github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/tcpip/network/ipv4/ipv4_test.go

// Copyright 2021 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package ipv4_test

import (
	"bytes"
	"encoding/hex"
	"fmt"
	"io/ioutil"
	"math"
	"net"
	"testing"
	"time"

	"github.com/google/go-cmp/cmp"
	"github.com/SagerNet/gvisor/pkg/sync"
	"github.com/SagerNet/gvisor/pkg/tcpip"
	"github.com/SagerNet/gvisor/pkg/tcpip/buffer"
	"github.com/SagerNet/gvisor/pkg/tcpip/checker"
	"github.com/SagerNet/gvisor/pkg/tcpip/faketime"
	"github.com/SagerNet/gvisor/pkg/tcpip/header"
	"github.com/SagerNet/gvisor/pkg/tcpip/link/channel"
	"github.com/SagerNet/gvisor/pkg/tcpip/link/loopback"
	"github.com/SagerNet/gvisor/pkg/tcpip/link/sniffer"
	"github.com/SagerNet/gvisor/pkg/tcpip/network/arp"
	iptestutil "github.com/SagerNet/gvisor/pkg/tcpip/network/internal/testutil"
	"github.com/SagerNet/gvisor/pkg/tcpip/network/ipv4"
	"github.com/SagerNet/gvisor/pkg/tcpip/stack"
	"github.com/SagerNet/gvisor/pkg/tcpip/testutil"
	"github.com/SagerNet/gvisor/pkg/tcpip/transport/icmp"
	"github.com/SagerNet/gvisor/pkg/tcpip/transport/raw"
	"github.com/SagerNet/gvisor/pkg/tcpip/transport/tcp"
	"github.com/SagerNet/gvisor/pkg/tcpip/transport/udp"
	"github.com/SagerNet/gvisor/pkg/waiter"
)

const (
	extraHeaderReserve = 50
	defaultMTU         = 65536
)

func TestExcludeBroadcast(t *testing.T) {
	s := stack.New(stack.Options{
		NetworkProtocols:   []stack.NetworkProtocolFactory{ipv4.NewProtocol},
		TransportProtocols: []stack.TransportProtocolFactory{udp.NewProtocol},
	})

	ep := stack.LinkEndpoint(channel.New(256, defaultMTU, ""))
	if testing.Verbose() {
		ep = sniffer.New(ep)
	}
	if err := s.CreateNIC(1, ep); err != nil {
		t.Fatalf("CreateNIC failed: %v", err)
	}

	s.SetRouteTable([]tcpip.Route{{
		Destination: header.IPv4EmptySubnet,
		NIC:         1,
	}})

	randomAddr := tcpip.FullAddress{NIC: 1, Addr: "\x0a\x00\x00\x01", Port: 53}

	var wq waiter.Queue
	t.Run("WithoutPrimaryAddress", func(t *testing.T) {
		ep, err := s.NewEndpoint(udp.ProtocolNumber, ipv4.ProtocolNumber, &wq)
		if err != nil {
			t.Fatal(err)
		}
		defer ep.Close()

		// Cannot connect using a broadcast address as the source.
		{
			err := ep.Connect(randomAddr)
			if _, ok := err.(*tcpip.ErrNoRoute); !ok {
				t.Errorf("got ep.Connect(...) = %v, want = %v", err, &tcpip.ErrNoRoute{})
			}
		}

		// However, we can bind to a broadcast address to listen.
		if err := ep.Bind(tcpip.FullAddress{Addr: header.IPv4Broadcast, Port: 53, NIC: 1}); err != nil {
			t.Errorf("Bind failed: %v", err)
		}
	})

	t.Run("WithPrimaryAddress", func(t *testing.T) {
		ep, err := s.NewEndpoint(udp.ProtocolNumber, ipv4.ProtocolNumber, &wq)
		if err != nil {
			t.Fatal(err)
		}
		defer ep.Close()

		// Add a valid primary endpoint address, now we can connect.
		if err := s.AddAddress(1, ipv4.ProtocolNumber, "\x0a\x00\x00\x02"); err != nil {
			t.Fatalf("AddAddress failed: %v", err)
		}
		if err := ep.Connect(randomAddr); err != nil {
			t.Errorf("Connect failed: %v", err)
		}
	})
}

func TestForwarding(t *testing.T) {
	const (
		incomingNICID    = 1
		outgoingNICID    = 2
		randomSequence   = 123
		randomIdent      = 42
		randomTimeOffset = 0x10203040
	)

	incomingIPv4Addr := tcpip.AddressWithPrefix{
		Address:   tcpip.Address(net.ParseIP("10.0.0.1").To4()),
		PrefixLen: 8,
	}
	outgoingIPv4Addr := tcpip.AddressWithPrefix{
		Address:   tcpip.Address(net.ParseIP("11.0.0.1").To4()),
		PrefixLen: 8,
	}
	outgoingLinkAddr := tcpip.LinkAddress("\x02\x03\x03\x04\x05\x06")
	remoteIPv4Addr1 := testutil.MustParse4("10.0.0.2")
	remoteIPv4Addr2 := testutil.MustParse4("11.0.0.2")
	unreachableIPv4Addr := testutil.MustParse4("12.0.0.2")
	multicastIPv4Addr := testutil.MustParse4("225.0.0.0")
	linkLocalIPv4Addr := testutil.MustParse4("169.254.0.0")

	tests := []struct {
		name                         string
		TTL                          uint8
		sourceAddr                   tcpip.Address
		destAddr                     tcpip.Address
		expectErrorICMP              bool
		ipFlags                      uint8
		mtu                          uint32
		payloadLength                int
		options                      header.IPv4Options
		forwardedOptions             header.IPv4Options
		icmpType                     header.ICMPv4Type
		icmpCode                     header.ICMPv4Code
		expectPacketUnrouteableError bool
		expectLinkLocalSourceError   bool
		expectLinkLocalDestError     bool
		expectPacketForwarded        bool
		expectedFragmentsForwarded   []fragmentInfo
	}{
		{
			name:            "TTL of zero",
			TTL:             0,
			sourceAddr:      remoteIPv4Addr1,
			destAddr:        remoteIPv4Addr2,
			expectErrorICMP: true,
			icmpType:        header.ICMPv4TimeExceeded,
			icmpCode:        header.ICMPv4TTLExceeded,
			mtu:             ipv4.MaxTotalSize,
		},
		{
			name:                  "TTL of one",
			TTL:                   1,
			sourceAddr:            remoteIPv4Addr1,
			destAddr:              remoteIPv4Addr2,
			expectPacketForwarded: true,
			mtu:                   ipv4.MaxTotalSize,
		},
		{
			name:                  "TTL of two",
			TTL:                   2,
			sourceAddr:            remoteIPv4Addr1,
			destAddr:              remoteIPv4Addr2,
			expectPacketForwarded: true,
			mtu:                   ipv4.MaxTotalSize,
		},
		{
			name:                  "Max TTL",
			TTL:                   math.MaxUint8,
			sourceAddr:            remoteIPv4Addr1,
			destAddr:              remoteIPv4Addr2,
			expectPacketForwarded: true,
			mtu:                   ipv4.MaxTotalSize,
		},
		{
			name:                  "four EOL options",
			TTL:                   2,
			sourceAddr:            remoteIPv4Addr1,
			destAddr:              remoteIPv4Addr2,
			expectPacketForwarded: true,
			mtu:                   ipv4.MaxTotalSize,
			options:               header.IPv4Options{0, 0, 0, 0},
			forwardedOptions:      header.IPv4Options{0, 0, 0, 0},
		},
		{
			name:       "TS type 1 full",
			TTL:        2,
			sourceAddr: remoteIPv4Addr1,
			destAddr:   remoteIPv4Addr2,
			mtu:        ipv4.MaxTotalSize,
			options: header.IPv4Options{
				68, 12, 13, 0xF1,
				192, 168, 1, 12,
				1, 2, 3, 4,
			},
			expectErrorICMP: true,
			icmpType:        header.ICMPv4ParamProblem,
			icmpCode:        header.ICMPv4UnusedCode,
		},
		{
			name:       "TS type 0",
			TTL:        2,
			sourceAddr: remoteIPv4Addr1,
			destAddr:   remoteIPv4Addr2,
			mtu:        ipv4.MaxTotalSize,
			options: header.IPv4Options{
				68, 24, 21, 0x00,
				1, 2, 3, 4,
				5, 6, 7, 8,
				9, 10, 11, 12,
				13, 14, 15, 16,
				0, 0, 0, 0,
			},
			forwardedOptions: header.IPv4Options{
				68, 24, 25, 0x00,
				1, 2, 3, 4,
				5, 6, 7, 8,
				9, 10, 11, 12,
				13, 14, 15, 16,
				0x00, 0xad, 0x1c, 0x40, // time we expect from fakeclock
			},
			expectPacketForwarded: true,
		},
		{
			name:       "end of options list",
			TTL:        2,
			sourceAddr: remoteIPv4Addr1,
			destAddr:   remoteIPv4Addr2,
			mtu:        ipv4.MaxTotalSize,
			options: header.IPv4Options{
				68, 12, 13, 0x11,
				192, 168, 1, 12,
				1, 2, 3, 4,
				0, 10, 3, 99, // EOL followed by junk
				1, 2, 3, 4,
			},
			forwardedOptions: header.IPv4Options{
				68, 12, 13, 0x21,
				192, 168, 1, 12,
				1, 2, 3, 4,
				0,       // End of Options hides following bytes.
				0, 0, 0, // 7 bytes unknown option removed.
				0, 0, 0, 0,
			},
			expectPacketForwarded: true,
		},
		{
			name:                         "Network unreachable",
			TTL:                          2,
			sourceAddr:                   remoteIPv4Addr1,
			destAddr:                     unreachableIPv4Addr,
			expectErrorICMP:              true,
			mtu:                          ipv4.MaxTotalSize,
			icmpType:                     header.ICMPv4DstUnreachable,
			icmpCode:                     header.ICMPv4NetUnreachable,
			expectPacketUnrouteableError: true,
		},
		{
			name:                         "Multicast destination",
			TTL:                          2,
			destAddr:                     multicastIPv4Addr,
			expectPacketUnrouteableError: true,
		},
		{
			name:                     "Link local destination",
			TTL:                      2,
			sourceAddr:               remoteIPv4Addr1,
			destAddr:                 linkLocalIPv4Addr,
			expectLinkLocalDestError: true,
		},
		{
			name:                       "Link local source",
			TTL:                        2,
			sourceAddr:                 linkLocalIPv4Addr,
			destAddr:                   remoteIPv4Addr2,
			expectLinkLocalSourceError: true,
		},
		{
			name:       "Fragmentation needed and DF set",
			TTL:        2,
			sourceAddr: remoteIPv4Addr1,
			destAddr:   remoteIPv4Addr2,
			ipFlags:    header.IPv4FlagDontFragment,
			// We've picked this MTU because it is:
			//
			// 1) Greater than the minimum MTU that IPv4 hosts are required to process
			// (576 bytes). As per RFC 1812, Section 4.3.2.3:
			//
			//   The ICMP datagram SHOULD contain as much of the original datagram as
			//   possible without the length of the ICMP datagram exceeding 576 bytes.
			//
			// Therefore, setting an MTU greater than 576 bytes ensures that we can fit a
			// complete ICMP packet on the incoming endpoint (and make assertions about
			// it).
			//
			// 2) Less than `ipv4.MaxTotalSize`, which lets us build an IPv4 packet whose
			// size exceeds the MTU.
			mtu:             1000,
			payloadLength:   1004,
			expectErrorICMP: true,
			icmpType:        header.ICMPv4DstUnreachable,
			icmpCode:        header.ICMPv4FragmentationNeeded,
		},
		{
			name:                  "Fragmentation needed and DF not set",
			TTL:                   2,
			sourceAddr:            remoteIPv4Addr1,
			destAddr:              remoteIPv4Addr2,
			mtu:                   1000,
			payloadLength:         1004,
			expectPacketForwarded: true,
			// Combined, these fragments have length of 1012 octets, which is equal to
			// the length of the payload (1004 octets), plus the length of the ICMP
			// header (8 octets).
			expectedFragmentsForwarded: []fragmentInfo{
				// The first fragment has a length of the greatest multiple of 8 which is
				// less than or equal to to `mtu - header.IPv4MinimumSize`.
				{offset: 0, payloadSize: uint16(976), more: true},
				// The next fragment holds the rest of the packet.
				{offset: uint16(976), payloadSize: 36, more: false},
			},
		},
	}
	for _, test := range tests {
		t.Run(test.name, func(t *testing.T) {
			clock := faketime.NewManualClock()

			s := stack.New(stack.Options{
				NetworkProtocols:   []stack.NetworkProtocolFactory{ipv4.NewProtocol},
				TransportProtocols: []stack.TransportProtocolFactory{icmp.NewProtocol4},
				Clock:              clock,
			})

			// Advance the clock by some unimportant amount to make
			// it give a more recognisable signature than 00,00,00,00.
			clock.Advance(time.Millisecond * randomTimeOffset)

			// We expect at most a single packet in response to our ICMP Echo Request.
			incomingEndpoint := channel.New(1, test.mtu, "")
			if err := s.CreateNIC(incomingNICID, incomingEndpoint); err != nil {
				t.Fatalf("CreateNIC(%d, _): %s", incomingNICID, err)
			}
			incomingIPv4ProtoAddr := tcpip.ProtocolAddress{Protocol: header.IPv4ProtocolNumber, AddressWithPrefix: incomingIPv4Addr}
			if err := s.AddProtocolAddress(incomingNICID, incomingIPv4ProtoAddr); err != nil {
				t.Fatalf("AddProtocolAddress(%d, %#v): %s", incomingNICID, incomingIPv4ProtoAddr, err)
			}

			expectedEmittedPacketCount := 1
			if len(test.expectedFragmentsForwarded) > expectedEmittedPacketCount {
				expectedEmittedPacketCount = len(test.expectedFragmentsForwarded)
			}
			outgoingEndpoint := channel.New(expectedEmittedPacketCount, test.mtu, outgoingLinkAddr)
			if err := s.CreateNIC(outgoingNICID, outgoingEndpoint); err != nil {
				t.Fatalf("CreateNIC(%d, _): %s", outgoingNICID, err)
			}
			outgoingIPv4ProtoAddr := tcpip.ProtocolAddress{Protocol: header.IPv4ProtocolNumber, AddressWithPrefix: outgoingIPv4Addr}
			if err := s.AddProtocolAddress(outgoingNICID, outgoingIPv4ProtoAddr); err != nil {
				t.Fatalf("AddProtocolAddress(%d, %#v): %s", outgoingNICID, outgoingIPv4ProtoAddr, err)
			}

			s.SetRouteTable([]tcpip.Route{
				{
					Destination: incomingIPv4Addr.Subnet(),
					NIC:         incomingNICID,
				},
				{
					Destination: outgoingIPv4Addr.Subnet(),
					NIC:         outgoingNICID,
				},
			})

			if err := s.SetForwardingDefaultAndAllNICs(header.IPv4ProtocolNumber, true); err != nil {
				t.Fatalf("SetForwardingDefaultAndAllNICs(%d, true): %s", header.IPv4ProtocolNumber, err)
			}

			ipHeaderLength := header.IPv4MinimumSize + len(test.options)
			if ipHeaderLength > header.IPv4MaximumHeaderSize {
				t.Fatalf("got ipHeaderLength = %d, want <= %d ", ipHeaderLength, header.IPv4MaximumHeaderSize)
			}
			icmpHeaderLength := header.ICMPv4MinimumSize
			totalLength := ipHeaderLength + icmpHeaderLength + test.payloadLength
			hdr := buffer.NewPrependable(totalLength)
			hdr.Prepend(test.payloadLength)
			icmpH := header.ICMPv4(hdr.Prepend(icmpHeaderLength))
			icmpH.SetIdent(randomIdent)
			icmpH.SetSequence(randomSequence)
			icmpH.SetType(header.ICMPv4Echo)
			icmpH.SetCode(header.ICMPv4UnusedCode)
			icmpH.SetChecksum(0)
			icmpH.SetChecksum(^header.Checksum(icmpH, 0))
			ip := header.IPv4(hdr.Prepend(ipHeaderLength))
			ip.Encode(&header.IPv4Fields{
				TotalLength: uint16(totalLength),
				Protocol:    uint8(header.ICMPv4ProtocolNumber),
				TTL:         test.TTL,
				SrcAddr:     test.sourceAddr,
				DstAddr:     test.destAddr,
				Flags:       test.ipFlags,
			})
			if len(test.options) != 0 {
				ip.SetHeaderLength(uint8(ipHeaderLength))
				// Copy options manually. We do not use Encode for options so we can
				// verify malformed options with handcrafted payloads.
				if want, got := copy(ip.Options(), test.options), len(test.options); want != got {
					t.Fatalf("got copy(ip.Options(), test.options) = %d, want = %d", got, want)
				}
			}
			ip.SetChecksum(0)
			ip.SetChecksum(^ip.CalculateChecksum())
			requestPkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
				Data: hdr.View().ToVectorisedView(),
			})
			requestPkt.NetworkProtocolNumber = header.IPv4ProtocolNumber
			incomingEndpoint.InjectInbound(header.IPv4ProtocolNumber, requestPkt)

			reply, ok := incomingEndpoint.Read()

			if test.expectErrorICMP {
				if !ok {
					t.Fatalf("expected ICMP packet type %d through incoming NIC", test.icmpType)
				}

				// We expect the ICMP packet to contain as much of the original packet as
				// possible up to a limit of 576 bytes, split between payload, IP header,
				// and ICMP header.
				expectedICMPPayloadLength := func() int {
					maxICMPPacketLength := header.IPv4MinimumProcessableDatagramSize
					maxICMPPayloadLength := maxICMPPacketLength - icmpHeaderLength - ipHeaderLength
					if len(hdr.View()) > maxICMPPayloadLength {
						return maxICMPPayloadLength
					}
					return len(hdr.View())
				}

				checker.IPv4(t, stack.PayloadSince(reply.Pkt.NetworkHeader()),
					checker.SrcAddr(incomingIPv4Addr.Address),
					checker.DstAddr(test.sourceAddr),
					checker.TTL(ipv4.DefaultTTL),
					checker.ICMPv4(
						checker.ICMPv4Checksum(),
						checker.ICMPv4Type(test.icmpType),
						checker.ICMPv4Code(test.icmpCode),
						checker.ICMPv4Payload(hdr.View()[:expectedICMPPayloadLength()]),
					),
				)
			} else if ok {
				t.Fatalf("expected no ICMP packet through incoming NIC, instead found: %#v", reply)
			}

			if test.expectPacketForwarded {
				if len(test.expectedFragmentsForwarded) != 0 {
					var fragmentedPackets []*stack.PacketBuffer
					for i := 0; i < len(test.expectedFragmentsForwarded); i++ {
						reply, ok = outgoingEndpoint.Read()
						if !ok {
							t.Fatal("expected ICMP Echo fragment through outgoing NIC")
						}
						fragmentedPackets = append(fragmentedPackets, reply.Pkt)
					}

					// The forwarded packet's TTL will have been decremented.
					ipHeader := header.IPv4(requestPkt.NetworkHeader().View())
					ipHeader.SetTTL(ipHeader.TTL() - 1)

					// Forwarded packets have available header bytes equalling the sum of the
					// maximum IP header size and the maximum size allocated for link layer
					// headers. In this case, no size is allocated for link layer headers.
					expectedAvailableHeaderBytes := header.IPv4MaximumHeaderSize
					if err := compareFragments(fragmentedPackets, requestPkt, test.mtu, test.expectedFragmentsForwarded, header.ICMPv4ProtocolNumber, true /* withIPHeader */, expectedAvailableHeaderBytes); err != nil {
						t.Error(err)
					}
				} else {
					reply, ok = outgoingEndpoint.Read()
					if !ok {
						t.Fatal("expected ICMP Echo packet through outgoing NIC")
					}

					checker.IPv4(t, stack.PayloadSince(reply.Pkt.NetworkHeader()),
						checker.SrcAddr(test.sourceAddr),
						checker.DstAddr(test.destAddr),
						checker.TTL(test.TTL-1),
						checker.IPv4Options(test.forwardedOptions),
						checker.ICMPv4(
							checker.ICMPv4Checksum(),
							checker.ICMPv4Type(header.ICMPv4Echo),
							checker.ICMPv4Code(header.ICMPv4UnusedCode),
							checker.ICMPv4Payload(nil),
						),
					)
				}
			} else {
				if reply, ok = outgoingEndpoint.Read(); ok {
					t.Fatalf("expected no ICMP Echo packet through outgoing NIC, instead found: %#v", reply)
				}
			}
			boolToInt := func(val bool) uint64 {
				if val {
					return 1
				}
				return 0
			}

			if got, want := s.Stats().IP.Forwarding.LinkLocalSource.Value(), boolToInt(test.expectLinkLocalSourceError); got != want {
				t.Errorf("got s.Stats().IP.Forwarding.LinkLocalSource.Value() = %d, want = %d", got, want)
			}

			if got, want := s.Stats().IP.Forwarding.LinkLocalDestination.Value(), boolToInt(test.expectLinkLocalDestError); got != want {
				t.Errorf("got s.Stats().IP.Forwarding.LinkLocalDestination.Value() = %d, want = %d", got, want)
			}

			if got, want := s.Stats().IP.MalformedPacketsReceived.Value(), boolToInt(test.icmpType == header.ICMPv4ParamProblem); got != want {
				t.Errorf("got s.Stats().IP.MalformedPacketsReceived.Value() = %d, want = %d", got, want)
			}

			if got, want := s.Stats().IP.Forwarding.ExhaustedTTL.Value(), boolToInt(test.TTL <= 0); got != want {
				t.Errorf("got s.Stats().IP.Forwarding.ExhaustedTTL.Value() = %d, want = %d", got, want)
			}

			if got, want := s.Stats().IP.Forwarding.Unrouteable.Value(), boolToInt(test.expectPacketUnrouteableError); got != want {
				t.Errorf("got s.Stats().IP.Forwarding.Unrouteable.Value() = %d, want = %d", got, want)
			}

			if got, want := s.Stats().IP.Forwarding.Errors.Value(), boolToInt(!test.expectPacketForwarded); got != want {
				t.Errorf("got s.Stats().IP.Forwarding.Errors.Value() = %d, want = %d", got, want)
			}

			if got, want := s.Stats().IP.Forwarding.PacketTooBig.Value(), boolToInt(test.icmpCode == header.ICMPv4FragmentationNeeded); got != want {
				t.Errorf("got s.Stats().IP.Forwarding.PacketTooBig.Value() = %d, want = %d", got, want)
			}
		})
	}
}

// TestIPv4Sanity sends IP/ICMP packets with various problems to the stack and
// checks the response.
func TestIPv4Sanity(t *testing.T) {
	const (
		ttl            = 255
		nicID          = 1
		randomSequence = 123
		randomIdent    = 42
		// In some cases Linux sets the error pointer to the start of the option
		// (offset 0) instead of the actual wrong value, which is the length byte
		// (offset 1). For compatibility we must do the same. Use this constant
		// to indicate where this happens.
		pointerOffsetForInvalidLength = 0
		randomTimeOffset              = 0x10203040
	)
	var (
		ipv4Addr = tcpip.AddressWithPrefix{
			Address:   tcpip.Address(net.ParseIP("192.168.1.58").To4()),
			PrefixLen: 24,
		}
		remoteIPv4Addr = tcpip.Address(net.ParseIP("10.0.0.1").To4())
	)

	tests := []struct {
		name                string
		headerLength        uint8 // value of 0 means "use correct size"
		badHeaderChecksum   bool
		maxTotalLength      uint16
		transportProtocol   uint8
		TTL                 uint8
		options             header.IPv4Options
		replyOptions        header.IPv4Options // reply should look like this
		shouldFail          bool
		expectErrorICMP     bool
		ICMPType            header.ICMPv4Type
		ICMPCode            header.ICMPv4Code
		paramProblemPointer uint8
	}{
		{
			name:              "valid no options",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
		},
		{
			name:              "bad header checksum",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			badHeaderChecksum: true,
			shouldFail:        true,
		},
		// The TTL tests check that we are not rejecting an incoming packet
		// with a zero or one TTL, which has been a point of confusion in the
		// past as RFC 791 says: "If this field contains the value zero, then the
		// datagram must be destroyed". However RFC 1122 section 3.2.1.7 clarifies
		// for the case of the destination host, stating as follows.
		//
		//      A host MUST NOT send a datagram with a Time-to-Live (TTL)
		//      value of zero.
		//
		//      A host MUST NOT discard a datagram just because it was
		//      received with TTL less than 2.
		{
			name:              "zero TTL",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               0,
		},
		{
			name:              "one TTL",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               1,
		},
		{
			name:              "End options",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options:           header.IPv4Options{0, 0, 0, 0},
			replyOptions:      header.IPv4Options{0, 0, 0, 0},
		},
		{
			name:              "NOP options",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options:           header.IPv4Options{1, 1, 1, 1},
			replyOptions:      header.IPv4Options{1, 1, 1, 1},
		},
		{
			name:              "NOP and End options",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options:           header.IPv4Options{1, 1, 0, 0},
			replyOptions:      header.IPv4Options{1, 1, 0, 0},
		},
		{
			name:              "bad header length",
			headerLength:      header.IPv4MinimumSize - 1,
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			shouldFail:        true,
		},
		{
			name:              "bad total length (0)",
			maxTotalLength:    0,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			shouldFail:        true,
		},
		{
			name:              "bad total length (ip - 1)",
			maxTotalLength:    uint16(header.IPv4MinimumSize - 1),
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			shouldFail:        true,
		},
		{
			name:              "bad total length (ip + icmp - 1)",
			maxTotalLength:    uint16(header.IPv4MinimumSize + header.ICMPv4MinimumSize - 1),
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			shouldFail:        true,
		},
		{
			name:              "bad protocol",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: 99,
			TTL:               ttl,
			shouldFail:        true,
			expectErrorICMP:   true,
			ICMPType:          header.ICMPv4DstUnreachable,
			ICMPCode:          header.ICMPv4ProtoUnreachable,
		},
		{
			name:              "timestamp option overflow",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				68, 12, 13, 0x11,
				192, 168, 1, 12,
				1, 2, 3, 4,
			},
			replyOptions: header.IPv4Options{
				68, 12, 13, 0x21,
				192, 168, 1, 12,
				1, 2, 3, 4,
			},
		},
		{
			name:              "timestamp option overflow full",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				68, 12, 13, 0xF1,
				//            ^   Counter full (15/0xF)
				192, 168, 1, 12,
				1, 2, 3, 4,
			},
			shouldFail:          true,
			expectErrorICMP:     true,
			ICMPType:            header.ICMPv4ParamProblem,
			ICMPCode:            header.ICMPv4UnusedCode,
			paramProblemPointer: header.IPv4MinimumSize + 3,
			replyOptions:        header.IPv4Options{},
		},
		{
			name:              "unknown option",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options:           header.IPv4Options{10, 4, 9, 0},
			//                        ^^
			// The unknown option should be stripped out of the reply.
			replyOptions: header.IPv4Options{},
		},
		{
			name:              "bad option - no length",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				1, 1, 1, 68,
				//        ^-start of timestamp.. but no length..
			},
			shouldFail:          true,
			expectErrorICMP:     true,
			ICMPType:            header.ICMPv4ParamProblem,
			ICMPCode:            header.ICMPv4UnusedCode,
			paramProblemPointer: header.IPv4MinimumSize + 3,
		},
		{
			name:              "bad option - length 0",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				68, 0, 9, 0,
				//  ^
				1, 2, 3, 4,
			},
			shouldFail:          true,
			expectErrorICMP:     true,
			ICMPType:            header.ICMPv4ParamProblem,
			ICMPCode:            header.ICMPv4UnusedCode,
			paramProblemPointer: header.IPv4MinimumSize + pointerOffsetForInvalidLength,
		},
		{
			name:              "bad option - length 1",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				68, 1, 9, 0,
				//  ^
				1, 2, 3, 4,
			},
			shouldFail:          true,
			expectErrorICMP:     true,
			ICMPType:            header.ICMPv4ParamProblem,
			ICMPCode:            header.ICMPv4UnusedCode,
			paramProblemPointer: header.IPv4MinimumSize + pointerOffsetForInvalidLength,
		},
		{
			name:              "bad option - length big",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				68, 9, 9, 0,
				//  ^
				// There are only 8 bytes allocated to options so 9 bytes of timestamp
				// space is not possible. (Second byte)
				1, 2, 3, 4,
			},
			shouldFail:          true,
			expectErrorICMP:     true,
			ICMPType:            header.ICMPv4ParamProblem,
			ICMPCode:            header.ICMPv4UnusedCode,
			paramProblemPointer: header.IPv4MinimumSize + pointerOffsetForInvalidLength,
		},
		{
			// This tests for some linux compatible behaviour.
			// The ICMP pointer returned is 22 for Linux but the
			// error is actually in spot 21.
			name:              "bad option - length bad",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			// Timestamps are in multiples of 4 or 8 but never 7.
			// The option space should be padded out.
			options: header.IPv4Options{
				68, 7, 5, 0,
				//  ^  ^ Linux points here which is wrong.
				//  | Not a multiple of 4
				1, 2, 3, 0,
			},
			shouldFail:          true,
			expectErrorICMP:     true,
			ICMPType:            header.ICMPv4ParamProblem,
			ICMPCode:            header.ICMPv4UnusedCode,
			paramProblemPointer: header.IPv4MinimumSize + header.IPv4OptTSPointerOffset,
		},
		{
			name:              "multiple type 0 with room",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				68, 24, 21, 0x00,
				1, 2, 3, 4,
				5, 6, 7, 8,
				9, 10, 11, 12,
				13, 14, 15, 16,
				0, 0, 0, 0,
			},
			replyOptions: header.IPv4Options{
				68, 24, 25, 0x00,
				1, 2, 3, 4,
				5, 6, 7, 8,
				9, 10, 11, 12,
				13, 14, 15, 16,
				0x00, 0xad, 0x1c, 0x40, // time we expect from fakeclock
			},
		},
		{
			// The timestamp area is full so add to the overflow count.
			name:              "multiple type 1 timestamps",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				68, 20, 21, 0x11,
				//            ^
				192, 168, 1, 12,
				1, 2, 3, 4,
				192, 168, 1, 13,
				5, 6, 7, 8,
			},
			// Overflow count is the top nibble of the 4th byte.
			replyOptions: header.IPv4Options{
				68, 20, 21, 0x21,
				//            ^
				192, 168, 1, 12,
				1, 2, 3, 4,
				192, 168, 1, 13,
				5, 6, 7, 8,
			},
		},
		{
			name:              "multiple type 1 timestamps with room",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				68, 28, 21, 0x01,
				192, 168, 1, 12,
				1, 2, 3, 4,
				192, 168, 1, 13,
				5, 6, 7, 8,
				0, 0, 0, 0,
				0, 0, 0, 0,
			},
			replyOptions: header.IPv4Options{
				68, 28, 29, 0x01,
				192, 168, 1, 12,
				1, 2, 3, 4,
				192, 168, 1, 13,
				5, 6, 7, 8,
				192, 168, 1, 58, // New IP Address.
				0x00, 0xad, 0x1c, 0x40, // time we expect from fakeclock
			},
		},
		{
			// Timestamp pointer uses one based counting so 0 is invalid.
			name:              "timestamp pointer invalid",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				68, 8, 0, 0x00,
				//      ^ 0 instead of 5 or more.
				0, 0, 0, 0,
			},
			shouldFail:          true,
			expectErrorICMP:     true,
			ICMPType:            header.ICMPv4ParamProblem,
			ICMPCode:            header.ICMPv4UnusedCode,
			paramProblemPointer: header.IPv4MinimumSize + 2,
		},
		{
			// Timestamp pointer cannot be less than 5. It must point past the header
			// which is 4 bytes. (1 based counting)
			name:              "timestamp pointer too small by 1",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				68, 8, header.IPv4OptionTimestampHdrLength, 0x00,
				//          ^ header is 4 bytes, so 4 should fail.
				0, 0, 0, 0,
			},
			shouldFail:          true,
			expectErrorICMP:     true,
			ICMPType:            header.ICMPv4ParamProblem,
			ICMPCode:            header.ICMPv4UnusedCode,
			paramProblemPointer: header.IPv4MinimumSize + header.IPv4OptTSPointerOffset,
		},
		{
			name:              "valid timestamp pointer",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				68, 8, header.IPv4OptionTimestampHdrLength + 1, 0x00,
				//          ^ header is 4 bytes, so 5 should succeed.
				0, 0, 0, 0,
			},
			replyOptions: header.IPv4Options{
				68, 8, 9, 0x00,
				0x00, 0xad, 0x1c, 0x40, // time we expect from fakeclock
			},
		},
		{
			// Needs 8 bytes for a type 1 timestamp but there are only 4 free.
			name:              "bad timer element alignment",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				68, 20, 17, 0x01,
				//  ^^  ^^   20 byte area, next free spot at 17.
				192, 168, 1, 12,
				1, 2, 3, 4,
				0, 0, 0, 0,
				0, 0, 0, 0,
			},
			shouldFail:          true,
			expectErrorICMP:     true,
			ICMPType:            header.ICMPv4ParamProblem,
			ICMPCode:            header.ICMPv4UnusedCode,
			paramProblemPointer: header.IPv4MinimumSize + header.IPv4OptTSPointerOffset,
		},
		// End of option list with illegal option after it, which should be ignored.
		{
			name:              "end of options list",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				68, 12, 13, 0x11,
				192, 168, 1, 12,
				1, 2, 3, 4,
				0, 10, 3, 99, // EOL followed by junk
			},
			replyOptions: header.IPv4Options{
				68, 12, 13, 0x21,
				192, 168, 1, 12,
				1, 2, 3, 4,
				0,       // End of Options hides following bytes.
				0, 0, 0, // 3 bytes unknown option removed.
			},
		},
		{
			// Timestamp with a size much too small.
			name:              "timestamp truncated",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				68, 1, 0, 0,
				//  ^ Smallest possible is 8. Linux points at the 68.
			},
			shouldFail:          true,
			expectErrorICMP:     true,
			ICMPType:            header.ICMPv4ParamProblem,
			ICMPCode:            header.ICMPv4UnusedCode,
			paramProblemPointer: header.IPv4MinimumSize + pointerOffsetForInvalidLength,
		},
		{
			name:              "single record route with room",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				7, 7, 4, //  3 byte header
				0, 0, 0, 0,
				0,
			},
			replyOptions: header.IPv4Options{
				7, 7, 8, // 3 byte header
				192, 168, 1, 58, // New IP Address.
				0, // padding to multiple of 4 bytes.
			},
		},
		{
			name:              "multiple record route with room",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				7, 23, 20, //  3 byte header
				1, 2, 3, 4,
				5, 6, 7, 8,
				9, 10, 11, 12,
				13, 14, 15, 16,
				0, 0, 0, 0,
				0,
			},
			replyOptions: header.IPv4Options{
				7, 23, 24,
				1, 2, 3, 4,
				5, 6, 7, 8,
				9, 10, 11, 12,
				13, 14, 15, 16,
				192, 168, 1, 58, // New IP Address.
				0, // padding to multiple of 4 bytes.
			},
		},
		{
			name:              "single record route with no room",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				7, 7, 8, // 3 byte header
				1, 2, 3, 4,
				0,
			},
			replyOptions: header.IPv4Options{
				7, 7, 8, // 3 byte header
				1, 2, 3, 4,
				0, // padding to multiple of 4 bytes.
			},
		},
		{
			// Unlike timestamp, this should just succeed.
			name:              "multiple record route with no room",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				7, 23, 24, // 3 byte header
				1, 2, 3, 4,
				5, 6, 7, 8,
				9, 10, 11, 12,
				13, 14, 15, 16,
				17, 18, 19, 20,
				0,
			},
			replyOptions: header.IPv4Options{
				7, 23, 24,
				1, 2, 3, 4,
				5, 6, 7, 8,
				9, 10, 11, 12,
				13, 14, 15, 16,
				17, 18, 19, 20,
				0, // padding to multiple of 4 bytes.
			},
		},
		{
			// Pointer uses one based counting so 0 is invalid.
			name:              "record route pointer zero",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				7, 8, 0, // 3 byte header
				0, 0, 0, 0,
				0,
			},
			shouldFail:          true,
			expectErrorICMP:     true,
			ICMPType:            header.ICMPv4ParamProblem,
			ICMPCode:            header.ICMPv4UnusedCode,
			paramProblemPointer: header.IPv4MinimumSize + header.IPv4OptRRPointerOffset,
		},
		{
			// Pointer must be 4 or more as it must point past the 3 byte header
			// using 1 based counting. 3 should fail.
			name:              "record route pointer too small by 1",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				7, 8, header.IPv4OptionRecordRouteHdrLength, // 3 byte header
				0, 0, 0, 0,
				0,
			},
			shouldFail:          true,
			expectErrorICMP:     true,
			ICMPType:            header.ICMPv4ParamProblem,
			ICMPCode:            header.ICMPv4UnusedCode,
			paramProblemPointer: header.IPv4MinimumSize + header.IPv4OptRRPointerOffset,
		},
		{
			// Pointer must be 4 or more as it must point past the 3 byte header
			// using 1 based counting. Check 4 passes. (Duplicates "single
			// record route with room")
			name:              "valid record route pointer",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				7, 7, header.IPv4OptionRecordRouteHdrLength + 1, // 3 byte header
				0, 0, 0, 0,
				0,
			},
			replyOptions: header.IPv4Options{
				7, 7, 8, // 3 byte header
				192, 168, 1, 58, // New IP Address.
				0, // padding to multiple of 4 bytes.
			},
		},
		{
			// Confirm Linux bug for bug compatibility.
			// Linux returns slot 22 but the error is in slot 21.
			name:              "multiple record route with not enough room",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				7, 8, 8, // 3 byte header
				// ^  ^ Linux points here. We must too.
				// | Not enough room. 1 byte free, need 4.
				1, 2, 3, 4,
				0,
			},
			shouldFail:          true,
			expectErrorICMP:     true,
			ICMPType:            header.ICMPv4ParamProblem,
			ICMPCode:            header.ICMPv4UnusedCode,
			paramProblemPointer: header.IPv4MinimumSize + header.IPv4OptRRPointerOffset,
		},
		{
			name:              "duplicate record route",
			maxTotalLength:    ipv4.MaxTotalSize,
			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
			TTL:               ttl,
			options: header.IPv4Options{
				7, 7, 8, // 3 byte header
				1, 2, 3, 4,
				7, 7, 8, // 3 byte header
				1, 2, 3, 4,
				0, 0, // pad
			},
			shouldFail:          true,
			expectErrorICMP:     true,
			ICMPType:            header.ICMPv4ParamProblem,
			ICMPCode:            header.ICMPv4UnusedCode,
			paramProblemPointer: header.IPv4MinimumSize + 7,
		},
	}

	for _, test := range tests {
		t.Run(test.name, func(t *testing.T) {
			clock := faketime.NewManualClock()
			s := stack.New(stack.Options{
				NetworkProtocols:   []stack.NetworkProtocolFactory{ipv4.NewProtocol},
				TransportProtocols: []stack.TransportProtocolFactory{icmp.NewProtocol4},
				Clock:              clock,
			})
			// Advance the clock by some unimportant amount to make
			// it give a more recognisable signature than 00,00,00,00.
			clock.Advance(time.Millisecond * randomTimeOffset)

			// We expect at most a single packet in response to our ICMP Echo Request.
			e := channel.New(1, ipv4.MaxTotalSize, "")
			if err := s.CreateNIC(nicID, e); err != nil {
				t.Fatalf("CreateNIC(%d, _): %s", nicID, err)
			}
			ipv4ProtoAddr := tcpip.ProtocolAddress{Protocol: header.IPv4ProtocolNumber, AddressWithPrefix: ipv4Addr}
			if err := s.AddProtocolAddress(nicID, ipv4ProtoAddr); err != nil {
				t.Fatalf("AddProtocolAddress(%d, %#v): %s", nicID, ipv4ProtoAddr, err)
			}

			// Default routes for IPv4 so ICMP can find a route to the remote
			// node when attempting to send the ICMP Echo Reply.
			s.SetRouteTable([]tcpip.Route{
				{
					Destination: header.IPv4EmptySubnet,
					NIC:         nicID,
				},
			})

			if len(test.options)%4 != 0 {
				t.Fatalf("options must be aligned to 32 bits, invalid test options: %x (len=%d)", test.options, len(test.options))
			}
			ipHeaderLength := header.IPv4MinimumSize + len(test.options)
			if ipHeaderLength > header.IPv4MaximumHeaderSize {
				t.Fatalf("IP header length too large: got = %d, want <= %d ", ipHeaderLength, header.IPv4MaximumHeaderSize)
			}
			totalLen := uint16(ipHeaderLength + header.ICMPv4MinimumSize)
			hdr := buffer.NewPrependable(int(totalLen))
			icmpH := header.ICMPv4(hdr.Prepend(header.ICMPv4MinimumSize))

			// Specify ident/seq to make sure we get the same in the response.
			icmpH.SetIdent(randomIdent)
			icmpH.SetSequence(randomSequence)
			icmpH.SetType(header.ICMPv4Echo)
			icmpH.SetCode(header.ICMPv4UnusedCode)
			icmpH.SetChecksum(0)
			icmpH.SetChecksum(^header.Checksum(icmpH, 0))
			ip := header.IPv4(hdr.Prepend(ipHeaderLength))
			if test.maxTotalLength < totalLen {
				totalLen = test.maxTotalLength
			}
			ip.Encode(&header.IPv4Fields{
				TotalLength: totalLen,
				Protocol:    test.transportProtocol,
				TTL:         test.TTL,
				SrcAddr:     remoteIPv4Addr,
				DstAddr:     ipv4Addr.Address,
			})
			if test.headerLength != 0 {
				ip.SetHeaderLength(test.headerLength)
			} else {
				// Set the calculated header length, since we may manually add options.
				ip.SetHeaderLength(uint8(ipHeaderLength))
			}
			if len(test.options) != 0 {
				// Copy options manually. We do not use Encode for options so we can
				// verify malformed options with handcrafted payloads.
				if want, got := copy(ip.Options(), test.options), len(test.options); want != got {
					t.Fatalf("got copy(ip.Options(), test.options) = %d, want = %d", got, want)
				}
			}
			ip.SetChecksum(0)
			ipHeaderChecksum := ip.CalculateChecksum()
			if test.badHeaderChecksum {
				ipHeaderChecksum += 42
			}
			ip.SetChecksum(^ipHeaderChecksum)
			requestPkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
				Data: hdr.View().ToVectorisedView(),
			})
			e.InjectInbound(header.IPv4ProtocolNumber, requestPkt)
			reply, ok := e.Read()
			if !ok {
				if test.shouldFail {
					if test.expectErrorICMP {
						t.Fatalf("ICMP error response (type %d, code %d) missing", test.ICMPType, test.ICMPCode)
					}
					return // Expected silent failure.
				}
				t.Fatal("expected ICMP echo reply missing")
			}

			// We didn't expect a packet. Register our surprise but carry on to
			// provide more information about what we got.
			if test.shouldFail && !test.expectErrorICMP {
				t.Error("unexpected packet response")
			}

			// Check the route that brought the packet to us.
			if reply.Route.LocalAddress != ipv4Addr.Address {
				t.Errorf("got pkt.Route.LocalAddress = %s, want = %s", reply.Route.LocalAddress, ipv4Addr.Address)
			}
			if reply.Route.RemoteAddress != remoteIPv4Addr {
				t.Errorf("got pkt.Route.RemoteAddress = %s, want = %s", reply.Route.RemoteAddress, remoteIPv4Addr)
			}

			// Make sure it's all in one buffer for checker.
			replyIPHeader := header.IPv4(stack.PayloadSince(reply.Pkt.NetworkHeader()))

			// At this stage we only know it's probably an IP+ICMP header so verify
			// that much.
			checker.IPv4(t, replyIPHeader,
				checker.SrcAddr(ipv4Addr.Address),
				checker.DstAddr(remoteIPv4Addr),
				checker.ICMPv4(
					checker.ICMPv4Checksum(),
				),
			)

			// Don't proceed any further if the checker found problems.
			if t.Failed() {
				t.FailNow()
			}

			// OK it's ICMP. We can safely look at the type now.
			replyICMPHeader := header.ICMPv4(replyIPHeader.Payload())
			switch replyICMPHeader.Type() {
			case header.ICMPv4ParamProblem:
				if !test.shouldFail {
					t.Fatalf("got Parameter Problem with pointer %d, wanted Echo Reply", replyICMPHeader.Pointer())
				}
				if !test.expectErrorICMP {
					t.Fatalf("got Parameter Problem with pointer %d, wanted no response", replyICMPHeader.Pointer())
				}
				checker.IPv4(t, replyIPHeader,
					checker.IPFullLength(uint16(header.IPv4MinimumSize+header.ICMPv4MinimumSize+requestPkt.Size())),
					checker.IPv4HeaderLength(header.IPv4MinimumSize),
					checker.ICMPv4(
						checker.ICMPv4Type(test.ICMPType),
						checker.ICMPv4Code(test.ICMPCode),
						checker.ICMPv4Pointer(test.paramProblemPointer),
						checker.ICMPv4Payload(hdr.View()),
					),
				)
				return
			case header.ICMPv4DstUnreachable:
				if !test.shouldFail {
					t.Fatalf("got ICMP error packet type %d, code %d, wanted Echo Reply",
						header.ICMPv4DstUnreachable, replyICMPHeader.Code())
				}
				if !test.expectErrorICMP {
					t.Fatalf("got ICMP error packet type %d, code %d, wanted no response",
						header.ICMPv4DstUnreachable, replyICMPHeader.Code())
				}
				checker.IPv4(t, replyIPHeader,
					checker.IPFullLength(uint16(header.IPv4MinimumSize+header.ICMPv4MinimumSize+requestPkt.Size())),
					checker.IPv4HeaderLength(header.IPv4MinimumSize),
					checker.ICMPv4(
						checker.ICMPv4Type(test.ICMPType),
						checker.ICMPv4Code(test.ICMPCode),
						checker.ICMPv4Payload(hdr.View()),
					),
				)
				return
			case header.ICMPv4EchoReply:
				if test.shouldFail {
					if !test.expectErrorICMP {
						t.Error("got Echo Reply packet, want no response")
					} else {
						t.Errorf("got Echo Reply, want ICMP error type %d, code %d", test.ICMPType, test.ICMPCode)
					}
				}
				// If the IP options change size then the packet will change size, so
				// some IP header fields will need to be adjusted for the checks.
				sizeChange := len(test.replyOptions) - len(test.options)

				checker.IPv4(t, replyIPHeader,
					checker.IPv4HeaderLength(ipHeaderLength+sizeChange),
					checker.IPv4Options(test.replyOptions),
					checker.IPFullLength(uint16(requestPkt.Size()+sizeChange)),
					checker.ICMPv4(
						checker.ICMPv4Checksum(),
						checker.ICMPv4Code(header.ICMPv4UnusedCode),
						checker.ICMPv4Seq(randomSequence),
						checker.ICMPv4Ident(randomIdent),
					),
				)
			default:
				t.Fatalf("unexpected ICMP response, got type %d, want = %d, %d or %d",
					replyICMPHeader.Type(), header.ICMPv4EchoReply, header.ICMPv4DstUnreachable, header.ICMPv4ParamProblem)
			}
		})
	}
}

// compareFragments compares the contents of a set of fragmented packets against
// the contents of a source packet.
//
// If withIPHeader is set to true, we will validate the fragmented packets' IP
// headers against the source packet's IP header. If set to false, we validate
// the fragmented packets' IP headers against each other.
func compareFragments(packets []*stack.PacketBuffer, sourcePacket *stack.PacketBuffer, mtu uint32, wantFragments []fragmentInfo, proto tcpip.TransportProtocolNumber, withIPHeader bool, expectedAvailableHeaderBytes int) error {
	// Make a complete array of the sourcePacket packet.
	var source header.IPv4
	vv := buffer.NewVectorisedView(sourcePacket.Size(), sourcePacket.Views())

	// If the packet to be fragmented contains an IPv4 header, use that header for
	// validating fragment headers. Else, use the header of the first fragment.
	if withIPHeader {
		source = header.IPv4(vv.ToView())
	} else {
		source = header.IPv4(packets[0].NetworkHeader().View())
		source = append(source, vv.ToView()...)
	}

	// Make a copy of the IP header, which will be modified in some fields to make
	// an expected header.
	sourceCopy := header.IPv4(append(buffer.View(nil), source[:source.HeaderLength()]...))
	sourceCopy.SetChecksum(0)
	sourceCopy.SetFlagsFragmentOffset(0, 0)
	sourceCopy.SetTotalLength(0)
	// Build up an array of the bytes sent.
	var reassembledPayload buffer.VectorisedView
	for i, packet := range packets {
		// Confirm that the packet is valid.
		allBytes := buffer.NewVectorisedView(packet.Size(), packet.Views())
		fragmentIPHeader := header.IPv4(allBytes.ToView())
		if !fragmentIPHeader.IsValid(len(fragmentIPHeader)) {
			return fmt.Errorf("fragment #%d: IP packet is invalid:\n%s", i, hex.Dump(fragmentIPHeader))
		}
		if got := len(fragmentIPHeader); got > int(mtu) {
			return fmt.Errorf("fragment #%d: got len(fragmentIPHeader) = %d, want <= %d", i, got, mtu)
		}
		if got := fragmentIPHeader.TransportProtocol(); got != proto {
			return fmt.Errorf("fragment #%d: got fragmentIPHeader.TransportProtocol() = %d, want = %d", i, got, uint8(proto))
		}
		if got, want := packet.NetworkProtocolNumber, sourcePacket.NetworkProtocolNumber; got != want {
			return fmt.Errorf("fragment #%d: got fragment.NetworkProtocolNumber = %d, want = %d", i, got, want)
		}
		if got := packet.AvailableHeaderBytes(); got != expectedAvailableHeaderBytes {
			return fmt.Errorf("fragment #%d: got packet.AvailableHeaderBytes() = %d, want = %d", i, got, expectedAvailableHeaderBytes)
		}
		if got, want := fragmentIPHeader.CalculateChecksum(), uint16(0xffff); got != want {
			return fmt.Errorf("fragment #%d: got ip.CalculateChecksum() = %#x, want = %#x", i, got, want)
		}
		if wantFragments[i].more {
			sourceCopy.SetFlagsFragmentOffset(sourceCopy.Flags()|header.IPv4FlagMoreFragments, wantFragments[i].offset)
		} else {
			sourceCopy.SetFlagsFragmentOffset(sourceCopy.Flags()&^header.IPv4FlagMoreFragments, wantFragments[i].offset)
		}
		reassembledPayload.AppendView(packet.TransportHeader().View())
		reassembledPayload.AppendView(packet.Data().AsRange().ToOwnedView())
		// Clear out the checksum and length from the ip because we can't compare
		// it.
		sourceCopy.SetTotalLength(wantFragments[i].payloadSize + header.IPv4MinimumSize)
		sourceCopy.SetChecksum(0)
		sourceCopy.SetChecksum(^sourceCopy.CalculateChecksum())

		// If we are validating against the original IP header, we should exclude the
		// ID field, which will only be set fo fragmented packets.
		if withIPHeader {
			fragmentIPHeader.SetID(0)
			fragmentIPHeader.SetChecksum(0)
			fragmentIPHeader.SetChecksum(^fragmentIPHeader.CalculateChecksum())
		}
		if diff := cmp.Diff(fragmentIPHeader[:fragmentIPHeader.HeaderLength()], sourceCopy[:sourceCopy.HeaderLength()]); diff != "" {
			return fmt.Errorf("fragment #%d: fragmentIPHeader mismatch (-want +got):\n%s", i, diff)
		}
	}

	expected := buffer.View(source[source.HeaderLength():])
	if diff := cmp.Diff(expected, reassembledPayload.ToView()); diff != "" {
		return fmt.Errorf("reassembledPayload mismatch (-want +got):\n%s", diff)
	}

	return nil
}

type fragmentInfo struct {
	offset      uint16
	more        bool
	payloadSize uint16
}

var fragmentationTests = []struct {
	description           string
	mtu                   uint32
	transportHeaderLength int
	payloadSize           int
	wantFragments         []fragmentInfo
}{
	{
		description:           "No fragmentation",
		mtu:                   1280,
		transportHeaderLength: 0,
		payloadSize:           1000,
		wantFragments: []fragmentInfo{
			{offset: 0, payloadSize: 1000, more: false},
		},
	},
	{
		description:           "Fragmented",
		mtu:                   1280,
		transportHeaderLength: 0,
		payloadSize:           2000,
		wantFragments: []fragmentInfo{
			{offset: 0, payloadSize: 1256, more: true},
			{offset: 1256, payloadSize: 744, more: false},
		},
	},
	{
		description:           "Fragmented with the minimum mtu",
		mtu:                   header.IPv4MinimumMTU,
		transportHeaderLength: 0,
		payloadSize:           100,
		wantFragments: []fragmentInfo{
			{offset: 0, payloadSize: 48, more: true},
			{offset: 48, payloadSize: 48, more: true},
			{offset: 96, payloadSize: 4, more: false},
		},
	},
	{
		description:           "Fragmented with mtu not a multiple of 8",
		mtu:                   header.IPv4MinimumMTU + 1,
		transportHeaderLength: 0,
		payloadSize:           100,
		wantFragments: []fragmentInfo{
			{offset: 0, payloadSize: 48, more: true},
			{offset: 48, payloadSize: 48, more: true},
			{offset: 96, payloadSize: 4, more: false},
		},
	},
	{
		description:           "No fragmentation with big header",
		mtu:                   2000,
		transportHeaderLength: 100,
		payloadSize:           1000,
		wantFragments: []fragmentInfo{
			{offset: 0, payloadSize: 1100, more: false},
		},
	},
	{
		description:           "Fragmented with big header",
		mtu:                   1280,
		transportHeaderLength: 100,
		payloadSize:           1200,
		wantFragments: []fragmentInfo{
			{offset: 0, payloadSize: 1256, more: true},
			{offset: 1256, payloadSize: 44, more: false},
		},
	},
	{
		description:           "Fragmented with MTU smaller than header",
		mtu:                   300,
		transportHeaderLength: 1000,
		payloadSize:           500,
		wantFragments: []fragmentInfo{
			{offset: 0, payloadSize: 280, more: true},
			{offset: 280, payloadSize: 280, more: true},
			{offset: 560, payloadSize: 280, more: true},
			{offset: 840, payloadSize: 280, more: true},
			{offset: 1120, payloadSize: 280, more: true},
			{offset: 1400, payloadSize: 100, more: false},
		},
	},
}

func TestFragmentationWritePacket(t *testing.T) {
	const ttl = 42

	for _, ft := range fragmentationTests {
		t.Run(ft.description, func(t *testing.T) {
			ep := iptestutil.NewMockLinkEndpoint(ft.mtu, nil, math.MaxInt32)
			r := buildRoute(t, ep)
			pkt := iptestutil.MakeRandPkt(ft.transportHeaderLength, extraHeaderReserve+header.IPv4MinimumSize, []int{ft.payloadSize}, header.IPv4ProtocolNumber)
			source := pkt.Clone()
			err := r.WritePacket(stack.NetworkHeaderParams{
				Protocol: tcp.ProtocolNumber,
				TTL:      ttl,
				TOS:      stack.DefaultTOS,
			}, pkt)
			if err != nil {
				t.Fatalf("r.WritePacket(...): %s", err)
			}
			if got := len(ep.WrittenPackets); got != len(ft.wantFragments) {
				t.Errorf("got len(ep.WrittenPackets) = %d, want = %d", got, len(ft.wantFragments))
			}
			if got := int(r.Stats().IP.PacketsSent.Value()); got != len(ft.wantFragments) {
				t.Errorf("got c.Route.Stats().IP.PacketsSent.Value() = %d, want = %d", got, len(ft.wantFragments))
			}
			if got := r.Stats().IP.OutgoingPacketErrors.Value(); got != 0 {
				t.Errorf("got r.Stats().IP.OutgoingPacketErrors.Value() = %d, want = 0", got)
			}
			if err := compareFragments(ep.WrittenPackets, source, ft.mtu, ft.wantFragments, tcp.ProtocolNumber, false /* withIPHeader */, extraHeaderReserve); err != nil {
				t.Error(err)
			}
		})
	}
}

func TestFragmentationWritePackets(t *testing.T) {
	const ttl = 42
	writePacketsTests := []struct {
		description  string
		insertBefore int
		insertAfter  int
	}{
		{
			description:  "Single packet",
			insertBefore: 0,
			insertAfter:  0,
		},
		{
			description:  "With packet before",
			insertBefore: 1,
			insertAfter:  0,
		},
		{
			description:  "With packet after",
			insertBefore: 0,
			insertAfter:  1,
		},
		{
			description:  "With packet before and after",
			insertBefore: 1,
			insertAfter:  1,
		},
	}
	tinyPacket := iptestutil.MakeRandPkt(header.TCPMinimumSize, extraHeaderReserve+header.IPv4MinimumSize, []int{1}, header.IPv4ProtocolNumber)

	for _, test := range writePacketsTests {
		t.Run(test.description, func(t *testing.T) {
			for _, ft := range fragmentationTests {
				t.Run(ft.description, func(t *testing.T) {
					var pkts stack.PacketBufferList
					for i := 0; i < test.insertBefore; i++ {
						pkts.PushBack(tinyPacket.Clone())
					}
					pkt := iptestutil.MakeRandPkt(ft.transportHeaderLength, extraHeaderReserve+header.IPv4MinimumSize, []int{ft.payloadSize}, header.IPv4ProtocolNumber)
					pkts.PushBack(pkt.Clone())
					for i := 0; i < test.insertAfter; i++ {
						pkts.PushBack(tinyPacket.Clone())
					}

					ep := iptestutil.NewMockLinkEndpoint(ft.mtu, nil, math.MaxInt32)
					r := buildRoute(t, ep)

					wantTotalPackets := len(ft.wantFragments) + test.insertBefore + test.insertAfter
					n, err := r.WritePackets(pkts, stack.NetworkHeaderParams{
						Protocol: tcp.ProtocolNumber,
						TTL:      ttl,
						TOS:      stack.DefaultTOS,
					})
					if err != nil {
						t.Errorf("got WritePackets(_, _, _) = (_, %s), want = (_, nil)", err)
					}
					if n != wantTotalPackets {
						t.Errorf("got WritePackets(_, _, _) = (%d, _), want = (%d, _)", n, wantTotalPackets)
					}
					if got := len(ep.WrittenPackets); got != wantTotalPackets {
						t.Errorf("got len(ep.WrittenPackets) = %d, want = %d", got, wantTotalPackets)
					}
					if got := int(r.Stats().IP.PacketsSent.Value()); got != wantTotalPackets {
						t.Errorf("got c.Route.Stats().IP.PacketsSent.Value() = %d, want = %d", got, wantTotalPackets)
					}
					if got := int(r.Stats().IP.OutgoingPacketErrors.Value()); got != 0 {
						t.Errorf("got r.Stats().IP.OutgoingPacketErrors.Value() = %d, want = 0", got)
					}

					if wantTotalPackets == 0 {
						return
					}

					fragments := ep.WrittenPackets[test.insertBefore : len(ft.wantFragments)+test.insertBefore]
					if err := compareFragments(fragments, pkt, ft.mtu, ft.wantFragments, tcp.ProtocolNumber, false /* withIPHeader */, extraHeaderReserve); err != nil {
						t.Error(err)
					}
				})
			}
		})
	}
}

// TestFragmentationErrors checks that errors are returned from WritePacket
// correctly.
func TestFragmentationErrors(t *testing.T) {
	const ttl = 42

	tests := []struct {
		description           string
		mtu                   uint32
		transportHeaderLength int
		payloadSize           int
		allowPackets          int
		outgoingErrors        int
		mockError             tcpip.Error
		wantError             tcpip.Error
	}{
		{
			description:           "No frag",
			mtu:                   2000,
			payloadSize:           1000,
			transportHeaderLength: 0,
			allowPackets:          0,
			outgoingErrors:        1,
			mockError:             &tcpip.ErrAborted{},
			wantError:             &tcpip.ErrAborted{},
		},
		{
			description:           "Error on first frag",
			mtu:                   500,
			payloadSize:           1000,
			transportHeaderLength: 0,
			allowPackets:          0,
			outgoingErrors:        3,
			mockError:             &tcpip.ErrAborted{},
			wantError:             &tcpip.ErrAborted{},
		},
		{
			description:           "Error on second frag",
			mtu:                   500,
			payloadSize:           1000,
			transportHeaderLength: 0,
			allowPackets:          1,
			outgoingErrors:        2,
			mockError:             &tcpip.ErrAborted{},
			wantError:             &tcpip.ErrAborted{},
		},
		{
			description:           "Error on first frag MTU smaller than header",
			mtu:                   500,
			transportHeaderLength: 1000,
			payloadSize:           500,
			allowPackets:          0,
			outgoingErrors:        4,
			mockError:             &tcpip.ErrAborted{},
			wantError:             &tcpip.ErrAborted{},
		},
		{
			description:           "Error when MTU is smaller than IPv4 minimum MTU",
			mtu:                   header.IPv4MinimumMTU - 1,
			transportHeaderLength: 0,
			payloadSize:           500,
			allowPackets:          0,
			outgoingErrors:        1,
			mockError:             nil,
			wantError:             &tcpip.ErrInvalidEndpointState{},
		},
	}

	for _, ft := range tests {
		t.Run(ft.description, func(t *testing.T) {
			pkt := iptestutil.MakeRandPkt(ft.transportHeaderLength, extraHeaderReserve+header.IPv4MinimumSize, []int{ft.payloadSize}, header.IPv4ProtocolNumber)
			ep := iptestutil.NewMockLinkEndpoint(ft.mtu, ft.mockError, ft.allowPackets)
			r := buildRoute(t, ep)
			err := r.WritePacket(stack.NetworkHeaderParams{
				Protocol: tcp.ProtocolNumber,
				TTL:      ttl,
				TOS:      stack.DefaultTOS,
			}, pkt)
			if diff := cmp.Diff(ft.wantError, err); diff != "" {
				t.Fatalf("unexpected error from r.WritePacket(_, _, _), (-want, +got):\n%s", diff)
			}
			if got := int(r.Stats().IP.PacketsSent.Value()); got != ft.allowPackets {
				t.Errorf("got r.Stats().IP.PacketsSent.Value() = %d, want = %d", got, ft.allowPackets)
			}
			if got := int(r.Stats().IP.OutgoingPacketErrors.Value()); got != ft.outgoingErrors {
				t.Errorf("got r.Stats().IP.OutgoingPacketErrors.Value() = %d, want = %d", got, ft.outgoingErrors)
			}
		})
	}
}

func TestInvalidFragments(t *testing.T) {
	const (
		nicID    = 1
		linkAddr = tcpip.LinkAddress("\x0a\x0b\x0c\x0d\x0e\x0e")
		addr1    = "\x0a\x00\x00\x01"
		addr2    = "\x0a\x00\x00\x02"
		tos      = 0
		ident    = 1
		ttl      = 48
		protocol = 6
	)

	payloadGen := func(payloadLen int) []byte {
		payload := make([]byte, payloadLen)
		for i := 0; i < len(payload); i++ {
			payload[i] = 0x30
		}
		return payload
	}

	type fragmentData struct {
		ipv4fields header.IPv4Fields
		// 0 means insert the correct IHL. Non 0 means override the correct IHL.
		overrideIHL  int // For 0 use 1 as it is an int and will be divided by 4.
		payload      []byte
		autoChecksum bool // If true, the Checksum field will be overwritten.
	}

	tests := []struct {
		name                   string
		fragments              []fragmentData
		wantMalformedIPPackets uint64
		wantMalformedFragments uint64
	}{
		{
			name: "IHL and TotalLength zero, FragmentOffset non-zero",
			fragments: []fragmentData{
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    0,
						ID:             ident,
						Flags:          header.IPv4FlagDontFragment | header.IPv4FlagMoreFragments,
						FragmentOffset: 59776,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					overrideIHL:  1, // See note above.
					payload:      payloadGen(12),
					autoChecksum: true,
				},
			},
			wantMalformedIPPackets: 1,
			wantMalformedFragments: 0,
		},
		{
			name: "IHL and TotalLength zero, FragmentOffset zero",
			fragments: []fragmentData{
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    0,
						ID:             ident,
						Flags:          header.IPv4FlagMoreFragments,
						FragmentOffset: 0,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					overrideIHL:  1, // See note above.
					payload:      payloadGen(12),
					autoChecksum: true,
				},
			},
			wantMalformedIPPackets: 1,
			wantMalformedFragments: 0,
		},
		{
			// Payload 17 octets and Fragment offset 65520
			// Leading to the fragment end to be past 65536.
			name: "fragment ends past 65536",
			fragments: []fragmentData{
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    header.IPv4MinimumSize + 17,
						ID:             ident,
						Flags:          0,
						FragmentOffset: 65520,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload:      payloadGen(17),
					autoChecksum: true,
				},
			},
			wantMalformedIPPackets: 1,
			wantMalformedFragments: 1,
		},
		{
			// Payload 16 octets and fragment offset 65520
			// Leading to the fragment end to be exactly 65536.
			name: "fragment ends exactly at 65536",
			fragments: []fragmentData{
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    header.IPv4MinimumSize + 16,
						ID:             ident,
						Flags:          0,
						FragmentOffset: 65520,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload:      payloadGen(16),
					autoChecksum: true,
				},
			},
			wantMalformedIPPackets: 0,
			wantMalformedFragments: 0,
		},
		{
			name: "IHL less than IPv4 minimum size",
			fragments: []fragmentData{
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    header.IPv4MinimumSize + 28,
						ID:             ident,
						Flags:          0,
						FragmentOffset: 1944,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload:      payloadGen(28),
					overrideIHL:  header.IPv4MinimumSize - 12,
					autoChecksum: true,
				},
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    header.IPv4MinimumSize - 12,
						ID:             ident,
						Flags:          header.IPv4FlagMoreFragments,
						FragmentOffset: 0,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload:      payloadGen(28),
					overrideIHL:  header.IPv4MinimumSize - 12,
					autoChecksum: true,
				},
			},
			wantMalformedIPPackets: 2,
			wantMalformedFragments: 0,
		},
		{
			name: "fragment with short TotalLength and extra payload",
			fragments: []fragmentData{
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    header.IPv4MinimumSize + 28,
						ID:             ident,
						Flags:          0,
						FragmentOffset: 28816,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload:      payloadGen(28),
					overrideIHL:  header.IPv4MinimumSize + 4,
					autoChecksum: true,
				},
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    header.IPv4MinimumSize + 4,
						ID:             ident,
						Flags:          header.IPv4FlagMoreFragments,
						FragmentOffset: 0,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload:      payloadGen(28),
					overrideIHL:  header.IPv4MinimumSize + 4,
					autoChecksum: true,
				},
			},
			wantMalformedIPPackets: 1,
			wantMalformedFragments: 1,
		},
		{
			name: "multiple fragments with More Fragments flag set to false",
			fragments: []fragmentData{
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    header.IPv4MinimumSize + 8,
						ID:             ident,
						Flags:          0,
						FragmentOffset: 128,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload:      payloadGen(8),
					autoChecksum: true,
				},
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    header.IPv4MinimumSize + 8,
						ID:             ident,
						Flags:          0,
						FragmentOffset: 8,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload:      payloadGen(8),
					autoChecksum: true,
				},
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    header.IPv4MinimumSize + 8,
						ID:             ident,
						Flags:          header.IPv4FlagMoreFragments,
						FragmentOffset: 0,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload:      payloadGen(8),
					autoChecksum: true,
				},
			},
			wantMalformedIPPackets: 1,
			wantMalformedFragments: 1,
		},
	}

	for _, test := range tests {
		t.Run(test.name, func(t *testing.T) {
			s := stack.New(stack.Options{
				NetworkProtocols: []stack.NetworkProtocolFactory{
					ipv4.NewProtocol,
				},
			})
			e := channel.New(0, 1500, linkAddr)
			if err := s.CreateNIC(nicID, e); err != nil {
				t.Fatalf("CreateNIC(%d, _) = %s", nicID, err)
			}
			if err := s.AddAddress(nicID, ipv4.ProtocolNumber, addr2); err != nil {
				t.Fatalf("AddAddress(%d, %d, %s) = %s", nicID, header.IPv4ProtocolNumber, addr2, err)
			}

			for _, f := range test.fragments {
				pktSize := header.IPv4MinimumSize + len(f.payload)
				hdr := buffer.NewPrependable(pktSize)

				ip := header.IPv4(hdr.Prepend(pktSize))
				ip.Encode(&f.ipv4fields)
				if want, got := len(f.payload), copy(ip[header.IPv4MinimumSize:], f.payload); want != got {
					t.Fatalf("copied %d bytes, expected %d bytes.", got, want)
				}
				// Encode sets this up correctly. If we want a different value for
				// testing then we need to overwrite the good value.
				if f.overrideIHL != 0 {
					ip.SetHeaderLength(uint8(f.overrideIHL))
					// If we are asked to add options (type not specified) then pad
					// with 0 (EOL). RFC 791 page 23 says "The padding is zero".
					for i := header.IPv4MinimumSize; i < f.overrideIHL; i++ {
						ip[i] = byte(header.IPv4OptionListEndType)
					}
				}

				if f.autoChecksum {
					ip.SetChecksum(0)
					ip.SetChecksum(^ip.CalculateChecksum())
				}

				vv := hdr.View().ToVectorisedView()
				e.InjectInbound(header.IPv4ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
					Data: vv,
				}))
			}

			if got, want := s.Stats().IP.MalformedPacketsReceived.Value(), test.wantMalformedIPPackets; got != want {
				t.Errorf("incorrect Stats.IP.MalformedPacketsReceived, got: %d, want: %d", got, want)
			}
			if got, want := s.Stats().IP.MalformedFragmentsReceived.Value(), test.wantMalformedFragments; got != want {
				t.Errorf("incorrect Stats.IP.MalformedFragmentsReceived, got: %d, want: %d", got, want)
			}
		})
	}
}

func TestFragmentReassemblyTimeout(t *testing.T) {
	const (
		nicID    = 1
		linkAddr = tcpip.LinkAddress("\x0a\x0b\x0c\x0d\x0e\x0e")
		addr1    = "\x0a\x00\x00\x01"
		addr2    = "\x0a\x00\x00\x02"
		tos      = 0
		ident    = 1
		ttl      = 48
		protocol = 99
		data     = "TEST_FRAGMENT_REASSEMBLY_TIMEOUT"
	)

	type fragmentData struct {
		ipv4fields header.IPv4Fields
		payload    []byte
	}

	tests := []struct {
		name       string
		fragments  []fragmentData
		expectICMP bool
	}{
		{
			name: "first fragment only",
			fragments: []fragmentData{
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    header.IPv4MinimumSize + 16,
						ID:             ident,
						Flags:          header.IPv4FlagMoreFragments,
						FragmentOffset: 0,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload: []byte(data)[:16],
				},
			},
			expectICMP: true,
		},
		{
			name: "two first fragments",
			fragments: []fragmentData{
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    header.IPv4MinimumSize + 16,
						ID:             ident,
						Flags:          header.IPv4FlagMoreFragments,
						FragmentOffset: 0,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload: []byte(data)[:16],
				},
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    header.IPv4MinimumSize + 16,
						ID:             ident,
						Flags:          header.IPv4FlagMoreFragments,
						FragmentOffset: 0,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload: []byte(data)[:16],
				},
			},
			expectICMP: true,
		},
		{
			name: "second fragment only",
			fragments: []fragmentData{
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    uint16(header.IPv4MinimumSize + len(data) - 16),
						ID:             ident,
						Flags:          0,
						FragmentOffset: 8,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload: []byte(data)[16:],
				},
			},
			expectICMP: false,
		},
		{
			name: "two fragments with a gap",
			fragments: []fragmentData{
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    header.IPv4MinimumSize + 8,
						ID:             ident,
						Flags:          header.IPv4FlagMoreFragments,
						FragmentOffset: 0,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload: []byte(data)[:8],
				},
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    uint16(header.IPv4MinimumSize + len(data) - 16),
						ID:             ident,
						Flags:          0,
						FragmentOffset: 16,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload: []byte(data)[16:],
				},
			},
			expectICMP: true,
		},
		{
			name: "two fragments with a gap in reverse order",
			fragments: []fragmentData{
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    uint16(header.IPv4MinimumSize + len(data) - 16),
						ID:             ident,
						Flags:          0,
						FragmentOffset: 16,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload: []byte(data)[16:],
				},
				{
					ipv4fields: header.IPv4Fields{
						TOS:            tos,
						TotalLength:    header.IPv4MinimumSize + 8,
						ID:             ident,
						Flags:          header.IPv4FlagMoreFragments,
						FragmentOffset: 0,
						TTL:            ttl,
						Protocol:       protocol,
						SrcAddr:        addr1,
						DstAddr:        addr2,
					},
					payload: []byte(data)[:8],
				},
			},
			expectICMP: true,
		},
	}

	for _, test := range tests {
		t.Run(test.name, func(t *testing.T) {
			clock := faketime.NewManualClock()
			s := stack.New(stack.Options{
				NetworkProtocols: []stack.NetworkProtocolFactory{
					ipv4.NewProtocol,
				},
				Clock: clock,
			})
			e := channel.New(1, 1500, linkAddr)
			if err := s.CreateNIC(nicID, e); err != nil {
				t.Fatalf("CreateNIC(%d, _) = %s", nicID, err)
			}
			if err := s.AddAddress(nicID, ipv4.ProtocolNumber, addr2); err != nil {
				t.Fatalf("AddAddress(%d, %d, %s) = %s", nicID, header.IPv4ProtocolNumber, addr2, err)
			}
			s.SetRouteTable([]tcpip.Route{{
				Destination: header.IPv4EmptySubnet,
				NIC:         nicID,
			}})

			var firstFragmentSent buffer.View
			for _, f := range test.fragments {
				pktSize := header.IPv4MinimumSize
				hdr := buffer.NewPrependable(pktSize)

				ip := header.IPv4(hdr.Prepend(pktSize))
				ip.Encode(&f.ipv4fields)

				ip.SetChecksum(0)
				ip.SetChecksum(^ip.CalculateChecksum())

				vv := hdr.View().ToVectorisedView()
				vv.AppendView(f.payload)

				pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
					Data: vv,
				})

				if firstFragmentSent == nil && ip.FragmentOffset() == 0 {
					firstFragmentSent = stack.PayloadSince(pkt.NetworkHeader())
				}

				e.InjectInbound(header.IPv4ProtocolNumber, pkt)
			}

			clock.Advance(ipv4.ReassembleTimeout)

			reply, ok := e.Read()
			if !test.expectICMP {
				if ok {
					t.Fatalf("unexpected ICMP error message received: %#v", reply)
				}
				return
			}
			if !ok {
				t.Fatal("expected ICMP error message missing")
			}
			if firstFragmentSent == nil {
				t.Fatalf("unexpected ICMP error message received: %#v", reply)
			}

			checker.IPv4(t, stack.PayloadSince(reply.Pkt.NetworkHeader()),
				checker.SrcAddr(addr2),
				checker.DstAddr(addr1),
				checker.IPFullLength(uint16(header.IPv4MinimumSize+header.ICMPv4MinimumSize+firstFragmentSent.Size())),
				checker.IPv4HeaderLength(header.IPv4MinimumSize),
				checker.ICMPv4(
					checker.ICMPv4Type(header.ICMPv4TimeExceeded),
					checker.ICMPv4Code(header.ICMPv4ReassemblyTimeout),
					checker.ICMPv4Checksum(),
					checker.ICMPv4Payload(firstFragmentSent),
				),
			)
		})
	}
}

// TestReceiveFragments feeds fragments in through the incoming packet path to
// test reassembly
func TestReceiveFragments(t *testing.T) {
	const (
		nicID = 1

		addr1 = "\x0c\xa8\x00\x01" // 192.168.0.1
		addr2 = "\x0c\xa8\x00\x02" // 192.168.0.2
		addr3 = "\x0c\xa8\x00\x03" // 192.168.0.3
	)

	// Build and return a UDP header containing payload.
	udpGen := func(payloadLen int, multiplier uint8, src, dst tcpip.Address) buffer.View {
		payload := buffer.NewView(payloadLen)
		for i := 0; i < len(payload); i++ {
			payload[i] = uint8(i) * multiplier
		}

		udpLength := header.UDPMinimumSize + len(payload)

		hdr := buffer.NewPrependable(udpLength)
		u := header.UDP(hdr.Prepend(udpLength))
		u.Encode(&header.UDPFields{
			SrcPort: 5555,
			DstPort: 80,
			Length:  uint16(udpLength),
		})
		copy(u.Payload(), payload)
		sum := header.PseudoHeaderChecksum(udp.ProtocolNumber, src, dst, uint16(udpLength))
		sum = header.Checksum(payload, sum)
		u.SetChecksum(^u.CalculateChecksum(sum))
		return hdr.View()
	}

	// UDP header plus a payload of 0..256
	ipv4Payload1Addr1ToAddr2 := udpGen(256, 1, addr1, addr2)
	udpPayload1Addr1ToAddr2 := ipv4Payload1Addr1ToAddr2[header.UDPMinimumSize:]
	ipv4Payload1Addr3ToAddr2 := udpGen(256, 1, addr3, addr2)
	udpPayload1Addr3ToAddr2 := ipv4Payload1Addr3ToAddr2[header.UDPMinimumSize:]
	// UDP header plus a payload of 0..256 in increments of 2.
	ipv4Payload2Addr1ToAddr2 := udpGen(128, 2, addr1, addr2)
	udpPayload2Addr1ToAddr2 := ipv4Payload2Addr1ToAddr2[header.UDPMinimumSize:]
	// UDP header plus a payload of 0..256 in increments of 3.
	// Used to test cases where the fragment blocks are not a multiple of
	// the fragment block size of 8 (RFC 791 section 3.1 page 14).
	ipv4Payload3Addr1ToAddr2 := udpGen(127, 3, addr1, addr2)
	udpPayload3Addr1ToAddr2 := ipv4Payload3Addr1ToAddr2[header.UDPMinimumSize:]
	// Used to test the max reassembled IPv4 payload length.
	ipv4Payload4Addr1ToAddr2 := udpGen(header.UDPMaximumSize-header.UDPMinimumSize, 4, addr1, addr2)
	udpPayload4Addr1ToAddr2 := ipv4Payload4Addr1ToAddr2[header.UDPMinimumSize:]

	type fragmentData struct {
		srcAddr        tcpip.Address
		dstAddr        tcpip.Address
		id             uint16
		flags          uint8
		fragmentOffset uint16
		payload        buffer.View
	}

	tests := []struct {
		name             string
		fragments        []fragmentData
		expectedPayloads [][]byte
	}{
		{
			name: "No fragmentation",
			fragments: []fragmentData{
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          0,
					fragmentOffset: 0,
					payload:        ipv4Payload1Addr1ToAddr2,
				},
			},
			expectedPayloads: [][]byte{udpPayload1Addr1ToAddr2},
		},
		{
			name: "No fragmentation with size not a multiple of fragment block size",
			fragments: []fragmentData{
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          0,
					fragmentOffset: 0,
					payload:        ipv4Payload3Addr1ToAddr2,
				},
			},
			expectedPayloads: [][]byte{udpPayload3Addr1ToAddr2},
		},
		{
			name: "More fragments without payload",
			fragments: []fragmentData{
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 0,
					payload:        ipv4Payload1Addr1ToAddr2,
				},
			},
			expectedPayloads: nil,
		},
		{
			name: "Non-zero fragment offset without payload",
			fragments: []fragmentData{
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          0,
					fragmentOffset: 8,
					payload:        ipv4Payload1Addr1ToAddr2,
				},
			},
			expectedPayloads: nil,
		},
		{
			name: "Two fragments",
			fragments: []fragmentData{
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 0,
					payload:        ipv4Payload1Addr1ToAddr2[:64],
				},
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          0,
					fragmentOffset: 64,
					payload:        ipv4Payload1Addr1ToAddr2[64:],
				},
			},
			expectedPayloads: [][]byte{udpPayload1Addr1ToAddr2},
		},
		{
			name: "Two fragments out of order",
			fragments: []fragmentData{
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          0,
					fragmentOffset: 64,
					payload:        ipv4Payload1Addr1ToAddr2[64:],
				},
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 0,
					payload:        ipv4Payload1Addr1ToAddr2[:64],
				},
			},
			expectedPayloads: [][]byte{udpPayload1Addr1ToAddr2},
		},
		{
			name: "Two fragments with last fragment size not a multiple of fragment block size",
			fragments: []fragmentData{
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 0,
					payload:        ipv4Payload3Addr1ToAddr2[:64],
				},
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          0,
					fragmentOffset: 64,
					payload:        ipv4Payload3Addr1ToAddr2[64:],
				},
			},
			expectedPayloads: [][]byte{udpPayload3Addr1ToAddr2},
		},
		{
			name: "Two fragments with first fragment size not a multiple of fragment block size",
			fragments: []fragmentData{
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 0,
					payload:        ipv4Payload3Addr1ToAddr2[:63],
				},
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          0,
					fragmentOffset: 63,
					payload:        ipv4Payload3Addr1ToAddr2[63:],
				},
			},
			expectedPayloads: nil,
		},
		{
			name: "Second fragment has MoreFlags set",
			fragments: []fragmentData{
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 0,
					payload:        ipv4Payload1Addr1ToAddr2[:64],
				},
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 64,
					payload:        ipv4Payload1Addr1ToAddr2[64:],
				},
			},
			expectedPayloads: nil,
		},
		{
			name: "Two fragments with different IDs",
			fragments: []fragmentData{
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 0,
					payload:        ipv4Payload1Addr1ToAddr2[:64],
				},
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             2,
					flags:          0,
					fragmentOffset: 64,
					payload:        ipv4Payload1Addr1ToAddr2[64:],
				},
			},
			expectedPayloads: nil,
		},
		{
			name: "Two interleaved fragmented packets",
			fragments: []fragmentData{
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 0,
					payload:        ipv4Payload1Addr1ToAddr2[:64],
				},
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             2,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 0,
					payload:        ipv4Payload2Addr1ToAddr2[:64],
				},
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          0,
					fragmentOffset: 64,
					payload:        ipv4Payload1Addr1ToAddr2[64:],
				},
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             2,
					flags:          0,
					fragmentOffset: 64,
					payload:        ipv4Payload2Addr1ToAddr2[64:],
				},
			},
			expectedPayloads: [][]byte{udpPayload1Addr1ToAddr2, udpPayload2Addr1ToAddr2},
		},
		{
			name: "Two interleaved fragmented packets from different sources but with same ID",
			fragments: []fragmentData{
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 0,
					payload:        ipv4Payload1Addr1ToAddr2[:64],
				},
				{
					srcAddr:        addr3,
					dstAddr:        addr2,
					id:             1,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 0,
					payload:        ipv4Payload1Addr3ToAddr2[:32],
				},
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          0,
					fragmentOffset: 64,
					payload:        ipv4Payload1Addr1ToAddr2[64:],
				},
				{
					srcAddr:        addr3,
					dstAddr:        addr2,
					id:             1,
					flags:          0,
					fragmentOffset: 32,
					payload:        ipv4Payload1Addr3ToAddr2[32:],
				},
			},
			expectedPayloads: [][]byte{udpPayload1Addr1ToAddr2, udpPayload1Addr3ToAddr2},
		},
		{
			name: "Fragment without followup",
			fragments: []fragmentData{
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 0,
					payload:        ipv4Payload1Addr1ToAddr2[:64],
				},
			},
			expectedPayloads: nil,
		},
		{
			name: "Two fragments reassembled into a maximum UDP packet",
			fragments: []fragmentData{
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 0,
					payload:        ipv4Payload4Addr1ToAddr2[:65512],
				},
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          0,
					fragmentOffset: 65512,
					payload:        ipv4Payload4Addr1ToAddr2[65512:],
				},
			},
			expectedPayloads: [][]byte{udpPayload4Addr1ToAddr2},
		},
		{
			name: "Two fragments with MF flag reassembled into a maximum UDP packet",
			fragments: []fragmentData{
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 0,
					payload:        ipv4Payload4Addr1ToAddr2[:65512],
				},
				{
					srcAddr:        addr1,
					dstAddr:        addr2,
					id:             1,
					flags:          header.IPv4FlagMoreFragments,
					fragmentOffset: 65512,
					payload:        ipv4Payload4Addr1ToAddr2[65512:],
				},
			},
			expectedPayloads: nil,
		},
	}

	for _, test := range tests {
		t.Run(test.name, func(t *testing.T) {
			// Setup a stack and endpoint.
			s := stack.New(stack.Options{
				NetworkProtocols:   []stack.NetworkProtocolFactory{ipv4.NewProtocol},
				TransportProtocols: []stack.TransportProtocolFactory{udp.NewProtocol},
				RawFactory:         raw.EndpointFactory{},
			})
			e := channel.New(0, 1280, "\xf0\x00")
			if err := s.CreateNIC(nicID, e); err != nil {
				t.Fatalf("CreateNIC(%d, _) = %s", nicID, err)
			}
			if err := s.AddAddress(nicID, header.IPv4ProtocolNumber, addr2); err != nil {
				t.Fatalf("AddAddress(%d, %d, %s) = %s", nicID, header.IPv4ProtocolNumber, addr2, err)
			}

			wq := waiter.Queue{}
			we, ch := waiter.NewChannelEntry(nil)
			wq.EventRegister(&we, waiter.ReadableEvents)
			defer wq.EventUnregister(&we)
			defer close(ch)
			ep, err := s.NewEndpoint(udp.ProtocolNumber, header.IPv4ProtocolNumber, &wq)
			if err != nil {
				t.Fatalf("NewEndpoint(%d, %d, _): %s", udp.ProtocolNumber, header.IPv4ProtocolNumber, err)
			}
			defer ep.Close()

			bindAddr := tcpip.FullAddress{Addr: addr2, Port: 80}
			if err := ep.Bind(bindAddr); err != nil {
				t.Fatalf("Bind(%+v): %s", bindAddr, err)
			}

			// Bring up a raw endpoint so we can examine network headers.
			epRaw, err := s.NewRawEndpoint(udp.ProtocolNumber, header.IPv4ProtocolNumber, &wq, true /* associated */)
			if err != nil {
				t.Fatalf("NewRawEndpoint(%d, %d, _, true): %s", udp.ProtocolNumber, header.IPv4ProtocolNumber, err)
			}
			defer epRaw.Close()

			// Prepare and send the fragments.
			for _, frag := range test.fragments {
				hdr := buffer.NewPrependable(header.IPv4MinimumSize)

				// Serialize IPv4 fixed header.
				ip := header.IPv4(hdr.Prepend(header.IPv4MinimumSize))
				ip.Encode(&header.IPv4Fields{
					TotalLength:    header.IPv4MinimumSize + uint16(len(frag.payload)),
					ID:             frag.id,
					Flags:          frag.flags,
					FragmentOffset: frag.fragmentOffset,
					TTL:            64,
					Protocol:       uint8(header.UDPProtocolNumber),
					SrcAddr:        frag.srcAddr,
					DstAddr:        frag.dstAddr,
				})
				ip.SetChecksum(^ip.CalculateChecksum())

				vv := hdr.View().ToVectorisedView()
				vv.AppendView(frag.payload)

				e.InjectInbound(header.IPv4ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
					Data: vv,
				}))
			}

			if got, want := s.Stats().UDP.PacketsReceived.Value(), uint64(len(test.expectedPayloads)); got != want {
				t.Errorf("got UDP Rx Packets = %d, want = %d", got, want)
			}

			for i, expectedPayload := range test.expectedPayloads {
				// Check UDP payload delivered by UDP endpoint.
				var buf bytes.Buffer
				result, err := ep.Read(&buf, tcpip.ReadOptions{})
				if err != nil {
					t.Fatalf("(i=%d) ep.Read: %s", i, err)
				}
				if diff := cmp.Diff(tcpip.ReadResult{
					Count: len(expectedPayload),
					Total: len(expectedPayload),
				}, result, checker.IgnoreCmpPath("ControlMessages")); diff != "" {
					t.Errorf("(i=%d) ep.Read: unexpected result (-want +got):\n%s", i, diff)
				}
				if diff := cmp.Diff(expectedPayload, buf.Bytes()); diff != "" {
					t.Errorf("(i=%d) ep.Read: UDP payload mismatch (-want +got):\n%s", i, diff)
				}

				// Check IPv4 header in packet delivered by raw endpoint.
				buf.Reset()
				result, err = epRaw.Read(&buf, tcpip.ReadOptions{})
				if err != nil {
					t.Fatalf("(i=%d) epRaw.Read: %s", i, err)
				}
				// Reassambly does not take care of checksum. Here we write our own
				// check routine instead of using checker.IPv4.
				ip := header.IPv4(buf.Bytes())
				for _, check := range []checker.NetworkChecker{
					checker.FragmentFlags(0),
					checker.FragmentOffset(0),
					checker.IPFullLength(uint16(header.IPv4MinimumSize + header.UDPMinimumSize + len(expectedPayload))),
				} {
					check(t, []header.Network{ip})
				}
			}

			res, err := ep.Read(ioutil.Discard, tcpip.ReadOptions{})
			if _, ok := err.(*tcpip.ErrWouldBlock); !ok {
				t.Fatalf("(last) got Read = (%#v, %v), want = (_, %s)", res, err, &tcpip.ErrWouldBlock{})
			}
		})
	}
}

func TestWriteStats(t *testing.T) {
	const nPackets = 3

	tests := []struct {
		name                     string
		setup                    func(*testing.T, *stack.Stack)
		allowPackets             int
		expectSent               int
		expectOutputDropped      int
		expectPostroutingDropped int
		expectWritten            int
	}{
		{
			name: "Accept all",
			// No setup needed, tables accept everything by default.
			setup:                    func(*testing.T, *stack.Stack) {},
			allowPackets:             math.MaxInt32,
			expectSent:               nPackets,
			expectOutputDropped:      0,
			expectPostroutingDropped: 0,
			expectWritten:            nPackets,
		}, {
			name: "Accept all with error",
			// No setup needed, tables accept everything by default.
			setup:                    func(*testing.T, *stack.Stack) {},
			allowPackets:             nPackets - 1,
			expectSent:               nPackets - 1,
			expectOutputDropped:      0,
			expectPostroutingDropped: 0,
			expectWritten:            nPackets - 1,
		}, {
			name: "Drop all with Output chain",
			setup: func(t *testing.T, stk *stack.Stack) {
				// Install Output DROP rule.
				ipt := stk.IPTables()
				filter := ipt.GetTable(stack.FilterID, false /* ipv6 */)
				ruleIdx := filter.BuiltinChains[stack.Output]
				filter.Rules[ruleIdx].Target = &stack.DropTarget{}
				if err := ipt.ReplaceTable(stack.FilterID, filter, false /* ipv6 */); err != nil {
					t.Fatalf("failed to replace table: %s", err)
				}
			},
			allowPackets:             math.MaxInt32,
			expectSent:               0,
			expectOutputDropped:      nPackets,
			expectPostroutingDropped: 0,
			expectWritten:            nPackets,
		}, {
			name: "Drop all with Postrouting chain",
			setup: func(t *testing.T, stk *stack.Stack) {
				ipt := stk.IPTables()
				filter := ipt.GetTable(stack.NATID, false /* ipv6 */)
				ruleIdx := filter.BuiltinChains[stack.Postrouting]
				filter.Rules[ruleIdx].Target = &stack.DropTarget{}
				if err := ipt.ReplaceTable(stack.NATID, filter, false /* ipv6 */); err != nil {
					t.Fatalf("failed to replace table: %s", err)
				}
			},
			allowPackets:             math.MaxInt32,
			expectSent:               0,
			expectOutputDropped:      0,
			expectPostroutingDropped: nPackets,
			expectWritten:            nPackets,
		}, {
			name: "Drop some with Output chain",
			setup: func(t *testing.T, stk *stack.Stack) {
				// Install Output DROP rule that matches only 1
				// of the 3 packets.
				ipt := stk.IPTables()
				filter := ipt.GetTable(stack.FilterID, false /* ipv6 */)
				// We'll match and DROP the last packet.
				ruleIdx := filter.BuiltinChains[stack.Output]
				filter.Rules[ruleIdx].Target = &stack.DropTarget{}
				filter.Rules[ruleIdx].Matchers = []stack.Matcher{&limitedMatcher{nPackets - 1}}
				// Make sure the next rule is ACCEPT.
				filter.Rules[ruleIdx+1].Target = &stack.AcceptTarget{}
				if err := ipt.ReplaceTable(stack.FilterID, filter, false /* ipv6 */); err != nil {
					t.Fatalf("failed to replace table: %s", err)
				}
			},
			allowPackets:             math.MaxInt32,
			expectSent:               nPackets - 1,
			expectOutputDropped:      1,
			expectPostroutingDropped: 0,
			expectWritten:            nPackets,
		}, {
			name: "Drop some with Postrouting chain",
			setup: func(t *testing.T, stk *stack.Stack) {
				// Install Postrouting DROP rule that matches only 1
				// of the 3 packets.
				ipt := stk.IPTables()
				filter := ipt.GetTable(stack.NATID, false /* ipv6 */)
				// We'll match and DROP the last packet.
				ruleIdx := filter.BuiltinChains[stack.Postrouting]
				filter.Rules[ruleIdx].Target = &stack.DropTarget{}
				filter.Rules[ruleIdx].Matchers = []stack.Matcher{&limitedMatcher{nPackets - 1}}
				// Make sure the next rule is ACCEPT.
				filter.Rules[ruleIdx+1].Target = &stack.AcceptTarget{}
				if err := ipt.ReplaceTable(stack.NATID, filter, false /* ipv6 */); err != nil {
					t.Fatalf("failed to replace table: %s", err)
				}
			},
			allowPackets:             math.MaxInt32,
			expectSent:               nPackets - 1,
			expectOutputDropped:      0,
			expectPostroutingDropped: 1,
			expectWritten:            nPackets,
		},
	}

	// Parameterize the tests to run with both WritePacket and WritePackets.
	writers := []struct {
		name         string
		writePackets func(*stack.Route, stack.PacketBufferList) (int, tcpip.Error)
	}{
		{
			name: "WritePacket",
			writePackets: func(rt *stack.Route, pkts stack.PacketBufferList) (int, tcpip.Error) {
				nWritten := 0
				for pkt := pkts.Front(); pkt != nil; pkt = pkt.Next() {
					if err := rt.WritePacket(stack.NetworkHeaderParams{}, pkt); err != nil {
						return nWritten, err
					}
					nWritten++
				}
				return nWritten, nil
			},
		}, {
			name: "WritePackets",
			writePackets: func(rt *stack.Route, pkts stack.PacketBufferList) (int, tcpip.Error) {
				return rt.WritePackets(pkts, stack.NetworkHeaderParams{})
			},
		},
	}

	for _, writer := range writers {
		t.Run(writer.name, func(t *testing.T) {
			for _, test := range tests {
				t.Run(test.name, func(t *testing.T) {
					ep := iptestutil.NewMockLinkEndpoint(header.IPv4MinimumMTU, &tcpip.ErrInvalidEndpointState{}, test.allowPackets)
					rt := buildRoute(t, ep)

					var pkts stack.PacketBufferList
					for i := 0; i < nPackets; i++ {
						pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
							ReserveHeaderBytes: header.UDPMinimumSize + int(rt.MaxHeaderLength()),
							Data:               buffer.NewView(0).ToVectorisedView(),
						})
						pkt.TransportHeader().Push(header.UDPMinimumSize)
						pkts.PushBack(pkt)
					}

					test.setup(t, rt.Stack())

					nWritten, _ := writer.writePackets(rt, pkts)

					if got := int(rt.Stats().IP.PacketsSent.Value()); got != test.expectSent {
						t.Errorf("got rt.Stats().IP.PacketsSent.Value() = %d, want = %d", got, test.expectSent)
					}
					if got := int(rt.Stats().IP.IPTablesOutputDropped.Value()); got != test.expectOutputDropped {
						t.Errorf("got rt.Stats().IP.IPTablesOutputDropped.Value() = %d, want = %d", got, test.expectOutputDropped)
					}
					if got := int(rt.Stats().IP.IPTablesPostroutingDropped.Value()); got != test.expectPostroutingDropped {
						t.Errorf("got rt.Stats().IP.IPTablesPostroutingDropped.Value() = %d, want = %d", got, test.expectPostroutingDropped)
					}
					if nWritten != test.expectWritten {
						t.Errorf("got nWritten = %d, want = %d", nWritten, test.expectWritten)
					}
				})
			}
		})
	}
}

func buildRoute(t *testing.T, ep stack.LinkEndpoint) *stack.Route {
	s := stack.New(stack.Options{
		NetworkProtocols: []stack.NetworkProtocolFactory{ipv4.NewProtocol},
	})
	if err := s.CreateNIC(1, ep); err != nil {
		t.Fatalf("CreateNIC(1, _) failed: %s", err)
	}
	const (
		src = "\x10\x00\x00\x01"
		dst = "\x10\x00\x00\x02"
	)
	if err := s.AddAddress(1, ipv4.ProtocolNumber, src); err != nil {
		t.Fatalf("AddAddress(1, %d, %s) failed: %s", ipv4.ProtocolNumber, src, err)
	}
	{
		mask := tcpip.AddressMask(header.IPv4Broadcast)
		subnet, err := tcpip.NewSubnet(dst, mask)
		if err != nil {
			t.Fatalf("NewSubnet(%s, %s) failed: %v", dst, mask, err)
		}
		s.SetRouteTable([]tcpip.Route{{
			Destination: subnet,
			NIC:         1,
		}})
	}
	rt, err := s.FindRoute(1, src, dst, ipv4.ProtocolNumber, false /* multicastLoop */)
	if err != nil {
		t.Fatalf("FindRoute(1, %s, %s, %d, false) = %s", src, dst, ipv4.ProtocolNumber, err)
	}
	return rt
}

// limitedMatcher is an iptables matcher that matches after a certain number of
// packets are checked against it.
type limitedMatcher struct {
	limit int
}

// Name implements Matcher.Name.
func (*limitedMatcher) Name() string {
	return "limitedMatcher"
}

// Match implements Matcher.Match.
func (lm *limitedMatcher) Match(stack.Hook, *stack.PacketBuffer, string, string) (bool, bool) {
	if lm.limit == 0 {
		return true, false
	}
	lm.limit--
	return false, false
}

func TestPacketQueuing(t *testing.T) {
	const nicID = 1

	var (
		host1NICLinkAddr = tcpip.LinkAddress("\x02\x03\x03\x04\x05\x06")
		host2NICLinkAddr = tcpip.LinkAddress("\x02\x03\x03\x04\x05\x09")

		host1IPv4Addr = tcpip.ProtocolAddress{
			Protocol: ipv4.ProtocolNumber,
			AddressWithPrefix: tcpip.AddressWithPrefix{
				Address:   tcpip.Address(net.ParseIP("192.168.0.1").To4()),
				PrefixLen: 24,
			},
		}
		host2IPv4Addr = tcpip.ProtocolAddress{
			Protocol: ipv4.ProtocolNumber,
			AddressWithPrefix: tcpip.AddressWithPrefix{
				Address:   tcpip.Address(net.ParseIP("192.168.0.2").To4()),
				PrefixLen: 8,
			},
		}
	)

	tests := []struct {
		name      string
		rxPkt     func(*channel.Endpoint)
		checkResp func(*testing.T, *channel.Endpoint)
	}{
		{
			name: "ICMP Error",
			rxPkt: func(e *channel.Endpoint) {
				hdr := buffer.NewPrependable(header.IPv4MinimumSize + header.UDPMinimumSize)
				u := header.UDP(hdr.Prepend(header.UDPMinimumSize))
				u.Encode(&header.UDPFields{
					SrcPort: 5555,
					DstPort: 80,
					Length:  header.UDPMinimumSize,
				})
				sum := header.PseudoHeaderChecksum(udp.ProtocolNumber, host2IPv4Addr.AddressWithPrefix.Address, host1IPv4Addr.AddressWithPrefix.Address, header.UDPMinimumSize)
				sum = header.Checksum(nil, sum)
				u.SetChecksum(^u.CalculateChecksum(sum))
				ip := header.IPv4(hdr.Prepend(header.IPv4MinimumSize))
				ip.Encode(&header.IPv4Fields{
					TotalLength: header.IPv4MinimumSize + header.UDPMinimumSize,
					TTL:         ipv4.DefaultTTL,
					Protocol:    uint8(udp.ProtocolNumber),
					SrcAddr:     host2IPv4Addr.AddressWithPrefix.Address,
					DstAddr:     host1IPv4Addr.AddressWithPrefix.Address,
				})
				ip.SetChecksum(^ip.CalculateChecksum())
				e.InjectInbound(ipv4.ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
					Data: hdr.View().ToVectorisedView(),
				}))
			},
			checkResp: func(t *testing.T, e *channel.Endpoint) {
				p, ok := e.Read()
				if !ok {
					t.Fatalf("timed out waiting for packet")
				}
				if p.Proto != header.IPv4ProtocolNumber {
					t.Errorf("got p.Proto = %d, want = %d", p.Proto, header.IPv4ProtocolNumber)
				}
				if p.Route.RemoteLinkAddress != host2NICLinkAddr {
					t.Errorf("got p.Route.RemoteLinkAddress = %s, want = %s", p.Route.RemoteLinkAddress, host2NICLinkAddr)
				}
				checker.IPv4(t, stack.PayloadSince(p.Pkt.NetworkHeader()),
					checker.SrcAddr(host1IPv4Addr.AddressWithPrefix.Address),
					checker.DstAddr(host2IPv4Addr.AddressWithPrefix.Address),
					checker.ICMPv4(
						checker.ICMPv4Type(header.ICMPv4DstUnreachable),
						checker.ICMPv4Code(header.ICMPv4PortUnreachable)))
			},
		},

		{
			name: "Ping",
			rxPkt: func(e *channel.Endpoint) {
				totalLen := header.IPv4MinimumSize + header.ICMPv4MinimumSize
				hdr := buffer.NewPrependable(totalLen)
				pkt := header.ICMPv4(hdr.Prepend(header.ICMPv4MinimumSize))
				pkt.SetType(header.ICMPv4Echo)
				pkt.SetCode(0)
				pkt.SetChecksum(0)
				pkt.SetChecksum(^header.Checksum(pkt, 0))
				ip := header.IPv4(hdr.Prepend(header.IPv4MinimumSize))
				ip.Encode(&header.IPv4Fields{
					TotalLength: uint16(totalLen),
					Protocol:    uint8(icmp.ProtocolNumber4),
					TTL:         ipv4.DefaultTTL,
					SrcAddr:     host2IPv4Addr.AddressWithPrefix.Address,
					DstAddr:     host1IPv4Addr.AddressWithPrefix.Address,
				})
				ip.SetChecksum(^ip.CalculateChecksum())
				e.InjectInbound(header.IPv4ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
					Data: hdr.View().ToVectorisedView(),
				}))
			},
			checkResp: func(t *testing.T, e *channel.Endpoint) {
				p, ok := e.Read()
				if !ok {
					t.Fatalf("timed out waiting for packet")
				}
				if p.Proto != header.IPv4ProtocolNumber {
					t.Errorf("got p.Proto = %d, want = %d", p.Proto, header.IPv4ProtocolNumber)
				}
				if p.Route.RemoteLinkAddress != host2NICLinkAddr {
					t.Errorf("got p.Route.RemoteLinkAddress = %s, want = %s", p.Route.RemoteLinkAddress, host2NICLinkAddr)
				}
				checker.IPv4(t, stack.PayloadSince(p.Pkt.NetworkHeader()),
					checker.SrcAddr(host1IPv4Addr.AddressWithPrefix.Address),
					checker.DstAddr(host2IPv4Addr.AddressWithPrefix.Address),
					checker.ICMPv4(
						checker.ICMPv4Type(header.ICMPv4EchoReply),
						checker.ICMPv4Code(header.ICMPv4UnusedCode)))
			},
		},
	}

	for _, test := range tests {
		t.Run(test.name, func(t *testing.T) {
			e := channel.New(1, defaultMTU, host1NICLinkAddr)
			e.LinkEPCapabilities |= stack.CapabilityResolutionRequired
			clock := faketime.NewManualClock()
			s := stack.New(stack.Options{
				NetworkProtocols:   []stack.NetworkProtocolFactory{arp.NewProtocol, ipv4.NewProtocol},
				TransportProtocols: []stack.TransportProtocolFactory{udp.NewProtocol},
				Clock:              clock,
			})

			if err := s.CreateNIC(nicID, e); err != nil {
				t.Fatalf("s.CreateNIC(%d, _): %s", nicID, err)
			}
			if err := s.AddProtocolAddress(nicID, host1IPv4Addr); err != nil {
				t.Fatalf("s.AddProtocolAddress(%d, %#v): %s", nicID, host1IPv4Addr, err)
			}

			s.SetRouteTable([]tcpip.Route{
				{
					Destination: host1IPv4Addr.AddressWithPrefix.Subnet(),
					NIC:         nicID,
				},
			})

			// Receive a packet to trigger link resolution before a response is sent.
			test.rxPkt(e)

			// Wait for a ARP request since link address resolution should be
			// performed.
			{
				clock.RunImmediatelyScheduledJobs()
				p, ok := e.Read()
				if !ok {
					t.Fatalf("timed out waiting for packet")
				}
				if p.Proto != arp.ProtocolNumber {
					t.Errorf("got p.Proto = %d, want = %d", p.Proto, arp.ProtocolNumber)
				}
				if p.Route.RemoteLinkAddress != header.EthernetBroadcastAddress {
					t.Errorf("got p.Route.RemoteLinkAddress = %s, want = %s", p.Route.RemoteLinkAddress, header.EthernetBroadcastAddress)
				}
				rep := header.ARP(p.Pkt.NetworkHeader().View())
				if got := rep.Op(); got != header.ARPRequest {
					t.Errorf("got Op() = %d, want = %d", got, header.ARPRequest)
				}
				if got := tcpip.LinkAddress(rep.HardwareAddressSender()); got != host1NICLinkAddr {
					t.Errorf("got HardwareAddressSender = %s, want = %s", got, host1NICLinkAddr)
				}
				if got := tcpip.Address(rep.ProtocolAddressSender()); got != host1IPv4Addr.AddressWithPrefix.Address {
					t.Errorf("got ProtocolAddressSender = %s, want = %s", got, host1IPv4Addr.AddressWithPrefix.Address)
				}
				if got := tcpip.Address(rep.ProtocolAddressTarget()); got != host2IPv4Addr.AddressWithPrefix.Address {
					t.Errorf("got ProtocolAddressTarget = %s, want = %s", got, host2IPv4Addr.AddressWithPrefix.Address)
				}
			}

			// Send an ARP reply to complete link address resolution.
			{
				hdr := buffer.View(make([]byte, header.ARPSize))
				packet := header.ARP(hdr)
				packet.SetIPv4OverEthernet()
				packet.SetOp(header.ARPReply)
				copy(packet.HardwareAddressSender(), host2NICLinkAddr)
				copy(packet.ProtocolAddressSender(), host2IPv4Addr.AddressWithPrefix.Address)
				copy(packet.HardwareAddressTarget(), host1NICLinkAddr)
				copy(packet.ProtocolAddressTarget(), host1IPv4Addr.AddressWithPrefix.Address)
				e.InjectInbound(arp.ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
					Data: hdr.ToVectorisedView(),
				}))
			}

			// Expect the response now that the link address has resolved.
			clock.RunImmediatelyScheduledJobs()
			test.checkResp(t, e)

			// Since link resolution was already performed, it shouldn't be performed
			// again.
			test.rxPkt(e)
			test.checkResp(t, e)
		})
	}
}

// TestCloseLocking test that lock ordering is followed when closing an
// endpoint.
func TestCloseLocking(t *testing.T) {
	const (
		nicID1 = 1
		nicID2 = 2

		iterations = 1000
	)

	var (
		src = testutil.MustParse4("16.0.0.1")
		dst = testutil.MustParse4("16.0.0.2")
	)

	s := stack.New(stack.Options{
		NetworkProtocols:   []stack.NetworkProtocolFactory{ipv4.NewProtocol},
		TransportProtocols: []stack.TransportProtocolFactory{udp.NewProtocol},
	})

	// Perform NAT so that the endpoint tries to search for a sibling endpoint
	// which ends up taking the protocol and endpoint lock (in that order).
	table := stack.Table{
		Rules: []stack.Rule{
			{Target: &stack.AcceptTarget{NetworkProtocol: header.IPv4ProtocolNumber}},
			{Target: &stack.AcceptTarget{NetworkProtocol: header.IPv4ProtocolNumber}},
			{Target: &stack.RedirectTarget{Port: 5, NetworkProtocol: header.IPv4ProtocolNumber}},
			{Target: &stack.AcceptTarget{NetworkProtocol: header.IPv4ProtocolNumber}},
			{Target: &stack.ErrorTarget{NetworkProtocol: header.IPv4ProtocolNumber}},
		},
		BuiltinChains: [stack.NumHooks]int{
			stack.Prerouting:  0,
			stack.Input:       1,
			stack.Forward:     stack.HookUnset,
			stack.Output:      2,
			stack.Postrouting: 3,
		},
		Underflows: [stack.NumHooks]int{
			stack.Prerouting:  0,
			stack.Input:       1,
			stack.Forward:     stack.HookUnset,
			stack.Output:      2,
			stack.Postrouting: 3,
		},
	}
	if err := s.IPTables().ReplaceTable(stack.NATID, table, false /* ipv6 */); err != nil {
		t.Fatalf("s.IPTables().ReplaceTable(...): %s", err)
	}

	e := channel.New(0, defaultMTU, "")
	if err := s.CreateNIC(nicID1, e); err != nil {
		t.Fatalf("CreateNIC(%d, _): %s", nicID1, err)
	}

	if err := s.AddAddress(nicID1, ipv4.ProtocolNumber, src); err != nil {
		t.Fatalf("AddAddress(%d, %d, %s) failed: %s", nicID1, ipv4.ProtocolNumber, src, err)
	}

	s.SetRouteTable([]tcpip.Route{{
		Destination: header.IPv4EmptySubnet,
		NIC:         nicID1,
	}})

	var wq waiter.Queue
	ep, err := s.NewEndpoint(udp.ProtocolNumber, ipv4.ProtocolNumber, &wq)
	if err != nil {
		t.Fatal(err)
	}
	defer ep.Close()

	addr := tcpip.FullAddress{NIC: nicID1, Addr: dst, Port: 53}
	if err := ep.Connect(addr); err != nil {
		t.Errorf("ep.Connect(%#v): %s", addr, err)
	}

	var wg sync.WaitGroup
	defer wg.Wait()

	// Writing packets should trigger NAT which requires the stack to search the
	// protocol for network endpoints with the destination address.
	//
	// Creating and removing interfaces should modify the protocol and endpoint
	// which requires taking the locks of each.
	//
	// We expect the protocol > endpoint lock ordering to be followed here.
	wg.Add(2)
	go func() {
		defer wg.Done()

		data := []byte{1, 2, 3, 4}

		for i := 0; i < iterations; i++ {
			var r bytes.Reader
			r.Reset(data)
			if n, err := ep.Write(&r, tcpip.WriteOptions{}); err != nil {
				t.Errorf("ep.Write(_, _): %s", err)
				return
			} else if want := int64(len(data)); n != want {
				t.Errorf("got ep.Write(_, _) = (%d, _), want = (%d, _)", n, want)
				return
			}
		}
	}()
	go func() {
		defer wg.Done()

		for i := 0; i < iterations; i++ {
			if err := s.CreateNIC(nicID2, loopback.New()); err != nil {
				t.Errorf("CreateNIC(%d, _): %s", nicID2, err)
				return
			}
			if err := s.RemoveNIC(nicID2); err != nil {
				t.Errorf("RemoveNIC(%d): %s", nicID2, err)
				return
			}
		}
	}()
}