[client] Use the prerouting chain to mark for masquerading to support older systems (#2808)

client/firewall/iptables/acl_linux.go

@@ -352,14 +352,14 @@ func (m *aclManager) seedInitialEntries() {
 func (m *aclManager) seedInitialOptionalEntries() {
 	m.optionalEntries["FORWARD"] = []entry{
 		{
-			spec:     []string{"-m", "mark", "--mark", fmt.Sprintf("%#x", nbnet.PreroutingFwmark), "-j", chainNameInputRules},
+			spec:     []string{"-m", "mark", "--mark", fmt.Sprintf("%#x", nbnet.PreroutingFwmarkRedirected), "-j", chainNameInputRules},
 			position: 2,
 		},
 	}
 
 	m.optionalEntries["PREROUTING"] = []entry{
 		{
-			spec:     []string{"-t", "mangle", "-i", m.wgIface.Name(), "-m", "addrtype", "--dst-type", "LOCAL", "-j", "MARK", "--set-mark", fmt.Sprintf("%#x", nbnet.PreroutingFwmark)},
+			spec:     []string{"-t", "mangle", "-i", m.wgIface.Name(), "-m", "addrtype", "--dst-type", "LOCAL", "-j", "MARK", "--set-mark", fmt.Sprintf("%#x", nbnet.PreroutingFwmarkRedirected)},
 			position: 1,
 		},
 	}

client/firewall/iptables/router_linux.go

@@ -18,22 +18,24 @@ import (
 	"github.com/netbirdio/netbird/client/internal/acl/id"
 	"github.com/netbirdio/netbird/client/internal/routemanager/refcounter"
 	"github.com/netbirdio/netbird/client/internal/statemanager"
-)
+	nbnet "github.com/netbirdio/netbird/util/net"
-
-const (
-	ipv4Nat = "netbird-rt-nat"
 )
 
 // constants needed to manage and create iptable rules
 const (
 	tableFilter             = "filter"
 	tableNat                = "nat"
+	tableMangle             = "mangle"
 	chainPOSTROUTING        = "POSTROUTING"
+	chainPREROUTING         = "PREROUTING"
 	chainRTNAT              = "NETBIRD-RT-NAT"
 	chainRTFWD              = "NETBIRD-RT-FWD"
+	chainRTPRE              = "NETBIRD-RT-PRE"
 	routingFinalForwardJump = "ACCEPT"
 	routingFinalNatJump     = "MASQUERADE"
 
+	jumpPre  = "jump-pre"
+	jumpNat  = "jump-nat"
 	matchSet = "--match-set"
 )
 
@@ -323,24 +325,25 @@ func (r *router) Reset() error {
 }
 
 func (r *router) cleanUpDefaultForwardRules() error {
-	err := r.cleanJumpRules()
+	if err := r.cleanJumpRules(); err != nil {
-	if err != nil {
+		return fmt.Errorf("clean jump rules: %w", err)
-		return err
 	}
 
 	log.Debug("flushing routing related tables")
-	for _, chain := range []string{chainRTFWD, chainRTNAT} {
+	for _, chainInfo := range []struct {
-		table := r.getTableForChain(chain)
+		chain string
-
+		table string
-		ok, err := r.iptablesClient.ChainExists(table, chain)
+	}{
+		{chainRTFWD, tableFilter},
+		{chainRTNAT, tableNat},
+		{chainRTPRE, tableMangle},
+	} {
+		ok, err := r.iptablesClient.ChainExists(chainInfo.table, chainInfo.chain)
 		if err != nil {
-			log.Errorf("failed check chain %s, error: %v", chain, err)
+			return fmt.Errorf("check chain %s in table %s: %w", chainInfo.chain, chainInfo.table, err)
-			return err
 		} else if ok {
-			err = r.iptablesClient.ClearAndDeleteChain(table, chain)
+			if err = r.iptablesClient.ClearAndDeleteChain(chainInfo.table, chainInfo.chain); err != nil {
-			if err != nil {
+				return fmt.Errorf("clear and delete chain %s in table %s: %w", chainInfo.chain, chainInfo.table, err)
-				log.Errorf("failed cleaning chain %s, error: %v", chain, err)
-				return err
 			}
 		}
 	}
@@ -349,9 +352,16 @@ func (r *router) cleanUpDefaultForwardRules() error {
 }
 
 func (r *router) createContainers() error {
-	for _, chain := range []string{chainRTFWD, chainRTNAT} {
+	for _, chainInfo := range []struct {
-		if err := r.createAndSetupChain(chain); err != nil {
+		chain string
-			return fmt.Errorf("create chain %s: %w", chain, err)
+		table string
+	}{
+		{chainRTFWD, tableFilter},
+		{chainRTPRE, tableMangle},
+		{chainRTNAT, tableNat},
+	} {
+		if err := r.createAndSetupChain(chainInfo.chain); err != nil {
+			return fmt.Errorf("create chain %s in table %s: %w", chainInfo.chain, chainInfo.table, err)
 		}
 	}
 
@@ -359,6 +369,10 @@ func (r *router) createContainers() error {
 		return fmt.Errorf("insert established rule: %w", err)
 	}
 
+	if err := r.addPostroutingRules(); err != nil {
+		return fmt.Errorf("add static nat rules: %w", err)
+	}
+
 	if err := r.addJumpRules(); err != nil {
 		return fmt.Errorf("add jump rules: %w", err)
 	}
@@ -366,6 +380,32 @@ func (r *router) createContainers() error {
 	return nil
 }
 
+func (r *router) addPostroutingRules() error {
+	// First rule for outbound masquerade
+	rule1 := []string{
+		"-m", "mark", "--mark", fmt.Sprintf("%#x", nbnet.PreroutingFwmarkMasquerade),
+		"!", "-o", "lo",
+		"-j", routingFinalNatJump,
+	}
+	if err := r.iptablesClient.Append(tableNat, chainRTNAT, rule1...); err != nil {
+		return fmt.Errorf("add outbound masquerade rule: %v", err)
+	}
+	r.rules["static-nat-outbound"] = rule1
+
+	// Second rule for return traffic masquerade
+	rule2 := []string{
+		"-m", "mark", "--mark", fmt.Sprintf("%#x", nbnet.PreroutingFwmarkMasqueradeReturn),
+		"-o", r.wgIface.Name(),
+		"-j", routingFinalNatJump,
+	}
+	if err := r.iptablesClient.Append(tableNat, chainRTNAT, rule2...); err != nil {
+		return fmt.Errorf("add return masquerade rule: %v", err)
+	}
+	r.rules["static-nat-return"] = rule2
+
+	return nil
+}
+
 func (r *router) createAndSetupChain(chain string) error {
 	table := r.getTableForChain(chain)
 
@@ -377,10 +417,14 @@ func (r *router) createAndSetupChain(chain string) error {
 }
 
 func (r *router) getTableForChain(chain string) string {
-	if chain == chainRTNAT {
+	switch chain {
+	case chainRTNAT:
 		return tableNat
+	case chainRTPRE:
+		return tableMangle
+	default:
+		return tableFilter
 	}
-	return tableFilter
 }
 
 func (r *router) insertEstablishedRule(chain string) error {
@@ -398,25 +442,39 @@ func (r *router) insertEstablishedRule(chain string) error {
 }
 
 func (r *router) addJumpRules() error {
-	rule := []string{"-j", chainRTNAT}
+	// Jump to NAT chain
-	err := r.iptablesClient.Insert(tableNat, chainPOSTROUTING, 1, rule...)
+	natRule := []string{"-j", chainRTNAT}
-	if err != nil {
+	if err := r.iptablesClient.Insert(tableNat, chainPOSTROUTING, 1, natRule...); err != nil {
-		return err
+		return fmt.Errorf("add nat jump rule: %v", err)
 	}
-	r.rules[ipv4Nat] = rule
+	r.rules[jumpNat] = natRule
+
+	// Jump to prerouting chain
+	preRule := []string{"-j", chainRTPRE}
+	if err := r.iptablesClient.Insert(tableMangle, chainPREROUTING, 1, preRule...); err != nil {
+		return fmt.Errorf("add prerouting jump rule: %v", err)
+	}
+	r.rules[jumpPre] = preRule
 
 	return nil
 }
 
 func (r *router) cleanJumpRules() error {
-	rule, found := r.rules[ipv4Nat]
+	for _, ruleKey := range []string{jumpNat, jumpPre} {
-	if found {
+		if rule, exists := r.rules[ruleKey]; exists {
-		err := r.iptablesClient.DeleteIfExists(tableNat, chainPOSTROUTING, rule...)
+			table := tableNat
-		if err != nil {
+			chain := chainPOSTROUTING
-			return fmt.Errorf("failed cleaning rule from chain %s, err: %v", chainPOSTROUTING, err)
+			if ruleKey == jumpPre {
+				table = tableMangle
+				chain = chainPREROUTING
+			}
+
+			if err := r.iptablesClient.DeleteIfExists(table, chain, rule...); err != nil {
+				return fmt.Errorf("delete rule from chain %s in table %s, err: %v", chain, table, err)
+			}
+			delete(r.rules, ruleKey)
 		}
 	}
-
 	return nil
 }
 
@@ -424,19 +482,35 @@ func (r *router) addNatRule(pair firewall.RouterPair) error {
 	ruleKey := firewall.GenKey(firewall.NatFormat, pair)
 
 	if rule, exists := r.rules[ruleKey]; exists {
-		if err := r.iptablesClient.DeleteIfExists(tableNat, chainRTNAT, rule...); err != nil {
+		if err := r.iptablesClient.DeleteIfExists(tableMangle, chainRTPRE, rule...); err != nil {
-			return fmt.Errorf("error while removing existing NAT rule for %s: %v", pair.Destination, err)
+			return fmt.Errorf("error while removing existing marking rule for %s: %v", pair.Destination, err)
 		}
 		delete(r.rules, ruleKey)
 	}
 
-	rule := genRuleSpec(routingFinalNatJump, pair.Source, pair.Destination, r.wgIface.Name(), pair.Inverse)
+	markValue := nbnet.PreroutingFwmarkMasquerade
-	if err := r.iptablesClient.Append(tableNat, chainRTNAT, rule...); err != nil {
+	if pair.Inverse {
-		return fmt.Errorf("error while appending new NAT rule for %s: %v", pair.Destination, err)
+		markValue = nbnet.PreroutingFwmarkMasqueradeReturn
+	}
+
+	rule := []string{"-i", r.wgIface.Name()}
+	if pair.Inverse {
+		rule = []string{"!", "-i", r.wgIface.Name()}
+	}
+
+	rule = append(rule,
+		"-m", "conntrack",
+		"--ctstate", "NEW",
+		"-s", pair.Source.String(),
+		"-d", pair.Destination.String(),
+		"-j", "MARK", "--set-mark", fmt.Sprintf("%#x", markValue),
+	)
+
+	if err := r.iptablesClient.Append(tableMangle, chainRTPRE, rule...); err != nil {
+		return fmt.Errorf("error while adding marking rule for %s: %v", pair.Destination, err)
 	}
 
 	r.rules[ruleKey] = rule
-
 	return nil
 }
 
@@ -444,13 +518,12 @@ func (r *router) removeNatRule(pair firewall.RouterPair) error {
 	ruleKey := firewall.GenKey(firewall.NatFormat, pair)
 
 	if rule, exists := r.rules[ruleKey]; exists {
-		if err := r.iptablesClient.DeleteIfExists(tableNat, chainRTNAT, rule...); err != nil {
+		if err := r.iptablesClient.DeleteIfExists(tableMangle, chainRTPRE, rule...); err != nil {
-			return fmt.Errorf("error while removing existing nat rule for %s: %v", pair.Destination, err)
+			return fmt.Errorf("error while removing marking rule for %s: %v", pair.Destination, err)
 		}
-
 		delete(r.rules, ruleKey)
 	} else {
-		log.Debugf("nat rule %s not found", ruleKey)
+		log.Debugf("marking rule %s not found", ruleKey)
 	}
 
 	return nil
@@ -482,16 +555,6 @@ func (r *router) updateState() {
 	}
 }
 
-func genRuleSpec(jump string, source, destination netip.Prefix, intf string, inverse bool) []string {
-	intdir := "-i"
-	lointdir := "-o"
-	if inverse {
-		intdir = "-o"
-		lointdir = "-i"
-	}
-	return []string{intdir, intf, "!", lointdir, "lo", "-s", source.String(), "-d", destination.String(), "-j", jump}
-}
-
 func genRouteFilteringRuleSpec(params routeFilteringRuleParams) []string {
 	var rule []string
 

client/firewall/iptables/router_linux_test.go

@@ -3,17 +3,18 @@
 package iptables
 
 import (
+	"fmt"
 	"net/netip"
 	"os/exec"
 	"testing"
 
 	"github.com/coreos/go-iptables/iptables"
-	log "github.com/sirupsen/logrus"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
 	firewall "github.com/netbirdio/netbird/client/firewall/manager"
 	"github.com/netbirdio/netbird/client/firewall/test"
+	nbnet "github.com/netbirdio/netbird/util/net"
 )
 
 func isIptablesSupported() bool {
@@ -34,14 +35,24 @@ func TestIptablesManager_RestoreOrCreateContainers(t *testing.T) {
 	require.NoError(t, manager.init(nil))
 
 	defer func() {
-		_ = manager.Reset()
+		assert.NoError(t, manager.Reset(), "shouldn't return error")
 	}()
 
-	require.Len(t, manager.rules, 2, "should have created rules map")
+	// Now 5 rules:
+	// 1. established rule in forward chain
+	// 2. jump rule to NAT chain
+	// 3. jump rule to PRE chain
+	// 4. static outbound masquerade rule
+	// 5. static return masquerade rule
+	require.Len(t, manager.rules, 5, "should have created rules map")
 
-	exists, err := manager.iptablesClient.Exists(tableNat, chainPOSTROUTING, manager.rules[ipv4Nat]...)
+	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)
-	require.True(t, exists, "postrouting rule should exist")
+	require.True(t, exists, "postrouting jump rule should exist")
+
+	exists, err = manager.iptablesClient.Exists(tableMangle, chainPREROUTING, "-j", chainRTPRE)
+	require.NoError(t, err, "should be able to query the iptables %s table and %s chain", tableMangle, chainPREROUTING)
+	require.True(t, exists, "prerouting jump rule should exist")
 
 	pair := firewall.RouterPair{
 		ID:          "abc",
@@ -49,22 +60,15 @@ func TestIptablesManager_RestoreOrCreateContainers(t *testing.T) {
 		Destination: netip.MustParsePrefix("100.100.100.0/24"),
 		Masquerade:  true,
 	}
-	forward4Rule := []string{"-s", pair.Source.String(), "-d", pair.Destination.String(), "-j", routingFinalForwardJump}
 
-	err = manager.iptablesClient.Insert(tableFilter, chainRTFWD, 1, forward4Rule...)
+	err = manager.AddNatRule(pair)
-	require.NoError(t, err, "inserting rule should not return error")
+	require.NoError(t, err, "adding NAT rule should not return error")
-
-	nat4Rule := genRuleSpec(routingFinalNatJump, pair.Source, pair.Destination, ifaceMock.Name(), false)
-
-	err = manager.iptablesClient.Insert(tableNat, chainRTNAT, 1, nat4Rule...)
-	require.NoError(t, err, "inserting rule should not return error")
 
 	err = manager.Reset()
 	require.NoError(t, err, "shouldn't return error")
 }
 
 func TestIptablesManager_AddNatRule(t *testing.T) {
-
 	if !isIptablesSupported() {
 		t.SkipNow()
 	}
@@ -79,52 +83,66 @@ func TestIptablesManager_AddNatRule(t *testing.T) {
 			require.NoError(t, manager.init(nil))
 
 			defer func() {
-				err := manager.Reset()
+				assert.NoError(t, manager.Reset(), "shouldn't return error")
-				if err != nil {
-					log.Errorf("failed to reset iptables manager: %s", err)
-				}
 			}()
 
 			err = manager.AddNatRule(testCase.InputPair)
-			require.NoError(t, err, "forwarding pair should be inserted")
+			require.NoError(t, err, "marking rule should be inserted")
 
 			natRuleKey := firewall.GenKey(firewall.NatFormat, testCase.InputPair)
-			natRule := genRuleSpec(routingFinalNatJump, testCase.InputPair.Source, testCase.InputPair.Destination, ifaceMock.Name(), false)
+			markingRule := []string{
-
+				"-i", ifaceMock.Name(),
-			exists, err := iptablesClient.Exists(tableNat, chainRTNAT, natRule...)
+				"-m", "conntrack",
-			require.NoError(t, err, "should be able to query the iptables %s table and %s chain", tableNat, chainRTNAT)
+				"--ctstate", "NEW",
-			if testCase.InputPair.Masquerade {
+				"-s", testCase.InputPair.Source.String(),
-				require.True(t, exists, "nat rule should be created")
+				"-d", testCase.InputPair.Destination.String(),
-				foundNatRule, foundNat := manager.rules[natRuleKey]
+				"-j", "MARK", "--set-mark",
-				require.True(t, foundNat, "nat rule should exist in the map")
+				fmt.Sprintf("%#x", nbnet.PreroutingFwmarkMasquerade),
-				require.Equal(t, natRule[:4], foundNatRule[:4], "stored nat rule should match")
-			} else {
-				require.False(t, exists, "nat rule should not be created")
-				_, foundNat := manager.rules[natRuleKey]
-				require.False(t, foundNat, "nat rule should not exist in the map")
 			}
 
-			inNatRuleKey := firewall.GenKey(firewall.NatFormat, firewall.GetInversePair(testCase.InputPair))
+			exists, err := iptablesClient.Exists(tableMangle, chainRTPRE, markingRule...)
-			inNatRule := genRuleSpec(routingFinalNatJump, firewall.GetInversePair(testCase.InputPair).Source, firewall.GetInversePair(testCase.InputPair).Destination, ifaceMock.Name(), true)
+			require.NoError(t, err, "should be able to query the iptables %s table and %s chain", tableMangle, chainRTPRE)
-
-			exists, err = iptablesClient.Exists(tableNat, chainRTNAT, inNatRule...)
-			require.NoError(t, err, "should be able to query the iptables %s table and %s chain", tableNat, chainRTNAT)
 			if testCase.InputPair.Masquerade {
-				require.True(t, exists, "income nat rule should be created")
+				require.True(t, exists, "marking rule should be created")
-				foundNatRule, foundNat := manager.rules[inNatRuleKey]
+				foundRule, found := manager.rules[natRuleKey]
-				require.True(t, foundNat, "income nat rule should exist in the map")
+				require.True(t, found, "marking rule should exist in the map")
-				require.Equal(t, inNatRule[:4], foundNatRule[:4], "stored income nat rule should match")
+				require.Equal(t, markingRule, foundRule, "stored marking rule should match")
 			} else {
-				require.False(t, exists, "nat rule should not be created")
+				require.False(t, exists, "marking rule should not be created")
-				_, foundNat := manager.rules[inNatRuleKey]
+				_, found := manager.rules[natRuleKey]
-				require.False(t, foundNat, "income nat rule should not exist in the map")
+				require.False(t, found, "marking rule should not exist in the map")
+			}
+
+			// Check inverse rule
+			inversePair := firewall.GetInversePair(testCase.InputPair)
+			inverseRuleKey := firewall.GenKey(firewall.NatFormat, inversePair)
+			inverseMarkingRule := []string{
+				"!", "-i", ifaceMock.Name(),
+				"-m", "conntrack",
+				"--ctstate", "NEW",
+				"-s", inversePair.Source.String(),
+				"-d", inversePair.Destination.String(),
+				"-j", "MARK", "--set-mark",
+				fmt.Sprintf("%#x", nbnet.PreroutingFwmarkMasqueradeReturn),
+			}
+
+			exists, err = iptablesClient.Exists(tableMangle, chainRTPRE, inverseMarkingRule...)
+			require.NoError(t, err, "should be able to query the iptables %s table and %s chain", tableMangle, chainRTPRE)
+			if testCase.InputPair.Masquerade {
+				require.True(t, exists, "inverse marking rule should be created")
+				foundRule, found := manager.rules[inverseRuleKey]
+				require.True(t, found, "inverse marking rule should exist in the map")
+				require.Equal(t, inverseMarkingRule, foundRule, "stored inverse marking rule should match")
+			} else {
+				require.False(t, exists, "inverse marking rule should not be created")
+				_, found := manager.rules[inverseRuleKey]
+				require.False(t, found, "inverse marking rule should not exist in the map")
 			}
 		})
 	}
 }
 
 func TestIptablesManager_RemoveNatRule(t *testing.T) {
-
 	if !isIptablesSupported() {
 		t.SkipNow()
 	}
@@ -137,42 +155,52 @@ func TestIptablesManager_RemoveNatRule(t *testing.T) {
 			require.NoError(t, err, "shouldn't return error")
 			require.NoError(t, manager.init(nil))
 			defer func() {
-				_ = manager.Reset()
+				assert.NoError(t, manager.Reset(), "shouldn't return error")
 			}()
 
-			require.NoError(t, err, "shouldn't return error")
+			err = manager.AddNatRule(testCase.InputPair)
-
+			require.NoError(t, err, "should add NAT rule without error")
-			natRuleKey := firewall.GenKey(firewall.NatFormat, testCase.InputPair)
-			natRule := genRuleSpec(routingFinalNatJump, testCase.InputPair.Source, testCase.InputPair.Destination, ifaceMock.Name(), false)
-
-			err = iptablesClient.Insert(tableNat, chainRTNAT, 1, natRule...)
-			require.NoError(t, err, "inserting rule should not return error")
-
-			inNatRuleKey := firewall.GenKey(firewall.NatFormat, firewall.GetInversePair(testCase.InputPair))
-			inNatRule := genRuleSpec(routingFinalNatJump, firewall.GetInversePair(testCase.InputPair).Source, firewall.GetInversePair(testCase.InputPair).Destination, ifaceMock.Name(), true)
-
-			err = iptablesClient.Insert(tableNat, chainRTNAT, 1, inNatRule...)
-			require.NoError(t, err, "inserting rule should not return error")
-
-			err = manager.Reset()
-			require.NoError(t, err, "shouldn't return error")
 
 			err = manager.RemoveNatRule(testCase.InputPair)
 			require.NoError(t, err, "shouldn't return error")
 
-			exists, err := iptablesClient.Exists(tableNat, chainRTNAT, natRule...)
+			natRuleKey := firewall.GenKey(firewall.NatFormat, testCase.InputPair)
-			require.NoError(t, err, "should be able to query the iptables %s table and %s chain", tableNat, chainRTNAT)
+			markingRule := []string{
-			require.False(t, exists, "nat rule should not exist")
+				"-i", ifaceMock.Name(),
+				"-m", "conntrack",
+				"--ctstate", "NEW",
+				"-s", testCase.InputPair.Source.String(),
+				"-d", testCase.InputPair.Destination.String(),
+				"-j", "MARK", "--set-mark",
+				fmt.Sprintf("%#x", nbnet.PreroutingFwmarkMasquerade),
+			}
+
+			exists, err := iptablesClient.Exists(tableMangle, chainRTPRE, markingRule...)
+			require.NoError(t, err, "should be able to query the iptables %s table and %s chain", tableMangle, chainRTPRE)
+			require.False(t, exists, "marking rule should not exist")
 
 			_, found := manager.rules[natRuleKey]
-			require.False(t, found, "nat rule should exist in the manager map")
+			require.False(t, found, "marking rule should not exist in the manager map")
 
-			exists, err = iptablesClient.Exists(tableNat, chainRTNAT, inNatRule...)
+			// Check inverse rule removal
-			require.NoError(t, err, "should be able to query the iptables %s table and %s chain", tableNat, chainRTNAT)
+			inversePair := firewall.GetInversePair(testCase.InputPair)
-			require.False(t, exists, "income nat rule should not exist")
+			inverseRuleKey := firewall.GenKey(firewall.NatFormat, inversePair)
+			inverseMarkingRule := []string{
+				"!", "-i", ifaceMock.Name(),
+				"-m", "conntrack",
+				"--ctstate", "NEW",
+				"-s", inversePair.Source.String(),
+				"-d", inversePair.Destination.String(),
+				"-j", "MARK", "--set-mark",
+				fmt.Sprintf("%#x", nbnet.PreroutingFwmarkMasqueradeReturn),
+			}
 
-			_, found = manager.rules[inNatRuleKey]
+			exists, err = iptablesClient.Exists(tableMangle, chainRTPRE, inverseMarkingRule...)
-			require.False(t, found, "income nat rule should exist in the manager map")
+			require.NoError(t, err, "should be able to query the iptables %s table and %s chain", tableMangle, chainRTPRE)
+			require.False(t, exists, "inverse marking rule should not exist")
+
+			_, found = manager.rules[inverseRuleKey]
+			require.False(t, found, "inverse marking rule should not exist in the map")
 		})
 	}
 }

client/firewall/manager/firewall.go

@@ -17,6 +17,7 @@ import (
 const (
 	ForwardingFormatPrefix = "netbird-fwd-"
 	ForwardingFormat       = "netbird-fwd-%s-%t"
+	PreroutingFormat       = "netbird-prerouting-%s-%t"
 	NatFormat              = "netbird-nat-%s-%t"
 )
 

client/firewall/nftables/acl_linux.go

@@ -520,7 +520,7 @@ func (m *AclManager) addPreroutingRule(preroutingChain *nftables.Chain) {
 			},
 			&expr.Immediate{
 				Register: 1,
-				Data:     binaryutil.NativeEndian.PutUint32(nbnet.PreroutingFwmark),
+				Data:     binaryutil.NativeEndian.PutUint32(nbnet.PreroutingFwmarkRedirected),
 			},
 			&expr.Meta{
 				Key:            expr.MetaKeyMARK,
@@ -543,7 +543,7 @@ func (m *AclManager) addFwmarkToForward(chainFwFilter *nftables.Chain) {
 			&expr.Cmp{
 				Op:       expr.CmpOpEq,
 				Register: 1,
-				Data:     binaryutil.NativeEndian.PutUint32(nbnet.PreroutingFwmark),
+				Data:     binaryutil.NativeEndian.PutUint32(nbnet.PreroutingFwmarkRedirected),
 			},
 			&expr.Verdict{
 				Kind:  expr.VerdictJump,

client/firewall/nftables/router_linux.go

@@ -21,6 +21,7 @@ import (
 	firewall "github.com/netbirdio/netbird/client/firewall/manager"
 	"github.com/netbirdio/netbird/client/internal/acl/id"
 	"github.com/netbirdio/netbird/client/internal/routemanager/refcounter"
+	nbnet "github.com/netbirdio/netbird/util/net"
 )
 
 const (
@@ -124,7 +125,6 @@ func (r *router) createContainers() error {
 	insertReturnTrafficRule(r.conn, r.workTable, r.chains[chainNameRoutingFw])
 
 	prio := *nftables.ChainPriorityNATSource - 1
-
 	r.chains[chainNameRoutingNat] = r.conn.AddChain(&nftables.Chain{
 		Name:     chainNameRoutingNat,
 		Table:    r.workTable,
@@ -133,6 +133,21 @@ func (r *router) createContainers() error {
 		Type:     nftables.ChainTypeNAT,
 	})
 
+	// Chain is created by acl manager
+	// TODO: move creation to a common place
+	r.chains[chainNamePrerouting] = &nftables.Chain{
+		Name:     chainNamePrerouting,
+		Table:    r.workTable,
+		Type:     nftables.ChainTypeFilter,
+		Hooknum:  nftables.ChainHookPrerouting,
+		Priority: nftables.ChainPriorityMangle,
+	}
+
+	// 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.acceptForwardRules(); err != nil {
 		log.Errorf("failed to add accept rules for the forward chain: %s", err)
 	}
@@ -422,59 +437,149 @@ func (r *router) addNatRule(pair firewall.RouterPair) error {
 	sourceExp := generateCIDRMatcherExpressions(true, pair.Source)
 	destExp := generateCIDRMatcherExpressions(false, pair.Destination)
 
-	dir := expr.MetaKeyIIFNAME
+	op := expr.CmpOpEq
-	notDir := expr.MetaKeyOIFNAME
 	if pair.Inverse {
-		dir = expr.MetaKeyOIFNAME
+		op = expr.CmpOpNeq
-		notDir = expr.MetaKeyIIFNAME
 	}
 
-	lo := ifname("lo")
-	intf := ifname(r.wgIface.Name())
-
 	exprs := []expr.Any{
-		&expr.Meta{
+		// We only care about NEW connections to mark them and later identify them in the postrouting chain for masquerading.
-			Key:      dir,
+		// Masquerading will take care of the conntrack state, which means we won't need to mark established connections.
+		&expr.Ct{
+			Key:      expr.CtKeySTATE,
 			Register: 1,
 		},
-		&expr.Cmp{
+		&expr.Bitwise{
-			Op:       expr.CmpOpEq,
+			SourceRegister: 1,
-			Register: 1,
+			DestRegister:   1,
-			Data:     intf,
+			Len:            4,
-		},
+			Mask:           binaryutil.NativeEndian.PutUint32(expr.CtStateBitNEW),
-
+			Xor:            binaryutil.NativeEndian.PutUint32(0),
-		// We need to exclude the loopback interface as this changes the ebpf proxy port
-		&expr.Meta{
-			Key:      notDir,
-			Register: 1,
 		},
 		&expr.Cmp{
 			Op:       expr.CmpOpNeq,
 			Register: 1,
-			Data:     lo,
+			Data:     []byte{0, 0, 0, 0},
+		},
+
+		// interface matching
+		&expr.Meta{
+			Key:      expr.MetaKeyIIFNAME,
+			Register: 1,
+		},
+		&expr.Cmp{
+			Op:       op,
+			Register: 1,
+			Data:     ifname(r.wgIface.Name()),
 		},
 	}
 
 	exprs = append(exprs, sourceExp...)
 	exprs = append(exprs, destExp...)
+
+	var markValue uint32 = nbnet.PreroutingFwmarkMasquerade
+	if pair.Inverse {
+		markValue = nbnet.PreroutingFwmarkMasqueradeReturn
+	}
+
 	exprs = append(exprs,
-		&expr.Counter{}, &expr.Masq{},
+		&expr.Immediate{
+			Register: 1,
+			Data:     binaryutil.NativeEndian.PutUint32(markValue),
+		},
+		&expr.Meta{
+			Key:            expr.MetaKeyMARK,
+			SourceRegister: true,
+			Register:       1,
+		},
 	)
 
-	ruleKey := firewall.GenKey(firewall.NatFormat, pair)
+	ruleKey := firewall.GenKey(firewall.PreroutingFormat, pair)
 
 	if _, exists := r.rules[ruleKey]; exists {
 		if err := r.removeNatRule(pair); err != nil {
-			return fmt.Errorf("remove routing rule: %w", err)
+			return fmt.Errorf("remove prerouting rule: %w", err)
 		}
 	}
 
 	r.rules[ruleKey] = r.conn.AddRule(&nftables.Rule{
 		Table:    r.workTable,
-		Chain:    r.chains[chainNameRoutingNat],
+		Chain:    r.chains[chainNamePrerouting],
 		Exprs:    exprs,
 		UserData: []byte(ruleKey),
 	})
+
+	return nil
+}
+
+// addPostroutingRules adds the masquerade rules
+func (r *router) addPostroutingRules() error {
+	// First masquerade rule for traffic coming in from WireGuard interface
+	exprs := []expr.Any{
+		// Match on the first fwmark
+		&expr.Meta{
+			Key:      expr.MetaKeyMARK,
+			Register: 1,
+		},
+		&expr.Cmp{
+			Op:       expr.CmpOpEq,
+			Register: 1,
+			Data:     binaryutil.NativeEndian.PutUint32(nbnet.PreroutingFwmarkMasquerade),
+		},
+
+		// We need to exclude the loopback interface as this changes the ebpf proxy port
+		&expr.Meta{
+			Key:      expr.MetaKeyOIFNAME,
+			Register: 1,
+		},
+		&expr.Cmp{
+			Op:       expr.CmpOpNeq,
+			Register: 1,
+			Data:     ifname("lo"),
+		},
+		&expr.Counter{},
+		&expr.Masq{},
+	}
+
+	r.conn.AddRule(&nftables.Rule{
+		Table: r.workTable,
+		Chain: r.chains[chainNameRoutingNat],
+		Exprs: exprs,
+	})
+
+	// Second masquerade rule for traffic going out through WireGuard interface
+	exprs2 := []expr.Any{
+		// Match on the second fwmark
+		&expr.Meta{
+			Key:      expr.MetaKeyMARK,
+			Register: 1,
+		},
+		&expr.Cmp{
+			Op:       expr.CmpOpEq,
+			Register: 1,
+			Data:     binaryutil.NativeEndian.PutUint32(nbnet.PreroutingFwmarkMasqueradeReturn),
+		},
+
+		// Match WireGuard interface
+		&expr.Meta{
+			Key:      expr.MetaKeyOIFNAME,
+			Register: 1,
+		},
+		&expr.Cmp{
+			Op:       expr.CmpOpEq,
+			Register: 1,
+			Data:     ifname(r.wgIface.Name()),
+		},
+		&expr.Counter{},
+		&expr.Masq{},
+	}
+
+	r.conn.AddRule(&nftables.Rule{
+		Table: r.workTable,
+		Chain: r.chains[chainNameRoutingNat],
+		Exprs: exprs2,
+	})
+
 	return nil
 }
 
@@ -723,18 +828,18 @@ func (r *router) removeAcceptForwardRulesIptables(ipt *iptables.IPTables) error
 	return nberrors.FormatErrorOrNil(merr)
 }
 
-// RemoveNatRule removes a nftables rule pair from nat chains
+// RemoveNatRule removes the prerouting mark rule
 func (r *router) RemoveNatRule(pair firewall.RouterPair) error {
 	if err := r.refreshRulesMap(); err != nil {
 		return fmt.Errorf(refreshRulesMapError, err)
 	}
 
 	if err := r.removeNatRule(pair); err != nil {
-		return fmt.Errorf("remove nat rule: %w", err)
+		return fmt.Errorf("remove prerouting rule: %w", err)
 	}
 
 	if err := r.removeNatRule(firewall.GetInversePair(pair)); err != nil {
-		return fmt.Errorf("remove inverse nat rule: %w", err)
+		return fmt.Errorf("remove inverse prerouting rule: %w", err)
 	}
 
 	if err := r.removeLegacyRouteRule(pair); err != nil {
@@ -749,21 +854,20 @@ func (r *router) RemoveNatRule(pair firewall.RouterPair) error {
 	return nil
 }
 
-// removeNatRule adds a nftables rule to the removal queue and deletes it from the rules map
 func (r *router) removeNatRule(pair firewall.RouterPair) error {
-	ruleKey := firewall.GenKey(firewall.NatFormat, pair)
+	ruleKey := firewall.GenKey(firewall.PreroutingFormat, pair)
 
 	if rule, exists := r.rules[ruleKey]; exists {
 		err := r.conn.DelRule(rule)
 		if err != nil {
-			return fmt.Errorf("remove nat rule %s -> %s: %v", pair.Source, pair.Destination, err)
+			return fmt.Errorf("remove prerouting rule %s -> %s: %v", pair.Source, pair.Destination, err)
 		}
 
-		log.Debugf("nftables: removed nat rule %s -> %s", pair.Source, pair.Destination)
+		log.Debugf("nftables: removed prerouting rule %s -> %s", pair.Source, pair.Destination)
 
 		delete(r.rules, ruleKey)
 	} else {
-		log.Debugf("nftables: nat rule %s not found", ruleKey)
+		log.Debugf("nftables: prerouting rule %s not found", ruleKey)
 	}
 
 	return nil

client/firewall/nftables/router_linux_test.go

@@ -10,6 +10,7 @@ import (
 
 	"github.com/coreos/go-iptables/iptables"
 	"github.com/google/nftables"
+	"github.com/google/nftables/binaryutil"
 	"github.com/google/nftables/expr"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -32,100 +33,87 @@ func TestNftablesManager_AddNatRule(t *testing.T) {
 		t.Skip("nftables not supported on this OS")
 	}
 
-	table, err := createWorkTable()
-	require.NoError(t, err, "Failed to create work table")
-
-	defer deleteWorkTable()
-
 	for _, testCase := range test.InsertRuleTestCases {
 		t.Run(testCase.Name, func(t *testing.T) {
-			manager, err := newRouter(table, ifaceMock)
+			// need fw manager to init both acl mgr and router for all chains to be present
-			require.NoError(t, err, "failed to create router")
+			manager, err := Create(ifaceMock)
-			require.NoError(t, manager.init(table))
+			t.Cleanup(func() {
+				require.NoError(t, manager.Reset(nil))
+			})
+			require.NoError(t, err)
+			require.NoError(t, manager.Init(nil))
 
 			nftablesTestingClient := &nftables.Conn{}
 
-			defer func(manager *router) {
+			rtr := manager.router
-				require.NoError(t, manager.Reset(), "failed to reset rules")
+			err = rtr.AddNatRule(testCase.InputPair)
-			}(manager)
-
-			require.NoError(t, err, "shouldn't return error")
-
-			err = manager.AddNatRule(testCase.InputPair)
 			require.NoError(t, err, "pair should be inserted")
 
-			defer func(manager *router, pair firewall.RouterPair) {
+			t.Cleanup(func() {
-				require.NoError(t, manager.RemoveNatRule(pair), "failed to remove rule")
+				require.NoError(t, rtr.RemoveNatRule(testCase.InputPair), "failed to remove rule")
-			}(manager, testCase.InputPair)
+			})
 
 			if testCase.InputPair.Masquerade {
-				sourceExp := generateCIDRMatcherExpressions(true, testCase.InputPair.Source)
+				// Build expected expressions for connection tracking
-				destExp := generateCIDRMatcherExpressions(false, testCase.InputPair.Destination)
+				conntrackExprs := []expr.Any{
-				testingExpression := append(sourceExp, destExp...) //nolint:gocritic
+					&expr.Ct{
-				testingExpression = append(testingExpression,
+						Key:      expr.CtKeySTATE,
-					&expr.Meta{Key: expr.MetaKeyIIFNAME, Register: 1},
+						Register: 1,
+					},
+					&expr.Bitwise{
+						SourceRegister: 1,
+						DestRegister:   1,
+						Len:            4,
+						Mask:           binaryutil.NativeEndian.PutUint32(expr.CtStateBitNEW),
+						Xor:            binaryutil.NativeEndian.PutUint32(0),
+					},
+					&expr.Cmp{
+						Op:       expr.CmpOpNeq,
+						Register: 1,
+						Data:     []byte{0, 0, 0, 0},
+					},
+				}
+
+				// Build interface matching expression
+				ifaceExprs := []expr.Any{
+					&expr.Meta{
+						Key:      expr.MetaKeyIIFNAME,
+						Register: 1,
+					},
 					&expr.Cmp{
 						Op:       expr.CmpOpEq,
 						Register: 1,
 						Data:     ifname(ifaceMock.Name()),
 					},
-					&expr.Meta{Key: expr.MetaKeyOIFNAME, Register: 1},
-					&expr.Cmp{
-						Op:       expr.CmpOpNeq,
-						Register: 1,
-						Data:     ifname("lo"),
-					},
-				)
-
-				natRuleKey := firewall.GenKey(firewall.NatFormat, testCase.InputPair)
-				found := 0
-				for _, chain := range manager.chains {
-					rules, err := nftablesTestingClient.GetRules(chain.Table, chain)
-					require.NoError(t, err, "should list rules for %s table and %s chain", chain.Table.Name, chain.Name)
-					for _, rule := range rules {
-						if len(rule.UserData) > 0 && string(rule.UserData) == natRuleKey {
-							require.ElementsMatchf(t, rule.Exprs[:len(testingExpression)], testingExpression, "nat rule elements should match")
-							found = 1
-						}
-					}
 				}
-				require.Equal(t, 1, found, "should find at least 1 rule to test")
-			}
 
-			if testCase.InputPair.Masquerade {
+				// Build CIDR matching expressions
 				sourceExp := generateCIDRMatcherExpressions(true, testCase.InputPair.Source)
 				destExp := generateCIDRMatcherExpressions(false, testCase.InputPair.Destination)
-				testingExpression := append(sourceExp, destExp...) //nolint:gocritic
-				testingExpression = append(testingExpression,
-					&expr.Meta{Key: expr.MetaKeyOIFNAME, Register: 1},
-					&expr.Cmp{
-						Op:       expr.CmpOpEq,
-						Register: 1,
-						Data:     ifname(ifaceMock.Name()),
-					},
-					&expr.Meta{Key: expr.MetaKeyIIFNAME, Register: 1},
-					&expr.Cmp{
-						Op:       expr.CmpOpNeq,
-						Register: 1,
-						Data:     ifname("lo"),
-					},
-				)
 
-				inNatRuleKey := firewall.GenKey(firewall.NatFormat, firewall.GetInversePair(testCase.InputPair))
+				// Combine all expressions in the correct order
+				// nolint:gocritic
+				testingExpression := append(conntrackExprs, ifaceExprs...)
+				testingExpression = append(testingExpression, sourceExp...)
+				testingExpression = append(testingExpression, destExp...)
+
+				natRuleKey := firewall.GenKey(firewall.PreroutingFormat, testCase.InputPair)
 				found := 0
-				for _, chain := range manager.chains {
+				for _, chain := range rtr.chains {
-					rules, err := nftablesTestingClient.GetRules(chain.Table, chain)
+					if chain.Name == chainNamePrerouting {
-					require.NoError(t, err, "should list rules for %s table and %s chain", chain.Table.Name, chain.Name)
+						rules, err := nftablesTestingClient.GetRules(chain.Table, chain)
-					for _, rule := range rules {
+						require.NoError(t, err, "should list rules for %s table and %s chain", chain.Table.Name, chain.Name)
-						if len(rule.UserData) > 0 && string(rule.UserData) == inNatRuleKey {
+						for _, rule := range rules {
-							require.ElementsMatchf(t, rule.Exprs[:len(testingExpression)], testingExpression, "income nat rule elements should match")
+							if len(rule.UserData) > 0 && string(rule.UserData) == natRuleKey {
-							found = 1
+								// Compare expressions up to the mark setting expressions
+								require.ElementsMatchf(t, rule.Exprs[:len(testingExpression)], testingExpression, "prerouting nat rule elements should match")
+								found = 1
+							}
 						}
 					}
 				}
-				require.Equal(t, 1, found, "should find at least 1 rule to test")
+				require.Equal(t, 1, found, "should find at least 1 rule in prerouting chain")
 			}
-
 		})
 	}
 }
@@ -135,68 +123,66 @@ func TestNftablesManager_RemoveNatRule(t *testing.T) {
 		t.Skip("nftables not supported on this OS")
 	}
 
-	table, err := createWorkTable()
-	require.NoError(t, err, "Failed to create work table")
-
-	defer deleteWorkTable()
-
 	for _, testCase := range test.RemoveRuleTestCases {
 		t.Run(testCase.Name, func(t *testing.T) {
-			manager, err := newRouter(table, ifaceMock)
+			manager, err := Create(ifaceMock)
-			require.NoError(t, err, "failed to create router")
+			t.Cleanup(func() {
-			require.NoError(t, manager.init(table))
+				require.NoError(t, manager.Reset(nil))
-
-			nftablesTestingClient := &nftables.Conn{}
-
-			defer func(manager *router) {
-				require.NoError(t, manager.Reset(), "failed to reset rules")
-			}(manager)
-
-			sourceExp := generateCIDRMatcherExpressions(true, testCase.InputPair.Source)
-			destExp := generateCIDRMatcherExpressions(false, testCase.InputPair.Destination)
-
-			natExp := append(sourceExp, append(destExp, &expr.Counter{}, &expr.Masq{})...) //nolint:gocritic
-			natRuleKey := firewall.GenKey(firewall.NatFormat, testCase.InputPair)
-
-			insertedNat := nftablesTestingClient.InsertRule(&nftables.Rule{
-				Table:    manager.workTable,
-				Chain:    manager.chains[chainNameRoutingNat],
-				Exprs:    natExp,
-				UserData: []byte(natRuleKey),
 			})
+			require.NoError(t, err)
+			require.NoError(t, manager.Init(nil))
 
-			sourceExp = generateCIDRMatcherExpressions(true, firewall.GetInversePair(testCase.InputPair).Source)
+			rtr := manager.router
-			destExp = generateCIDRMatcherExpressions(false, firewall.GetInversePair(testCase.InputPair).Destination)
 
-			natExp = append(sourceExp, append(destExp, &expr.Counter{}, &expr.Masq{})...) //nolint:gocritic
+			// First add the NAT rule using the router's method
-			inNatRuleKey := firewall.GenKey(firewall.NatFormat, firewall.GetInversePair(testCase.InputPair))
+			err = rtr.AddNatRule(testCase.InputPair)
+			require.NoError(t, err, "should add NAT rule")
 
-			insertedInNat := nftablesTestingClient.InsertRule(&nftables.Rule{
+			// Verify the rule was added
-				Table:    manager.workTable,
+			natRuleKey := firewall.GenKey(firewall.PreroutingFormat, testCase.InputPair)
-				Chain:    manager.chains[chainNameRoutingNat],
+			found := false
-				Exprs:    natExp,
+			rules, err := rtr.conn.GetRules(rtr.workTable, rtr.chains[chainNamePrerouting])
-				UserData: []byte(inNatRuleKey),
+			require.NoError(t, err, "should list rules")
-			})
+			for _, rule := range rules {
-
+				if len(rule.UserData) > 0 && string(rule.UserData) == natRuleKey {
-			err = nftablesTestingClient.Flush()
+					found = true
-			require.NoError(t, err, "shouldn't return error")
+					break
-
-			err = manager.Reset()
-			require.NoError(t, err, "shouldn't return error")
-
-			err = manager.RemoveNatRule(testCase.InputPair)
-			require.NoError(t, err, "shouldn't return error")
-
-			for _, chain := range manager.chains {
-				rules, err := nftablesTestingClient.GetRules(chain.Table, chain)
-				require.NoError(t, err, "should list rules for %s table and %s chain", chain.Table.Name, chain.Name)
-				for _, rule := range rules {
-					if len(rule.UserData) > 0 {
-						require.NotEqual(t, insertedNat.UserData, rule.UserData, "nat rule should not exist")
-						require.NotEqual(t, insertedInNat.UserData, rule.UserData, "income nat rule should not exist")
-					}
 				}
 			}
+			require.True(t, found, "NAT rule should exist before removal")
+
+			// Now remove the rule
+			err = rtr.RemoveNatRule(testCase.InputPair)
+			require.NoError(t, err, "shouldn't return error when removing rule")
+
+			// Verify the rule was removed
+			found = false
+			rules, err = rtr.conn.GetRules(rtr.workTable, rtr.chains[chainNamePrerouting])
+			require.NoError(t, err, "should list rules after removal")
+			for _, rule := range rules {
+				if len(rule.UserData) > 0 && string(rule.UserData) == natRuleKey {
+					found = true
+					break
+				}
+			}
+			require.False(t, found, "NAT rule should not exist after removal")
+
+			// Verify the static postrouting rules still exist
+			rules, err = rtr.conn.GetRules(rtr.workTable, rtr.chains[chainNameRoutingNat])
+			require.NoError(t, err, "should list postrouting rules")
+			foundCounter := false
+			for _, rule := range rules {
+				for _, e := range rule.Exprs {
+					if _, ok := e.(*expr.Counter); ok {
+						foundCounter = true
+						break
+					}
+				}
+				if foundCounter {
+					break
+				}
+			}
+			require.True(t, foundCounter, "static postrouting rule should remain")
 		})
 	}
 }

util/net/net.go

@@ -11,8 +11,11 @@ import (
 
 const (
 	// NetbirdFwmark is the fwmark value used by Netbird via wireguard
-	NetbirdFwmark    = 0x1BD00
+	NetbirdFwmark = 0x1BD00
-	PreroutingFwmark = 0x1BD01
+
+	PreroutingFwmarkRedirected       = 0x1BD01
+	PreroutingFwmarkMasquerade       = 0x1BD11
+	PreroutingFwmarkMasqueradeReturn = 0x1BD12
 
 	envDisableCustomRouting = "NB_DISABLE_CUSTOM_ROUTING"
 )