diff --git a/tun/checksum_generic_test.go b/tun/checksum_generic_test.go
new file mode 100644
index 000000000..a0c945740
--- /dev/null
+++ b/tun/checksum_generic_test.go
@@ -0,0 +1,9 @@
+package tun
+
+var archChecksumFuncs = []archChecksumDetails{
+	{
+		name:      "generic",
+		available: true,
+		f:         checksum,
+	},
+}
diff --git a/tun/checksum_test.go b/tun/checksum_test.go
index c1ccff531..b3a358378 100644
--- a/tun/checksum_test.go
+++ b/tun/checksum_test.go
@@ -2,33 +2,596 @@ package tun
 
 import (
 	"fmt"
+	"math"
 	"math/rand"
+	"net/netip"
+	"sort"
+	"syscall"
 	"testing"
+	"unsafe"
+
+	"gvisor.dev/gvisor/pkg/tcpip"
+	gvisorChecksum "gvisor.dev/gvisor/pkg/tcpip/checksum"
+	"gvisor.dev/gvisor/pkg/tcpip/header"
 )
 
+type archChecksumDetails struct {
+	name      string
+	available bool
+	f         func([]byte, uint64) uint16
+}
+
+func deterministicRandomBytes(seed int64, length int) []byte {
+	rng := rand.New(rand.NewSource(seed))
+	buf := make([]byte, length)
+	n, err := rng.Read(buf)
+	if err != nil {
+		panic(err)
+	}
+	if n != length {
+		panic("incomplete random buffer")
+	}
+	return buf
+}
+
+func getPageAlignedRandomBytes(seed int64, length int) []byte {
+	alignment := syscall.Getpagesize()
+	buf := deterministicRandomBytes(seed, length+(alignment-1))
+	bufPtr := uintptr(unsafe.Pointer(&buf[0]))
+	alignedBufPtr := (bufPtr + uintptr(alignment-1)) & ^uintptr(alignment-1)
+	alignedStart := int(alignedBufPtr - bufPtr)
+	return buf[alignedStart:]
+}
+
+func TestChecksum(t *testing.T) {
+	alignedBuf := getPageAlignedRandomBytes(10, 8192)
+	allOnes := make([]byte, 65535)
+	for i := range allOnes {
+		allOnes[i] = 0xff
+	}
+	allFE := make([]byte, 65535)
+	for i := range allFE {
+		allFE[i] = 0xfe
+	}
+
+	tests := []struct {
+		name    string
+		data    []byte
+		initial uint16
+		want    uint16
+	}{
+		{
+			name:    "empty",
+			data:    []byte{},
+			initial: 0,
+			want:    0,
+		},
+		{
+			name:    "max initial",
+			data:    []byte{},
+			initial: math.MaxUint16,
+			want:    0xffff,
+		},
+		{
+			name:    "odd length",
+			data:    []byte{0x01, 0x02, 0x01},
+			initial: 0,
+			want:    0x0202,
+		},
+		{
+			name:    "tiny",
+			data:    []byte{0x01, 0x02, 0x01, 0x02, 0x01, 0x02},
+			initial: 0,
+			want:    0x0306,
+		},
+		{
+			name:    "initial",
+			data:    []byte{0x01, 0x02, 0x01, 0x02, 0x01, 0x02},
+			initial: 0x1000,
+			want:    0x1306,
+		},
+		// cleanup0 through cleanup15 is 1024 (handled by large SIMD loops) +
+		// 32 (handled by small SIMD loops) + n, where n ranges from 0 to 15
+		// to cover all of the leftover byte sizes that are possible after small
+		// SIMD loops that handle 16 bytes.
+		{
+			name:    "cleanup0",
+			data:    deterministicRandomBytes(1, 1056),
+			initial: 0,
+			want:    0x11ec,
+		},
+		{
+			name:    "cleanup1",
+			data:    deterministicRandomBytes(1, 1057),
+			initial: 0,
+			want:    0xc5ec,
+		},
+		{
+			name:    "cleanup2",
+			data:    deterministicRandomBytes(1, 1058),
+			initial: 0,
+			want:    0xc6ad,
+		},
+		{
+			name:    "cleanup3",
+			data:    deterministicRandomBytes(1, 1059),
+			initial: 0,
+			want:    0x86ae,
+		},
+		{
+			name:    "cleanup4",
+			data:    deterministicRandomBytes(1, 1060),
+			initial: 0,
+			want:    0x878e,
+		},
+		{
+			name:    "cleanup5",
+			data:    deterministicRandomBytes(1, 1061),
+			initial: 0,
+			want:    0xdb8e,
+		},
+		{
+			name:    "cleanup6",
+			data:    deterministicRandomBytes(1, 1062),
+			initial: 0,
+			want:    0xdbd5,
+		},
+		{
+			name:    "cleanup7",
+			data:    deterministicRandomBytes(1, 1063),
+			initial: 0,
+			want:    0xcfd6,
+		},
+		{
+			name:    "cleanup8",
+			data:    deterministicRandomBytes(1, 1064),
+			initial: 0,
+			want:    0xd090,
+		},
+		{
+			name:    "cleanup9",
+			data:    deterministicRandomBytes(1, 1065),
+			initial: 0,
+			want:    0x0791,
+		},
+		{
+			name:    "cleanup10",
+			data:    deterministicRandomBytes(1, 1066),
+			initial: 0,
+			want:    0x079f,
+		},
+		{
+			name:    "cleanup11",
+			data:    deterministicRandomBytes(1, 1067),
+			initial: 0,
+			want:    0xba9f,
+		},
+		{
+			name:    "cleanup12",
+			data:    deterministicRandomBytes(1, 1068),
+			initial: 0,
+			want:    0xbb0c,
+		},
+		{
+			name:    "cleanup13",
+			data:    deterministicRandomBytes(1, 1069),
+			initial: 0,
+			want:    0x770d,
+		},
+		{
+			name:    "cleanup14",
+			data:    deterministicRandomBytes(1, 1070),
+			initial: 0,
+			want:    0x780a,
+		},
+		{
+			name:    "cleanup15",
+			data:    deterministicRandomBytes(1, 1071),
+			initial: 0,
+			want:    0x640b,
+		},
+		// small1 through small15 covers small sizes that are not large enough
+		// to do overlapped reads.
+		{
+			name:    "small1",
+			data:    deterministicRandomBytes(2, 1),
+			initial: 0x1122,
+			want:    0x4022,
+		},
+		{
+			name:    "small2",
+			data:    deterministicRandomBytes(2, 2),
+			initial: 0x1122,
+			want:    0x40a4,
+		},
+		{
+			name:    "small3",
+			data:    deterministicRandomBytes(2, 3),
+			initial: 0x1122,
+			want:    0xc2a4,
+		},
+		{
+			name:    "small4",
+			data:    deterministicRandomBytes(2, 4),
+			initial: 0x1122,
+			want:    0xc36f,
+		},
+		{
+			name:    "small5",
+			data:    deterministicRandomBytes(2, 5),
+			initial: 0x1122,
+			want:    0xa570,
+		},
+		{
+			name:    "small6",
+			data:    deterministicRandomBytes(2, 6),
+			initial: 0x1122,
+			want:    0xa669,
+		},
+		{
+			name:    "small7",
+			data:    deterministicRandomBytes(2, 7),
+			initial: 0x1122,
+			want:    0x0f6a,
+		},
+		{
+			name:    "small8",
+			data:    deterministicRandomBytes(2, 8),
+			initial: 0x1122,
+			want:    0x0fd9,
+		},
+		{
+			name:    "small9",
+			data:    deterministicRandomBytes(2, 9),
+			initial: 0x1122,
+			want:    0x40d9,
+		},
+		{
+			name:    "small10",
+			data:    deterministicRandomBytes(2, 10),
+			initial: 0x1122,
+			want:    0x411d,
+		},
+		{
+			name:    "small11",
+			data:    deterministicRandomBytes(2, 11),
+			initial: 0x1122,
+			want:    0x011e,
+		},
+		{
+			name:    "small12",
+			data:    deterministicRandomBytes(2, 12),
+			initial: 0x1122,
+			want:    0x01c8,
+		},
+		{
+			name:    "small13",
+			data:    deterministicRandomBytes(2, 13),
+			initial: 0x1122,
+			want:    0x4dc8,
+		},
+		{
+			name:    "small14",
+			data:    deterministicRandomBytes(2, 14),
+			initial: 0x1122,
+			want:    0x4eb5,
+		},
+		{
+			name:    "small15",
+			data:    deterministicRandomBytes(2, 15),
+			initial: 0x1122,
+			want:    0xa4b5,
+		},
+		// other small-ish sizes
+		{
+			name:    "small16",
+			data:    deterministicRandomBytes(1, 16),
+			initial: 0,
+			want:    0x02fa,
+		},
+		{
+			name:    "small32",
+			data:    deterministicRandomBytes(1, 32),
+			initial: 0,
+			want:    0x03ee,
+		},
+		{
+			name:    "small64",
+			data:    deterministicRandomBytes(1, 64),
+			initial: 0,
+			want:    0x3f85,
+		},
+		{
+			name:    "medium",
+			data:    deterministicRandomBytes(1, 1400),
+			initial: 0,
+			want:    0xbea5,
+		},
+		{
+			name:    "big",
+			data:    deterministicRandomBytes(2, 65000),
+			initial: 0,
+			want:    0x3ba7,
+		},
+		{
+			name:    "big-initial",
+			data:    deterministicRandomBytes(2, 65000),
+			initial: 0x1234,
+			want:    0x4ddb,
+		},
+		{
+			// big-small-loop is intended to exercise a few iterations of a big
+			// initial loop of 128 bytes or larger + a smaller loop of 16 bytes
+			// + some leftover
+			name:    "big-small-loop",
+			data:    deterministicRandomBytes(3, 1094),
+			initial: 0x9999,
+			want:    0xe65b,
+		},
+		{
+			name:    "page-aligned",
+			data:    alignedBuf[:4096],
+			initial: 0,
+			want:    0x963b,
+		},
+		{
+			name:    "32-aligned",
+			data:    alignedBuf[32:4128],
+			initial: 0,
+			want:    0x30c4,
+		},
+		{
+			name:    "16-aligned",
+			data:    alignedBuf[16:4112],
+			initial: 0,
+			want:    0xaeff,
+		},
+		{
+			name:    "8-aligned",
+			data:    alignedBuf[8:4104],
+			initial: 0,
+			want:    0x6c3b,
+		},
+		{
+			name:    "4-aligned",
+			data:    alignedBuf[4:4100],
+			initial: 0,
+			want:    0x2e4a,
+		},
+		{
+			name:    "2-aligned",
+			data:    alignedBuf[2:4098],
+			initial: 0,
+			want:    0xc702,
+		},
+		{
+			name:    "unaligned",
+			data:    alignedBuf[1:4097],
+			initial: 0,
+			want:    0x3bc7,
+		},
+		{
+			name:    "unalignedAndOdd",
+			data:    alignedBuf[1:4096],
+			initial: 0,
+			want:    0x3b13,
+		},
+		{
+			name:    "fe1282",
+			data:    allFE[:1282],
+			initial: 0,
+			want:    0x7c7c,
+		},
+		{
+			name:    "fe",
+			data:    allFE,
+			initial: 0,
+			want:    0x7e81,
+		},
+		{
+			name:    "maximum",
+			data:    allOnes,
+			initial: 0,
+			want:    0xff00,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			for _, fd := range archChecksumFuncs {
+				t.Run(fd.name, func(t *testing.T) {
+					if !fd.available {
+						t.Skip("can not run on this system")
+					}
+					if got := fd.f(tt.data, uint64(tt.initial)); got != tt.want {
+						t.Errorf("%s checksum = %04x, want %04x", fd.name, got, tt.want)
+					}
+				})
+			}
+			t.Run("reference", func(t *testing.T) {
+				if got := gvisorChecksum.Checksum(tt.data, tt.initial); got != tt.want {
+					t.Errorf("reference checksum = %04x, want %04x", got, tt.want)
+				}
+			})
+		})
+	}
+}
+
+func TestPseudoHeaderChecksumNoFold(t *testing.T) {
+	tests := []struct {
+		name     string
+		protocol uint8
+		srcAddr  []byte
+		dstAddr  []byte
+		totalLen uint16
+		want     uint16
+	}{
+		{
+			name:     "ipv4",
+			protocol: syscall.IPPROTO_TCP,
+			srcAddr:  netip.MustParseAddr("192.168.1.1").AsSlice(),
+			dstAddr:  netip.MustParseAddr("192.168.1.2").AsSlice(),
+			totalLen: 1492,
+			want:     0x892e,
+		},
+		{
+			name:     "ipv6",
+			protocol: syscall.IPPROTO_TCP,
+			srcAddr:  netip.MustParseAddr("2001:db8:3333:4444:5555:6666:7777:8888").AsSlice(),
+			dstAddr:  netip.MustParseAddr("2001:db8:aaaa:bbbb:cccc:dddd:eeee:ffff").AsSlice(),
+			totalLen: 1492,
+			want:     0x947f,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotNoFold := pseudoHeaderChecksumNoFold(tt.protocol, tt.srcAddr, tt.dstAddr, tt.totalLen)
+			got := checksum([]byte{}, gotNoFold)
+			if got != tt.want {
+				t.Errorf("pseudoHeaderChecksumNoFold() = %x, folds to %04x, want %04x", gotNoFold, got, tt.want)
+			}
+
+			got = header.PseudoHeaderChecksum(
+				tcpip.TransportProtocolNumber(tt.protocol),
+				tcpip.AddrFromSlice(tt.srcAddr),
+				tcpip.AddrFromSlice(tt.dstAddr),
+				tt.totalLen)
+			if got != tt.want {
+				t.Errorf("header.PseudoHeaderChecksum() = %04x, want %04x", got, tt.want)
+			}
+		})
+	}
+}
+
+func FuzzChecksum(f *testing.F) {
+	buf := getPageAlignedRandomBytes(1234, 65536)
+
+	f.Add([]byte{}, uint16(0))
+	f.Add([]byte{}, uint16(0x1234))
+	f.Add([]byte{}, uint16(0))
+	f.Add(buf[:15], uint16(0x1234))
+	f.Add(buf[:256], uint16(0x1234))
+	f.Add(buf[:1280], uint16(0x1234))
+	f.Add(buf[:1288], uint16(0x1234))
+	f.Add(buf[1:1050], uint16(0x1234))
+
+	f.Fuzz(func(t *testing.T, data []byte, initial uint16) {
+		want := gvisorChecksum.Checksum(data, initial)
+
+		for _, fd := range archChecksumFuncs {
+			t.Run(fd.name, func(t *testing.T) {
+				if !fd.available {
+					t.Skip("can not run on this system")
+				}
+				if got := fd.f(data, uint64(initial)); got != want {
+					t.Errorf("%s checksum = %04x, want %04x", fd.name, got, want)
+				}
+			})
+		}
+	})
+}
+
+var result uint16
+var result64 uint64
+
 func BenchmarkChecksum(b *testing.B) {
+	offsets := []int{ // offsets from page alignment
+		0,
+		1,
+		2,
+		4,
+		8,
+		16,
+	}
 	lengths := []int{
+		0,
+		7,
+		15,
+		16,
+		31,
 		64,
+		90,
+		95,
 		128,
 		256,
 		512,
 		1024,
+		1240,
 		1500,
 		2048,
 		4096,
 		8192,
 		9000,
 		9001,
+		16384,
+		65536,
+	}
+	if !sort.IntsAreSorted(offsets) {
+		b.Fatal("offsets are not sorted")
+	}
+	largestLength := lengths[len(lengths)-1]
+	if !sort.IntsAreSorted(lengths) {
+		b.Fatal("lengths are not sorted")
 	}
+	largestOffset := lengths[len(offsets)-1]
+	alignedBuf := getPageAlignedRandomBytes(1, largestOffset+largestLength)
+	var r uint16
+	for _, offset := range offsets {
+		name := fmt.Sprintf("%vAligned", offset)
+		if offset == 0 {
+			name = "pageAligned"
+		}
+		offsetBuf := alignedBuf[offset:]
+		b.Run(name, func(b *testing.B) {
+			for _, length := range lengths {
+				b.Run(fmt.Sprintf("%d", length), func(b *testing.B) {
+					for _, fd := range archChecksumFuncs {
+						b.Run(fd.name, func(b *testing.B) {
+							if !fd.available {
+								b.Skip("can not run on this system")
+							}
+							b.SetBytes(int64(length))
+							for i := 0; i < b.N; i++ {
+								r += fd.f(offsetBuf[:length], 0)
+							}
+						})
+					}
+				})
+			}
+		})
+	}
+	result = r
+}
 
-	for _, length := range lengths {
-		b.Run(fmt.Sprintf("%d", length), func(b *testing.B) {
-			buf := make([]byte, length)
-			rng := rand.New(rand.NewSource(1))
-			rng.Read(buf)
-			b.ResetTimer()
+func BenchmarkPseudoHeaderChecksum(b *testing.B) {
+	tests := []struct {
+		name     string
+		protocol uint8
+		srcAddr  []byte
+		dstAddr  []byte
+		totalLen uint16
+		want     uint16
+	}{
+		{
+			name:     "ipv4",
+			protocol: syscall.IPPROTO_TCP,
+			srcAddr:  []byte{192, 168, 1, 1},
+			dstAddr:  []byte{192, 168, 1, 2},
+			totalLen: 1492,
+			want:     0x892e,
+		},
+		{
+			name:     "ipv6",
+			protocol: syscall.IPPROTO_TCP,
+			srcAddr:  netip.MustParseAddr("2001:db8:3333:4444:5555:6666:7777:8888").AsSlice(),
+			dstAddr:  netip.MustParseAddr("2001:db8:aaaa:bbbb:cccc:dddd:eeee:ffff").AsSlice(),
+			totalLen: 1492,
+			want:     0x892e,
+		},
+	}
+	for _, tt := range tests {
+		b.Run(tt.name, func(b *testing.B) {
 			for i := 0; i < b.N; i++ {
-				checksum(buf, 0)
+				result64 += pseudoHeaderChecksumNoFold(tt.protocol, tt.srcAddr, tt.dstAddr, tt.totalLen)
 			}
 		})
 	}