TUN-6744: On posix platforms, assign unique echo ID per (src, dst, echo ID)

This also refactor FunnelTracker to provide a GetOrRegister method to prevent race condition

ingress/icmp_darwin.go

@@ -37,9 +37,9 @@ type icmpProxy struct {
 // then from the beginning to lastAssignment.
 // ICMP echo are short lived. By the time an ID is revisited, it should have been released.
 type echoIDTracker struct {
-	lock sync.RWMutex
+	lock sync.Mutex
-	// maps the source IP to an echo ID obtained from assignment
+	// maps the source IP, destination IP and original echo ID to a unique echo ID obtained from assignment
-	srcIPMapping map[netip.Addr]uint16
+	mapping map[flow3Tuple]uint16
 	// assignment tracks if an ID is assigned using index as the ID
 	// The size of the array is math.MaxUint16 because echo ID is 2 bytes
 	assignment [math.MaxUint16]bool
@@ -49,20 +49,18 @@ type echoIDTracker struct {
 
 func newEchoIDTracker() *echoIDTracker {
 	return &echoIDTracker{
-		srcIPMapping: make(map[netip.Addr]uint16),
+		mapping: make(map[flow3Tuple]uint16),
 	}
 }
 
-func (eit *echoIDTracker) get(srcIP netip.Addr) (uint16, bool) {
+// Get assignment or assign a new ID.
-	eit.lock.RLock()
+func (eit *echoIDTracker) getOrAssign(key flow3Tuple) (id uint16, success bool) {
-	defer eit.lock.RUnlock()
-	id, ok := eit.srcIPMapping[srcIP]
-	return id, ok
-}
-
-func (eit *echoIDTracker) assign(srcIP netip.Addr) (uint16, bool) {
 	eit.lock.Lock()
 	defer eit.lock.Unlock()
+	id, exists := eit.mapping[key]
+	if exists {
+		return id, true
+	}
 
 	if eit.nextAssignment == math.MaxUint16 {
 		eit.nextAssignment = 0
@@ -71,14 +69,14 @@ func (eit *echoIDTracker) assign(srcIP netip.Addr) (uint16, bool) {
 	for i, assigned := range eit.assignment[eit.nextAssignment:] {
 		if !assigned {
 			echoID := uint16(i) + eit.nextAssignment
-			eit.set(srcIP, echoID)
+			eit.set(key, echoID)
 			return echoID, true
 		}
 	}
 	for i, assigned := range eit.assignment[0:eit.nextAssignment] {
 		if !assigned {
 			echoID := uint16(i)
-			eit.set(srcIP, echoID)
+			eit.set(key, echoID)
 			return echoID, true
 		}
 	}
@@ -86,20 +84,20 @@ func (eit *echoIDTracker) assign(srcIP netip.Addr) (uint16, bool) {
 }
 
 // Caller should hold the lock
-func (eit *echoIDTracker) set(srcIP netip.Addr, echoID uint16) {
+func (eit *echoIDTracker) set(key flow3Tuple, assignedEchoID uint16) {
-	eit.assignment[echoID] = true
+	eit.assignment[assignedEchoID] = true
-	eit.srcIPMapping[srcIP] = echoID
+	eit.mapping[key] = assignedEchoID
-	eit.nextAssignment = echoID + 1
+	eit.nextAssignment = assignedEchoID + 1
 }
 
-func (eit *echoIDTracker) release(srcIP netip.Addr, id uint16) bool {
+func (eit *echoIDTracker) release(key flow3Tuple, assigned uint16) bool {
 	eit.lock.Lock()
 	defer eit.lock.Unlock()
 
-	currentID, exists := eit.srcIPMapping[srcIP]
+	currentEchoID, exists := eit.mapping[key]
-	if exists && id == currentID {
+	if exists && assigned == currentEchoID {
-		delete(eit.srcIPMapping, srcIP)
+		delete(eit.mapping, key)
-		eit.assignment[id] = false
+		eit.assignment[assigned] = false
 		return true
 	}
 	return false
@@ -134,33 +132,46 @@ func (ip *icmpProxy) Request(pk *packet.ICMP, responder packet.FunnelUniPipe) er
 	if pk == nil {
 		return errPacketNil
 	}
+	originalEcho, err := getICMPEcho(pk.Message)
+	if err != nil {
+		return err
+	}
+	echoIDTrackerKey := flow3Tuple{
+		srcIP:          pk.Src,
+		dstIP:          pk.Dst,
+		originalEchoID: originalEcho.ID,
+	}
 	// TODO: TUN-6744 assign unique flow per (src, echo ID)
-	echoID, exists := ip.echoIDTracker.get(pk.Src)
+	assignedEchoID, success := ip.echoIDTracker.getOrAssign(echoIDTrackerKey)
-	if !exists {
+	if !success {
+		return fmt.Errorf("failed to assign unique echo ID")
+	}
+	newFunnelFunc := func() (packet.Funnel, error) {
 		originalEcho, err := getICMPEcho(pk.Message)
 		if err != nil {
-			return err
+			return nil, err
 		}
-		echoID, exists = ip.echoIDTracker.assign(pk.Src)
-		if !exists {
-			return fmt.Errorf("failed to assign unique echo ID")
-		}
-		funnelID := echoFunnelID(echoID)
 		originSender := originSender{
-			conn:          ip.conn,
+			conn:             ip.conn,
-			echoIDTracker: ip.echoIDTracker,
+			echoIDTracker:    ip.echoIDTracker,
-			srcIP:         pk.Src,
+			echoIDTrackerKey: echoIDTrackerKey,
-			echoID:        echoID,
+			assignedEchoID:   assignedEchoID,
 		}
-		icmpFlow := newICMPEchoFlow(pk.Src, &originSender, responder, int(echoID), originalEcho.ID, ip.encoder)
+		icmpFlow := newICMPEchoFlow(pk.Src, &originSender, responder, int(assignedEchoID), originalEcho.ID, ip.encoder)
-		if replaced := ip.srcFunnelTracker.Register(funnelID, icmpFlow); replaced {
+		return icmpFlow, nil
-			ip.logger.Info().Str("src", pk.Src.String()).Msg("Replaced funnel")
-		}
-		return icmpFlow.sendToDst(pk.Dst, pk.Message)
 	}
-	funnel, exists := ip.srcFunnelTracker.Get(echoFunnelID(echoID))
+	funnelID := echoFunnelID(assignedEchoID)
-	if !exists {
+	funnel, isNew, err := ip.srcFunnelTracker.GetOrRegister(funnelID, newFunnelFunc)
-		return packet.ErrFunnelNotFound
+	if err != nil {
+		return err
+	}
+	if isNew {
+		ip.logger.Debug().
+			Str("src", pk.Src.String()).
+			Str("dst", pk.Dst.String()).
+			Int("originalEchoID", originalEcho.ID).
+			Int("assignedEchoID", int(assignedEchoID)).
+			Msg("New flow")
 	}
 	icmpFlow, err := toICMPEchoFlow(funnel)
 	if err != nil {
@@ -199,7 +210,7 @@ func (ip *icmpProxy) Serve(ctx context.Context) error {
 			ip.logger.Debug().Str("dst", from.String()).Msgf("Drop ICMP %s from reply", reply.msg.Type)
 			continue
 		}
-		if ip.sendReply(reply); err != nil {
+		if err := ip.sendReply(reply); err != nil {
 			ip.logger.Error().Err(err).Str("dst", from.String()).Msg("Failed to send ICMP reply")
 			continue
 		}
@@ -227,7 +238,8 @@ func (ip *icmpProxy) handleFullPacket(decoder *packet.ICMPDecoder, rawPacket []b
 }
 
 func (ip *icmpProxy) sendReply(reply *echoReply) error {
-	funnel, ok := ip.srcFunnelTracker.Get(echoFunnelID(reply.echo.ID))
+	funnelID := echoFunnelID(reply.echo.ID)
+	funnel, ok := ip.srcFunnelTracker.Get(funnelID)
 	if !ok {
 		return packet.ErrFunnelNotFound
 	}
@@ -240,10 +252,10 @@ func (ip *icmpProxy) sendReply(reply *echoReply) error {
 
 // originSender wraps icmp.PacketConn to implement packet.FunnelUniPipe interface
 type originSender struct {
-	conn          *icmp.PacketConn
+	conn             *icmp.PacketConn
-	echoIDTracker *echoIDTracker
+	echoIDTracker    *echoIDTracker
-	srcIP         netip.Addr
+	echoIDTrackerKey flow3Tuple
-	echoID        uint16
+	assignedEchoID   uint16
 }
 
 func (os *originSender) SendPacket(dst netip.Addr, pk packet.RawPacket) error {
@@ -254,6 +266,6 @@ func (os *originSender) SendPacket(dst netip.Addr, pk packet.RawPacket) error {
 }
 
 func (os *originSender) Close() error {
-	os.echoIDTracker.release(os.srcIP, os.echoID)
+	os.echoIDTracker.release(os.echoIDTrackerKey, os.assignedEchoID)
 	return nil
 }

ingress/icmp_darwin_test.go

@@ -12,80 +12,110 @@ import (
 
 func TestSingleEchoIDTracker(t *testing.T) {
 	tracker := newEchoIDTracker()
-	srcIP := netip.MustParseAddr("127.0.0.1")
+	key := flow3Tuple{
-	echoID, ok := tracker.get(srcIP)
+		srcIP:          netip.MustParseAddr("172.16.0.1"),
-	require.False(t, ok)
+		dstIP:          netip.MustParseAddr("172.16.0.2"),
-	require.Equal(t, uint16(0), echoID)
+		originalEchoID: 5182,
+	}
 
 	// not assigned yet, so nothing to release
-	require.False(t, tracker.release(srcIP, echoID))
+	require.False(t, tracker.release(key, 0))
 
-	echoID, ok = tracker.assign(srcIP)
+	echoID, ok := tracker.getOrAssign(key)
 	require.True(t, ok)
 	require.Equal(t, uint16(0), echoID)
 
-	echoID, ok = tracker.get(srcIP)
+	//  Second time should return the same echo ID
+	echoID, ok = tracker.getOrAssign(key)
 	require.True(t, ok)
 	require.Equal(t, uint16(0), echoID)
 
 	// releasing a different ID returns false
-	require.False(t, tracker.release(srcIP, 1999))
+	require.False(t, tracker.release(key, 1999))
-	require.True(t, tracker.release(srcIP, echoID))
+	require.True(t, tracker.release(key, echoID))
 	// releasing the second time returns false
-	require.False(t, tracker.release(srcIP, echoID))
+	require.False(t, tracker.release(key, echoID))
-
-	echoID, ok = tracker.get(srcIP)
-	require.False(t, ok)
-	require.Equal(t, uint16(0), echoID)
 
 	// Move to the next IP
-	echoID, ok = tracker.assign(srcIP)
+	echoID, ok = tracker.getOrAssign(key)
 	require.True(t, ok)
 	require.Equal(t, uint16(1), echoID)
 }
 
 func TestFullEchoIDTracker(t *testing.T) {
+	var (
+		dstIP          = netip.MustParseAddr("192.168.0.1")
+		originalEchoID = 41820
+	)
 	tracker := newEchoIDTracker()
-	firstIP := netip.MustParseAddr("172.16.0.1")
+	firstSrcIP := netip.MustParseAddr("172.16.0.1")
-	srcIP := firstIP
+	srcIP := firstSrcIP
 
 	for i := uint16(0); i < math.MaxUint16; i++ {
-		echoID, ok := tracker.assign(srcIP)
+		key := flow3Tuple{
+			srcIP:          srcIP,
+			dstIP:          dstIP,
+			originalEchoID: originalEchoID,
+		}
+		echoID, ok := tracker.getOrAssign(key)
 		require.True(t, ok)
 		require.Equal(t, i, echoID)
 
-		echoID, ok = tracker.get(srcIP)
+		echoID, ok = tracker.get(key)
 		require.True(t, ok)
 		require.Equal(t, i, echoID)
+
 		srcIP = srcIP.Next()
 	}
 
+	key := flow3Tuple{
+		srcIP:          srcIP.Next(),
+		dstIP:          dstIP,
+		originalEchoID: originalEchoID,
+	}
 	// All echo IDs are assigned
-	echoID, ok := tracker.assign(srcIP.Next())
+	echoID, ok := tracker.getOrAssign(key)
 	require.False(t, ok)
 	require.Equal(t, uint16(0), echoID)
 
-	srcIP = firstIP
+	srcIP = firstSrcIP
 	for i := uint16(0); i < math.MaxUint16; i++ {
-		ok := tracker.release(srcIP, i)
+		key := flow3Tuple{
+			srcIP:          srcIP,
+			dstIP:          dstIP,
+			originalEchoID: originalEchoID,
+		}
+		ok := tracker.release(key, i)
 		require.True(t, ok)
 
-		echoID, ok = tracker.get(srcIP)
+		echoID, ok = tracker.get(key)
 		require.False(t, ok)
 		require.Equal(t, uint16(0), echoID)
 		srcIP = srcIP.Next()
 	}
 
 	// The IDs are assignable again
-	srcIP = firstIP
+	srcIP = firstSrcIP
 	for i := uint16(0); i < math.MaxUint16; i++ {
-		echoID, ok := tracker.assign(srcIP)
+		key := flow3Tuple{
+			srcIP:          srcIP,
+			dstIP:          dstIP,
+			originalEchoID: originalEchoID,
+		}
+		echoID, ok := tracker.getOrAssign(key)
 		require.True(t, ok)
 		require.Equal(t, i, echoID)
 
-		echoID, ok = tracker.get(srcIP)
+		echoID, ok = tracker.get(key)
 		require.True(t, ok)
 		require.Equal(t, i, echoID)
 		srcIP = srcIP.Next()
 	}
 }
+
+func (eit *echoIDTracker) get(key flow3Tuple) (id uint16, exist bool) {
+	eit.lock.Lock()
+	defer eit.lock.Unlock()
+	id, exists := eit.mapping[key]
+	return id, exists
+}

ingress/icmp_linux.go

@@ -57,45 +57,57 @@ func (ip *icmpProxy) Request(pk *packet.ICMP, responder packet.FunnelUniPipe) er
 	if pk == nil {
 		return errPacketNil
 	}
-	funnelID := srcIPFunnelID(pk.Src)
+	originalEcho, err := getICMPEcho(pk.Message)
-	funnel, exists := ip.srcFunnelTracker.Get(funnelID)
+	if err != nil {
-	if !exists {
+		return err
-		originalEcho, err := getICMPEcho(pk.Message)
+	}
-		if err != nil {
+	newConnChan := make(chan *icmp.PacketConn, 1)
-			return err
+	newFunnelFunc := func() (packet.Funnel, error) {
-		}
 		conn, err := newICMPConn(ip.listenIP)
 		if err != nil {
-			return errors.Wrap(err, "failed to open ICMP socket")
+			return nil, errors.Wrap(err, "failed to open ICMP socket")
 		}
+		newConnChan <- conn
 		localUDPAddr, ok := conn.LocalAddr().(*net.UDPAddr)
 		if !ok {
-			return fmt.Errorf("ICMP listener address %s is not net.UDPAddr", conn.LocalAddr())
+			return nil, fmt.Errorf("ICMP listener address %s is not net.UDPAddr", conn.LocalAddr())
 		}
 		originSender := originSender{conn: conn}
 		echoID := localUDPAddr.Port
 		icmpFlow := newICMPEchoFlow(pk.Src, &originSender, responder, echoID, originalEcho.ID, packet.NewEncoder())
-		if replaced := ip.srcFunnelTracker.Register(funnelID, icmpFlow); replaced {
+		return icmpFlow, nil
-			ip.logger.Info().Str("src", pk.Src.String()).Msg("Replaced funnel")
+	}
-		}
+	funnelID := flow3Tuple{
-		if err := icmpFlow.sendToDst(pk.Dst, pk.Message); err != nil {
+		srcIP:          pk.Src,
-			return errors.Wrap(err, "failed to send ICMP echo request")
+		dstIP:          pk.Dst,
-		}
+		originalEchoID: originalEcho.ID,
-		go func() {
+	}
-			defer ip.srcFunnelTracker.Unregister(funnelID, icmpFlow)
+	funnel, isNew, err := ip.srcFunnelTracker.GetOrRegister(funnelID, newFunnelFunc)
-			if err := ip.listenResponse(icmpFlow, conn); err != nil {
+	if err != nil {
-				ip.logger.Err(err).
+		return err
-					Str("funnelID", funnelID.String()).
-					Int("echoID", echoID).
-					Msg("Failed to listen for ICMP echo response")
-			}
-		}()
-		return nil
 	}
 	icmpFlow, err := toICMPEchoFlow(funnel)
 	if err != nil {
 		return err
 	}
+	if isNew {
+		ip.logger.Debug().
+			Str("src", pk.Src.String()).
+			Str("dst", pk.Dst.String()).
+			Int("originalEchoID", originalEcho.ID).
+			Msg("New flow")
+		conn := <-newConnChan
+		go func() {
+			defer ip.srcFunnelTracker.Unregister(funnelID, icmpFlow)
+			if err := ip.listenResponse(icmpFlow, conn); err != nil {
+				ip.logger.Debug().Err(err).
+					Str("src", pk.Src.String()).
+					Str("dst", pk.Dst.String()).
+					Int("originalEchoID", originalEcho.ID).
+					Msg("Failed to listen for ICMP echo response")
+			}
+		}()
+	}
 	if err := icmpFlow.sendToDst(pk.Dst, pk.Message); err != nil {
 		return errors.Wrap(err, "failed to send ICMP echo request")
 	}
@@ -146,12 +158,11 @@ func (os *originSender) Close() error {
 	return os.conn.Close()
 }
 
-type srcIPFunnelID netip.Addr
+// Only linux uses flow3Tuple as FunnelID
-
+func (ft flow3Tuple) Type() string {
-func (sifd srcIPFunnelID) Type() string {
+	return "srcIP_dstIP_echoID"
-	return "srcIP"
 }
 
-func (sifd srcIPFunnelID) String() string {
+func (ft flow3Tuple) String() string {
-	return netip.Addr(sifd).String()
+	return fmt.Sprintf("%s:%s:%d", ft.srcIP, ft.dstIP, ft.originalEchoID)
 }

ingress/icmp_posix.go

@@ -32,17 +32,10 @@ func netipAddr(addr net.Addr) (netip.Addr, bool) {
 	return netip.AddrFromSlice(udpAddr.IP)
 }
 
-type flowID struct {
+type flow3Tuple struct {
-	srcIP  netip.Addr
+	srcIP          netip.Addr
-	echoID int
+	dstIP          netip.Addr
-}
+	originalEchoID int
-
-func (fi *flowID) Type() string {
-	return "srcIP_echoID"
-}
-
-func (fi *flowID) String() string {
-	return fmt.Sprintf("%s:%d", fi.srcIP, fi.echoID)
 }
 
 // icmpEchoFlow implements the packet.Funnel interface.

ingress/icmp_windows.go

@@ -315,23 +315,22 @@ func (ip *icmpProxy) handleEchoReply(request *packet.ICMP, echoReq *icmp.Echo, d
 		},
 	}
 
-	serializedPacket, err := ip.encodeICMPReply(&pk)
+	cachedEncoder := ip.encoderPool.Get()
+	// The encoded packet is a slice to of the encoder, so we shouldn't return the encoder back to the pool until
+	// the encoded packet is sent.
+	defer ip.encoderPool.Put(cachedEncoder)
+	encoder, ok := cachedEncoder.(*packet.Encoder)
+	if !ok {
+		return fmt.Errorf("encoderPool returned %T, expect *packet.Encoder", cachedEncoder)
+	}
+
+	serializedPacket, err := encoder.Encode(&pk)
 	if err != nil {
 		return err
 	}
 	return responder.SendPacket(request.Src, serializedPacket)
 }
 
-func (ip *icmpProxy) encodeICMPReply(pk *packet.ICMP) (packet.RawPacket, error) {
-	cachedEncoder := ip.encoderPool.Get()
-	defer ip.encoderPool.Put(cachedEncoder)
-	encoder, ok := cachedEncoder.(*packet.Encoder)
-	if !ok {
-		return packet.RawPacket{}, fmt.Errorf("encoderPool returned %T, expect *packet.Encoder", cachedEncoder)
-	}
-	return encoder.Encode(pk)
-}
-
 func (ip *icmpProxy) icmpEchoRoundtrip(dst netip.Addr, echo *icmp.Echo) ([]byte, error) {
 	if dst.Is6() {
 		if ip.srcSocketAddr == nil {

ingress/origin_icmp_proxy_test.go

@@ -6,6 +6,7 @@ import (
 	"net"
 	"net/netip"
 	"strings"
+	"sync"
 	"testing"
 
 	"github.com/google/gopacket/layers"
@@ -97,6 +98,91 @@ func testICMPRouterEcho(t *testing.T, sendIPv4 bool) {
 	<-proxyDone
 }
 
+// TestConcurrentRequests makes sure icmpRouter can send concurrent requests to the same destination with different
+// echo ID. This simulates concurrent ping to the same destination.
+func TestConcurrentRequestsToSameDst(t *testing.T) {
+	const (
+		concurrentPings = 5
+		endSeq          = 5
+	)
+
+	router, err := NewICMPRouter(&noopLogger)
+	require.NoError(t, err)
+
+	proxyDone := make(chan struct{})
+	ctx, cancel := context.WithCancel(context.Background())
+	go func() {
+		router.Serve(ctx)
+		close(proxyDone)
+	}()
+
+	var wg sync.WaitGroup
+	// icmpv4 and icmpv6 each has concurrentPings
+	wg.Add(concurrentPings * 2)
+	for i := 0; i < concurrentPings; i++ {
+		echoID := 38451 + i
+		go func() {
+			defer wg.Done()
+			responder := echoFlowResponder{
+				decoder:  packet.NewICMPDecoder(),
+				respChan: make(chan []byte, 1),
+			}
+			for seq := 0; seq < endSeq; seq++ {
+				pk := &packet.ICMP{
+					IP: &packet.IP{
+						Src:      localhostIP,
+						Dst:      localhostIP,
+						Protocol: layers.IPProtocolICMPv4,
+						TTL:      packet.DefaultTTL,
+					},
+					Message: &icmp.Message{
+						Type: ipv4.ICMPTypeEcho,
+						Code: 0,
+						Body: &icmp.Echo{
+							ID:   echoID,
+							Seq:  seq,
+							Data: []byte(fmt.Sprintf("icmpv4 echo id %d, seq %d", echoID, seq)),
+						},
+					},
+				}
+				require.NoError(t, router.Request(pk, &responder))
+				responder.validate(t, pk)
+			}
+		}()
+		go func() {
+			defer wg.Done()
+			responder := echoFlowResponder{
+				decoder:  packet.NewICMPDecoder(),
+				respChan: make(chan []byte, 1),
+			}
+			for seq := 0; seq < endSeq; seq++ {
+				pk := &packet.ICMP{
+					IP: &packet.IP{
+						Src:      localhostIPv6,
+						Dst:      localhostIPv6,
+						Protocol: layers.IPProtocolICMPv6,
+						TTL:      packet.DefaultTTL,
+					},
+					Message: &icmp.Message{
+						Type: ipv6.ICMPTypeEchoRequest,
+						Code: 0,
+						Body: &icmp.Echo{
+							ID:   echoID,
+							Seq:  seq,
+							Data: []byte(fmt.Sprintf("icmpv6 echo id %d, seq %d", echoID, seq)),
+						},
+					},
+				}
+				require.NoError(t, router.Request(pk, &responder))
+				responder.validate(t, pk)
+			}
+		}()
+	}
+	wg.Wait()
+	cancel()
+	<-proxyDone
+}
+
 // TestICMPProxyRejectNotEcho makes sure it rejects messages other than echo
 func TestICMPRouterRejectNotEcho(t *testing.T) {
 	msgs := []icmp.Message{

packet/funnel.go

@@ -158,20 +158,19 @@ func (ft *FunnelTracker) Get(id FunnelID) (Funnel, bool) {
 }
 
 // Registers a funnel. It replaces the current funnel.
-func (ft *FunnelTracker) Register(id FunnelID, funnel Funnel) (replaced bool) {
+func (ft *FunnelTracker) GetOrRegister(id FunnelID, newFunnelFunc func() (Funnel, error)) (funnel Funnel, new bool, err error) {
 	ft.lock.Lock()
 	defer ft.lock.Unlock()
 	currentFunnel, exists := ft.funnels[id]
-	if !exists {
+	if exists {
-		ft.funnels[id] = funnel
+		return currentFunnel, false, nil
-		return false
 	}
-	replaced = !currentFunnel.Equal(funnel)
+	newFunnel, err := newFunnelFunc()
-	if replaced {
+	if err != nil {
-		currentFunnel.Close()
+		return nil, false, err
 	}
-	ft.funnels[id] = funnel
+	ft.funnels[id] = newFunnel
-	return replaced
+	return newFunnel, true, nil
 }
 
 // Unregisters a funnel if the funnel equals to the current funnel