Add iptablesProto helper, filter table fallback, DNAT compat tests

client/firewall/nftables/manager_linux.go

@@ -332,7 +332,13 @@ func (m *Manager) RemoveNatRule(pair firewall.RouterPair) error {
 	return nil
 }
 
-// AllowNetbird allows netbird interface traffic
+// AllowNetbird allows netbird interface traffic.
+// TODO: In USP mode this only adds ACCEPT to the netbird table's own chains,
+// which doesn't override DROP rules in external tables (e.g. firewalld).
+// Should add passthrough rules to external chains (like the native mode router's
+// addExternalChainsRules does) for both the netbird table family and inet tables.
+// The netbird table itself is fine (routing chains already exist there), but
+// non-netbird tables with INPUT/FORWARD hooks can still DROP our WG traffic.
 func (m *Manager) AllowNetbird() error {
 	if !m.wgIface.IsUserspaceBind() {
 		return nil

client/firewall/nftables/manager_linux_test.go

@@ -385,6 +385,18 @@ func TestNftablesManagerCompatibilityWithIptables(t *testing.T) {
 	err = manager.AddNatRule(pair)
 	require.NoError(t, err, "failed to add NAT rule")
 
+	dnatRule, err := manager.AddDNATRule(fw.ForwardRule{
+		Protocol:          fw.ProtocolTCP,
+		DestinationPort:   fw.Port{Values: []uint16{8080}},
+		TranslatedAddress: netip.MustParseAddr("100.96.0.2"),
+		TranslatedPort:    fw.Port{Values: []uint16{80}},
+	})
+	require.NoError(t, err, "failed to add DNAT rule")
+
+	t.Cleanup(func() {
+		require.NoError(t, manager.DeleteDNATRule(dnatRule), "failed to delete DNAT rule")
+	})
+
 	stdout, stderr = runIptablesSave(t)
 	verifyIptablesOutput(t, stdout, stderr)
 }
@@ -446,7 +458,22 @@ func TestNftablesManagerIPv6CompatibilityWithIp6tables(t *testing.T) {
 	})
 	require.NoError(t, err, "add v6 NAT rule")
 
-	stdout, stderr := runIp6tablesSave(t)
+	dnatRule, err := manager.AddDNATRule(fw.ForwardRule{
+		Protocol:          fw.ProtocolTCP,
+		DestinationPort:   fw.Port{Values: []uint16{8080}},
+		TranslatedAddress: netip.MustParseAddr("fd00::2"),
+		TranslatedPort:    fw.Port{Values: []uint16{80}},
+	})
+	require.NoError(t, err, "add v6 DNAT rule")
+
+	t.Cleanup(func() {
+		require.NoError(t, manager.DeleteDNATRule(dnatRule), "delete v6 DNAT rule")
+	})
+
+	stdout, stderr := runIptablesSave(t)
+	verifyIptablesOutput(t, stdout, stderr)
+
+	stdout, stderr = runIp6tablesSave(t)
 	verifyIp6tablesOutput(t, stdout, stderr)
 }
 

client/firewall/nftables/router_linux.go

@@ -474,6 +474,13 @@ func (r *router) getIpSet(set firewall.Set, prefixes []netip.Prefix, isSource bo
 	return r.getIpSetExprs(ref, isSource)
 }
 
+func (r *router) iptablesProto() iptables.Protocol {
+	if r.af.tableFamily == nftables.TableFamilyIPv6 {
+		return iptables.ProtocolIPv6
+	}
+	return iptables.ProtocolIPv4
+}
+
 func (r *router) hasRule(id string) bool {
 	_, ok := r.rules[id]
 	return ok
@@ -1063,17 +1070,22 @@ func (r *router) acceptFilterTableRules() error {
 		log.Debugf("Used %s to add accept forward and input rules", fw)
 	}()
 
-	// Try iptables first and fallback to nftables if iptables is not available
-	ipt, err := iptables.New()
+	// Try iptables first and fallback to nftables if iptables is not available.
+	// Use the correct protocol (iptables vs ip6tables) for the address family.
+	ipt, err := iptables.NewWithProtocol(r.iptablesProto())
 	if err != nil {
-		// iptables is not available but the filter table exists
 		log.Warnf("Will use nftables to manipulate the filter table because iptables is not available: %v", err)
 
 		fw = "nftables"
 		return r.acceptFilterRulesNftables(r.filterTable)
 	}
 
-	return r.acceptFilterRulesIptables(ipt)
+	if err := r.acceptFilterRulesIptables(ipt); err != nil {
+		log.Warnf("iptables failed (table may be incompatible), falling back to nftables: %v", err)
+		fw = "nftables"
+		return r.acceptFilterRulesNftables(r.filterTable)
+	}
+	return nil
 }
 
 func (r *router) acceptFilterRulesIptables(ipt *iptables.IPTables) error {
@@ -1242,13 +1254,17 @@ func (r *router) removeFilterTableRules() error {
 		return nil
 	}
 
-	ipt, err := iptables.New()
+	ipt, err := iptables.NewWithProtocol(r.iptablesProto())
 	if err != nil {
 		log.Debugf("iptables not available, using nftables to remove filter rules: %v", err)
 		return r.removeAcceptRulesFromTable(r.filterTable)
 	}
 
-	return r.removeAcceptFilterRulesIptables(ipt)
+	if err := r.removeAcceptFilterRulesIptables(ipt); err != nil {
+		log.Debugf("iptables removal failed (table may be incompatible), falling back to nftables: %v", err)
+		return r.removeAcceptRulesFromTable(r.filterTable)
+	}
+	return nil
 }
 
 func (r *router) removeAcceptRulesFromTable(table *nftables.Table) error {