fix(firewall): log warning if ipv6 nat filter not supported instead of returning an error

- Allow to port forward redirect for IPv4 and not IPv6 if IPv6 NAT is not supported
- Fix #2503

internal/firewall/interfaces.go

@@ -9,5 +9,6 @@ type CmdRunner interface {
 type Logger interface {
 	Debug(s string)
 	Info(s string)
+	Warn(s string)
 	Error(s string)
 }

internal/firewall/iptables.go

@@ -239,6 +239,13 @@ func (c *Config) redirectPort(ctx context.Context, intf string,
 			appendOrDelete(remove), interfaceFlag, destinationPort),
 	})
 	if err != nil {
+		errMessage := err.Error()
+		if strings.Contains(errMessage, "can't initialize ip6tables table `nat': Table does not exist") {
+			if !remove {
+				c.logger.Warn("IPv6 port redirection disabled because your kernel does not support IPv6 NAT: " + errMessage)
+			}
+			return nil
+		}
 		return fmt.Errorf("redirecting IPv6 source port %d to destination port %d on interface %s: %w",
 			sourcePort, destinationPort, intf, err)
 	}

internal/firewall/mocks_test.go

@@ -107,3 +107,15 @@ func (mr *MockLoggerMockRecorder) Info(arg0 interface{}) *gomock.Call {
 	mr.mock.ctrl.T.Helper()
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Info", reflect.TypeOf((*MockLogger)(nil).Info), arg0)
 }
+
+// Warn mocks base method.
+func (m *MockLogger) Warn(arg0 string) {
+	m.ctrl.T.Helper()
+	m.ctrl.Call(m, "Warn", arg0)
+}
+
+// Warn indicates an expected call of Warn.
+func (mr *MockLoggerMockRecorder) Warn(arg0 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Warn", reflect.TypeOf((*MockLogger)(nil).Warn), arg0)
+}