Support iterating an NDP options buffer.

This change helps support iterating over an NDP options buffer so that
implementations can handle all the NDP options present in an NDP packet.

Note, this change does not yet actually handle these options, it just provides
the tools to do so (in preparation for NDP's Prefix, Parameter, and a complete
implementation of Neighbor Discovery).

Tests: Unittests to make sure we can iterate over a valid NDP options buffer
that may contain multiple options. Also tests to check an iterator before
using it to see if the NDP options buffer is malformed.
PiperOrigin-RevId: 277312487

2 files changed, 475 insertions, 48 deletions

diff --git a/pkg/tcpip/header/ndp_options.go b/pkg/tcpip/header/ndp_options.go
index 98310ea23..a2b9d7435 100644
--- a/pkg/tcpip/header/ndp_options.go
+++ b/pkg/tcpip/header/ndp_options.go
@@ -16,6 +16,7 @@ package header
 
 import (
 	"encoding/binary"
+	"errors"
 	"time"
 
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -30,9 +31,9 @@ const (
 	// Link Layer Option for an Ethernet address.
 	ndpTargetEthernetLinkLayerAddressSize = 8
 
-	// ndpPrefixInformationType is the type of the Prefix Information
+	// NDPPrefixInformationType is the type of the Prefix Information
 	// option, as per RFC 4861 section 4.6.2.
-	ndpPrefixInformationType = 3
+	NDPPrefixInformationType = 3
 
 	// ndpPrefixInformationLength is the expected length, in bytes, of the
 	// body of an NDP Prefix Information option, as per RFC 4861 section
@@ -95,9 +96,122 @@ const (
 	lengthByteUnits = 8
 )
 
+// NDPOptionIterator is an iterator of NDPOption.
+//
+// Note, between when an NDPOptionIterator is obtained and last used, no changes
+// to the NDPOptions may happen. Doing so may cause undefined and unexpected
+// behaviour. It is fine to obtain an NDPOptionIterator, iterate over the first
+// few NDPOption then modify the backing NDPOptions so long as the
+// NDPOptionIterator obtained before modification is no longer used.
+type NDPOptionIterator struct {
+	// The NDPOptions this NDPOptionIterator is iterating over.
+	opts NDPOptions
+}
+
+// Potential errors when iterating over an NDPOptions.
+var (
+	ErrNDPOptBufExhausted  = errors.New("Buffer unexpectedly exhausted")
+	ErrNDPOptZeroLength    = errors.New("NDP option has zero-valued Length field")
+	ErrNDPOptMalformedBody = errors.New("NDP option has a malformed body")
+)
+
+// Next returns the next element in the backing NDPOptions, or true if we are
+// done, or false if an error occured.
+//
+// The return can be read as option, done, error. Note, option should only be
+// used if done is false and error is nil.
+func (i *NDPOptionIterator) Next() (NDPOption, bool, error) {
+	for {
+		// Do we still have elements to look at?
+		if len(i.opts) == 0 {
+			return nil, true, nil
+		}
+
+		// Do we have enough bytes for an NDP option that has a Length
+		// field of at least 1? Note, 0 in the Length field is invalid.
+		if len(i.opts) < lengthByteUnits {
+			return nil, true, ErrNDPOptBufExhausted
+		}
+
+		// Get the Type field.
+		t := i.opts[0]
+
+		// Get the Length field.
+		l := i.opts[1]
+
+		// This would indicate an erroneous NDP option as the Length
+		// field should never be 0.
+		if l == 0 {
+			return nil, true, ErrNDPOptZeroLength
+		}
+
+		// How many bytes are in the option body?
+		numBytes := int(l) * lengthByteUnits
+		numBodyBytes := numBytes - 2
+
+		potentialBody := i.opts[2:]
+
+		// This would indicate an erroenous NDPOptions buffer as we ran
+		// out of the buffer in the middle of an NDP option.
+		if left := len(potentialBody); left < numBodyBytes {
+			return nil, true, ErrNDPOptBufExhausted
+		}
+
+		// Get only the options body, leaving the rest of the options
+		// buffer alone.
+		body := potentialBody[:numBodyBytes]
+
+		// Update opts with the remaining options body.
+		i.opts = i.opts[numBytes:]
+
+		switch t {
+		case NDPTargetLinkLayerAddressOptionType:
+			return NDPTargetLinkLayerAddressOption(body), false, nil
+
+		case NDPPrefixInformationType:
+			// Make sure the length of a Prefix Information option
+			// body is ndpPrefixInformationLength, as per RFC 4861
+			// section 4.6.2.
+			if numBodyBytes != ndpPrefixInformationLength {
+				return nil, true, ErrNDPOptMalformedBody
+			}
+
+			return NDPPrefixInformation(body), false, nil
+		default:
+			// We do not yet recognize the option, just skip for
+			// now. This is okay because RFC 4861 allows us to
+			// skip/ignore any unrecognized options. However,
+			// we MUST recognized all the options in RFC 4861.
+			//
+			// TODO(b/141487990): Handle all NDP options as defined
+			//                    by RFC 4861.
+		}
+	}
+}
+
 // NDPOptions is a buffer of NDP options as defined by RFC 4861 section 4.6.
 type NDPOptions []byte
 
+// Iter returns an iterator of NDPOption.
+//
+// If check is true, Iter will do an integrity check on the options by iterating
+// over it and returning an error if detected.
+//
+// See NDPOptionIterator for more information.
+func (b NDPOptions) Iter(check bool) (NDPOptionIterator, error) {
+	it := NDPOptionIterator{opts: b}
+
+	if check {
+		for it2 := it; true; {
+			if _, done, err := it2.Next(); err != nil || done {
+				return it, err
+			}
+		}
+	}
+
+	return it, nil
+}
+
 // Serialize serializes the provided list of NDP options into o.
 //
 // Note, b must be of sufficient size to hold all the options in s. See
@@ -137,15 +251,15 @@ func (b NDPOptions) Serialize(s NDPOptionsSerializer) int {
 	return done
 }
 
-// ndpOption is the set of functions to be implemented by all NDP option types.
-type ndpOption interface {
-	// Type returns the type of this ndpOption.
+// NDPOption is the set of functions to be implemented by all NDP option types.
+type NDPOption interface {
+	// Type returns the type of the receiver.
 	Type() uint8
 
-	// Length returns the length of the body of this ndpOption, in bytes.
+	// Length returns the length of the body of the receiver, in bytes.
 	Length() int
 
-	// serializeInto serializes this ndpOption into the provided byte
+	// serializeInto serializes the receiver into the provided byte
 	// buffer.
 	//
 	// Note, the caller MUST provide a byte buffer with size of at least
@@ -154,15 +268,15 @@ type ndpOption interface {
 	// buffer is not of sufficient size.
 	//
 	// serializeInto will return the number of bytes that was used to
-	// serialize this ndpOption. Implementers must only use the number of
-	// bytes required to serialize this ndpOption. Callers MAY provide a
+	// serialize the receiver. Implementers must only use the number of
+	// bytes required to serialize the receiver. Callers MAY provide a
 	// larger buffer than required to serialize into.
 	serializeInto([]byte) int
 }
 
 // paddedLength returns the length of o, in bytes, with any padding bytes, if
 // required.
-func paddedLength(o ndpOption) int {
+func paddedLength(o NDPOption) int {
 	l := o.Length()
 
 	if l == 0 {
@@ -201,7 +315,7 @@ func paddedLength(o ndpOption) int {
 }
 
 // NDPOptionsSerializer is a serializer for NDP options.
-type NDPOptionsSerializer []ndpOption
+type NDPOptionsSerializer []NDPOption
 
 // Length returns the total number of bytes required to serialize.
 func (b NDPOptionsSerializer) Length() int {
@@ -221,21 +335,34 @@ func (b NDPOptionsSerializer) Length() int {
 // where X is the value in Length multiplied by lengthByteUnits - 2 bytes.
 type NDPTargetLinkLayerAddressOption tcpip.LinkAddress
 
-// Type implements ndpOption.Type.
+// Type implements NDPOption.Type.
 func (o NDPTargetLinkLayerAddressOption) Type() uint8 {
 	return NDPTargetLinkLayerAddressOptionType
 }
 
-// Length implements ndpOption.Length.
+// Length implements NDPOption.Length.
 func (o NDPTargetLinkLayerAddressOption) Length() int {
 	return len(o)
 }
 
-// serializeInto implements ndpOption.serializeInto.
+// serializeInto implements NDPOption.serializeInto.
 func (o NDPTargetLinkLayerAddressOption) serializeInto(b []byte) int {
 	return copy(b, o)
 }
 
+// EthernetAddress will return an ethernet (MAC) address if the
+// NDPTargetLinkLayerAddressOption's body has at minimum EthernetAddressSize
+// bytes. If the body has more than EthernetAddressSize bytes, only the first
+// EthernetAddressSize bytes are returned as that is all that is needed for an
+// Ethernet address.
+func (o NDPTargetLinkLayerAddressOption) EthernetAddress() tcpip.LinkAddress {
+	if len(o) >= EthernetAddressSize {
+		return tcpip.LinkAddress(o[:EthernetAddressSize])
+	}
+
+	return tcpip.LinkAddress([]byte(nil))
+}
+
 // NDPPrefixInformation is the NDP Prefix Information option as defined by
 // RFC 4861 section 4.6.2.
 //
@@ -243,17 +370,17 @@ func (o NDPTargetLinkLayerAddressOption) serializeInto(b []byte) int {
 // ndpPrefixInformationLength bytes.
 type NDPPrefixInformation []byte
 
-// Type implements ndpOption.Type.
+// Type implements NDPOption.Type.
 func (o NDPPrefixInformation) Type() uint8 {
-	return ndpPrefixInformationType
+	return NDPPrefixInformationType
 }
 
-// Length implements ndpOption.Length.
+// Length implements NDPOption.Length.
 func (o NDPPrefixInformation) Length() int {
 	return ndpPrefixInformationLength
 }
 
-// serializeInto implements ndpOption.serializeInto.
+// serializeInto implements NDPOption.serializeInto.
 func (o NDPPrefixInformation) serializeInto(b []byte) int {
 	used := copy(b, o)
 
diff --git a/pkg/tcpip/header/ndp_test.go b/pkg/tcpip/header/ndp_test.go
index 0bbf67a2b..ad6daafcd 100644
--- a/pkg/tcpip/header/ndp_test.go
+++ b/pkg/tcpip/header/ndp_test.go
@@ -36,18 +36,18 @@ func TestNDPNeighborSolicit(t *testing.T) {
 	ns := NDPNeighborSolicit(b)
 	addr := tcpip.Address("\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f\x10")
 	if got := ns.TargetAddress(); got != addr {
-		t.Fatalf("got ns.TargetAddress = %s, want %s", got, addr)
+		t.Errorf("got ns.TargetAddress = %s, want %s", got, addr)
 	}
 
 	// Test updating the Target Address.
 	addr2 := tcpip.Address("\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f\x11")
 	ns.SetTargetAddress(addr2)
 	if got := ns.TargetAddress(); got != addr2 {
-		t.Fatalf("got ns.TargetAddress = %s, want %s", got, addr2)
+		t.Errorf("got ns.TargetAddress = %s, want %s", got, addr2)
 	}
 	// Make sure the address got updated in the backing buffer.
 	if got := tcpip.Address(b[ndpNSTargetAddessOffset:][:IPv6AddressSize]); got != addr2 {
-		t.Fatalf("got targetaddress buffer = %s, want %s", got, addr2)
+		t.Errorf("got targetaddress buffer = %s, want %s", got, addr2)
 	}
 }
 
@@ -65,56 +65,56 @@ func TestNDPNeighborAdvert(t *testing.T) {
 	na := NDPNeighborAdvert(b)
 	addr := tcpip.Address("\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f\x10")
 	if got := na.TargetAddress(); got != addr {
-		t.Fatalf("got TargetAddress = %s, want %s", got, addr)
+		t.Errorf("got TargetAddress = %s, want %s", got, addr)
 	}
 
 	// Test getting the Router Flag.
 	if got := na.RouterFlag(); !got {
-		t.Fatalf("got RouterFlag = false, want = true")
+		t.Errorf("got RouterFlag = false, want = true")
 	}
 
 	// Test getting the Solicited Flag.
 	if got := na.SolicitedFlag(); got {
-		t.Fatalf("got SolicitedFlag = true, want = false")
+		t.Errorf("got SolicitedFlag = true, want = false")
 	}
 
 	// Test getting the Override Flag.
 	if got := na.OverrideFlag(); !got {
-		t.Fatalf("got OverrideFlag = false, want = true")
+		t.Errorf("got OverrideFlag = false, want = true")
 	}
 
 	// Test updating the Target Address.
 	addr2 := tcpip.Address("\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f\x11")
 	na.SetTargetAddress(addr2)
 	if got := na.TargetAddress(); got != addr2 {
-		t.Fatalf("got TargetAddress = %s, want %s", got, addr2)
+		t.Errorf("got TargetAddress = %s, want %s", got, addr2)
 	}
 	// Make sure the address got updated in the backing buffer.
 	if got := tcpip.Address(b[ndpNATargetAddressOffset:][:IPv6AddressSize]); got != addr2 {
-		t.Fatalf("got targetaddress buffer = %s, want %s", got, addr2)
+		t.Errorf("got targetaddress buffer = %s, want %s", got, addr2)
 	}
 
 	// Test updating the Router Flag.
 	na.SetRouterFlag(false)
 	if got := na.RouterFlag(); got {
-		t.Fatalf("got RouterFlag = true, want = false")
+		t.Errorf("got RouterFlag = true, want = false")
 	}
 
 	// Test updating the Solicited Flag.
 	na.SetSolicitedFlag(true)
 	if got := na.SolicitedFlag(); !got {
-		t.Fatalf("got SolicitedFlag = false, want = true")
+		t.Errorf("got SolicitedFlag = false, want = true")
 	}
 
 	// Test updating the Override Flag.
 	na.SetOverrideFlag(false)
 	if got := na.OverrideFlag(); got {
-		t.Fatalf("got OverrideFlag = true, want = false")
+		t.Errorf("got OverrideFlag = true, want = false")
 	}
 
 	// Make sure flags got updated in the backing buffer.
 	if got := b[ndpNAFlagsOffset]; got != 64 {
-		t.Fatalf("got flags byte = %d, want = 64")
+		t.Errorf("got flags byte = %d, want = 64")
 	}
 }
 
@@ -128,30 +128,66 @@ func TestNDPRouterAdvert(t *testing.T) {
 	ra := NDPRouterAdvert(b)
 
 	if got := ra.CurrHopLimit(); got != 64 {
-		t.Fatalf("got ra.CurrHopLimit = %d, want = 64", got)
+		t.Errorf("got ra.CurrHopLimit = %d, want = 64", got)
 	}
 
 	if got := ra.ManagedAddrConfFlag(); !got {
-		t.Fatalf("got ManagedAddrConfFlag = false, want = true")
+		t.Errorf("got ManagedAddrConfFlag = false, want = true")
 	}
 
 	if got := ra.OtherConfFlag(); got {
-		t.Fatalf("got OtherConfFlag = true, want = false")
+		t.Errorf("got OtherConfFlag = true, want = false")
 	}
 
 	if got, want := ra.RouterLifetime(), time.Second*258; got != want {
-		t.Fatalf("got ra.RouterLifetime = %d, want = %d", got, want)
+		t.Errorf("got ra.RouterLifetime = %d, want = %d", got, want)
 	}
 
 	if got, want := ra.ReachableTime(), time.Millisecond*50595078; got != want {
-		t.Fatalf("got ra.ReachableTime = %d, want = %d", got, want)
+		t.Errorf("got ra.ReachableTime = %d, want = %d", got, want)
 	}
 
 	if got, want := ra.RetransTimer(), time.Millisecond*117967114; got != want {
-		t.Fatalf("got ra.RetransTimer = %d, want = %d", got, want)
+		t.Errorf("got ra.RetransTimer = %d, want = %d", got, want)
 	}
 }
 
+// TestNDPTargetLinkLayerAddressOptionEthernetAddress tests getting the
+// Ethernet address from an NDPTargetLinkLayerAddressOption.
+func TestNDPTargetLinkLayerAddressOptionEthernetAddress(t *testing.T) {
+	tests := []struct {
+		name     string
+		buf      []byte
+		expected tcpip.LinkAddress
+	}{
+		{
+			"ValidMAC",
+			[]byte{1, 2, 3, 4, 5, 6},
+			tcpip.LinkAddress("\x01\x02\x03\x04\x05\x06"),
+		},
+		{
+			"TLLBodyTooShort",
+			[]byte{1, 2, 3, 4, 5},
+			tcpip.LinkAddress([]byte(nil)),
+		},
+		{
+			"TLLBodyLargerThanNeeded",
+			[]byte{1, 2, 3, 4, 5, 6, 7, 8},
+			tcpip.LinkAddress("\x01\x02\x03\x04\x05\x06"),
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			tll := NDPTargetLinkLayerAddressOption(test.buf)
+			if got := tll.EthernetAddress(); got != test.expected {
+				t.Errorf("got tll.EthernetAddress = %s, want = %s", got, test.expected)
+			}
+		})
+	}
+
+}
+
 // TestNDPTargetLinkLayerAddressOptionSerialize tests serializing a
 // NDPTargetLinkLayerAddressOption.
 func TestNDPTargetLinkLayerAddressOptionSerialize(t *testing.T) {
@@ -194,6 +230,44 @@ func TestNDPTargetLinkLayerAddressOptionSerialize(t *testing.T) {
 			if !bytes.Equal(test.buf, test.expectedBuf) {
 				t.Fatalf("got b = %d, want = %d", test.buf, test.expectedBuf)
 			}
+
+			it, err := opts.Iter(true)
+			if err != nil {
+				t.Fatalf("got Iter = (_, %s), want = (_, nil)", err)
+			}
+
+			if len(test.expectedBuf) > 0 {
+				next, done, err := it.Next()
+				if err != nil {
+					t.Fatalf("got Next = (_, _, %s), want = (_, _, nil)", err)
+				}
+				if done {
+					t.Fatal("got Next = (_, true, _), want = (_, false, _)")
+				}
+				if got := next.Type(); got != NDPTargetLinkLayerAddressOptionType {
+					t.Fatalf("got Type %= %d, want = %d", got, NDPTargetLinkLayerAddressOptionType)
+				}
+				tll := next.(NDPTargetLinkLayerAddressOption)
+				if got, want := []byte(tll), test.expectedBuf[2:]; !bytes.Equal(got, want) {
+					t.Fatalf("got Next = (%x, _, _), want = (%x, _, _)", got, want)
+				}
+
+				if got, want := tll.EthernetAddress(), tcpip.LinkAddress(test.expectedBuf[2:][:EthernetAddressSize]); got != want {
+					t.Errorf("got tll.MACAddress = %s, want = %s", got, want)
+				}
+			}
+
+			// Iterator should not return anything else.
+			next, done, err := it.Next()
+			if err != nil {
+				t.Errorf("got Next = (_, _, %s), want = (_, _, nil)", err)
+			}
+			if !done {
+				t.Error("got Next = (_, false, _), want = (_, true, _)")
+			}
+			if next != nil {
+				t.Errorf("got Next = (%x, _, _), want = (nil, _, _)", next)
+			}
 		})
 	}
 }
@@ -232,39 +306,265 @@ func TestNDPPrefixInformationOption(t *testing.T) {
 		t.Fatalf("got targetBuf = %x, want = %x", targetBuf, expectedBuf)
 	}
 
-	// First two bytes are the Type and Length fields, which are not part of
-	// the option body.
-	pi := NDPPrefixInformation(targetBuf[2:])
+	it, err := opts.Iter(true)
+	if err != nil {
+		t.Fatalf("got Iter = (_, %s), want = (_, nil)", err)
+	}
+
+	next, done, err := it.Next()
+	if err != nil {
+		t.Fatalf("got Next = (_, _, %s), want = (_, _, nil)", err)
+	}
+	if done {
+		t.Fatal("got Next = (_, true, _), want = (_, false, _)")
+	}
+	if got := next.Type(); got != NDPPrefixInformationType {
+		t.Errorf("got Type = %d, want = %d", got, NDPPrefixInformationType)
+	}
+
+	pi := next.(NDPPrefixInformation)
 
 	if got := pi.Type(); got != 3 {
-		t.Fatalf("got Type = %d, want = 3", got)
+		t.Errorf("got Type = %d, want = 3", got)
 	}
 
 	if got := pi.Length(); got != 30 {
-		t.Fatalf("got Length = %d, want = 30", got)
+		t.Errorf("got Length = %d, want = 30", got)
 	}
 
 	if got := pi.PrefixLength(); got != 43 {
-		t.Fatalf("got PrefixLength = %d, want = 43", got)
+		t.Errorf("got PrefixLength = %d, want = 43", got)
 	}
 
 	if pi.OnLinkFlag() {
-		t.Fatalf("got OnLinkFlag = true, want = false")
+		t.Error("got OnLinkFlag = true, want = false")
 	}
 
 	if !pi.AutonomousAddressConfigurationFlag() {
-		t.Fatalf("got AutonomousAddressConfigurationFlag = false, want = true")
+		t.Error("got AutonomousAddressConfigurationFlag = false, want = true")
 	}
 
 	if got, want := pi.ValidLifetime(), 16909060*time.Second; got != want {
-		t.Fatalf("got ValidLifetime = %d, want = %d", got, want)
+		t.Errorf("got ValidLifetime = %d, want = %d", got, want)
 	}
 
 	if got, want := pi.PreferredLifetime(), 84281096*time.Second; got != want {
-		t.Fatalf("got PreferredLifetime = %d, want = %d", got, want)
+		t.Errorf("got PreferredLifetime = %d, want = %d", got, want)
 	}
 
 	if got, want := pi.Prefix(), tcpip.Address("\x09\x0a\x0b\x0c\x0d\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18"); got != want {
-		t.Fatalf("got Prefix = %s, want = %s", got, want)
+		t.Errorf("got Prefix = %s, want = %s", got, want)
+	}
+
+	// Iterator should not return anything else.
+	next, done, err = it.Next()
+	if err != nil {
+		t.Errorf("got Next = (_, _, %s), want = (_, _, nil)", err)
+	}
+	if !done {
+		t.Error("got Next = (_, false, _), want = (_, true, _)")
+	}
+	if next != nil {
+		t.Errorf("got Next = (%x, _, _), want = (nil, _, _)", next)
+	}
+}
+
+// TestNDPOptionsIterCheck tests that Iter will return false if the NDPOptions
+// the iterator was returned for is malformed.
+func TestNDPOptionsIterCheck(t *testing.T) {
+	tests := []struct {
+		name     string
+		buf      []byte
+		expected error
+	}{
+		{
+			"ZeroLengthField",
+			[]byte{0, 0, 0, 0, 0, 0, 0, 0},
+			ErrNDPOptZeroLength,
+		},
+		{
+			"ValidTargetLinkLayerAddressOption",
+			[]byte{2, 1, 1, 2, 3, 4, 5, 6},
+			nil,
+		},
+		{
+			"TooSmallTargetLinkLayerAddressOption",
+			[]byte{2, 1, 1, 2, 3, 4, 5},
+			ErrNDPOptBufExhausted,
+		},
+		{
+			"ValidPrefixInformation",
+			[]byte{
+				3, 4, 43, 64,
+				1, 2, 3, 4,
+				5, 6, 7, 8,
+				0, 0, 0, 0,
+				9, 10, 11, 12,
+				13, 14, 15, 16,
+				17, 18, 19, 20,
+				21, 22, 23, 24,
+			},
+			nil,
+		},
+		{
+			"TooSmallPrefixInformation",
+			[]byte{
+				3, 4, 43, 64,
+				1, 2, 3, 4,
+				5, 6, 7, 8,
+				0, 0, 0, 0,
+				9, 10, 11, 12,
+				13, 14, 15, 16,
+				17, 18, 19, 20,
+				21, 22, 23,
+			},
+			ErrNDPOptBufExhausted,
+		},
+		{
+			"InvalidPrefixInformationLength",
+			[]byte{
+				3, 3, 43, 64,
+				1, 2, 3, 4,
+				5, 6, 7, 8,
+				0, 0, 0, 0,
+				9, 10, 11, 12,
+				13, 14, 15, 16,
+			},
+			ErrNDPOptMalformedBody,
+		},
+		{
+			"ValidTargetLinkLayerAddressWithPrefixInformation",
+			[]byte{
+				// Target Link-Layer Address.
+				2, 1, 1, 2, 3, 4, 5, 6,
+
+				// Prefix information.
+				3, 4, 43, 64,
+				1, 2, 3, 4,
+				5, 6, 7, 8,
+				0, 0, 0, 0,
+				9, 10, 11, 12,
+				13, 14, 15, 16,
+				17, 18, 19, 20,
+				21, 22, 23, 24,
+			},
+			nil,
+		},
+		{
+			"ValidTargetLinkLayerAddressWithPrefixInformationWithUnrecognized",
+			[]byte{
+				// Target Link-Layer Address.
+				2, 1, 1, 2, 3, 4, 5, 6,
+
+				// 255 is an unrecognized type. If 255 ends up
+				// being the type for some recognized type,
+				// update 255 to some other unrecognized value.
+				255, 2, 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 7, 8,
+
+				// Prefix information.
+				3, 4, 43, 64,
+				1, 2, 3, 4,
+				5, 6, 7, 8,
+				0, 0, 0, 0,
+				9, 10, 11, 12,
+				13, 14, 15, 16,
+				17, 18, 19, 20,
+				21, 22, 23, 24,
+			},
+			nil,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			opts := NDPOptions(test.buf)
+
+			if _, err := opts.Iter(true); err != test.expected {
+				t.Fatalf("got Iter(true) = (_, %v), want = (_, %v)", err, test.expected)
+			}
+
+			// test.buf may be malformed but we chose not to check
+			// the iterator so it must return true.
+			if _, err := opts.Iter(false); err != nil {
+				t.Fatalf("got Iter(false) = (_, %s), want = (_, nil)", err)
+			}
+		})
+	}
+}
+
+// TestNDPOptionsIter tests that we can iterator over a valid NDPOptions. Note,
+// this test does not actually check any of the option's getters, it simply
+// checks the option Type and Body. We have other tests that tests the option
+// field gettings given an option body and don't need to duplicate those tests
+// here.
+func TestNDPOptionsIter(t *testing.T) {
+	buf := []byte{
+		// Target Link-Layer Address.
+		2, 1, 1, 2, 3, 4, 5, 6,
+
+		// 255 is an unrecognized type. If 255 ends up being the type
+		// for some recognized type, update 255 to some other
+		// unrecognized value. Note, this option should be skipped when
+		// iterating.
+		255, 2, 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 7, 8,
+
+		// Prefix information.
+		3, 4, 43, 64,
+		1, 2, 3, 4,
+		5, 6, 7, 8,
+		0, 0, 0, 0,
+		9, 10, 11, 12,
+		13, 14, 15, 16,
+		17, 18, 19, 20,
+		21, 22, 23, 24,
+	}
+
+	opts := NDPOptions(buf)
+	it, err := opts.Iter(true)
+	if err != nil {
+		t.Fatalf("got Iter = (_, %s), want = (_, nil)", err)
+	}
+
+	// Test the first (Taret Link-Layer) option.
+	next, done, err := it.Next()
+	if err != nil {
+		t.Fatalf("got Next = (_, _, %s), want = (_, _, nil)", err)
+	}
+	if done {
+		t.Fatal("got Next = (_, true, _), want = (_, false, _)")
+	}
+	if got, want := []byte(next.(NDPTargetLinkLayerAddressOption)), buf[2:][:6]; !bytes.Equal(got, want) {
+		t.Errorf("got Next = (%x, _, _), want = (%x, _, _)", got, want)
+	}
+	if got := next.Type(); got != NDPTargetLinkLayerAddressOptionType {
+		t.Errorf("got Type = %d, want = %d", got, NDPTargetLinkLayerAddressOptionType)
+	}
+
+	// Test the next (Prefix Information) option.
+	// Note, the unrecognized option should be skipped.
+	next, done, err = it.Next()
+	if err != nil {
+		t.Fatalf("got Next = (_, _, %s), want = (_, _, nil)", err)
+	}
+	if done {
+		t.Fatal("got Next = (_, true, _), want = (_, false, _)")
+	}
+	if got, want := next.(NDPPrefixInformation), buf[26:][:30]; !bytes.Equal(got, want) {
+		t.Errorf("got Next = (%x, _, _), want = (%x, _, _)", got, want)
+	}
+	if got := next.Type(); got != NDPPrefixInformationType {
+		t.Errorf("got Type = %d, want = %d", got, NDPPrefixInformationType)
+	}
+
+	// Iterator should not return anything else.
+	next, done, err = it.Next()
+	if err != nil {
+		t.Errorf("got Next = (_, _, %s), want = (_, _, nil)", err)
+	}
+	if !done {
+		t.Error("got Next = (_, false, _), want = (_, true, _)")
+	}
+	if next != nil {
+		t.Errorf("got Next = (%x, _, _), want = (nil, _, _)", next)
 	}
 }