NAT ICMPv4 errors

...so a NAT-ed connection's socket can handle ICMP errors.

Updates #5916.

PiperOrigin-RevId: 405970089

3 files changed, 495 insertions, 68 deletions

diff --git a/pkg/tcpip/stack/conntrack.go b/pkg/tcpip/stack/conntrack.go
index a3f403855..4a28be585 100644
--- a/pkg/tcpip/stack/conntrack.go
+++ b/pkg/tcpip/stack/conntrack.go
@@ -209,19 +209,120 @@ type bucket struct {
 	tuples tupleList
 }
 
-func getTransportHeader(pkt *PacketBuffer) (header.ChecksummableTransport, bool) {
+func getHeaders(pkt *PacketBuffer) (netHdr header.Network, transHdr header.ChecksummableTransport, isICMPError bool, ok bool) {
 	switch pkt.TransportProtocolNumber {
 	case header.TCPProtocolNumber:
 		if tcpHeader := header.TCP(pkt.TransportHeader().View()); len(tcpHeader) >= header.TCPMinimumSize {
-			return tcpHeader, true
+			return pkt.Network(), tcpHeader, false, true
 		}
 	case header.UDPProtocolNumber:
 		if udpHeader := header.UDP(pkt.TransportHeader().View()); len(udpHeader) >= header.UDPMinimumSize {
-			return udpHeader, true
+			return pkt.Network(), udpHeader, false, true
+		}
+	case header.ICMPv4ProtocolNumber:
+		h, ok := pkt.Data().PullUp(header.IPv4MinimumSize)
+		if !ok {
+			panic(fmt.Sprintf("should have a valid IPv4 packet; only have %d bytes, want at least %d bytes", pkt.Data().Size(), header.IPv4MinimumSize))
+		}
+
+		ipv4 := header.IPv4(h)
+		if ipv4.HeaderLength() > header.IPv4MinimumSize {
+			// TODO(https://gvisor.dev/issue/6765): Handle IPv4 options.
+			panic("should have dropped packets with IPv4 options")
+		}
+
+		switch pkt.tuple.id().transProto {
+		case header.TCPProtocolNumber:
+			// TODO(https://gvisor.dev/issue/6765): Handle IPv4 options.
+			netAndTransHeader, ok := pkt.Data().PullUp(header.IPv4MinimumSize + header.TCPMinimumSize)
+			if !ok {
+				return nil, nil, false, false
+			}
+			netHeader := header.IPv4(netAndTransHeader)
+			return netHeader, header.TCP(netHeader.Payload()), true, true
+		case header.UDPProtocolNumber:
+			// TODO(https://gvisor.dev/issue/6765): Handle IPv4 options.
+			netAndTransHeader, ok := pkt.Data().PullUp(header.IPv4MinimumSize + header.UDPMinimumSize)
+			if !ok {
+				return nil, nil, false, false
+			}
+			netHeader := header.IPv4(netAndTransHeader)
+			return netHeader, header.UDP(netHeader.Payload()), true, true
 		}
 	}
 
-	return nil, false
+	return nil, nil, false, false
+}
+
+func getTupleIDForRegularPacket(netHdr header.Network, netProto tcpip.NetworkProtocolNumber, transHdr header.Transport, transProto tcpip.TransportProtocolNumber) tupleID {
+	return tupleID{
+		srcAddr:    netHdr.SourceAddress(),
+		srcPort:    transHdr.SourcePort(),
+		dstAddr:    netHdr.DestinationAddress(),
+		dstPort:    transHdr.DestinationPort(),
+		transProto: transProto,
+		netProto:   netProto,
+	}
+}
+
+func getTupleIDForPacketInICMPError(netHdr header.Network, netProto tcpip.NetworkProtocolNumber, transHdr header.Transport, transProto tcpip.TransportProtocolNumber) tupleID {
+	return tupleID{
+		srcAddr:    netHdr.DestinationAddress(),
+		srcPort:    transHdr.DestinationPort(),
+		dstAddr:    netHdr.SourceAddress(),
+		dstPort:    transHdr.SourcePort(),
+		transProto: transProto,
+		netProto:   netProto,
+	}
+}
+
+func getTupleID(pkt *PacketBuffer) (tid tupleID, isICMPError bool, ok bool) {
+	switch pkt.TransportProtocolNumber {
+	case header.TCPProtocolNumber:
+		if transHeader := header.TCP(pkt.TransportHeader().View()); len(transHeader) >= header.TCPMinimumSize {
+			return getTupleIDForRegularPacket(pkt.Network(), pkt.NetworkProtocolNumber, transHeader, pkt.TransportProtocolNumber), false, true
+		}
+	case header.UDPProtocolNumber:
+		if transHeader := header.UDP(pkt.TransportHeader().View()); len(transHeader) >= header.UDPMinimumSize {
+			return getTupleIDForRegularPacket(pkt.Network(), pkt.NetworkProtocolNumber, transHeader, pkt.TransportProtocolNumber), false, true
+		}
+	case header.ICMPv4ProtocolNumber:
+		icmp := header.ICMPv4(pkt.TransportHeader().View())
+		if len(icmp) < header.ICMPv4MinimumSize {
+			return tupleID{}, false, false
+		}
+
+		switch icmp.Type() {
+		case header.ICMPv4DstUnreachable, header.ICMPv4TimeExceeded, header.ICMPv4ParamProblem:
+		default:
+			return tupleID{}, false, false
+		}
+
+		h, ok := pkt.Data().PullUp(header.IPv4MinimumSize)
+		if !ok {
+			return tupleID{}, false, false
+		}
+
+		ipv4 := header.IPv4(h)
+		if ipv4.HeaderLength() > header.IPv4MinimumSize {
+			// TODO(https://gvisor.dev/issue/6765): Handle IPv4 options.
+			return tupleID{}, false, false
+		}
+		switch ipv4.TransportProtocol() {
+		case header.TCPProtocolNumber:
+			if netAndTransHeader, ok := pkt.Data().PullUp(header.IPv4MinimumSize + header.TCPMinimumSize); ok {
+				netHdr := header.IPv4(netAndTransHeader)
+				return getTupleIDForPacketInICMPError(netHdr, header.IPv4ProtocolNumber, header.TCP(netHdr.Payload()), header.TCPProtocolNumber), true, true
+			}
+		case header.UDPProtocolNumber:
+			if netAndTransHeader, ok := pkt.Data().PullUp(header.IPv4MinimumSize + header.UDPMinimumSize); ok {
+				netHdr := header.IPv4(netAndTransHeader)
+				return getTupleIDForPacketInICMPError(netHdr, header.IPv4ProtocolNumber, header.UDP(netHdr.Payload()), header.UDPProtocolNumber), true, true
+			}
+		}
+	}
+
+	return tupleID{}, false, false
 }
 
 func (ct *ConnTrack) init() {
@@ -231,21 +332,11 @@ func (ct *ConnTrack) init() {
 }
 
 func (ct *ConnTrack) getConnOrMaybeInsertNoop(pkt *PacketBuffer) *tuple {
-	netHeader := pkt.Network()
-	transportHeader, ok := getTransportHeader(pkt)
+	tid, isICMPError, ok := getTupleID(pkt)
 	if !ok {
 		return nil
 	}
 
-	tid := tupleID{
-		srcAddr:    netHeader.SourceAddress(),
-		srcPort:    transportHeader.SourcePort(),
-		dstAddr:    netHeader.DestinationAddress(),
-		dstPort:    transportHeader.DestinationPort(),
-		transProto: pkt.TransportProtocolNumber,
-		netProto:   pkt.NetworkProtocolNumber,
-	}
-
 	bktID := ct.bucket(tid)
 
 	ct.mu.RLock()
@@ -257,6 +348,11 @@ func (ct *ConnTrack) getConnOrMaybeInsertNoop(pkt *PacketBuffer) *tuple {
 		return t
 	}
 
+	if isICMPError {
+		// Do not create a noop entry in response to an ICMP error.
+		return nil
+	}
+
 	bkt.mu.Lock()
 	defer bkt.mu.Unlock()
 
@@ -407,7 +503,7 @@ func (cn *conn) performNATIfNoop(port uint16, address tcpip.Address, dnat bool)
 //
 // Returns true if the packet can skip the NAT table.
 func (cn *conn) handlePacket(pkt *PacketBuffer, hook Hook, rt *Route) bool {
-	transportHeader, ok := getTransportHeader(pkt)
+	netHdr, transHdr, isICMPError, ok := getHeaders(pkt)
 	if !ok {
 		return false
 	}
@@ -498,9 +594,9 @@ func (cn *conn) handlePacket(pkt *PacketBuffer, hook Hook, rt *Route) bool {
 	}
 
 	rewritePacket(
-		pkt.Network(),
-		transportHeader,
-		!dnat,
+		netHdr,
+		transHdr,
+		!dnat != isICMPError,
 		fullChecksum,
 		updatePseudoHeader,
 		newPort,
@@ -508,6 +604,28 @@ func (cn *conn) handlePacket(pkt *PacketBuffer, hook Hook, rt *Route) bool {
 	)
 
 	*natDone = true
+
+	if !isICMPError {
+		return true
+	}
+
+	// We performed NAT on (erroneous) packet that triggered an ICMP response, but
+	// not the ICMP packet itself.
+	switch pkt.TransportProtocolNumber {
+	case header.ICMPv4ProtocolNumber:
+		icmp := header.ICMPv4(pkt.TransportHeader().View())
+		// TODO(https://gvisor.dev/issue/6788): Incrementally update ICMP checksum.
+		icmp.SetChecksum(0)
+		icmp.SetChecksum(header.ICMPv4Checksum(icmp, pkt.Data().AsRange().Checksum()))
+
+		network := header.IPv4(pkt.NetworkHeader().View())
+		if dnat {
+			network.SetDestinationAddressWithChecksumUpdate(tid.srcAddr)
+		} else {
+			network.SetSourceAddressWithChecksumUpdate(tid.dstAddr)
+		}
+	}
+
 	return true
 }
 
diff --git a/pkg/tcpip/tests/integration/iptables_test.go b/pkg/tcpip/tests/integration/iptables_test.go
index 957a779bf..9e00a6350 100644
--- a/pkg/tcpip/tests/integration/iptables_test.go
+++ b/pkg/tcpip/tests/integration/iptables_test.go
@@ -1779,3 +1779,296 @@ func TestNAT(t *testing.T) {
 		})
 	}
 }
+
+func TestNATICMPError(t *testing.T) {
+	const srcPort = 1234
+	const dstPort = 5432
+
+	type icmpTypeTest struct {
+		name           string
+		val            uint8
+		expectResponse bool
+	}
+
+	type transportTypeTest struct {
+		name       string
+		proto      tcpip.TransportProtocolNumber
+		buf        buffer.View
+		checkNATed func(*testing.T, buffer.View)
+	}
+
+	ipHdr := func(v buffer.View, totalLen int, transProto tcpip.TransportProtocolNumber, srcAddr, dstAddr tcpip.Address) {
+		ip := header.IPv4(v)
+		ip.Encode(&header.IPv4Fields{
+			TotalLength: uint16(totalLen),
+			Protocol:    uint8(transProto),
+			TTL:         64,
+			SrcAddr:     srcAddr,
+			DstAddr:     dstAddr,
+		})
+		ip.SetChecksum(^ip.CalculateChecksum())
+	}
+
+	tests := []struct {
+		name            string
+		netProto        tcpip.NetworkProtocolNumber
+		host1Addr       tcpip.Address
+		icmpError       func(*testing.T, buffer.View, uint8) buffer.View
+		decrementTTL    func(buffer.View)
+		checkNATedError func(*testing.T, buffer.View, buffer.View, uint8)
+
+		transportTypes []transportTypeTest
+		icmpTypes      []icmpTypeTest
+	}{
+		{
+			name:      "IPv4",
+			netProto:  ipv4.ProtocolNumber,
+			host1Addr: utils.Host1IPv4Addr.AddressWithPrefix.Address,
+			icmpError: func(t *testing.T, original buffer.View, icmpType uint8) buffer.View {
+				totalLen := header.IPv4MinimumSize + header.ICMPv4MinimumSize + len(original)
+				hdr := buffer.NewPrependable(totalLen)
+				if n := copy(hdr.Prepend(len(original)), original); n != len(original) {
+					t.Fatalf("got copy(...) = %d, want = %d", n, len(original))
+				}
+				icmp := header.ICMPv4(hdr.Prepend(header.ICMPv4MinimumSize))
+				icmp.SetType(header.ICMPv4Type(icmpType))
+				icmp.SetChecksum(0)
+				icmp.SetChecksum(header.ICMPv4Checksum(icmp, 0))
+				ipHdr(hdr.Prepend(header.IPv4MinimumSize),
+					totalLen,
+					header.ICMPv4ProtocolNumber,
+					utils.Host1IPv4Addr.AddressWithPrefix.Address,
+					utils.RouterNIC1IPv4Addr.AddressWithPrefix.Address,
+				)
+				return hdr.View()
+			},
+			decrementTTL: func(v buffer.View) {
+				ip := header.IPv4(v)
+				ip.SetTTL(ip.TTL() - 1)
+				ip.SetChecksum(0)
+				ip.SetChecksum(^ip.CalculateChecksum())
+			},
+			checkNATedError: func(t *testing.T, v buffer.View, original buffer.View, icmpType uint8) {
+				checker.IPv4(t, v,
+					checker.SrcAddr(utils.RouterNIC2IPv4Addr.AddressWithPrefix.Address),
+					checker.DstAddr(utils.Host2IPv4Addr.AddressWithPrefix.Address),
+					checker.ICMPv4(
+						checker.ICMPv4Type(header.ICMPv4Type(icmpType)),
+						checker.ICMPv4Checksum(),
+						checker.ICMPv4Payload(original),
+					),
+				)
+			},
+			transportTypes: []transportTypeTest{
+				{
+					name:  "UDP",
+					proto: header.UDPProtocolNumber,
+					buf: func() buffer.View {
+						totalLen := header.IPv4MinimumSize + header.UDPMinimumSize
+						hdr := buffer.NewPrependable(totalLen)
+						udp := header.UDP(hdr.Prepend(header.UDPMinimumSize))
+						udp.SetSourcePort(srcPort)
+						udp.SetDestinationPort(dstPort)
+						udp.SetChecksum(0)
+						udp.SetChecksum(^udp.CalculateChecksum(header.PseudoHeaderChecksum(
+							header.UDPProtocolNumber,
+							utils.Host2IPv4Addr.AddressWithPrefix.Address,
+							utils.RouterNIC2IPv4Addr.AddressWithPrefix.Address,
+							uint16(len(udp)),
+						)))
+						ipHdr(hdr.Prepend(header.IPv4MinimumSize),
+							totalLen,
+							header.UDPProtocolNumber,
+							utils.Host2IPv4Addr.AddressWithPrefix.Address,
+							utils.RouterNIC2IPv4Addr.AddressWithPrefix.Address,
+						)
+						return hdr.View()
+					}(),
+					checkNATed: func(t *testing.T, v buffer.View) {
+						checker.IPv4(t, v,
+							checker.SrcAddr(utils.RouterNIC1IPv4Addr.AddressWithPrefix.Address),
+							checker.DstAddr(utils.Host1IPv4Addr.AddressWithPrefix.Address),
+							checker.UDP(
+								checker.SrcPort(srcPort),
+								checker.DstPort(dstPort),
+							),
+						)
+					},
+				},
+				{
+					name:  "TCP",
+					proto: header.TCPProtocolNumber,
+					buf: func() buffer.View {
+						totalLen := header.IPv4MinimumSize + header.TCPMinimumSize
+						hdr := buffer.NewPrependable(totalLen)
+						tcp := header.TCP(hdr.Prepend(header.TCPMinimumSize))
+						tcp.SetSourcePort(srcPort)
+						tcp.SetDestinationPort(dstPort)
+						tcp.SetDataOffset(header.TCPMinimumSize)
+						tcp.SetChecksum(0)
+						tcp.SetChecksum(^tcp.CalculateChecksum(header.PseudoHeaderChecksum(
+							header.TCPProtocolNumber,
+							utils.Host2IPv4Addr.AddressWithPrefix.Address,
+							utils.RouterNIC2IPv4Addr.AddressWithPrefix.Address,
+							uint16(len(tcp)),
+						)))
+						ipHdr(hdr.Prepend(header.IPv4MinimumSize),
+							totalLen,
+							header.TCPProtocolNumber,
+							utils.Host2IPv4Addr.AddressWithPrefix.Address,
+							utils.RouterNIC2IPv4Addr.AddressWithPrefix.Address,
+						)
+						return hdr.View()
+					}(),
+					checkNATed: func(t *testing.T, v buffer.View) {
+						checker.IPv4(t, v,
+							checker.SrcAddr(utils.RouterNIC1IPv4Addr.AddressWithPrefix.Address),
+							checker.DstAddr(utils.Host1IPv4Addr.AddressWithPrefix.Address),
+							checker.TCP(
+								checker.SrcPort(srcPort),
+								checker.DstPort(dstPort),
+							),
+						)
+					},
+				},
+			},
+			icmpTypes: []icmpTypeTest{
+				{
+					name:           "Destination Unreachable",
+					val:            uint8(header.ICMPv4DstUnreachable),
+					expectResponse: true,
+				},
+				{
+					name:           "Time Exceeded",
+					val:            uint8(header.ICMPv4TimeExceeded),
+					expectResponse: true,
+				},
+				{
+					name:           "Parameter Problem",
+					val:            uint8(header.ICMPv4ParamProblem),
+					expectResponse: true,
+				},
+				{
+					name:           "Echo Request",
+					val:            uint8(header.ICMPv4Echo),
+					expectResponse: false,
+				},
+				{
+					name:           "Echo Reply",
+					val:            uint8(header.ICMPv4EchoReply),
+					expectResponse: false,
+				},
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			for _, transportType := range test.transportTypes {
+				t.Run(transportType.name, func(t *testing.T) {
+					for _, icmpType := range test.icmpTypes {
+						t.Run(icmpType.name, func(t *testing.T) {
+							s := stack.New(stack.Options{
+								NetworkProtocols:   []stack.NetworkProtocolFactory{ipv4.NewProtocol, ipv6.NewProtocol},
+								TransportProtocols: []stack.TransportProtocolFactory{udp.NewProtocol, tcp.NewProtocol},
+							})
+
+							ep1 := channel.New(1, header.IPv6MinimumMTU, "")
+							ep2 := channel.New(1, header.IPv6MinimumMTU, "")
+							utils.SetupRouterStack(t, s, ep1, ep2)
+
+							ipv6 := test.netProto == ipv6.ProtocolNumber
+							ipt := s.IPTables()
+
+							table := stack.Table{
+								Rules: []stack.Rule{
+									// Prerouting
+									{
+										Filter: stack.IPHeaderFilter{
+											Protocol:       transportType.proto,
+											CheckProtocol:  true,
+											InputInterface: utils.RouterNIC2Name,
+										},
+										Target: &stack.DNATTarget{NetworkProtocol: test.netProto, Addr: test.host1Addr, Port: dstPort},
+									},
+									{
+										Target: &stack.AcceptTarget{},
+									},
+
+									// Input
+									{
+										Target: &stack.AcceptTarget{},
+									},
+
+									// Forward
+									{
+										Target: &stack.AcceptTarget{},
+									},
+
+									// Output
+									{
+										Target: &stack.AcceptTarget{},
+									},
+
+									// Postrouting
+									{
+										Filter: stack.IPHeaderFilter{
+											Protocol:        transportType.proto,
+											CheckProtocol:   true,
+											OutputInterface: utils.RouterNIC1Name,
+										},
+										Target: &stack.MasqueradeTarget{NetworkProtocol: test.netProto},
+									},
+									{
+										Target: &stack.AcceptTarget{},
+									},
+								},
+								BuiltinChains: [stack.NumHooks]int{
+									stack.Prerouting:  0,
+									stack.Input:       2,
+									stack.Forward:     3,
+									stack.Output:      4,
+									stack.Postrouting: 5,
+								},
+							}
+
+							if err := ipt.ReplaceTable(stack.NATID, table, ipv6); err != nil {
+								t.Fatalf("ipt.ReplaceTable(%d, _, %t): %s", stack.NATID, ipv6, err)
+							}
+
+							ep2.InjectInbound(test.netProto, stack.NewPacketBuffer(stack.PacketBufferOptions{
+								Data: append(buffer.View(nil), transportType.buf...).ToVectorisedView(),
+							}))
+
+							{
+								pkt, ok := ep1.Read()
+								if !ok {
+									t.Fatal("expected to read a packet on ep1")
+								}
+								pktView := stack.PayloadSince(pkt.Pkt.NetworkHeader())
+								transportType.checkNATed(t, pktView)
+								if t.Failed() {
+									t.FailNow()
+								}
+
+								ep1.InjectInbound(test.netProto, stack.NewPacketBuffer(stack.PacketBufferOptions{
+									Data: test.icmpError(t, pktView, icmpType.val).ToVectorisedView(),
+								}))
+							}
+
+							pkt, ok := ep2.Read()
+							if ok != icmpType.expectResponse {
+								t.Fatalf("got ep2.Read() = (%#v, %t), want = (_, %t)", pkt, ok, icmpType.expectResponse)
+							}
+							if !icmpType.expectResponse {
+								return
+							}
+							test.decrementTTL(transportType.buf)
+							test.checkNATedError(t, stack.PayloadSince(pkt.Pkt.NetworkHeader()), transportType.buf, icmpType.val)
+						})
+					}
+				})
+			}
+		})
+	}
+}
diff --git a/pkg/tcpip/tests/utils/utils.go b/pkg/tcpip/tests/utils/utils.go
index c69410859..654309584 100644
--- a/pkg/tcpip/tests/utils/utils.go
+++ b/pkg/tcpip/tests/utils/utils.go
@@ -213,12 +213,77 @@ func (e *EndpointWithDestinationCheck) DeliverNetworkPacket(src, dst tcpip.LinkA
 	}
 }
 
+// SetupRouterStack creates the NICs, sets forwarding, adds addresses and sets
+// the route table for a stack that should operate as a router.
+func SetupRouterStack(t *testing.T, s *stack.Stack, ep1, ep2 stack.LinkEndpoint) {
+
+	if err := s.SetForwardingDefaultAndAllNICs(ipv4.ProtocolNumber, true); err != nil {
+		t.Fatalf("s.SetForwardingDefaultAndAllNICs(%d): %s", ipv4.ProtocolNumber, err)
+	}
+	if err := s.SetForwardingDefaultAndAllNICs(ipv6.ProtocolNumber, true); err != nil {
+		t.Fatalf("s.SetForwardingDefaultAndAllNICs(%d): %s", ipv6.ProtocolNumber, err)
+	}
+
+	for _, setup := range []struct {
+		nicID   tcpip.NICID
+		nicName string
+		ep      stack.LinkEndpoint
+
+		addresses [2]tcpip.ProtocolAddress
+	}{
+		{
+			nicID:     RouterNICID1,
+			nicName:   RouterNIC1Name,
+			ep:        ep1,
+			addresses: [2]tcpip.ProtocolAddress{RouterNIC1IPv4Addr, RouterNIC1IPv6Addr},
+		},
+		{
+			nicID:     RouterNICID2,
+			nicName:   RouterNIC2Name,
+			ep:        ep2,
+			addresses: [2]tcpip.ProtocolAddress{RouterNIC2IPv4Addr, RouterNIC2IPv6Addr},
+		},
+	} {
+		opts := stack.NICOptions{Name: setup.nicName}
+		if err := s.CreateNICWithOptions(setup.nicID, setup.ep, opts); err != nil {
+			t.Fatalf("s.CreateNICWithOptions(%d, _, %#v): %s", setup.nicID, opts, err)
+		}
+
+		for _, addr := range setup.addresses {
+			if err := s.AddProtocolAddress(setup.nicID, addr, stack.AddressProperties{}); err != nil {
+				t.Fatalf("s.AddProtocolAddress(%d, %#v, {}): %s", setup.nicID, addr, err)
+			}
+		}
+	}
+
+	s.SetRouteTable([]tcpip.Route{
+		{
+			Destination: RouterNIC1IPv4Addr.AddressWithPrefix.Subnet(),
+			NIC:         RouterNICID1,
+		},
+		{
+			Destination: RouterNIC1IPv6Addr.AddressWithPrefix.Subnet(),
+			NIC:         RouterNICID1,
+		},
+		{
+			Destination: RouterNIC2IPv4Addr.AddressWithPrefix.Subnet(),
+			NIC:         RouterNICID2,
+		},
+		{
+			Destination: RouterNIC2IPv6Addr.AddressWithPrefix.Subnet(),
+			NIC:         RouterNICID2,
+		},
+	})
+}
+
 // SetupRoutedStacks creates the NICs, sets forwarding, adds addresses and sets
 // the route tables for the passed stacks.
 func SetupRoutedStacks(t *testing.T, host1Stack, routerStack, host2Stack *stack.Stack) {
 	host1NIC, routerNIC1 := pipe.New(LinkAddr1, LinkAddr2)
 	routerNIC2, host2NIC := pipe.New(LinkAddr3, LinkAddr4)
 
+	SetupRouterStack(t, routerStack, NewEthernetEndpoint(routerNIC1), NewEthernetEndpoint(routerNIC2))
+
 	{
 		opts := stack.NICOptions{Name: Host1NICName}
 		if err := host1Stack.CreateNICWithOptions(Host1NICID, NewEthernetEndpoint(host1NIC), opts); err != nil {
@@ -226,52 +291,21 @@ func SetupRoutedStacks(t *testing.T, host1Stack, routerStack, host2Stack *stack.
 		}
 	}
 	{
-		opts := stack.NICOptions{Name: RouterNIC1Name}
-		if err := routerStack.CreateNICWithOptions(RouterNICID1, NewEthernetEndpoint(routerNIC1), opts); err != nil {
-			t.Fatalf("routerStack.CreateNICWithOptions(%d, _, %#v): %s", RouterNICID1, opts, err)
-		}
-	}
-	{
-		opts := stack.NICOptions{Name: RouterNIC2Name}
-		if err := routerStack.CreateNICWithOptions(RouterNICID2, NewEthernetEndpoint(routerNIC2), opts); err != nil {
-			t.Fatalf("routerStack.CreateNICWithOptions(%d, _, %#v): %s", RouterNICID2, opts, err)
-		}
-	}
-	{
 		opts := stack.NICOptions{Name: Host2NICName}
 		if err := host2Stack.CreateNICWithOptions(Host2NICID, NewEthernetEndpoint(host2NIC), opts); err != nil {
 			t.Fatalf("host2Stack.CreateNICWithOptions(%d, _, %#v): %s", Host2NICID, opts, err)
 		}
 	}
 
-	if err := routerStack.SetForwardingDefaultAndAllNICs(ipv4.ProtocolNumber, true); err != nil {
-		t.Fatalf("routerStack.SetForwardingDefaultAndAllNICs(%d): %s", ipv4.ProtocolNumber, err)
-	}
-	if err := routerStack.SetForwardingDefaultAndAllNICs(ipv6.ProtocolNumber, true); err != nil {
-		t.Fatalf("routerStack.SetForwardingDefaultAndAllNICs(%d): %s", ipv6.ProtocolNumber, err)
-	}
-
 	if err := host1Stack.AddProtocolAddress(Host1NICID, Host1IPv4Addr, stack.AddressProperties{}); err != nil {
 		t.Fatalf("host1Stack.AddProtocolAddress(%d, %+v, {}): %s", Host1NICID, Host1IPv4Addr, err)
 	}
-	if err := routerStack.AddProtocolAddress(RouterNICID1, RouterNIC1IPv4Addr, stack.AddressProperties{}); err != nil {
-		t.Fatalf("routerStack.AddProtocolAddress(%d, %+v, {}): %s", RouterNICID1, RouterNIC1IPv4Addr, err)
-	}
-	if err := routerStack.AddProtocolAddress(RouterNICID2, RouterNIC2IPv4Addr, stack.AddressProperties{}); err != nil {
-		t.Fatalf("routerStack.AddProtocolAddress(%d, %+v, {}): %s", RouterNICID2, RouterNIC2IPv4Addr, err)
-	}
 	if err := host2Stack.AddProtocolAddress(Host2NICID, Host2IPv4Addr, stack.AddressProperties{}); err != nil {
 		t.Fatalf("host2Stack.AddProtocolAddress(%d, %+v, {}): %s", Host2NICID, Host2IPv4Addr, err)
 	}
 	if err := host1Stack.AddProtocolAddress(Host1NICID, Host1IPv6Addr, stack.AddressProperties{}); err != nil {
 		t.Fatalf("host1Stack.AddProtocolAddress(%d, %+v, {}): %s", Host1NICID, Host1IPv6Addr, err)
 	}
-	if err := routerStack.AddProtocolAddress(RouterNICID1, RouterNIC1IPv6Addr, stack.AddressProperties{}); err != nil {
-		t.Fatalf("routerStack.AddProtocolAddress(%d, %+v, {}): %s", RouterNICID1, RouterNIC1IPv6Addr, err)
-	}
-	if err := routerStack.AddProtocolAddress(RouterNICID2, RouterNIC2IPv6Addr, stack.AddressProperties{}); err != nil {
-		t.Fatalf("routerStack.AddProtocolAddress(%d, %+v, {}): %s", RouterNICID2, RouterNIC2IPv6Addr, err)
-	}
 	if err := host2Stack.AddProtocolAddress(Host2NICID, Host2IPv6Addr, stack.AddressProperties{}); err != nil {
 		t.Fatalf("host2Stack.AddProtocolAddress(%d, %+v, {}): %s", Host2NICID, Host2IPv6Addr, err)
 	}
@@ -296,24 +330,6 @@ func SetupRoutedStacks(t *testing.T, host1Stack, routerStack, host2Stack *stack.
 			NIC:         Host1NICID,
 		},
 	})
-	routerStack.SetRouteTable([]tcpip.Route{
-		{
-			Destination: RouterNIC1IPv4Addr.AddressWithPrefix.Subnet(),
-			NIC:         RouterNICID1,
-		},
-		{
-			Destination: RouterNIC1IPv6Addr.AddressWithPrefix.Subnet(),
-			NIC:         RouterNICID1,
-		},
-		{
-			Destination: RouterNIC2IPv4Addr.AddressWithPrefix.Subnet(),
-			NIC:         RouterNICID2,
-		},
-		{
-			Destination: RouterNIC2IPv6Addr.AddressWithPrefix.Subnet(),
-			NIC:         RouterNICID2,
-		},
-	})
 	host2Stack.SetRouteTable([]tcpip.Route{
 		{
 			Destination: Host2IPv4Addr.AddressWithPrefix.Subnet(),