linux_test.go
+++ b/client/firewall/iptables/router_linux_test.go
@@ -14,6 +14,7 @@ import (
 
 	firewall "github.com/netbirdio/netbird/client/firewall/manager"
 	"github.com/netbirdio/netbird/client/firewall/test"
+	"github.com/netbirdio/netbird/client/iface"
 	nbnet "github.com/netbirdio/netbird/client/net"
 )
 
@@ -30,7 +31,7 @@ func TestIptablesManager_RestoreOrCreateContainers(t *testing.T) {
 	iptablesClient, err := iptables.NewWithProtocol(iptables.ProtocolIPv4)
 	require.NoError(t, err, "failed to init iptables client")
 
-	manager, err := newRouter(iptablesClient, ifaceMock)
+	manager, err := newRouter(iptablesClient, ifaceMock, iface.DefaultMTU)
 	require.NoError(t, err, "should return a valid iptables manager")
 	require.NoError(t, manager.init(nil))
 
@@ -38,7 +39,6 @@ func TestIptablesManager_RestoreOrCreateContainers(t *testing.T) {
 		assert.NoError(t, manager.Reset(), "shouldn't return error")
 	}()
 
-	// Now 5 rules:
 	// 1. established rule forward in
 	// 2. estbalished rule forward out
 	// 3. jump rule to POST nat chain
@@ -48,7 +48,9 @@ func TestIptablesManager_RestoreOrCreateContainers(t *testing.T) {
 	// 7. static return masquerade rule
 	// 8. mangle prerouting mark rule
 	// 9. mangle postrouting mark rule
-	require.Len(t, manager.rules, 9, "should have created rules map")
+	// 10. jump rule to MSS clamping chain
+	// 11. MSS clamping rule for outbound traffic
+	require.Len(t, manager.rules, 11, "should have created rules map")
 
 	exists, err := manager.iptablesClient.Exists(tableNat, chainPOSTROUTING, "-j", chainRTNAT)
 	require.NoError(t, err, "should be able to query the iptables %s table and %s chain", tableNat, chainPOSTROUTING)
@@ -82,7 +84,7 @@ func TestIptablesManager_AddNatRule(t *testing.T) {
 			iptablesClient, err := iptables.NewWithProtocol(iptables.ProtocolIPv4)
 			require.NoError(t, err, "failed to init iptables client")
 
-			manager, err := newRouter(iptablesClient, ifaceMock)
+			manager, err := newRouter(iptablesClient, ifaceMock, iface.DefaultMTU)
 			require.NoError(t, err, "shouldn't return error")
 			require.NoError(t, manager.init(nil))
 
@@ -155,7 +157,7 @@ func TestIptablesManager_RemoveNatRule(t *testing.T) {
 		t.Run(testCase.Name, func(t *testing.T) {
 			iptablesClient, _ := iptables.NewWithProtocol(iptables.ProtocolIPv4)
 
-			manager, err := newRouter(iptablesClient, ifaceMock)
+			manager, err := newRouter(iptablesClient, ifaceMock, iface.DefaultMTU)
 			require.NoError(t, err, "shouldn't return error")
 			require.NoError(t, manager.init(nil))
 			defer func() {
@@ -217,7 +219,7 @@ func TestRouter_AddRouteFiltering(t *testing.T) {
 	iptablesClient, err := iptables.NewWithProtocol(iptables.ProtocolIPv4)
 	require.NoError(t, err, "Failed to create iptables client")
 
-	r, err := newRouter(iptablesClient, ifaceMock)
+	r, err := newRouter(iptablesClient, ifaceMock, iface.DefaultMTU)
 	require.NoError(t, err, "Failed to create router manager")
 	require.NoError(t, r.init(nil))
 
diff --git a/client/firewall/iptables/state_linux.go b/client/firewall/iptables/state_linux.go
index 6ef159e01..c88774c1f 100644
--- a/client/firewall/iptables/state_linux.go
+++ b/client/firewall/iptables/state_linux.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"sync"
 
+	"github.com/netbirdio/netbird/client/iface"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 )
 
@@ -11,6 +12,7 @@ type InterfaceState struct {
 	NameStr       string         `json:"name"`
 	WGAddress     wgaddr.Address `json:"wg_address"`
 	UserspaceBind bool           `json:"userspace_bind"`
+	MTU           uint16         `json:"mtu"`
 }
 
 func (i *InterfaceState) Name() string {
@@ -42,7 +44,11 @@ func (s *ShutdownState) Name() string {
 }
 
 func (s *ShutdownState) Cleanup() error {
-	ipt, err := Create(s.InterfaceState)
+	mtu := s.InterfaceState.MTU
+	if mtu == 0 {
+		mtu = iface.DefaultMTU
+	}
+	ipt, err := Create(s.InterfaceState, mtu)
 	if err != nil {
 		return fmt.Errorf("create iptables manager: %w", err)
 	}
diff --git a/client/firewall/nftables/manager_linux.go b/client/firewall/nftables/manager_linux.go
index aa90d3b9a..d864914fe 100644
--- a/client/firewall/nftables/manager_linux.go
+++ b/client/firewall/nftables/manager_linux.go
@@ -44,7 +44,7 @@ type Manager struct {
 }
 
 // Create nftables firewall manager
-func Create(wgIface iFaceMapper) (*Manager, error) {
+func Create(wgIface iFaceMapper, mtu uint16) (*Manager, error) {
 	m := &Manager{
 		rConn:   &nftables.Conn{},
 		wgIface: wgIface,
@@ -53,7 +53,7 @@ func Create(wgIface iFaceMapper) (*Manager, error) {
 	workTable := &nftables.Table{Name: tableNameNetbird, Family: nftables.TableFamilyIPv4}
 
 	var err error
-	m.router, err = newRouter(workTable, wgIface)
+	m.router, err = newRouter(workTable, wgIface, mtu)
 	if err != nil {
 		return nil, fmt.Errorf("create router: %w", err)
 	}
@@ -93,6 +93,7 @@ func (m *Manager) Init(stateManager *statemanager.Manager) error {
 			NameStr:       m.wgIface.Name(),
 			WGAddress:     m.wgIface.Address(),
 			UserspaceBind: m.wgIface.IsUserspaceBind(),
+			MTU:           m.router.mtu,
 		},
 	}); err != nil {
 		log.Errorf("failed to update state: %v", err)
diff --git a/client/firewall/nftables/manager_linux_test.go b/client/firewall/nftables/manager_linux_test.go
index c7f05dcb7..adec802c8 100644
--- a/client/firewall/nftables/manager_linux_test.go
+++ b/client/firewall/nftables/manager_linux_test.go
@@ -16,6 +16,7 @@ import (
 	"golang.org/x/sys/unix"
 
 	fw "github.com/netbirdio/netbird/client/firewall/manager"
+	"github.com/netbirdio/netbird/client/iface"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 )
 
@@ -56,7 +57,7 @@ func (i *iFaceMock) IsUserspaceBind() bool { return false }
 func TestNftablesManager(t *testing.T) {
 
 	// just check on the local interface
-	manager, err := Create(ifaceMock)
+	manager, err := Create(ifaceMock, iface.DefaultMTU)
 	require.NoError(t, err)
 	require.NoError(t, manager.Init(nil))
 	time.Sleep(time.Second * 3)
@@ -168,7 +169,7 @@ func TestNftablesManager(t *testing.T) {
 func TestNftablesManagerRuleOrder(t *testing.T) {
 	// This test verifies rule insertion order in nftables peer ACLs
 	// We add accept rule first, then deny rule to test ordering behavior
-	manager, err := Create(ifaceMock)
+	manager, err := Create(ifaceMock, iface.DefaultMTU)
 	require.NoError(t, err)
 	require.NoError(t, manager.Init(nil))
 
@@ -261,7 +262,7 @@ func TestNFtablesCreatePerformance(t *testing.T) {
 	for _, testMax := range []int{10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000} {
 		t.Run(fmt.Sprintf("Testing %d rules", testMax), func(t *testing.T) {
 			// just check on the local interface
-			manager, err := Create(mock)
+			manager, err := Create(mock, iface.DefaultMTU)
 			require.NoError(t, err)
 			require.NoError(t, manager.Init(nil))
 			time.Sleep(time.Second * 3)
@@ -345,7 +346,7 @@ func TestNftablesManagerCompatibilityWithIptables(t *testing.T) {
 	stdout, stderr := runIptablesSave(t)
 	verifyIptablesOutput(t, stdout, stderr)
 
-	manager, err := Create(ifaceMock)
+	manager, err := Create(ifaceMock, iface.DefaultMTU)
 	require.NoError(t, err, "failed to create manager")
 	require.NoError(t, manager.Init(nil))
 
diff --git a/client/firewall/nftables/router_linux.go b/client/firewall/nftables/router_linux.go
index 648a6aedf..0a2c79186 100644
--- a/client/firewall/nftables/router_linux.go
+++ b/client/firewall/nftables/router_linux.go
@@ -16,6 +16,7 @@ import (
 	"github.com/google/nftables/xt"
 	"github.com/hashicorp/go-multierror"
 	log "github.com/sirupsen/logrus"
+	"golang.org/x/sys/unix"
 
 	nberrors "github.com/netbirdio/netbird/client/errors"
 	firewall "github.com/netbirdio/netbird/client/firewall/manager"
@@ -32,12 +33,16 @@ const (
 	chainNameRoutingNat    = "netbird-rt-postrouting"
 	chainNameRoutingRdr    = "netbird-rt-redirect"
 	chainNameForward       = "FORWARD"
+	chainNameMangleForward = "netbird-mangle-forward"
 
 	userDataAcceptForwardRuleIif = "frwacceptiif"
 	userDataAcceptForwardRuleOif = "frwacceptoif"
 
 	dnatSuffix = "_dnat"
 	snatSuffix = "_snat"
+
+	// ipTCPHeaderMinSize represents minimum IP (20) + TCP (20) header size for MSS calculation
+	ipTCPHeaderMinSize = 40
 )
 
 const refreshRulesMapError = "refresh rules map: %w"
@@ -63,9 +68,10 @@ type router struct {
 	wgIface          iFaceMapper
 	ipFwdState       *ipfwdstate.IPForwardingState
 	legacyManagement bool
+	mtu              uint16
 }
 
-func newRouter(workTable *nftables.Table, wgIface iFaceMapper) (*router, error) {
+func newRouter(workTable *nftables.Table, wgIface iFaceMapper, mtu uint16) (*router, error) {
 	r := &router{
 		conn:       &nftables.Conn{},
 		workTable:  workTable,
@@ -73,6 +79,7 @@ func newRouter(workTable *nftables.Table, wgIface iFaceMapper) (*router, error)
 		rules:      make(map[string]*nftables.Rule),
 		wgIface:    wgIface,
 		ipFwdState: ipfwdstate.NewIPForwardingState(),
+		mtu:        mtu,
 	}
 
 	r.ipsetCounter = refcounter.New(
@@ -220,11 +227,23 @@ func (r *router) createContainers() error {
 		Type:     nftables.ChainTypeFilter,
 	})
 
+	r.chains[chainNameMangleForward] = r.conn.AddChain(&nftables.Chain{
+		Name:     chainNameMangleForward,
+		Table:    r.workTable,
+		Hooknum:  nftables.ChainHookForward,
+		Priority: nftables.ChainPriorityMangle,
+		Type:     nftables.ChainTypeFilter,
+	})
+
 	// Add the single NAT rule that matches on mark
 	if err := r.addPostroutingRules(); err != nil {
 		return fmt.Errorf("add single nat rule: %v", err)
 	}
 
+	if err := r.addMSSClampingRules(); err != nil {
+		log.Errorf("failed to add MSS clamping rules: %s", err)
+	}
+
 	if err := r.acceptForwardRules(); err != nil {
 		log.Errorf("failed to add accept rules for the forward chain: %s", err)
 	}
@@ -745,6 +764,83 @@ func (r *router) addPostroutingRules() error {
 	return nil
 }
 
+// addMSSClampingRules adds MSS clamping rules to prevent fragmentation for forwarded traffic.
+// TODO: Add IPv6 support
+func (r *router) addMSSClampingRules() error {
+	mss := r.mtu - ipTCPHeaderMinSize
+
+	exprsOut := []expr.Any{
+		&expr.Meta{
+			Key:      expr.MetaKeyOIFNAME,
+			Register: 1,
+		},
+		&expr.Cmp{
+			Op:       expr.CmpOpEq,
+			Register: 1,
+			Data:     ifname(r.wgIface.Name()),
+		},
+		&expr.Meta{
+			Key:      expr.MetaKeyL4PROTO,
+			Register: 1,
+		},
+		&expr.Cmp{
+			Op:       expr.CmpOpEq,
+			Register: 1,
+			Data:     []byte{unix.IPPROTO_TCP},
+		},
+		&expr.Payload{
+			DestRegister: 1,
+			Base:         expr.PayloadBaseTransportHeader,
+			Offset:       13,
+			Len:          1,
+		},
+		&expr.Bitwise{
+			DestRegister:   1,
+			SourceRegister: 1,
+			Len:            1,
+			Mask:           []byte{0x02},
+			Xor:            []byte{0x00},
+		},
+		&expr.Cmp{
+			Op:       expr.CmpOpNeq,
+			Register: 1,
+			Data:     []byte{0x00},
+		},
+		&expr.Counter{},
+		&expr.Exthdr{
+			DestRegister: 1,
+			Type:         2,
+			Offset:       2,
+			Len:          2,
+			Op:           expr.ExthdrOpTcpopt,
+		},
+		&expr.Cmp{
+			Op:       expr.CmpOpGt,
+			Register: 1,
+			Data:     binaryutil.BigEndian.PutUint16(uint16(mss)),
+		},
+		&expr.Immediate{
+			Register: 1,
+			Data:     binaryutil.BigEndian.PutUint16(uint16(mss)),
+		},
+		&expr.Exthdr{
+			SourceRegister: 1,
+			Type:           2,
+			Offset:         2,
+			Len:            2,
+			Op:             expr.ExthdrOpTcpopt,
+		},
+	}
+
+	r.conn.AddRule(&nftables.Rule{
+		Table: r.workTable,
+		Chain: r.chains[chainNameMangleForward],
+		Exprs: exprsOut,
+	})
+
+	return nil
+}
+
 // addLegacyRouteRule adds a legacy routing rule for mgmt servers pre route acls
 func (r *router) addLegacyRouteRule(pair firewall.RouterPair) error {
 	sourceExp, err := r.applyNetwork(pair.Source, nil, true)
diff --git a/client/firewall/nftables/router_linux_test.go b/client/firewall/nftables/router_linux_test.go
index 4fdbf3505..3531b014b 100644
--- a/client/firewall/nftables/router_linux_test.go
+++ b/client/firewall/nftables/router_linux_test.go
@@ -17,6 +17,7 @@ import (
 
 	firewall "github.com/netbirdio/netbird/client/firewall/manager"
 	"github.com/netbirdio/netbird/client/firewall/test"
+	"github.com/netbirdio/netbird/client/iface"
 )
 
 const (
@@ -36,7 +37,7 @@ func TestNftablesManager_AddNatRule(t *testing.T) {
 	for _, testCase := range test.InsertRuleTestCases {
 		t.Run(testCase.Name, func(t *testing.T) {
 			// need fw manager to init both acl mgr and router for all chains to be present
-			manager, err := Create(ifaceMock)
+			manager, err := Create(ifaceMock, iface.DefaultMTU)
 			t.Cleanup(func() {
 				require.NoError(t, manager.Close(nil))
 			})
@@ -125,7 +126,7 @@ func TestNftablesManager_RemoveNatRule(t *testing.T) {
 
 	for _, testCase := range test.RemoveRuleTestCases {
 		t.Run(testCase.Name, func(t *testing.T) {
-			manager, err := Create(ifaceMock)
+			manager, err := Create(ifaceMock, iface.DefaultMTU)
 			t.Cleanup(func() {
 				require.NoError(t, manager.Close(nil))
 			})
@@ -197,7 +198,7 @@ func TestRouter_AddRouteFiltering(t *testing.T) {
 
 	defer deleteWorkTable()
 
-	r, err := newRouter(workTable, ifaceMock)
+	r, err := newRouter(workTable, ifaceMock, iface.DefaultMTU)
 	require.NoError(t, err, "Failed to create router")
 	require.NoError(t, r.init(workTable))
 
@@ -364,7 +365,7 @@ func TestNftablesCreateIpSet(t *testing.T) {
 
 	defer deleteWorkTable()
 
-	r, err := newRouter(workTable, ifaceMock)
+	r, err := newRouter(workTable, ifaceMock, iface.DefaultMTU)
 	require.NoError(t, err, "Failed to create router")
 	require.NoError(t, r.init(workTable))
 
diff --git a/client/firewall/nftables/state_linux.go b/client/firewall/nftables/state_linux.go
index f805623d6..48b7b3741 100644
--- a/client/firewall/nftables/state_linux.go
+++ b/client/firewall/nftables/state_linux.go
@@ -3,6 +3,7 @@ package nftables
 import (
 	"fmt"
 
+	"github.com/netbirdio/netbird/client/iface"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 )
 
@@ -10,6 +11,7 @@ type InterfaceState struct {
 	NameStr       string         `json:"name"`
 	WGAddress     wgaddr.Address `json:"wg_address"`
 	UserspaceBind bool           `json:"userspace_bind"`
+	MTU           uint16         `json:"mtu"`
 }
 
 func (i *InterfaceState) Name() string {
@@ -33,7 +35,11 @@ func (s *ShutdownState) Name() string {
 }
 
 func (s *ShutdownState) Cleanup() error {
-	nft, err := Create(s.InterfaceState)
+	mtu := s.InterfaceState.MTU
+	if mtu == 0 {
+		mtu = iface.DefaultMTU
+	}
+	nft, err := Create(s.InterfaceState, mtu)
 	if err != nil {
 		return fmt.Errorf("create nftables manager: %w", err)
 	}
diff --git a/client/firewall/uspfilter/filter.go b/client/firewall/uspfilter/filter.go
index ec2d2c57f..990630ee4 100644
--- a/client/firewall/uspfilter/filter.go
+++ b/client/firewall/uspfilter/filter.go
@@ -1,6 +1,7 @@
 package uspfilter
 
 import (
+	"encoding/binary"
 	"errors"
 	"fmt"
 	"net"
@@ -27,7 +28,12 @@ import (
 	"github.com/netbirdio/netbird/client/internal/statemanager"
 )
 
-const layerTypeAll = 0
+const (
+	layerTypeAll = 0
+
+	// ipTCPHeaderMinSize represents minimum IP (20) + TCP (20) header size for MSS calculation
+	ipTCPHeaderMinSize = 40
+)
 
 const (
 	// EnvDisableConntrack disables the stateful filter, replies to outbound traffic won't be allowed.
@@ -36,6 +42,9 @@ const (
 	// EnvDisableUserspaceRouting disables userspace routing, to-be-routed packets will be dropped.
 	EnvDisableUserspaceRouting = "NB_DISABLE_USERSPACE_ROUTING"
 
+	// EnvDisableMSSClamping disables TCP MSS clamping for forwarded traffic.
+	EnvDisableMSSClamping = "NB_DISABLE_MSS_CLAMPING"
+
 	// EnvForceUserspaceRouter forces userspace routing even if native routing is available.
 	EnvForceUserspaceRouter = "NB_FORCE_USERSPACE_ROUTER"
 
@@ -122,6 +131,10 @@ type Manager struct {
 
 	netstackServices     map[serviceKey]struct{}
 	netstackServiceMutex sync.RWMutex
+
+	mtu             uint16
+	mssClampValue   uint16
+	mssClampEnabled bool
 }
 
 // decoder for packages
@@ -140,16 +153,16 @@ type decoder struct {
 }
 
 // Create userspace firewall manager constructor
-func Create(iface common.IFaceMapper, disableServerRoutes bool, flowLogger nftypes.FlowLogger) (*Manager, error) {
-	return create(iface, nil, disableServerRoutes, flowLogger)
+func Create(iface common.IFaceMapper, disableServerRoutes bool, flowLogger nftypes.FlowLogger, mtu uint16) (*Manager, error) {
+	return create(iface, nil, disableServerRoutes, flowLogger, mtu)
 }
 
-func CreateWithNativeFirewall(iface common.IFaceMapper, nativeFirewall firewall.Manager, disableServerRoutes bool, flowLogger nftypes.FlowLogger) (*Manager, error) {
+func CreateWithNativeFirewall(iface common.IFaceMapper, nativeFirewall firewall.Manager, disableServerRoutes bool, flowLogger nftypes.FlowLogger, mtu uint16) (*Manager, error) {
 	if nativeFirewall == nil {
 		return nil, errors.New("native firewall is nil")
 	}
 
-	mgr, err := create(iface, nativeFirewall, disableServerRoutes, flowLogger)
+	mgr, err := create(iface, nativeFirewall, disableServerRoutes, flowLogger, mtu)
 	if err != nil {
 		return nil, err
 	}
@@ -157,8 +170,8 @@ func CreateWithNativeFirewall(iface common.IFaceMapper, nativeFirewall firewall.
 	return mgr, nil
 }
 
-func parseCreateEnv() (bool, bool) {
-	var disableConntrack, enableLocalForwarding bool
+func parseCreateEnv() (bool, bool, bool) {
+	var disableConntrack, enableLocalForwarding, disableMSSClamping bool
 	var err error
 	if val := os.Getenv(EnvDisableConntrack); val != "" {
 		disableConntrack, err = strconv.ParseBool(val)
@@ -177,12 +190,18 @@ func parseCreateEnv() (bool, bool) {
 			log.Warnf("failed to parse %s: %v", EnvEnableLocalForwarding, err)
 		}
 	}
+	if val := os.Getenv(EnvDisableMSSClamping); val != "" {
+		disableMSSClamping, err = strconv.ParseBool(val)
+		if err != nil {
+			log.Warnf("failed to parse %s: %v", EnvDisableMSSClamping, err)
+		}
+	}
 
-	return disableConntrack, enableLocalForwarding
+	return disableConntrack, enableLocalForwarding, disableMSSClamping
 }
 
-func create(iface common.IFaceMapper, nativeFirewall firewall.Manager, disableServerRoutes bool, flowLogger nftypes.FlowLogger) (*Manager, error) {
-	disableConntrack, enableLocalForwarding := parseCreateEnv()
+func create(iface common.IFaceMapper, nativeFirewall firewall.Manager, disableServerRoutes bool, flowLogger nftypes.FlowLogger, mtu uint16) (*Manager, error) {
+	disableConntrack, enableLocalForwarding, disableMSSClamping := parseCreateEnv()
 
 	m := &Manager{
 		decoders: sync.Pool{
@@ -213,13 +232,17 @@ func create(iface common.IFaceMapper, nativeFirewall firewall.Manager, disableSe
 		dnatMappings:        make(map[netip.Addr]netip.Addr),
 		portDNATRules:       []portDNATRule{},
 		netstackServices:    make(map[serviceKey]struct{}),
+		mtu:                 mtu,
 	}
 	m.routingEnabled.Store(false)
 
+	if !disableMSSClamping {
+		m.mssClampEnabled = true
+		m.mssClampValue = mtu - ipTCPHeaderMinSize
+	}
 	if err := m.localipmanager.UpdateLocalIPs(iface); err != nil {
 		return nil, fmt.Errorf("update local IPs: %w", err)
 	}
-
 	if disableConntrack {
 		log.Info("conntrack is disabled")
 	} else {
@@ -227,14 +250,11 @@ func create(iface common.IFaceMapper, nativeFirewall firewall.Manager, disableSe
 		m.icmpTracker = conntrack.NewICMPTracker(conntrack.DefaultICMPTimeout, m.logger, flowLogger)
 		m.tcpTracker = conntrack.NewTCPTracker(conntrack.DefaultTCPTimeout, m.logger, flowLogger)
 	}
-
-	// netstack needs the forwarder for local traffic
 	if m.netstack && m.localForwarding {
 		if err := m.initForwarder(); err != nil {
 			log.Errorf("failed to initialize forwarder: %v", err)
 		}
 	}
-
 	if err := iface.SetFilter(m); err != nil {
 		return nil, fmt.Errorf("set filter: %w", err)
 	}
@@ -337,7 +357,7 @@ func (m *Manager) initForwarder() error {
 		return errors.New("forwarding not supported")
 	}
 
-	forwarder, err := forwarder.New(m.wgIface, m.logger, m.flowLogger, m.netstack)
+	forwarder, err := forwarder.New(m.wgIface, m.logger, m.flowLogger, m.netstack, m.mtu)
 	if err != nil {
 		m.routingEnabled.Store(false)
 		return fmt.Errorf("create forwarder: %w", err)
@@ -643,8 +663,17 @@ func (m *Manager) filterOutbound(packetData []byte, size int) bool {
 		return false
 	}
 
-	if d.decoded[1] == layers.LayerTypeUDP && m.udpHooksDrop(uint16(d.udp.DstPort), dstIP, packetData) {
-		return true
+	switch d.decoded[1] {
+	case layers.LayerTypeUDP:
+		if m.udpHooksDrop(uint16(d.udp.DstPort), dstIP, packetData) {
+			return true
+		}
+	case layers.LayerTypeTCP:
+		// Clamp MSS on all TCP SYN packets, including those from local IPs.
+		// SNATed routed traffic may appear as local IP but still requires clamping.
+		if m.mssClampEnabled {
+			m.clampTCPMSS(packetData, d)
+		}
 	}
 
 	m.trackOutbound(d, srcIP, dstIP, packetData, size)
@@ -691,6 +720,97 @@ func getTCPFlags(tcp *layers.TCP) uint8 {
 	return flags
 }
 
+// clampTCPMSS clamps the TCP MSS option in SYN and SYN-ACK packets to prevent fragmentation.
+// Both sides advertise their MSS during connection establishment, so we need to clamp both.
+func (m *Manager) clampTCPMSS(packetData []byte, d *decoder) bool {
+	if !d.tcp.SYN {
+		return false
+	}
+	if len(d.tcp.Options) == 0 {
+		return false
+	}
+
+	mssOptionIndex := -1
+	var currentMSS uint16
+	for i, opt := range d.tcp.Options {
+		if opt.OptionType == layers.TCPOptionKindMSS && len(opt.OptionData) == 2 {
+			currentMSS = binary.BigEndian.Uint16(opt.OptionData)
+			if currentMSS > m.mssClampValue {
+				mssOptionIndex = i
+				break
+			}
+		}
+	}
+
+	if mssOptionIndex == -1 {
+		return false
+	}
+
+	ipHeaderSize := int(d.ip4.IHL) * 4
+	if ipHeaderSize < 20 {
+		return false
+	}
+
+	if !m.updateMSSOption(packetData, d, mssOptionIndex, ipHeaderSize) {
+		return false
+	}
+
+	m.logger.Trace2("Clamped TCP MSS from %d to %d", currentMSS, m.mssClampValue)
+	return true
+}
+
+func (m *Manager) updateMSSOption(packetData []byte, d *decoder, mssOptionIndex, ipHeaderSize int) bool {
+	tcpHeaderStart := ipHeaderSize
+	tcpOptionsStart := tcpHeaderStart + 20
+
+	optOffset := tcpOptionsStart
+	for j := 0; j < mssOptionIndex; j++ {
+		switch d.tcp.Options[j].OptionType {
+		case layers.TCPOptionKindEndList, layers.TCPOptionKindNop:
+			optOffset++
+		default:
+			optOffset += 2 + len(d.tcp.Options[j].OptionData)
+		}
+	}
+
+	mssValueOffset := optOffset + 2
+	binary.BigEndian.PutUint16(packetData[mssValueOffset:mssValueOffset+2], m.mssClampValue)
+
+	m.recalculateTCPChecksum(packetData, d, tcpHeaderStart)
+	return true
+}
+
+func (m *Manager) recalculateTCPChecksum(packetData []byte, d *decoder, tcpHeaderStart int) {
+	tcpLayer := packetData[tcpHeaderStart:]
+	tcpLength := len(packetData) - tcpHeaderStart
+
+	tcpLayer[16] = 0
+	tcpLayer[17] = 0
+
+	var pseudoSum uint32
+	pseudoSum += uint32(d.ip4.SrcIP[0])<<8 | uint32(d.ip4.SrcIP[1])
+	pseudoSum += uint32(d.ip4.SrcIP[2])<<8 | uint32(d.ip4.SrcIP[3])
+	pseudoSum += uint32(d.ip4.DstIP[0])<<8 | uint32(d.ip4.DstIP[1])
+	pseudoSum += uint32(d.ip4.DstIP[2])<<8 | uint32(d.ip4.DstIP[3])
+	pseudoSum += uint32(d.ip4.Protocol)
+	pseudoSum += uint32(tcpLength)
+
+	var sum uint32 = pseudoSum
+	for i := 0; i < tcpLength-1; i += 2 {
+		sum += uint32(tcpLayer[i])<<8 | uint32(tcpLayer[i+1])
+	}
+	if tcpLength%2 == 1 {
+		sum += uint32(tcpLayer[tcpLength-1]) << 8
+	}
+
+	for sum > 0xFFFF {
+		sum = (sum & 0xFFFF) + (sum >> 16)
+	}
+
+	checksum := ^uint16(sum)
+	binary.BigEndian.PutUint16(tcpLayer[16:18], checksum)
+}
+
 func (m *Manager) trackOutbound(d *decoder, srcIP, dstIP netip.Addr, packetData []byte, size int) {
 	transport := d.decoded[1]
 	switch transport {
diff --git a/client/firewall/uspfilter/filter_bench_test.go b/client/firewall/uspfilter/filter_bench_test.go
index 0cffcc1a7..5a2d0410f 100644
--- a/client/firewall/uspfilter/filter_bench_test.go
+++ b/client/firewall/uspfilter/filter_bench_test.go
@@ -17,6 +17,7 @@ import (
 
 	fw "github.com/netbirdio/netbird/client/firewall/manager"
 	"github.com/netbirdio/netbird/client/firewall/uspfilter/conntrack"
+	"github.com/netbirdio/netbird/client/iface"
 	"github.com/netbirdio/netbird/client/iface/device"
 )
 
@@ -169,7 +170,7 @@ func BenchmarkCoreFiltering(b *testing.B) {
 				// Create manager and basic setup
 				manager, _ := Create(&IFaceMock{
 					SetFilterFunc: func(device.PacketFilter) error { return nil },
-				}, false, flowLogger)
+				}, false, flowLogger, iface.DefaultMTU)
 				defer b.Cleanup(func() {
 					require.NoError(b, manager.Close(nil))
 				})
@@ -209,7 +210,7 @@ func BenchmarkStateScaling(b *testing.B) {
 		b.Run(fmt.Sprintf("conns_%d", count), func(b *testing.B) {
 			manager, _ := Create(&IFaceMock{
 				SetFilterFunc: func(device.PacketFilter) error { return nil },
-			}, false, flowLogger)
+			}, false, flowLogger, iface.DefaultMTU)
 			b.Cleanup(func() {
 				require.NoError(b, manager.Close(nil))
 			})
@@ -252,7 +253,7 @@ func BenchmarkEstablishmentOverhead(b *testing.B) {
 		b.Run(sc.name, func(b *testing.B) {
 			manager, _ := Create(&IFaceMock{
 				SetFilterFunc: func(device.PacketFilter) error { return nil },
-			}, false, flowLogger)
+			}, false, flowLogger, iface.DefaultMTU)
 			b.Cleanup(func() {
 				require.NoError(b, manager.Close(nil))
 			})
@@ -410,7 +411,7 @@ func BenchmarkRoutedNetworkReturn(b *testing.B) {
 		b.Run(sc.name, func(b *testing.B) {
 			manager, _ := Create(&IFaceMock{
 				SetFilterFunc: func(device.PacketFilter) error { return nil },
-			}, false, flowLogger)
+			}, false, flowLogger, iface.DefaultMTU)
 			b.Cleanup(func() {
 				require.NoError(b, manager.Close(nil))
 			})
@@ -537,7 +538,7 @@ func BenchmarkLongLivedConnections(b *testing.B) {
 
 			manager, _ := Create(&IFaceMock{
 				SetFilterFunc: func(device.PacketFilter) error { return nil },
-			}, false, flowLogger)
+			}, false, flowLogger, iface.DefaultMTU)
 			defer b.Cleanup(func() {
 				require.NoError(b, manager.Close(nil))
 			})
@@ -620,7 +621,7 @@ func BenchmarkShortLivedConnections(b *testing.B) {
 
 			manager, _ := Create(&IFaceMock{
 				SetFilterFunc: func(device.PacketFilter) error { return nil },
-			}, false, flowLogger)
+			}, false, flowLogger, iface.DefaultMTU)
 			defer b.Cleanup(func() {
 				require.NoError(b, manager.Close(nil))
 			})
@@ -731,7 +732,7 @@ func BenchmarkParallelLongLivedConnections(b *testing.B) {
 
 			manager, _ := Create(&IFaceMock{
 				SetFilterFunc: func(device.PacketFilter) error { return nil },
-			}, false, flowLogger)
+			}, false, flowLogger, iface.DefaultMTU)
 			defer b.Cleanup(func() {
 				require.NoError(b, manager.Close(nil))
 			})
@@ -811,7 +812,7 @@ func BenchmarkParallelShortLivedConnections(b *testing.B) {
 
 			manager, _ := Create(&IFaceMock{
 				SetFilterFunc: func(device.PacketFilter) error { return nil },
-			}, false, flowLogger)
+			}, false, flowLogger, iface.DefaultMTU)
 			defer b.Cleanup(func() {
 				require.NoError(b, manager.Close(nil))
 			})
@@ -896,38 +897,6 @@ func BenchmarkParallelShortLivedConnections(b *testing.B) {
 	}
 }
 
-// generateTCPPacketWithFlags creates a TCP packet with specific flags
-func generateTCPPacketWithFlags(b *testing.B, srcIP, dstIP net.IP, srcPort, dstPort, flags uint16) []byte {
-	b.Helper()
-
-	ipv4 := &layers.IPv4{
-		TTL:      64,
-		Version:  4,
-		SrcIP:    srcIP,
-		DstIP:    dstIP,
-		Protocol: layers.IPProtocolTCP,
-	}
-
-	tcp := &layers.TCP{
-		SrcPort: layers.TCPPort(srcPort),
-		DstPort: layers.TCPPort(dstPort),
-	}
-
-	// Set TCP flags
-	tcp.SYN = (flags & uint16(conntrack.TCPSyn)) != 0
-	tcp.ACK = (flags & uint16(conntrack.TCPAck)) != 0
-	tcp.PSH = (flags & uint16(conntrack.TCPPush)) != 0
-	tcp.RST = (flags & uint16(conntrack.TCPRst)) != 0
-	tcp.FIN = (flags & uint16(conntrack.TCPFin)) != 0
-
-	require.NoError(b, tcp.SetNetworkLayerForChecksum(ipv4))
-
-	buf := gopacket.NewSerializeBuffer()
-	opts := gopacket.SerializeOptions{ComputeChecksums: true, FixLengths: true}
-	require.NoError(b, gopacket.SerializeLayers(buf, opts, ipv4, tcp, gopacket.Payload("test")))
-	return buf.Bytes()
-}
-
 func BenchmarkRouteACLs(b *testing.B) {
 	manager := setupRoutedManager(b, "10.10.0.100/16")
 
@@ -990,3 +959,231 @@ func BenchmarkRouteACLs(b *testing.B) {
 		}
 	}
 }
+
+// BenchmarkMSSClamping benchmarks the MSS clamping impact on filterOutbound.
+// This shows the overhead difference between the common case (non-SYN packets, fast path)
+// and the rare case (SYN packets that need clamping, expensive path).
+func BenchmarkMSSClamping(b *testing.B) {
+	scenarios := []struct {
+		name        string
+		description string
+		genPacket   func(*testing.B, net.IP, net.IP) []byte
+		frequency   string
+	}{
+		{
+			name:        "syn_needs_clamp",
+			description: "SYN packet needing MSS clamping",
+			genPacket: func(b *testing.B, src, dst net.IP) []byte {
+				return generateSYNPacketWithMSS(b, src, dst, 12345, 80, 1460)
+			},
+			frequency: "~0.1% of traffic - EXPENSIVE",
+		},
+		{
+			name:        "syn_no_clamp_needed",
+			description: "SYN packet with already-small MSS",
+			genPacket: func(b *testing.B, src, dst net.IP) []byte {
+				return generateSYNPacketWithMSS(b, src, dst, 12345, 80, 1200)
+			},
+			frequency: "~0.05% of traffic",
+		},
+		{
+			name:        "tcp_ack",
+			description: "Non-SYN TCP packet (ACK, data transfer)",
+			genPacket: func(b *testing.B, src, dst net.IP) []byte {
+				return generateTCPPacketWithFlags(b, src, dst, 12345, 80, uint16(conntrack.TCPAck))
+			},
+			frequency: "~60-70% of traffic - FAST PATH",
+		},
+		{
+			name:        "tcp_psh_ack",
+			description: "TCP data packet (PSH+ACK)",
+			genPacket: func(b *testing.B, src, dst net.IP) []byte {
+				return generateTCPPacketWithFlags(b, src, dst, 12345, 80, uint16(conntrack.TCPPush|conntrack.TCPAck))
+			},
+			frequency: "~10-20% of traffic - FAST PATH",
+		},
+		{
+			name:        "udp",
+			description: "UDP packet",
+			genPacket: func(b *testing.B, src, dst net.IP) []byte {
+				return generatePacket(b, src, dst, 12345, 80, layers.IPProtocolUDP)
+			},
+			frequency: "~20-30% of traffic - FAST PATH",
+		},
+	}
+
+	for _, sc := range scenarios {
+		b.Run(sc.name, func(b *testing.B) {
+			manager, err := Create(&IFaceMock{
+				SetFilterFunc: func(device.PacketFilter) error { return nil },
+			}, false, flowLogger, iface.DefaultMTU)
+			require.NoError(b, err)
+			defer func() {
+				require.NoError(b, manager.Close(nil))
+			}()
+
+			manager.mssClampEnabled = true
+			manager.mssClampValue = 1240
+
+			srcIP := net.ParseIP("100.64.0.2")
+			dstIP := net.ParseIP("8.8.8.8")
+			packet := sc.genPacket(b, srcIP, dstIP)
+
+			b.ReportAllocs()
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				manager.filterOutbound(packet, len(packet))
+			}
+		})
+	}
+}
+
+// BenchmarkMSSClampingOverhead compares overhead of MSS clamping enabled vs disabled
+// for the common case (non-SYN TCP packets).
+func BenchmarkMSSClampingOverhead(b *testing.B) {
+	scenarios := []struct {
+		name      string
+		enabled   bool
+		genPacket func(*testing.B, net.IP, net.IP) []byte
+	}{
+		{
+			name:    "disabled_tcp_ack",
+			enabled: false,
+			genPacket: func(b *testing.B, src, dst net.IP) []byte {
+				return generateTCPPacketWithFlags(b, src, dst, 12345, 80, uint16(conntrack.TCPAck))
+			},
+		},
+		{
+			name:    "enabled_tcp_ack",
+			enabled: true,
+			genPacket: func(b *testing.B, src, dst net.IP) []byte {
+				return generateTCPPacketWithFlags(b, src, dst, 12345, 80, uint16(conntrack.TCPAck))
+			},
+		},
+		{
+			name:    "disabled_syn_needs_clamp",
+			enabled: false,
+			genPacket: func(b *testing.B, src, dst net.IP) []byte {
+				return generateSYNPacketWithMSS(b, src, dst, 12345, 80, 1460)
+			},
+		},
+		{
+			name:    "enabled_syn_needs_clamp",
+			enabled: true,
+			genPacket: func(b *testing.B, src, dst net.IP) []byte {
+				return generateSYNPacketWithMSS(b, src, dst, 12345, 80, 1460)
+			},
+		},
+	}
+
+	for _, sc := range scenarios {
+		b.Run(sc.name, func(b *testing.B) {
+			manager, err := Create(&IFaceMock{
+				SetFilterFunc: func(device.PacketFilter) error { return nil },
+			}, false, flowLogger, iface.DefaultMTU)
+			require.NoError(b, err)
+			defer func() {
+				require.NoError(b, manager.Close(nil))
+			}()
+
+			manager.mssClampEnabled = sc.enabled
+			if sc.enabled {
+				manager.mssClampValue = 1240
+			}
+
+			srcIP := net.ParseIP("100.64.0.2")
+			dstIP := net.ParseIP("8.8.8.8")
+			packet := sc.genPacket(b, srcIP, dstIP)
+
+			b.ReportAllocs()
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				manager.filterOutbound(packet, len(packet))
+			}
+		})
+	}
+}
+
+// BenchmarkMSSClampingMemory measures memory allocations for common vs rare cases
+func BenchmarkMSSClampingMemory(b *testing.B) {
+	scenarios := []struct {
+		name      string
+		genPacket func(*testing.B, net.IP, net.IP) []byte
+	}{
+		{
+			name: "tcp_ack_fast_path",
+			genPacket: func(b *testing.B, src, dst net.IP) []byte {
+				return generateTCPPacketWithFlags(b, src, dst, 12345, 80, uint16(conntrack.TCPAck))
+			},
+		},
+		{
+			name: "syn_needs_clamp",
+			genPacket: func(b *testing.B, src, dst net.IP) []byte {
+				return generateSYNPacketWithMSS(b, src, dst, 12345, 80, 1460)
+			},
+		},
+		{
+			name: "udp_fast_path",
+			genPacket: func(b *testing.B, src, dst net.IP) []byte {
+				return generatePacket(b, src, dst, 12345, 80, layers.IPProtocolUDP)
+			},
+		},
+	}
+
+	for _, sc := range scenarios {
+		b.Run(sc.name, func(b *testing.B) {
+			manager, err := Create(&IFaceMock{
+				SetFilterFunc: func(device.PacketFilter) error { return nil },
+			}, false, flowLogger, iface.DefaultMTU)
+			require.NoError(b, err)
+			defer func() {
+				require.NoError(b, manager.Close(nil))
+			}()
+
+			manager.mssClampEnabled = true
+			manager.mssClampValue = 1240
+
+			srcIP := net.ParseIP("100.64.0.2")
+			dstIP := net.ParseIP("8.8.8.8")
+			packet := sc.genPacket(b, srcIP, dstIP)
+
+			b.ReportAllocs()
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				manager.filterOutbound(packet, len(packet))
+			}
+		})
+	}
+}
+
+func generateSYNPacketNoMSS(b *testing.B, srcIP, dstIP net.IP, srcPort, dstPort uint16) []byte {
+	b.Helper()
+
+	ip := &layers.IPv4{
+		Version:  4,
+		IHL:      5,
+		TTL:      64,
+		Protocol: layers.IPProtocolTCP,
+		SrcIP:    srcIP,
+		DstIP:    dstIP,
+	}
+
+	tcp := &layers.TCP{
+		SrcPort: layers.TCPPort(srcPort),
+		DstPort: layers.TCPPort(dstPort),
+		SYN:     true,
+		Seq:     1000,
+		Window:  65535,
+	}
+
+	require.NoError(b, tcp.SetNetworkLayerForChecksum(ip))
+
+	buf := gopacket.NewSerializeBuffer()
+	opts := gopacket.SerializeOptions{
+		FixLengths:       true,
+		ComputeChecksums: true,
+	}
+
+	require.NoError(b, gopacket.SerializeLayers(buf, opts, ip, tcp, gopacket.Payload([]byte{})))
+	return buf.Bytes()
+}
diff --git a/client/firewall/uspfilter/filter_filter_test.go b/client/firewall/uspfilter/filter_filter_test.go
index 73f3face8..eb5aa3343 100644
--- a/client/firewall/uspfilter/filter_filter_test.go
+++ b/client/firewall/uspfilter/filter_filter_test.go
@@ -12,6 +12,7 @@ import (
 	wgdevice "golang.zx2c4.com/wireguard/device"
 
 	fw "github.com/netbirdio/netbird/client/firewall/manager"
+	"github.com/netbirdio/netbird/client/iface"
 	"github.com/netbirdio/netbird/client/iface/device"
 	"github.com/netbirdio/netbird/client/iface/mocks"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
@@ -31,7 +32,7 @@ func TestPeerACLFiltering(t *testing.T) {
 		},
 	}
 
-	manager, err := Create(ifaceMock, false, flowLogger)
+	manager, err := Create(ifaceMock, false, flowLogger, iface.DefaultMTU)
 	require.NoError(t, err)
 	require.NotNil(t, manager)
 
@@ -616,7 +617,7 @@ func setupRoutedManager(tb testing.TB, network string) *Manager {
 		},
 	}
 
-	manager, err := Create(ifaceMock, false, flowLogger)
+	manager, err := Create(ifaceMock, false, flowLogger, iface.DefaultMTU)
 	require.NoError(tb, err)
 	require.NoError(tb, manager.EnableRouting())
 	require.NotNil(tb, manager)
@@ -1462,7 +1463,7 @@ func TestRouteACLSet(t *testing.T) {
 		},
 	}
 
-	manager, err := Create(ifaceMock, false, flowLogger)
+	manager, err := Create(ifaceMock, false, flowLogger, iface.DefaultMTU)
 	require.NoError(t, err)
 	t.Cleanup(func() {
 		require.NoError(t, manager.Close(nil))
diff --git a/client/firewall/uspfilter/filter_test.go b/client/firewall/uspfilter/filter_test.go
index bac06814d..c56a078fc 100644
--- a/client/firewall/uspfilter/filter_test.go
+++ b/client/firewall/uspfilter/filter_test.go
@@ -1,6 +1,7 @@
 package uspfilter
 
 import (
+	"encoding/binary"
 	"fmt"
 	"net"
 	"net/netip"
@@ -17,6 +18,7 @@ import (
 	fw "github.com/netbirdio/netbird/client/firewall/manager"
 	"github.com/netbirdio/netbird/client/firewall/uspfilter/conntrack"
 	"github.com/netbirdio/netbird/client/firewall/uspfilter/log"
+	nbiface "github.com/netbirdio/netbird/client/iface"
 	"github.com/netbirdio/netbird/client/iface/device"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 	"github.com/netbirdio/netbird/client/internal/netflow"
@@ -66,7 +68,7 @@ func TestManagerCreate(t *testing.T) {
 		SetFilterFunc: func(device.PacketFilter) error { return nil },
 	}
 
-	m, err := Create(ifaceMock, false, flowLogger)
+	m, err := Create(ifaceMock, false, flowLogger, nbiface.DefaultMTU)
 	if err != nil {
 		t.Errorf("failed to create Manager: %v", err)
 		return
@@ -86,7 +88,7 @@ func TestManagerAddPeerFiltering(t *testing.T) {
 		},
 	}
 
-	m, err := Create(ifaceMock, false, flowLogger)
+	m, err := Create(ifaceMock, false, flowLogger, nbiface.DefaultMTU)
 	if err != nil {
 		t.Errorf("failed to create Manager: %v", err)
 		return
@@ -119,7 +121,7 @@ func TestManagerDeleteRule(t *testing.T) {
 		SetFilterFunc: func(device.PacketFilter) error { return nil },
 	}
 
-	m, err := Create(ifaceMock, false, flowLogger)
+	m, err := Create(ifaceMock, false, flowLogger, nbiface.DefaultMTU)
 	if err != nil {
 		t.Errorf("failed to create Manager: %v", err)
 		return
@@ -215,7 +217,7 @@ func TestAddUDPPacketHook(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			manager, err := Create(&IFaceMock{
 				SetFilterFunc: func(device.PacketFilter) error { return nil },
-			}, false, flowLogger)
+			}, false, flowLogger, nbiface.DefaultMTU)
 			require.NoError(t, err)
 
 			manager.AddUDPPacketHook(tt.in, tt.ip, tt.dPort, tt.hook)
@@ -265,7 +267,7 @@ func TestManagerReset(t *testing.T) {
 		SetFilterFunc: func(device.PacketFilter) error { return nil },
 	}
 
-	m, err := Create(ifaceMock, false, flowLogger)
+	m, err := Create(ifaceMock, false, flowLogger, nbiface.DefaultMTU)
 	if err != nil {
 		t.Errorf("failed to create Manager: %v", err)
 		return
@@ -304,7 +306,7 @@ func TestNotMatchByIP(t *testing.T) {
 		},
 	}
 
-	m, err := Create(ifaceMock, false, flowLogger)
+	m, err := Create(ifaceMock, false, flowLogger, nbiface.DefaultMTU)
 	if err != nil {
 		t.Errorf("failed to create Manager: %v", err)
 		return
@@ -367,7 +369,7 @@ func TestRemovePacketHook(t *testing.T) {
 	}
 
 	// creating manager instance
-	manager, err := Create(iface, false, flowLogger)
+	manager, err := Create(iface, false, flowLogger, nbiface.DefaultMTU)
 	if err != nil {
 		t.Fatalf("Failed to create Manager: %s", err)
 	}
@@ -413,7 +415,7 @@ func TestRemovePacketHook(t *testing.T) {
 func TestProcessOutgoingHooks(t *testing.T) {
 	manager, err := Create(&IFaceMock{
 		SetFilterFunc: func(device.PacketFilter) error { return nil },
-	}, false, flowLogger)
+	}, false, flowLogger, nbiface.DefaultMTU)
 	require.NoError(t, err)
 
 	manager.udpTracker.Close()
@@ -495,7 +497,7 @@ func TestUSPFilterCreatePerformance(t *testing.T) {
 			ifaceMock := &IFaceMock{
 				SetFilterFunc: func(device.PacketFilter) error { return nil },
 			}
-			manager, err := Create(ifaceMock, false, flowLogger)
+			manager, err := Create(ifaceMock, false, flowLogger, nbiface.DefaultMTU)
 			require.NoError(t, err)
 			time.Sleep(time.Second)
 
@@ -522,7 +524,7 @@ func TestUSPFilterCreatePerformance(t *testing.T) {
 func TestStatefulFirewall_UDPTracking(t *testing.T) {
 	manager, err := Create(&IFaceMock{
 		SetFilterFunc: func(device.PacketFilter) error { return nil },
-	}, false, flowLogger)
+	}, false, flowLogger, nbiface.DefaultMTU)
 	require.NoError(t, err)
 
 	manager.udpTracker.Close() // Close the existing tracker
@@ -729,7 +731,7 @@ func TestUpdateSetMerge(t *testing.T) {
 		SetFilterFunc: func(device.PacketFilter) error { return nil },
 	}
 
-	manager, err := Create(ifaceMock, false, flowLogger)
+	manager, err := Create(ifaceMock, false, flowLogger, nbiface.DefaultMTU)
 	require.NoError(t, err)
 	t.Cleanup(func() {
 		require.NoError(t, manager.Close(nil))
@@ -815,7 +817,7 @@ func TestUpdateSetDeduplication(t *testing.T) {
 		SetFilterFunc: func(device.PacketFilter) error { return nil },
 	}
 
-	manager, err := Create(ifaceMock, false, flowLogger)
+	manager, err := Create(ifaceMock, false, flowLogger, nbiface.DefaultMTU)
 	require.NoError(t, err)
 	t.Cleanup(func() {
 		require.NoError(t, manager.Close(nil))
@@ -923,3 +925,192 @@ func TestUpdateSetDeduplication(t *testing.T) {
 		require.Equal(t, tc.expected, isAllowed, tc.desc)
 	}
 }
+
+func TestMSSClamping(t *testing.T) {
+	ifaceMock := &IFaceMock{
+		SetFilterFunc: func(device.PacketFilter) error { return nil },
+		AddressFunc: func() wgaddr.Address {
+			return wgaddr.Address{
+				IP:      netip.MustParseAddr("100.10.0.100"),
+				Network: netip.MustParsePrefix("100.10.0.0/16"),
+			}
+		},
+	}
+
+	manager, err := Create(ifaceMock, false, flowLogger, 1280)
+	require.NoError(t, err)
+	defer func() {
+		require.NoError(t, manager.Close(nil))
+	}()
+
+	require.True(t, manager.mssClampEnabled, "MSS clamping should be enabled by default")
+	expectedMSSValue := uint16(1280 - ipTCPHeaderMinSize)
+	require.Equal(t, expectedMSSValue, manager.mssClampValue, "MSS clamp value should be MTU - 40")
+
+	err = manager.UpdateLocalIPs()
+	require.NoError(t, err)
+
+	srcIP := net.ParseIP("100.10.0.2")
+	dstIP := net.ParseIP("8.8.8.8")
+
+	t.Run("SYN packet with high MSS gets clamped", func(t *testing.T) {
+		highMSS := uint16(1460)
+		packet := generateSYNPacketWithMSS(t, srcIP, dstIP, 12345, 80, highMSS)
+
+		manager.filterOutbound(packet, len(packet))
+
+		d := parsePacket(t, packet)
+		require.Len(t, d.tcp.Options, 1, "Should have MSS option")
+		require.Equal(t, uint8(layers.TCPOptionKindMSS), uint8(d.tcp.Options[0].OptionType))
+		actualMSS := binary.BigEndian.Uint16(d.tcp.Options[0].OptionData)
+		require.Equal(t, expectedMSSValue, actualMSS, "MSS should be clamped to MTU - 40")
+	})
+
+	t.Run("SYN packet with low MSS unchanged", func(t *testing.T) {
+		lowMSS := uint16(1200)
+		packet := generateSYNPacketWithMSS(t, srcIP, dstIP, 12345, 80, lowMSS)
+
+		manager.filterOutbound(packet, len(packet))
+
+		d := parsePacket(t, packet)
+		require.Len(t, d.tcp.Options, 1, "Should have MSS option")
+		actualMSS := binary.BigEndian.Uint16(d.tcp.Options[0].OptionData)
+		require.Equal(t, lowMSS, actualMSS, "Low MSS should not be modified")
+	})
+
+	t.Run("SYN-ACK packet gets clamped", func(t *testing.T) {
+		highMSS := uint16(1460)
+		packet := generateSYNACKPacketWithMSS(t, srcIP, dstIP, 12345, 80, highMSS)
+
+		manager.filterOutbound(packet, len(packet))
+
+		d := parsePacket(t, packet)
+		require.Len(t, d.tcp.Options, 1, "Should have MSS option")
+		actualMSS := binary.BigEndian.Uint16(d.tcp.Options[0].OptionData)
+		require.Equal(t, expectedMSSValue, actualMSS, "MSS in SYN-ACK should be clamped")
+	})
+
+	t.Run("Non-SYN packet unchanged", func(t *testing.T) {
+		packet := generateTCPPacketWithFlags(t, srcIP, dstIP, 12345, 80, uint16(conntrack.TCPAck))
+
+		manager.filterOutbound(packet, len(packet))
+
+		d := parsePacket(t, packet)
+		require.Empty(t, d.tcp.Options, "ACK packet should have no options")
+	})
+}
+
+func generateSYNPacketWithMSS(tb testing.TB, srcIP, dstIP net.IP, srcPort, dstPort uint16, mss uint16) []byte {
+	tb.Helper()
+
+	ipLayer := &layers.IPv4{
+		Version:  4,
+		TTL:      64,
+		Protocol: layers.IPProtocolTCP,
+		SrcIP:    srcIP,
+		DstIP:    dstIP,
+	}
+
+	tcpLayer := &layers.TCP{
+		SrcPort: layers.TCPPort(srcPort),
+		DstPort: layers.TCPPort(dstPort),
+		SYN:     true,
+		Window:  65535,
+		Options: []layers.TCPOption{
+			{
+				OptionType:   layers.TCPOptionKindMSS,
+				OptionLength: 4,
+				OptionData:   binary.BigEndian.AppendUint16(nil, mss),
+			},
+		},
+	}
+	err := tcpLayer.SetNetworkLayerForChecksum(ipLayer)
+	require.NoError(tb, err)
+
+	buf := gopacket.NewSerializeBuffer()
+	opts := gopacket.SerializeOptions{ComputeChecksums: true, FixLengths: true}
+	err = gopacket.SerializeLayers(buf, opts, ipLayer, tcpLayer, gopacket.Payload([]byte{}))
+	require.NoError(tb, err)
+
+	return buf.Bytes()
+}
+
+func generateSYNACKPacketWithMSS(tb testing.TB, srcIP, dstIP net.IP, srcPort, dstPort uint16, mss uint16) []byte {
+	tb.Helper()
+
+	ipLayer := &layers.IPv4{
+		Version:  4,
+		TTL:      64,
+		Protocol: layers.IPProtocolTCP,
+		SrcIP:    srcIP,
+		DstIP:    dstIP,
+	}
+
+	tcpLayer := &layers.TCP{
+		SrcPort: layers.TCPPort(srcPort),
+		DstPort: layers.TCPPort(dstPort),
+		SYN:     true,
+		ACK:     true,
+		Window:  65535,
+		Options: []layers.TCPOption{
+			{
+				OptionType:   layers.TCPOptionKindMSS,
+				OptionLength: 4,
+				OptionData:   binary.BigEndian.AppendUint16(nil, mss),
+			},
+		},
+	}
+	err := tcpLayer.SetNetworkLayerForChecksum(ipLayer)
+	require.NoError(tb, err)
+
+	buf := gopacket.NewSerializeBuffer()
+	opts := gopacket.SerializeOptions{ComputeChecksums: true, FixLengths: true}
+	err = gopacket.SerializeLayers(buf, opts, ipLayer, tcpLayer, gopacket.Payload([]byte{}))
+	require.NoError(tb, err)
+
+	return buf.Bytes()
+}
+
+func generateTCPPacketWithFlags(tb testing.TB, srcIP, dstIP net.IP, srcPort, dstPort uint16, flags uint16) []byte {
+	tb.Helper()
+
+	ipLayer := &layers.IPv4{
+		Version:  4,
+		TTL:      64,
+		Protocol: layers.IPProtocolTCP,
+		SrcIP:    srcIP,
+		DstIP:    dstIP,
+	}
+
+	tcpLayer := &layers.TCP{
+		SrcPort: layers.TCPPort(srcPort),
+		DstPort: layers.TCPPort(dstPort),
+		Window:  65535,
+	}
+
+	if flags&uint16(conntrack.TCPSyn) != 0 {
+		tcpLayer.SYN = true
+	}
+	if flags&uint16(conntrack.TCPAck) != 0 {
+		tcpLayer.ACK = true
+	}
+	if flags&uint16(conntrack.TCPFin) != 0 {
+		tcpLayer.FIN = true
+	}
+	if flags&uint16(conntrack.TCPRst) != 0 {
+		tcpLayer.RST = true
+	}
+	if flags&uint16(conntrack.TCPPush) != 0 {
+		tcpLayer.PSH = true
+	}
+
+	err := tcpLayer.SetNetworkLayerForChecksum(ipLayer)
+	require.NoError(tb, err)
+
+	buf := gopacket.NewSerializeBuffer()
+	opts := gopacket.SerializeOptions{ComputeChecksums: true, FixLengths: true}
+	err = gopacket.SerializeLayers(buf, opts, ipLayer, tcpLayer, gopacket.Payload([]byte{}))
+	require.NoError(tb, err)
+
+	return buf.Bytes()
+}
diff --git a/client/firewall/uspfilter/forwarder/forwarder.go b/client/firewall/uspfilter/forwarder/forwarder.go
index 42a3e0800..00cb3f1df 100644
--- a/client/firewall/uspfilter/forwarder/forwarder.go
+++ b/client/firewall/uspfilter/forwarder/forwarder.go
@@ -45,7 +45,7 @@ type Forwarder struct {
 	netstack     bool
 }
 
-func New(iface common.IFaceMapper, logger *nblog.Logger, flowLogger nftypes.FlowLogger, netstack bool) (*Forwarder, error) {
+func New(iface common.IFaceMapper, logger *nblog.Logger, flowLogger nftypes.FlowLogger, netstack bool, mtu uint16) (*Forwarder, error) {
 	s := stack.New(stack.Options{
 		NetworkProtocols: []stack.NetworkProtocolFactory{ipv4.NewProtocol},
 		TransportProtocols: []stack.TransportProtocolFactory{
@@ -56,10 +56,6 @@ func New(iface common.IFaceMapper, logger *nblog.Logger, flowLogger nftypes.Flow
 		HandleLocal: false,
 	})
 
-	mtu, err := iface.GetDevice().MTU()
-	if err != nil {
-		return nil, fmt.Errorf("get MTU: %w", err)
-	}
 	nicID := tcpip.NICID(1)
 	endpoint := &endpoint{
 		logger: logger,
@@ -68,7 +64,7 @@ func New(iface common.IFaceMapper, logger *nblog.Logger, flowLogger nftypes.Flow
 	}
 
 	if err := s.CreateNIC(nicID, endpoint); err != nil {
-		return nil, fmt.Errorf("failed to create NIC: %v", err)
+		return nil, fmt.Errorf("create NIC: %v", err)
 	}
 
 	protoAddr := tcpip.ProtocolAddress{
diff --git a/client/firewall/uspfilter/forwarder/udp.go b/client/firewall/uspfilter/forwarder/udp.go
index d146de5e4..55743d975 100644
--- a/client/firewall/uspfilter/forwarder/udp.go
+++ b/client/firewall/uspfilter/forwarder/udp.go
@@ -49,7 +49,7 @@ type idleConn struct {
 	conn *udpPacketConn
 }
 
-func newUDPForwarder(mtu int, logger *nblog.Logger, flowLogger nftypes.FlowLogger) *udpForwarder {
+func newUDPForwarder(mtu uint16, logger *nblog.Logger, flowLogger nftypes.FlowLogger) *udpForwarder {
 	ctx, cancel := context.WithCancel(context.Background())
 	f := &udpForwarder{
 		logger:     logger,
diff --git a/client/firewall/uspfilter/nat_bench_test.go b/client/firewall/uspfilter/nat_bench_test.go
index d726474cf..d2599e577 100644
--- a/client/firewall/uspfilter/nat_bench_test.go
+++ b/client/firewall/uspfilter/nat_bench_test.go
@@ -12,6 +12,7 @@ import (
 
 	log "github.com/sirupsen/logrus"
 
+	"github.com/netbirdio/netbird/client/iface"
 	"github.com/netbirdio/netbird/client/iface/device"
 )
 
@@ -65,7 +66,7 @@ func BenchmarkDNATTranslation(b *testing.B) {
 		b.Run(sc.name, func(b *testing.B) {
 			manager, err := Create(&IFaceMock{
 				SetFilterFunc: func(device.PacketFilter) error { return nil },
-			}, false, flowLogger)
+			}, false, flowLogger, iface.DefaultMTU)
 			require.NoError(b, err)
 			defer func() {
 				require.NoError(b, manager.Close(nil))
@@ -125,7 +126,7 @@ func BenchmarkDNATTranslation(b *testing.B) {
 func BenchmarkDNATConcurrency(b *testing.B) {
 	manager, err := Create(&IFaceMock{
 		SetFilterFunc: func(device.PacketFilter) error { return nil },
-	}, false, flowLogger)
+	}, false, flowLogger, iface.DefaultMTU)
 	require.NoError(b, err)
 	defer func() {
 		require.NoError(b, manager.Close(nil))
@@ -197,7 +198,7 @@ func BenchmarkDNATScaling(b *testing.B) {
 		b.Run(fmt.Sprintf("mappings_%d", count), func(b *testing.B) {
 			manager, err := Create(&IFaceMock{
 				SetFilterFunc: func(device.PacketFilter) error { return nil },
-			}, false, flowLogger)
+			}, false, flowLogger, iface.DefaultMTU)
 			require.NoError(b, err)
 			defer func() {
 				require.NoError(b, manager.Close(nil))
@@ -309,7 +310,7 @@ func BenchmarkChecksumUpdate(b *testing.B) {
 func BenchmarkDNATMemoryAllocations(b *testing.B) {
 	manager, err := Create(&IFaceMock{
 		SetFilterFunc: func(device.PacketFilter) error { return nil },
-	}, false, flowLogger)
+	}, false, flowLogger, iface.DefaultMTU)
 	require.NoError(b, err)
 	defer func() {
 		require.NoError(b, manager.Close(nil))
@@ -472,7 +473,7 @@ func BenchmarkPortDNAT(b *testing.B) {
 		b.Run(sc.name, func(b *testing.B) {
 			manager, err := Create(&IFaceMock{
 				SetFilterFunc: func(device.PacketFilter) error { return nil },
-			}, false, flowLogger)
+			}, false, flowLogger, iface.DefaultMTU)
 			require.NoError(b, err)
 			defer func() {
 				require.NoError(b, manager.Close(nil))
diff --git a/client/firewall/uspfilter/nat_test.go b/client/firewall/uspfilter/nat_test.go
index 2a285484c..400d61020 100644
--- a/client/firewall/uspfilter/nat_test.go
+++ b/client/firewall/uspfilter/nat_test.go
@@ -9,6 +9,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	firewall "github.com/netbirdio/netbird/client/firewall/manager"
+	"github.com/netbirdio/netbird/client/iface"
 	"github.com/netbirdio/netbird/client/iface/device"
 )
 
@@ -16,7 +17,7 @@ import (
 func TestDNATTranslationCorrectness(t *testing.T) {
 	manager, err := Create(&IFaceMock{
 		SetFilterFunc: func(device.PacketFilter) error { return nil },
-	}, false, flowLogger)
+	}, false, flowLogger, iface.DefaultMTU)
 	require.NoError(t, err)
 	defer func() {
 		require.NoError(t, manager.Close(nil))
@@ -100,7 +101,7 @@ func parsePacket(t testing.TB, packetData []byte) *decoder {
 func TestDNATMappingManagement(t *testing.T) {
 	manager, err := Create(&IFaceMock{
 		SetFilterFunc: func(device.PacketFilter) error { return nil },
-	}, false, flowLogger)
+	}, false, flowLogger, iface.DefaultMTU)
 	require.NoError(t, err)
 	defer func() {
 		require.NoError(t, manager.Close(nil))
@@ -148,7 +149,7 @@ func TestDNATMappingManagement(t *testing.T) {
 func TestInboundPortDNAT(t *testing.T) {
 	manager, err := Create(&IFaceMock{
 		SetFilterFunc: func(device.PacketFilter) error { return nil },
-	}, false, flowLogger)
+	}, false, flowLogger, iface.DefaultMTU)
 	require.NoError(t, err)
 	defer func() {
 		require.NoError(t, manager.Close(nil))
@@ -198,7 +199,7 @@ func TestInboundPortDNAT(t *testing.T) {
 func TestInboundPortDNATNegative(t *testing.T) {
 	manager, err := Create(&IFaceMock{
 		SetFilterFunc: func(device.PacketFilter) error { return nil },
-	}, false, flowLogger)
+	}, false, flowLogger, iface.DefaultMTU)
 	require.NoError(t, err)
 	defer func() {
 		require.NoError(t, manager.Close(nil))
diff --git a/client/firewall/uspfilter/tracer_test.go b/client/firewall/uspfilter/tracer_test.go
index ee1bb8a23..d9f9f1aa8 100644
--- a/client/firewall/uspfilter/tracer_test.go
+++ b/client/firewall/uspfilter/tracer_test.go
@@ -10,6 +10,7 @@ import (
 	fw "github.com/netbirdio/netbird/client/firewall/manager"
 	"github.com/netbirdio/netbird/client/firewall/uspfilter/conntrack"
 	"github.com/netbirdio/netbird/client/firewall/uspfilter/forwarder"
+	"github.com/netbirdio/netbird/client/iface"
 	"github.com/netbirdio/netbird/client/iface/device"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 )
@@ -44,7 +45,7 @@ func TestTracePacket(t *testing.T) {
 			},
 		}
 
-		m, err := Create(ifaceMock, false, flowLogger)
+		m, err := Create(ifaceMock, false, flowLogger, iface.DefaultMTU)
 		require.NoError(t, err)
 
 		if !statefulMode {
diff --git a/client/internal/acl/manager_test.go b/client/internal/acl/manager_test.go
index daf4979ce..638245bf7 100644
--- a/client/internal/acl/manager_test.go
+++ b/client/internal/acl/manager_test.go
@@ -9,6 +9,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/netbirdio/netbird/client/firewall"
+	"github.com/netbirdio/netbird/client/iface"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 	"github.com/netbirdio/netbird/client/internal/acl/mocks"
 	"github.com/netbirdio/netbird/client/internal/netflow"
@@ -52,7 +53,7 @@ func TestDefaultManager(t *testing.T) {
 	}).AnyTimes()
 	ifaceMock.EXPECT().GetWGDevice().Return(nil).AnyTimes()
 
-	fw, err := firewall.NewFirewall(ifaceMock, nil, flowLogger, false)
+	fw, err := firewall.NewFirewall(ifaceMock, nil, flowLogger, false, iface.DefaultMTU)
 	require.NoError(t, err)
 	defer func() {
 		err = fw.Close(nil)
@@ -170,7 +171,7 @@ func TestDefaultManagerStateless(t *testing.T) {
 	}).AnyTimes()
 	ifaceMock.EXPECT().GetWGDevice().Return(nil).AnyTimes()
 
-	fw, err := firewall.NewFirewall(ifaceMock, nil, flowLogger, false)
+	fw, err := firewall.NewFirewall(ifaceMock, nil, flowLogger, false, iface.DefaultMTU)
 	require.NoError(t, err)
 	defer func() {
 		err = fw.Close(nil)
@@ -321,7 +322,7 @@ func TestDefaultManagerEnableSSHRules(t *testing.T) {
 	}).AnyTimes()
 	ifaceMock.EXPECT().GetWGDevice().Return(nil).AnyTimes()
 
-	fw, err := firewall.NewFirewall(ifaceMock, nil, flowLogger, false)
+	fw, err := firewall.NewFirewall(ifaceMock, nil, flowLogger, false, iface.DefaultMTU)
 	require.NoError(t, err)
 	defer func() {
 		err = fw.Close(nil)
diff --git a/client/internal/dns/server_test.go b/client/internal/dns/server_test.go
index 11575d500..451b83f92 100644
--- a/client/internal/dns/server_test.go
+++ b/client/internal/dns/server_test.go
@@ -944,7 +944,7 @@ func createWgInterfaceWithBind(t *testing.T) (*iface.WGIface, error) {
 		return nil, err
 	}
 
-	pf, err := uspfilter.Create(wgIface, false, flowLogger)
+	pf, err := uspfilter.Create(wgIface, false, flowLogger, iface.DefaultMTU)
 	if err != nil {
 		t.Fatalf("failed to create uspfilter: %v", err)
 		return nil, err
diff --git a/client/internal/engine.go b/client/internal/engine.go
index ad69bcf43..0c7bd9f0a 100644
--- a/client/internal/engine.go
+++ b/client/internal/engine.go
@@ -506,7 +506,7 @@ func (e *Engine) createFirewall() error {
 	}
 
 	var err error
-	e.firewall, err = firewall.NewFirewall(e.wgInterface, e.stateManager, e.flowManager.GetLogger(), e.config.DisableServerRoutes)
+	e.firewall, err = firewall.NewFirewall(e.wgInterface, e.stateManager, e.flowManager.GetLogger(), e.config.DisableServerRoutes, e.config.MTU)
 	if err != nil || e.firewall == nil {
 		log.Errorf("failed creating firewall manager: %s", err)
 		return nil

From 641eb5140bf51a5b6f2ca1b3a391662bffb86e32 Mon Sep 17 00:00:00 2001
From: Viktor Liu <17948409+lixmal@users.noreply.github.com>
Date: Tue, 4 Nov 2025 21:56:53 +0100
Subject: [PATCH 4/5] [client] Allow INPUT traffic on the compat iptables
 filter table for nftables (#4742)

---
 client/firewall/manager/firewall.go       |   3 +
 client/firewall/nftables/acl_linux.go     |  41 +++----
 client/firewall/nftables/manager_linux.go | 141 ++++------------------
 client/firewall/nftables/router_linux.go  |  94 +++++++++++----
 client/internal/dnsfwd/manager.go         |  42 ++++++-
 client/internal/engine.go                 |  35 +-----
 6 files changed, 146 insertions(+), 210 deletions(-)

diff --git a/client/firewall/manager/firewall.go b/client/firewall/manager/firewall.go
index 7ee33118b..72e6a5c68 100644
--- a/client/firewall/manager/firewall.go
+++ b/client/firewall/manager/firewall.go
@@ -100,6 +100,9 @@ type Manager interface {
 	//
 	// If comment argument is empty firewall manager should set
 	// rule ID as comment for the rule
+	//
+	// Note: Callers should call Flush() after adding rules to ensure
+	// they are applied to the kernel and rule handles are refreshed.
 	AddPeerFiltering(
 		id []byte,
 		ip net.IP,
diff --git a/client/firewall/nftables/acl_linux.go b/client/firewall/nftables/acl_linux.go
index 9ff5b8c92..a9d066e2f 100644
--- a/client/firewall/nftables/acl_linux.go
+++ b/client/firewall/nftables/acl_linux.go
@@ -29,8 +29,6 @@ const (
 	chainNameForwardFilter     = "netbird-acl-forward-filter"
 	chainNameManglePrerouting  = "netbird-mangle-prerouting"
 	chainNameManglePostrouting = "netbird-mangle-postrouting"
-
-	allowNetbirdInputRuleID = "allow Netbird incoming traffic"
 )
 
 const flushError = "flush: %w"
@@ -195,25 +193,6 @@ func (m *AclManager) DeletePeerRule(rule firewall.Rule) error {
 // createDefaultAllowRules creates default allow rules for the input and output chains
 func (m *AclManager) createDefaultAllowRules() error {
 	expIn := []expr.Any{
-		&expr.Payload{
-			DestRegister: 1,
-			Base:         expr.PayloadBaseNetworkHeader,
-			Offset:       12,
-			Len:          4,
-		},
-		// mask
-		&expr.Bitwise{
-			SourceRegister: 1,
-			DestRegister:   1,
-			Len:            4,
-			Mask:           []byte{0, 0, 0, 0},
-			Xor:            []byte{0, 0, 0, 0},
-		},
-		// net address
-		&expr.Cmp{
-			Register: 1,
-			Data:     []byte{0, 0, 0, 0},
-		},
 		&expr.Verdict{
 			Kind: expr.VerdictAccept,
 		},
@@ -258,7 +237,7 @@ func (m *AclManager) addIOFiltering(
 	action firewall.Action,
 	ipset *nftables.Set,
 ) (*Rule, error) {
-	ruleId := generatePeerRuleId(ip, sPort, dPort, action, ipset)
+	ruleId := generatePeerRuleId(ip, proto, sPort, dPort, action, ipset)
 	if r, ok := m.rules[ruleId]; ok {
 		return &Rule{
 			nftRule:    r.nftRule,
@@ -357,11 +336,12 @@ func (m *AclManager) addIOFiltering(
 	}
 
 	if err := m.rConn.Flush(); err != nil {
-		return nil, fmt.Errorf(flushError, err)
+		return nil, fmt.Errorf("flush input rule %s: %v", ruleId, err)
 	}
 
 	ruleStruct := &Rule{
-		nftRule:    nftRule,
+		nftRule: nftRule,
+		// best effort mangle rule
 		mangleRule: m.createPreroutingRule(expressions, userData),
 		nftSet:     ipset,
 		ruleID:     ruleId,
@@ -420,12 +400,19 @@ func (m *AclManager) createPreroutingRule(expressions []expr.Any, userData []byt
 		},
 	)
 
-	return m.rConn.AddRule(&nftables.Rule{
+	nfRule := m.rConn.AddRule(&nftables.Rule{
 		Table:    m.workTable,
 		Chain:    m.chainPrerouting,
 		Exprs:    preroutingExprs,
 		UserData: userData,
 	})
+
+	if err := m.rConn.Flush(); err != nil {
+		log.Errorf("failed to flush mangle rule %s: %v", string(userData), err)
+		return nil
+	}
+
+	return nfRule
 }
 
 func (m *AclManager) createDefaultChains() (err error) {
@@ -697,8 +684,8 @@ func (m *AclManager) refreshRuleHandles(chain *nftables.Chain, mangle bool) erro
 	return nil
 }
 
-func generatePeerRuleId(ip net.IP, sPort *firewall.Port, dPort *firewall.Port, action firewall.Action, ipset *nftables.Set) string {
-	rulesetID := ":"
+func generatePeerRuleId(ip net.IP, proto firewall.Protocol, sPort *firewall.Port, dPort *firewall.Port, action firewall.Action, ipset *nftables.Set) string {
+	rulesetID := ":" + string(proto) + ":"
 	if sPort != nil {
 		rulesetID += sPort.String()
 	}
diff --git a/client/firewall/nftables/manager_linux.go b/client/firewall/nftables/manager_linux.go
index d864914fe..bd19f1067 100644
--- a/client/firewall/nftables/manager_linux.go
+++ b/client/firewall/nftables/manager_linux.go
@@ -1,11 +1,11 @@
 package nftables
 
 import (
-	"bytes"
 	"context"
 	"fmt"
 	"net"
 	"net/netip"
+	"os"
 	"sync"
 
 	"github.com/google/nftables"
@@ -19,13 +19,22 @@ import (
 )
 
 const (
-	// tableNameNetbird is the name of the table that is used for filtering by the Netbird client
+	// tableNameNetbird is the default name of the table that is used for filtering by the Netbird client
 	tableNameNetbird = "netbird"
+	// envTableName is the environment variable to override the table name
+	envTableName = "NB_NFTABLES_TABLE"
 
 	tableNameFilter = "filter"
 	chainNameInput  = "INPUT"
 )
 
+func getTableName() string {
+	if name := os.Getenv(envTableName); name != "" {
+		return name
+	}
+	return tableNameNetbird
+}
+
 // iFaceMapper defines subset methods of interface required for manager
 type iFaceMapper interface {
 	Name() string
@@ -50,7 +59,7 @@ func Create(wgIface iFaceMapper, mtu uint16) (*Manager, error) {
 		wgIface: wgIface,
 	}
 
-	workTable := &nftables.Table{Name: tableNameNetbird, Family: nftables.TableFamilyIPv4}
+	workTable := &nftables.Table{Name: getTableName(), Family: nftables.TableFamilyIPv4}
 
 	var err error
 	m.router, err = newRouter(workTable, wgIface, mtu)
@@ -198,44 +207,11 @@ func (m *Manager) AllowNetbird() error {
 	m.mutex.Lock()
 	defer m.mutex.Unlock()
 
-	err := m.aclManager.createDefaultAllowRules()
-	if err != nil {
-		return fmt.Errorf("failed to create default allow rules: %v", err)
+	if err := m.aclManager.createDefaultAllowRules(); err != nil {
+		return fmt.Errorf("create default allow rules: %w", err)
 	}
-
-	chains, err := m.rConn.ListChainsOfTableFamily(nftables.TableFamilyIPv4)
-	if err != nil {
-		return fmt.Errorf("list of chains: %w", err)
-	}
-
-	var chain *nftables.Chain
-	for _, c := range chains {
-		if c.Table.Name == tableNameFilter && c.Name == chainNameInput {
-			chain = c
-			break
-		}
-	}
-
-	if chain == nil {
-		log.Debugf("chain INPUT not found. Skipping add allow netbird rule")
-		return nil
-	}
-
-	rules, err := m.rConn.GetRules(chain.Table, chain)
-	if err != nil {
-		return fmt.Errorf("failed to get rules for the INPUT chain: %v", err)
-	}
-
-	if rule := m.detectAllowNetbirdRule(rules); rule != nil {
-		log.Debugf("allow netbird rule already exists: %v", rule)
-		return nil
-	}
-
-	m.applyAllowNetbirdRules(chain)
-
-	err = m.rConn.Flush()
-	if err != nil {
-		return fmt.Errorf("failed to flush allow input netbird rules: %v", err)
+	if err := m.rConn.Flush(); err != nil {
+		return fmt.Errorf("flush allow input netbird rules: %w", err)
 	}
 
 	return nil
@@ -251,10 +227,6 @@ func (m *Manager) Close(stateManager *statemanager.Manager) error {
 	m.mutex.Lock()
 	defer m.mutex.Unlock()
 
-	if err := m.resetNetbirdInputRules(); err != nil {
-		return fmt.Errorf("reset netbird input rules: %v", err)
-	}
-
 	if err := m.router.Reset(); err != nil {
 		return fmt.Errorf("reset router: %v", err)
 	}
@@ -274,49 +246,15 @@ func (m *Manager) Close(stateManager *statemanager.Manager) error {
 	return nil
 }
 
-func (m *Manager) resetNetbirdInputRules() error {
-	chains, err := m.rConn.ListChains()
-	if err != nil {
-		return fmt.Errorf("list chains: %w", err)
-	}
-
-	m.deleteNetbirdInputRules(chains)
-
-	return nil
-}
-
-func (m *Manager) deleteNetbirdInputRules(chains []*nftables.Chain) {
-	for _, c := range chains {
-		if c.Table.Name == tableNameFilter && c.Name == chainNameInput {
-			rules, err := m.rConn.GetRules(c.Table, c)
-			if err != nil {
-				log.Errorf("get rules for chain %q: %v", c.Name, err)
-				continue
-			}
-
-			m.deleteMatchingRules(rules)
-		}
-	}
-}
-
-func (m *Manager) deleteMatchingRules(rules []*nftables.Rule) {
-	for _, r := range rules {
-		if bytes.Equal(r.UserData, []byte(allowNetbirdInputRuleID)) {
-			if err := m.rConn.DelRule(r); err != nil {
-				log.Errorf("delete rule: %v", err)
-			}
-		}
-	}
-}
-
 func (m *Manager) cleanupNetbirdTables() error {
 	tables, err := m.rConn.ListTables()
 	if err != nil {
 		return fmt.Errorf("list tables: %w", err)
 	}
 
+	tableName := getTableName()
 	for _, t := range tables {
-		if t.Name == tableNameNetbird {
+		if t.Name == tableName {
 			m.rConn.DelTable(t)
 		}
 	}
@@ -399,55 +337,18 @@ func (m *Manager) createWorkTable() (*nftables.Table, error) {
 		return nil, fmt.Errorf("list of tables: %w", err)
 	}
 
+	tableName := getTableName()
 	for _, t := range tables {
-		if t.Name == tableNameNetbird {
+		if t.Name == tableName {
 			m.rConn.DelTable(t)
 		}
 	}
 
-	table := m.rConn.AddTable(&nftables.Table{Name: tableNameNetbird, Family: nftables.TableFamilyIPv4})
+	table := m.rConn.AddTable(&nftables.Table{Name: getTableName(), Family: nftables.TableFamilyIPv4})
 	err = m.rConn.Flush()
 	return table, err
 }
 
-func (m *Manager) applyAllowNetbirdRules(chain *nftables.Chain) {
-	rule := &nftables.Rule{
-		Table: chain.Table,
-		Chain: chain,
-		Exprs: []expr.Any{
-			&expr.Meta{Key: expr.MetaKeyIIFNAME, Register: 1},
-			&expr.Cmp{
-				Op:       expr.CmpOpEq,
-				Register: 1,
-				Data:     ifname(m.wgIface.Name()),
-			},
-			&expr.Verdict{
-				Kind: expr.VerdictAccept,
-			},
-		},
-		UserData: []byte(allowNetbirdInputRuleID),
-	}
-	_ = m.rConn.InsertRule(rule)
-}
-
-func (m *Manager) detectAllowNetbirdRule(existedRules []*nftables.Rule) *nftables.Rule {
-	ifName := ifname(m.wgIface.Name())
-	for _, rule := range existedRules {
-		if rule.Table.Name == tableNameFilter && rule.Chain.Name == chainNameInput {
-			if len(rule.Exprs) < 4 {
-				if e, ok := rule.Exprs[0].(*expr.Meta); !ok || e.Key != expr.MetaKeyIIFNAME {
-					continue
-				}
-				if e, ok := rule.Exprs[1].(*expr.Cmp); !ok || e.Op != expr.CmpOpEq || !bytes.Equal(e.Data, ifName) {
-					continue
-				}
-				return rule
-			}
-		}
-	}
-	return nil
-}
-
 func insertReturnTrafficRule(conn *nftables.Conn, table *nftables.Table, chain *nftables.Chain) {
 	rule := &nftables.Rule{
 		Table: table,
diff --git a/client/firewall/nftables/router_linux.go b/client/firewall/nftables/router_linux.go
index 0a2c79186..6192c92aa 100644
--- a/client/firewall/nftables/router_linux.go
+++ b/client/firewall/nftables/router_linux.go
@@ -37,6 +37,7 @@ const (
 
 	userDataAcceptForwardRuleIif = "frwacceptiif"
 	userDataAcceptForwardRuleOif = "frwacceptoif"
+	userDataAcceptInputRule      = "inputaccept"
 
 	dnatSuffix = "_dnat"
 	snatSuffix = "_snat"
@@ -103,8 +104,8 @@ func newRouter(workTable *nftables.Table, wgIface iFaceMapper, mtu uint16) (*rou
 func (r *router) init(workTable *nftables.Table) error {
 	r.workTable = workTable
 
-	if err := r.removeAcceptForwardRules(); err != nil {
-		log.Errorf("failed to clean up rules from FORWARD chain: %s", err)
+	if err := r.removeAcceptFilterRules(); err != nil {
+		log.Errorf("failed to clean up rules from filter table: %s", err)
 	}
 
 	if err := r.createContainers(); err != nil {
@@ -118,15 +119,15 @@ func (r *router) init(workTable *nftables.Table) error {
 	return nil
 }
 
-// Reset cleans existing nftables default forward rules from the system
+// Reset cleans existing nftables filter table rules from the system
 func (r *router) Reset() error {
 	// clear without deleting the ipsets, the nf table will be deleted by the caller
 	r.ipsetCounter.Clear()
 
 	var merr *multierror.Error
 
-	if err := r.removeAcceptForwardRules(); err != nil {
-		merr = multierror.Append(merr, fmt.Errorf("remove accept forward rules: %w", err))
+	if err := r.removeAcceptFilterRules(); err != nil {
+		merr = multierror.Append(merr, fmt.Errorf("remove accept filter rules: %w", err))
 	}
 
 	if err := r.removeNatPreroutingRules(); err != nil {
@@ -936,6 +937,7 @@ func (r *router) RemoveAllLegacyRouteRules() error {
 // that our traffic is not dropped by existing rules there.
 // The existing FORWARD rules/policies decide outbound traffic towards our interface.
 // In case the FORWARD policy is set to "drop", we add an established/related rule to allow return traffic for the inbound rule.
+// This method also adds INPUT chain rules to allow traffic to the local interface.
 func (r *router) acceptForwardRules() error {
 	if r.filterTable == nil {
 		log.Debugf("table 'filter' not found for forward rules, skipping accept rules")
@@ -945,7 +947,7 @@ func (r *router) acceptForwardRules() error {
 	fw := "iptables"
 
 	defer func() {
-		log.Debugf("Used %s to add accept forward rules", fw)
+		log.Debugf("Used %s to add accept forward and input rules", fw)
 	}()
 
 	// Try iptables first and fallback to nftables if iptables is not available
@@ -955,22 +957,30 @@ func (r *router) acceptForwardRules() error {
 		log.Warnf("Will use nftables to manipulate the filter table because iptables is not available: %v", err)
 
 		fw = "nftables"
-		return r.acceptForwardRulesNftables()
+		return r.acceptFilterRulesNftables()
 	}
 
-	return r.acceptForwardRulesIptables(ipt)
+	return r.acceptFilterRulesIptables(ipt)
 }
 
-func (r *router) acceptForwardRulesIptables(ipt *iptables.IPTables) error {
+func (r *router) acceptFilterRulesIptables(ipt *iptables.IPTables) error {
 	var merr *multierror.Error
+
 	for _, rule := range r.getAcceptForwardRules() {
 		if err := ipt.Insert("filter", chainNameForward, 1, rule...); err != nil {
-			merr = multierror.Append(err, fmt.Errorf("add iptables rule: %v", err))
+			merr = multierror.Append(err, fmt.Errorf("add iptables forward rule: %v", err))
 		} else {
-			log.Debugf("added iptables rule: %v", rule)
+			log.Debugf("added iptables forward rule: %v", rule)
 		}
 	}
 
+	inputRule := r.getAcceptInputRule()
+	if err := ipt.Insert("filter", chainNameInput, 1, inputRule...); err != nil {
+		merr = multierror.Append(err, fmt.Errorf("add iptables input rule: %v", err))
+	} else {
+		log.Debugf("added iptables input rule: %v", inputRule)
+	}
+
 	return nberrors.FormatErrorOrNil(merr)
 }
 
@@ -982,10 +992,13 @@ func (r *router) getAcceptForwardRules() [][]string {
 	}
 }
 
-func (r *router) acceptForwardRulesNftables() error {
+func (r *router) getAcceptInputRule() []string {
+	return []string{"-i", r.wgIface.Name(), "-j", "ACCEPT"}
+}
+
+func (r *router) acceptFilterRulesNftables() error {
 	intf := ifname(r.wgIface.Name())
 
-	// Rule for incoming interface (iif) with counter
 	iifRule := &nftables.Rule{
 		Table: r.filterTable,
 		Chain: &nftables.Chain{
@@ -1018,11 +1031,10 @@ func (r *router) acceptForwardRulesNftables() error {
 		},
 	}
 
-	// Rule for outgoing interface (oif) with counter
 	oifRule := &nftables.Rule{
 		Table: r.filterTable,
 		Chain: &nftables.Chain{
-			Name:     "FORWARD",
+			Name:     chainNameForward,
 			Table:    r.filterTable,
 			Type:     nftables.ChainTypeFilter,
 			Hooknum:  nftables.ChainHookForward,
@@ -1031,35 +1043,60 @@ func (r *router) acceptForwardRulesNftables() error {
 		Exprs:    append(oifExprs, getEstablishedExprs(2)...),
 		UserData: []byte(userDataAcceptForwardRuleOif),
 	}
-
 	r.conn.InsertRule(oifRule)
 
+	inputRule := &nftables.Rule{
+		Table: r.filterTable,
+		Chain: &nftables.Chain{
+			Name:     chainNameInput,
+			Table:    r.filterTable,
+			Type:     nftables.ChainTypeFilter,
+			Hooknum:  nftables.ChainHookInput,
+			Priority: nftables.ChainPriorityFilter,
+		},
+		Exprs: []expr.Any{
+			&expr.Meta{Key: expr.MetaKeyIIFNAME, Register: 1},
+			&expr.Cmp{
+				Op:       expr.CmpOpEq,
+				Register: 1,
+				Data:     intf,
+			},
+			&expr.Counter{},
+			&expr.Verdict{Kind: expr.VerdictAccept},
+		},
+		UserData: []byte(userDataAcceptInputRule),
+	}
+	r.conn.InsertRule(inputRule)
+
 	return nil
 }
 
-func (r *router) removeAcceptForwardRules() error {
+func (r *router) removeAcceptFilterRules() error {
 	if r.filterTable == nil {
 		return nil
 	}
 
-	// Try iptables first and fallback to nftables if iptables is not available
 	ipt, err := iptables.New()
 	if err != nil {
 		log.Warnf("Will use nftables to manipulate the filter table because iptables is not available: %v", err)
-		return r.removeAcceptForwardRulesNftables()
+		return r.removeAcceptFilterRulesNftables()
 	}
 
-	return r.removeAcceptForwardRulesIptables(ipt)
+	return r.removeAcceptFilterRulesIptables(ipt)
 }
 
-func (r *router) removeAcceptForwardRulesNftables() error {
+func (r *router) removeAcceptFilterRulesNftables() error {
 	chains, err := r.conn.ListChainsOfTableFamily(nftables.TableFamilyIPv4)
 	if err != nil {
 		return fmt.Errorf("list chains: %v", err)
 	}
 
 	for _, chain := range chains {
-		if chain.Table.Name != r.filterTable.Name || chain.Name != chainNameForward {
+		if chain.Table.Name != r.filterTable.Name {
+			continue
+		}
+
+		if chain.Name != chainNameForward && chain.Name != chainNameInput {
 			continue
 		}
 
@@ -1070,7 +1107,8 @@ func (r *router) removeAcceptForwardRulesNftables() error {
 
 		for _, rule := range rules {
 			if bytes.Equal(rule.UserData, []byte(userDataAcceptForwardRuleIif)) ||
-				bytes.Equal(rule.UserData, []byte(userDataAcceptForwardRuleOif)) {
+				bytes.Equal(rule.UserData, []byte(userDataAcceptForwardRuleOif)) ||
+				bytes.Equal(rule.UserData, []byte(userDataAcceptInputRule)) {
 				if err := r.conn.DelRule(rule); err != nil {
 					return fmt.Errorf("delete rule: %v", err)
 				}
@@ -1085,14 +1123,20 @@ func (r *router) removeAcceptForwardRulesNftables() error {
 	return nil
 }
 
-func (r *router) removeAcceptForwardRulesIptables(ipt *iptables.IPTables) error {
+func (r *router) removeAcceptFilterRulesIptables(ipt *iptables.IPTables) error {
 	var merr *multierror.Error
+
 	for _, rule := range r.getAcceptForwardRules() {
 		if err := ipt.DeleteIfExists("filter", chainNameForward, rule...); err != nil {
-			merr = multierror.Append(err, fmt.Errorf("remove iptables rule: %v", err))
+			merr = multierror.Append(err, fmt.Errorf("remove iptables forward rule: %v", err))
 		}
 	}
 
+	inputRule := r.getAcceptInputRule()
+	if err := ipt.DeleteIfExists("filter", chainNameInput, inputRule...); err != nil {
+		merr = multierror.Append(err, fmt.Errorf("remove iptables input rule: %v", err))
+	}
+
 	return nberrors.FormatErrorOrNil(merr)
 }
 
diff --git a/client/internal/dnsfwd/manager.go b/client/internal/dnsfwd/manager.go
index b26836d17..58b88d9ef 100644
--- a/client/internal/dnsfwd/manager.go
+++ b/client/internal/dnsfwd/manager.go
@@ -15,6 +15,7 @@ import (
 	nberrors "github.com/netbirdio/netbird/client/errors"
 	firewall "github.com/netbirdio/netbird/client/firewall/manager"
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
+	nftypes "github.com/netbirdio/netbird/client/internal/netflow/types"
 	"github.com/netbirdio/netbird/client/internal/peer"
 	nbdns "github.com/netbirdio/netbird/dns"
 	"github.com/netbirdio/netbird/route"
@@ -134,6 +135,8 @@ func (m *Manager) Stop(ctx context.Context) error {
 		}
 	}
 
+	m.unregisterNetstackServices()
+
 	if err := m.dropDNSFirewall(); err != nil {
 		mErr = multierror.Append(mErr, err)
 	}
@@ -158,21 +161,50 @@ func (m *Manager) allowDNSFirewall() error {
 
 	dnsRules, err := m.firewall.AddPeerFiltering(nil, net.IP{0, 0, 0, 0}, firewall.ProtocolUDP, nil, dport, firewall.ActionAccept, "")
 	if err != nil {
-		log.Errorf("failed to add allow DNS router rules, err: %v", err)
-		return err
+		return fmt.Errorf("add udp firewall rule: %w", err)
 	}
-	m.fwRules = dnsRules
 
 	tcpRules, err := m.firewall.AddPeerFiltering(nil, net.IP{0, 0, 0, 0}, firewall.ProtocolTCP, nil, dport, firewall.ActionAccept, "")
 	if err != nil {
-		log.Errorf("failed to add allow DNS router rules, err: %v", err)
-		return err
+		return fmt.Errorf("add tcp firewall rule: %w", err)
 	}
+
+	if err := m.firewall.Flush(); err != nil {
+		return fmt.Errorf("flush: %w", err)
+	}
+
+	m.fwRules = dnsRules
 	m.tcpRules = tcpRules
 
+	m.registerNetstackServices()
+
 	return nil
 }
 
+func (m *Manager) registerNetstackServices() {
+	if netstackNet := m.wgIface.GetNet(); netstackNet != nil {
+		if registrar, ok := m.firewall.(interface {
+			RegisterNetstackService(protocol nftypes.Protocol, port uint16)
+		}); ok {
+			registrar.RegisterNetstackService(nftypes.TCP, m.serverPort)
+			registrar.RegisterNetstackService(nftypes.UDP, m.serverPort)
+			log.Debugf("registered DNS forwarder service with netstack for UDP/TCP:%d", m.serverPort)
+		}
+	}
+}
+
+func (m *Manager) unregisterNetstackServices() {
+	if netstackNet := m.wgIface.GetNet(); netstackNet != nil {
+		if registrar, ok := m.firewall.(interface {
+			UnregisterNetstackService(protocol nftypes.Protocol, port uint16)
+		}); ok {
+			registrar.UnregisterNetstackService(nftypes.TCP, m.serverPort)
+			registrar.UnregisterNetstackService(nftypes.UDP, m.serverPort)
+			log.Debugf("unregistered DNS forwarder service with netstack for UDP/TCP:%d", m.serverPort)
+		}
+	}
+}
+
 func (m *Manager) dropDNSFirewall() error {
 	var mErr *multierror.Error
 	for _, rule := range m.fwRules {
diff --git a/client/internal/engine.go b/client/internal/engine.go
index 0c7bd9f0a..3c7d52cb3 100644
--- a/client/internal/engine.go
+++ b/client/internal/engine.go
@@ -298,17 +298,12 @@ func (e *Engine) Stop() error {
 		e.ingressGatewayMgr = nil
 	}
 
+	e.stopDNSForwarder()
+
 	if e.routeManager != nil {
 		e.routeManager.Stop(e.stateManager)
 	}
 
-	if e.dnsForwardMgr != nil {
-		if err := e.dnsForwardMgr.Stop(context.Background()); err != nil {
-			log.Errorf("failed to stop DNS forward: %v", err)
-		}
-		e.dnsForwardMgr = nil
-	}
-
 	if e.srWatcher != nil {
 		e.srWatcher.Close()
 	}
@@ -1873,7 +1868,6 @@ func (e *Engine) updateDNSForwarder(
 
 func (e *Engine) startDNSForwarder(fwdEntries []*dnsfwd.ForwarderEntry) {
 	e.dnsForwardMgr = dnsfwd.NewManager(e.firewall, e.statusRecorder, e.wgInterface)
-	e.registerDNSServices()
 
 	if err := e.dnsForwardMgr.Start(fwdEntries); err != nil {
 		log.Errorf("failed to start DNS forward: %v", err)
@@ -1893,34 +1887,9 @@ func (e *Engine) stopDNSForwarder() {
 		log.Errorf("failed to stop DNS forward: %v", err)
 	}
 
-	e.unregisterDNSServices()
 	e.dnsForwardMgr = nil
 }
 
-func (e *Engine) registerDNSServices() {
-	if netstackNet := e.wgInterface.GetNet(); netstackNet != nil {
-		if registrar, ok := e.firewall.(interface {
-			RegisterNetstackService(protocol nftypes.Protocol, port uint16)
-		}); ok {
-			registrar.RegisterNetstackService(nftypes.UDP, nbdns.ForwarderServerPort)
-			registrar.RegisterNetstackService(nftypes.TCP, nbdns.ForwarderServerPort)
-			log.Debugf("registered DNS forwarder service with netstack for UDP/TCP:%d", nbdns.ForwarderServerPort)
-		}
-	}
-}
-
-func (e *Engine) unregisterDNSServices() {
-	if netstackNet := e.wgInterface.GetNet(); netstackNet != nil {
-		if registrar, ok := e.firewall.(interface {
-			UnregisterNetstackService(protocol nftypes.Protocol, port uint16)
-		}); ok {
-			registrar.UnregisterNetstackService(nftypes.UDP, nbdns.ForwarderServerPort)
-			registrar.UnregisterNetstackService(nftypes.TCP, nbdns.ForwarderServerPort)
-			log.Debugf("unregistered DNS forwarder service with netstack for UDP/TCP:%d", nbdns.ForwarderServerPort)
-		}
-	}
-}
-
 func (e *Engine) GetNet() (*netstack.Net, error) {
 	e.syncMsgMux.Lock()
 	intf := e.wgInterface

From c92e6c1b5fd040248b4fd36a2e397daeeb21ba9f Mon Sep 17 00:00:00 2001
From: Viktor Liu <17948409+lixmal@users.noreply.github.com>
Date: Wed, 5 Nov 2025 12:15:37 +0100
Subject: [PATCH 5/5] [client] Block on all subsystems on shutdown (#4709)

---
 client/internal/connect.go                    |  32 +++--
 client/internal/dns/server.go                 |   9 +-
 client/internal/engine.go                     | 119 +++++++++++++-----
 client/internal/netflow/manager.go            |  17 ++-
 client/internal/peer/guard/sr_watcher.go      |   9 +-
 client/internal/routemanager/manager.go       |  14 ++-
 .../internal/routeselector/routeselector.go   |   4 -
 7 files changed, 139 insertions(+), 65 deletions(-)

diff --git a/client/internal/connect.go b/client/internal/connect.go
index c9331baf5..bb7c2b38b 100644
--- a/client/internal/connect.go
+++ b/client/internal/connect.go
@@ -25,6 +25,7 @@ import (
 	"github.com/netbirdio/netbird/client/internal/peer"
 	"github.com/netbirdio/netbird/client/internal/profilemanager"
 	"github.com/netbirdio/netbird/client/internal/stdnet"
+	nbnet "github.com/netbirdio/netbird/client/net"
 	cProto "github.com/netbirdio/netbird/client/proto"
 	"github.com/netbirdio/netbird/client/ssh"
 	"github.com/netbirdio/netbird/client/system"
@@ -34,7 +35,6 @@ import (
 	relayClient "github.com/netbirdio/netbird/shared/relay/client"
 	signal "github.com/netbirdio/netbird/shared/signal/client"
 	"github.com/netbirdio/netbird/util"
-	nbnet "github.com/netbirdio/netbird/client/net"
 	"github.com/netbirdio/netbird/version"
 )
 
@@ -289,15 +289,18 @@ func (c *ConnectClient) run(mobileDependency MobileDependency, runningChan chan
 		}
 
 		<-engineCtx.Done()
+
 		c.engineMutex.Lock()
-		if c.engine != nil && c.engine.wgInterface != nil {
-			log.Infof("ensuring %s is removed, Netbird engine context cancelled", c.engine.wgInterface.Name())
-			if err := c.engine.Stop(); err != nil {
+		engine := c.engine
+		c.engine = nil
+		c.engineMutex.Unlock()
+
+		if engine != nil && engine.wgInterface != nil {
+			log.Infof("ensuring %s is removed, Netbird engine context cancelled", engine.wgInterface.Name())
+			if err := engine.Stop(); err != nil {
 				log.Errorf("Failed to stop engine: %v", err)
 			}
-			c.engine = nil
 		}
-		c.engineMutex.Unlock()
 		c.statusRecorder.ClientTeardown()
 
 		backOff.Reset()
@@ -382,19 +385,12 @@ func (c *ConnectClient) Status() StatusType {
 }
 
 func (c *ConnectClient) Stop() error {
-	if c == nil {
-		return nil
+	engine := c.Engine()
+	if engine != nil {
+		if err := engine.Stop(); err != nil {
+			return fmt.Errorf("stop engine: %w", err)
+		}
 	}
-	c.engineMutex.Lock()
-	defer c.engineMutex.Unlock()
-
-	if c.engine == nil {
-		return nil
-	}
-	if err := c.engine.Stop(); err != nil {
-		return fmt.Errorf("stop engine: %w", err)
-	}
-
 	return nil
 }
 
diff --git a/client/internal/dns/server.go b/client/internal/dns/server.go
index 8cb886203..afaf0579f 100644
--- a/client/internal/dns/server.go
+++ b/client/internal/dns/server.go
@@ -65,8 +65,9 @@ type hostManagerWithOriginalNS interface {
 
 // DefaultServer dns server object
 type DefaultServer struct {
-	ctx       context.Context
-	ctxCancel context.CancelFunc
+	ctx        context.Context
+	ctxCancel  context.CancelFunc
+	shutdownWg sync.WaitGroup
 	// disableSys disables system DNS management (e.g., /etc/resolv.conf updates) while keeping the DNS service running.
 	// This is different from ServiceEnable=false from management which completely disables the DNS service.
 	disableSys         bool
@@ -318,6 +319,7 @@ func (s *DefaultServer) DnsIP() netip.Addr {
 // Stop stops the server
 func (s *DefaultServer) Stop() {
 	s.ctxCancel()
+	s.shutdownWg.Wait()
 
 	s.mux.Lock()
 	defer s.mux.Unlock()
@@ -507,8 +509,9 @@ func (s *DefaultServer) applyConfiguration(update nbdns.Config) error {
 
 	s.applyHostConfig()
 
+	s.shutdownWg.Add(1)
 	go func() {
-		// persist dns state right away
+		defer s.shutdownWg.Done()
 		if err := s.stateManager.PersistState(s.ctx); err != nil {
 			log.Errorf("Failed to persist dns state: %v", err)
 		}
diff --git a/client/internal/engine.go b/client/internal/engine.go
index 3c7d52cb3..ebc05c453 100644
--- a/client/internal/engine.go
+++ b/client/internal/engine.go
@@ -148,6 +148,8 @@ type Engine struct {
 
 	// syncMsgMux is used to guarantee sequential Management Service message processing
 	syncMsgMux *sync.Mutex
+	// sshMux protects sshServer field access
+	sshMux sync.Mutex
 
 	config    *EngineConfig
 	mobileDep MobileDependency
@@ -200,8 +202,10 @@ type Engine struct {
 	flowManager         nftypes.FlowManager
 
 	// WireGuard interface monitor
-	wgIfaceMonitor   *WGIfaceMonitor
-	wgIfaceMonitorWg sync.WaitGroup
+	wgIfaceMonitor *WGIfaceMonitor
+
+	// shutdownWg tracks all long-running goroutines to ensure clean shutdown
+	shutdownWg sync.WaitGroup
 
 	probeStunTurn *relay.StunTurnProbe
 }
@@ -320,10 +324,6 @@ func (e *Engine) Stop() error {
 		e.cancel()
 	}
 
-	// very ugly but we want to remove peers from the WireGuard interface first before removing interface.
-	// Removing peers happens in the conn.Close() asynchronously
-	time.Sleep(500 * time.Millisecond)
-
 	e.close()
 
 	// stop flow manager after wg interface is gone
@@ -331,8 +331,6 @@ func (e *Engine) Stop() error {
 		e.flowManager.Close()
 	}
 
-	log.Infof("stopped Netbird Engine")
-
 	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
 	defer cancel()
 
@@ -343,12 +341,52 @@ func (e *Engine) Stop() error {
 		log.Errorf("failed to persist state: %v", err)
 	}
 
-	// Stop WireGuard interface monitor and wait for it to exit
-	e.wgIfaceMonitorWg.Wait()
+	timeout := e.calculateShutdownTimeout()
+	log.Debugf("waiting for goroutines to finish with timeout: %v", timeout)
+	shutdownCtx, cancel := context.WithTimeout(context.Background(), timeout)
+	defer cancel()
+
+	if err := waitWithContext(shutdownCtx, &e.shutdownWg); err != nil {
+		log.Warnf("shutdown timeout exceeded after %v, some goroutines may still be running", timeout)
+	}
+
+	log.Infof("stopped Netbird Engine")
 
 	return nil
 }
 
+// calculateShutdownTimeout returns shutdown timeout: 10s base + 100ms per peer, capped at 30s.
+func (e *Engine) calculateShutdownTimeout() time.Duration {
+	peerCount := len(e.peerStore.PeersPubKey())
+
+	baseTimeout := 10 * time.Second
+	perPeerTimeout := time.Duration(peerCount) * 100 * time.Millisecond
+	timeout := baseTimeout + perPeerTimeout
+
+	maxTimeout := 30 * time.Second
+	if timeout > maxTimeout {
+		timeout = maxTimeout
+	}
+
+	return timeout
+}
+
+// waitWithContext waits for WaitGroup with timeout, returns ctx.Err() on timeout.
+func waitWithContext(ctx context.Context, wg *sync.WaitGroup) error {
+	done := make(chan struct{})
+	go func() {
+		wg.Wait()
+		close(done)
+	}()
+
+	select {
+	case <-done:
+		return nil
+	case <-ctx.Done():
+		return ctx.Err()
+	}
+}
+
 // Start creates a new WireGuard tunnel interface and listens to events from Signal and Management services
 // Connections to remote peers are not established here.
 // However, they will be established once an event with a list of peers to connect to will be received from Management Service
@@ -478,14 +516,14 @@ func (e *Engine) Start(netbirdConfig *mgmProto.NetbirdConfig, mgmtURL *url.URL)
 
 	// monitor WireGuard interface lifecycle and restart engine on changes
 	e.wgIfaceMonitor = NewWGIfaceMonitor()
-	e.wgIfaceMonitorWg.Add(1)
+	e.shutdownWg.Add(1)
 
 	go func() {
-		defer e.wgIfaceMonitorWg.Done()
+		defer e.shutdownWg.Done()
 
 		if shouldRestart, err := e.wgIfaceMonitor.Start(e.ctx, e.wgInterface.Name()); shouldRestart {
 			log.Infof("WireGuard interface monitor: %s, restarting engine", err)
-			e.restartEngine()
+			e.triggerClientRestart()
 		} else if err != nil {
 			log.Warnf("WireGuard interface monitor: %s", err)
 		}
@@ -669,9 +707,11 @@ func (e *Engine) removeAllPeers() error {
 func (e *Engine) removePeer(peerKey string) error {
 	log.Debugf("removing peer from engine %s", peerKey)
 
+	e.sshMux.Lock()
 	if !isNil(e.sshServer) {
 		e.sshServer.RemoveAuthorizedKey(peerKey)
 	}
+	e.sshMux.Unlock()
 
 	e.connMgr.RemovePeerConn(peerKey)
 
@@ -873,6 +913,7 @@ func (e *Engine) updateSSH(sshConf *mgmProto.SSHConfig) error {
 			log.Warnf("running SSH server on %s is not supported", runtime.GOOS)
 			return nil
 		}
+		e.sshMux.Lock()
 		// start SSH server if it wasn't running
 		if isNil(e.sshServer) {
 			listenAddr := fmt.Sprintf("%s:%d", e.wgInterface.Address().IP.String(), nbssh.DefaultSSHPort)
@@ -880,34 +921,42 @@ func (e *Engine) updateSSH(sshConf *mgmProto.SSHConfig) error {
 				listenAddr = fmt.Sprintf("127.0.0.1:%d", nbssh.DefaultSSHPort)
 			}
 			// nil sshServer means it has not yet been started
-			var err error
-			e.sshServer, err = e.sshServerFunc(e.config.SSHKey, listenAddr)
-
+			server, err := e.sshServerFunc(e.config.SSHKey, listenAddr)
 			if err != nil {
+				e.sshMux.Unlock()
 				return fmt.Errorf("create ssh server: %w", err)
 			}
+
+			e.sshServer = server
+			e.sshMux.Unlock()
+
 			go func() {
 				// blocking
-				err = e.sshServer.Start()
+				err = server.Start()
 				if err != nil {
 					// will throw error when we stop it even if it is a graceful stop
 					log.Debugf("stopped SSH server with error %v", err)
 				}
-				e.syncMsgMux.Lock()
-				defer e.syncMsgMux.Unlock()
+				e.sshMux.Lock()
 				e.sshServer = nil
+				e.sshMux.Unlock()
 				log.Infof("stopped SSH server")
 			}()
 		} else {
+			e.sshMux.Unlock()
 			log.Debugf("SSH server is already running")
 		}
-	} else if !isNil(e.sshServer) {
-		// Disable SSH server request, so stop it if it was running
-		err := e.sshServer.Stop()
-		if err != nil {
-			log.Warnf("failed to stop SSH server %v", err)
+	} else {
+		e.sshMux.Lock()
+		if !isNil(e.sshServer) {
+			// Disable SSH server request, so stop it if it was running
+			err := e.sshServer.Stop()
+			if err != nil {
+				log.Warnf("failed to stop SSH server %v", err)
+			}
+			e.sshServer = nil
 		}
-		e.sshServer = nil
+		e.sshMux.Unlock()
 	}
 	return nil
 }
@@ -944,7 +993,9 @@ func (e *Engine) updateConfig(conf *mgmProto.PeerConfig) error {
 // receiveManagementEvents connects to the Management Service event stream to receive updates from the management service
 // E.g. when a new peer has been registered and we are allowed to connect to it.
 func (e *Engine) receiveManagementEvents() {
+	e.shutdownWg.Add(1)
 	go func() {
+		defer e.shutdownWg.Done()
 		info, err := system.GetInfoWithChecks(e.ctx, e.checks)
 		if err != nil {
 			log.Warnf("failed to get system info with checks: %v", err)
@@ -1120,6 +1171,7 @@ func (e *Engine) updateNetworkMap(networkMap *mgmProto.NetworkMap) error {
 		e.statusRecorder.FinishPeerListModifications()
 
 		// update SSHServer by adding remote peer SSH keys
+		e.sshMux.Lock()
 		if !isNil(e.sshServer) {
 			for _, config := range networkMap.GetRemotePeers() {
 				if config.GetSshConfig() != nil && config.GetSshConfig().GetSshPubKey() != nil {
@@ -1130,6 +1182,7 @@ func (e *Engine) updateNetworkMap(networkMap *mgmProto.NetworkMap) error {
 				}
 			}
 		}
+		e.sshMux.Unlock()
 	}
 
 	// must set the exclude list after the peers are added. Without it the manager can not figure out the peers parameters from the store
@@ -1372,7 +1425,9 @@ func (e *Engine) createPeerConn(pubKey string, allowedIPs []netip.Prefix, agentV
 
 // receiveSignalEvents connects to the Signal Service event stream to negotiate connection with remote peers
 func (e *Engine) receiveSignalEvents() {
+	e.shutdownWg.Add(1)
 	go func() {
+		defer e.shutdownWg.Done()
 		// connect to a stream of messages coming from the signal server
 		err := e.signal.Receive(e.ctx, func(msg *sProto.Message) error {
 			e.syncMsgMux.Lock()
@@ -1489,12 +1544,14 @@ func (e *Engine) close() {
 		e.statusRecorder.SetWgIface(nil)
 	}
 
+	e.sshMux.Lock()
 	if !isNil(e.sshServer) {
 		err := e.sshServer.Stop()
 		if err != nil {
 			log.Warnf("failed stopping the SSH server: %v", err)
 		}
 	}
+	e.sshMux.Unlock()
 
 	if e.firewall != nil {
 		err := e.firewall.Close(e.stateManager)
@@ -1725,8 +1782,10 @@ func (e *Engine) RunHealthProbes(waitForResult bool) bool {
 	return allHealthy
 }
 
-// restartEngine restarts the engine by cancelling the client context
-func (e *Engine) restartEngine() {
+// triggerClientRestart triggers a full client restart by cancelling the client context.
+// Note: This does NOT just restart the engine - it cancels the entire client context,
+// which causes the connect client's retry loop to create a completely new engine.
+func (e *Engine) triggerClientRestart() {
 	e.syncMsgMux.Lock()
 	defer e.syncMsgMux.Unlock()
 
@@ -1748,7 +1807,9 @@ func (e *Engine) startNetworkMonitor() {
 	}
 
 	e.networkMonitor = networkmonitor.New()
+	e.shutdownWg.Add(1)
 	go func() {
+		defer e.shutdownWg.Done()
 		if err := e.networkMonitor.Listen(e.ctx); err != nil {
 			if errors.Is(err, context.Canceled) {
 				log.Infof("network monitor stopped")
@@ -1758,8 +1819,8 @@ func (e *Engine) startNetworkMonitor() {
 			return
 		}
 
-		log.Infof("Network monitor: detected network change, restarting engine")
-		e.restartEngine()
+		log.Infof("Network monitor: detected network change, triggering client restart")
+		e.triggerClientRestart()
 	}()
 }
 
diff --git a/client/internal/netflow/manager.go b/client/internal/netflow/manager.go
index e3b188468..7752c97b0 100644
--- a/client/internal/netflow/manager.go
+++ b/client/internal/netflow/manager.go
@@ -24,6 +24,7 @@ import (
 // Manager handles netflow tracking and logging
 type Manager struct {
 	mux            sync.Mutex
+	shutdownWg     sync.WaitGroup
 	logger         nftypes.FlowLogger
 	flowConfig     *nftypes.FlowConfig
 	conntrack      nftypes.ConnTracker
@@ -105,8 +106,15 @@ func (m *Manager) resetClient() error {
 	ctx, cancel := context.WithCancel(context.Background())
 	m.cancel = cancel
 
-	go m.receiveACKs(ctx, flowClient)
-	go m.startSender(ctx)
+	m.shutdownWg.Add(2)
+	go func() {
+		defer m.shutdownWg.Done()
+		m.receiveACKs(ctx, flowClient)
+	}()
+	go func() {
+		defer m.shutdownWg.Done()
+		m.startSender(ctx)
+	}()
 
 	return nil
 }
@@ -176,11 +184,12 @@ func (m *Manager) Update(update *nftypes.FlowConfig) error {
 // Close cleans up all resources
 func (m *Manager) Close() {
 	m.mux.Lock()
-	defer m.mux.Unlock()
-
 	if err := m.disableFlow(); err != nil {
 		log.Warnf("failed to disable flow manager: %v", err)
 	}
+	m.mux.Unlock()
+
+	m.shutdownWg.Wait()
 }
 
 // GetLogger returns the flow logger
diff --git a/client/internal/peer/guard/sr_watcher.go b/client/internal/peer/guard/sr_watcher.go
index 686430752..6f4f5ad4f 100644
--- a/client/internal/peer/guard/sr_watcher.go
+++ b/client/internal/peer/guard/sr_watcher.go
@@ -19,11 +19,10 @@ type SRWatcher struct {
 	signalClient chNotifier
 	relayManager chNotifier
 
-	listeners     map[chan struct{}]struct{}
-	mu            sync.Mutex
-	iFaceDiscover stdnet.ExternalIFaceDiscover
-	iceConfig     ice.Config
-
+	listeners        map[chan struct{}]struct{}
+	mu               sync.Mutex
+	iFaceDiscover    stdnet.ExternalIFaceDiscover
+	iceConfig        ice.Config
 	cancelIceMonitor context.CancelFunc
 }
 
diff --git a/client/internal/routemanager/manager.go b/client/internal/routemanager/manager.go
index 37974cd17..26cf758d9 100644
--- a/client/internal/routemanager/manager.go
+++ b/client/internal/routemanager/manager.go
@@ -81,6 +81,7 @@ type DefaultManager struct {
 	ctx                  context.Context
 	stop                 context.CancelFunc
 	mux                  sync.Mutex
+	shutdownWg           sync.WaitGroup
 	clientNetworks       map[route.HAUniqueID]*client.Watcher
 	routeSelector        *routeselector.RouteSelector
 	serverRouter         *server.Router
@@ -283,6 +284,7 @@ func (m *DefaultManager) SetDNSForwarderPort(port uint16) {
 // Stop stops the manager watchers and clean firewall rules
 func (m *DefaultManager) Stop(stateManager *statemanager.Manager) {
 	m.stop()
+	m.shutdownWg.Wait()
 	if m.serverRouter != nil {
 		m.serverRouter.CleanUp()
 	}
@@ -485,7 +487,11 @@ func (m *DefaultManager) TriggerSelection(networks route.HAMap) {
 		}
 		clientNetworkWatcher := client.NewWatcher(config)
 		m.clientNetworks[id] = clientNetworkWatcher
-		go clientNetworkWatcher.Start()
+		m.shutdownWg.Add(1)
+		go func() {
+			defer m.shutdownWg.Done()
+			clientNetworkWatcher.Start()
+		}()
 		clientNetworkWatcher.SendUpdate(client.RoutesUpdate{Routes: routes})
 	}
 
@@ -527,7 +533,11 @@ func (m *DefaultManager) updateClientNetworks(updateSerial uint64, networks rout
 			}
 			clientNetworkWatcher = client.NewWatcher(config)
 			m.clientNetworks[id] = clientNetworkWatcher
-			go clientNetworkWatcher.Start()
+			m.shutdownWg.Add(1)
+			go func() {
+				defer m.shutdownWg.Done()
+				clientNetworkWatcher.Start()
+			}()
 		}
 		update := client.RoutesUpdate{
 			UpdateSerial: updateSerial,
diff --git a/client/internal/routeselector/routeselector.go b/client/internal/routeselector/routeselector.go
index e4a78599e..61c8bbc79 100644
--- a/client/internal/routeselector/routeselector.go
+++ b/client/internal/routeselector/routeselector.go
@@ -9,8 +9,6 @@ import (
 	"github.com/hashicorp/go-multierror"
 	"golang.org/x/exp/maps"
 
-	log "github.com/sirupsen/logrus"
-
 	"github.com/netbirdio/netbird/client/errors"
 	"github.com/netbirdio/netbird/route"
 )
@@ -128,13 +126,11 @@ func (rs *RouteSelector) IsSelected(routeID route.NetID) bool {
 	defer rs.mu.RUnlock()
 
 	if rs.deselectAll {
-		log.Debugf("Route %s not selected (deselect all)", routeID)
 		return false
 	}
 
 	_, deselected := rs.deselectedRoutes[routeID]
 	isSelected := !deselected
-	log.Debugf("Route %s selection status: %v (deselected: %v)", routeID, isSelected, deselected)
 	return isSelected
 }