Introduce IPv6 extension header serialization facilities

Adds IPv6 extension header serializer and Hop by Hop options serializer.
Add RouterAlert option serializer and use it in MLD.

Fixed #4996

Startblock:
  has LGTM from marinaciocea
  and then
  add reviewer ghanan
PiperOrigin-RevId: 347174537

19 files changed, 1247 insertions, 369 deletions

diff --git a/pkg/tcpip/checker/checker.go b/pkg/tcpip/checker/checker.go
index 8830c45d7..91971b687 100644
--- a/pkg/tcpip/checker/checker.go
+++ b/pkg/tcpip/checker/checker.go
@@ -117,6 +117,10 @@ func TTL(ttl uint8) NetworkChecker {
 			v = ip.TTL()
 		case header.IPv6:
 			v = ip.HopLimit()
+		case *ipv6HeaderWithExtHdr:
+			v = ip.HopLimit()
+		default:
+			t.Fatalf("unrecognized header type %T for TTL evaluation", ip)
 		}
 		if v != ttl {
 			t.Fatalf("Bad TTL, got = %d, want = %d", v, ttl)
@@ -1413,3 +1417,189 @@ func IGMPGroupAddress(want tcpip.Address) TransportChecker {
 		}
 	}
 }
+
+// IPv6ExtHdrChecker is a function to check an extension header.
+type IPv6ExtHdrChecker func(*testing.T, header.IPv6PayloadHeader)
+
+// IPv6WithExtHdr is like IPv6 but allows IPv6 packets with extension headers.
+func IPv6WithExtHdr(t *testing.T, b []byte, checkers ...NetworkChecker) {
+	t.Helper()
+
+	ipv6 := header.IPv6(b)
+	if !ipv6.IsValid(len(b)) {
+		t.Error("not a valid IPv6 packet")
+		return
+	}
+
+	payloadIterator := header.MakeIPv6PayloadIterator(
+		header.IPv6ExtensionHeaderIdentifier(ipv6.NextHeader()),
+		buffer.View(ipv6.Payload()).ToVectorisedView(),
+	)
+
+	var rawPayloadHeader header.IPv6RawPayloadHeader
+	for {
+		h, done, err := payloadIterator.Next()
+		if err != nil {
+			t.Errorf("payloadIterator.Next(): %s", err)
+			return
+		}
+		if done {
+			t.Errorf("got payloadIterator.Next() = (%T, %t, _), want = (_, true, _)", h, done)
+			return
+		}
+		r, ok := h.(header.IPv6RawPayloadHeader)
+		if ok {
+			rawPayloadHeader = r
+			break
+		}
+	}
+
+	networkHeader := ipv6HeaderWithExtHdr{
+		IPv6:      ipv6,
+		transport: tcpip.TransportProtocolNumber(rawPayloadHeader.Identifier),
+		payload:   rawPayloadHeader.Buf.ToView(),
+	}
+
+	for _, checker := range checkers {
+		checker(t, []header.Network{&networkHeader})
+	}
+}
+
+// IPv6ExtHdr checks for the presence of extension headers.
+//
+// All the extension headers in headers will be checked exhaustively in the
+// order provided.
+func IPv6ExtHdr(headers ...IPv6ExtHdrChecker) NetworkChecker {
+	return func(t *testing.T, h []header.Network) {
+		t.Helper()
+
+		extHdrs, ok := h[0].(*ipv6HeaderWithExtHdr)
+		if !ok {
+			t.Errorf("got network header = %T, want = *ipv6HeaderWithExtHdr", h[0])
+			return
+		}
+
+		payloadIterator := header.MakeIPv6PayloadIterator(
+			header.IPv6ExtensionHeaderIdentifier(extHdrs.IPv6.NextHeader()),
+			buffer.View(extHdrs.IPv6.Payload()).ToVectorisedView(),
+		)
+
+		for _, check := range headers {
+			h, done, err := payloadIterator.Next()
+			if err != nil {
+				t.Errorf("payloadIterator.Next(): %s", err)
+				return
+			}
+			if done {
+				t.Errorf("got payloadIterator.Next() = (%T, %t, _), want = (_, false, _)", h, done)
+				return
+			}
+			check(t, h)
+		}
+		// Validate we consumed all headers.
+		//
+		// The next one over should be a raw payload and then iterator should
+		// terminate.
+		wantDone := false
+		for {
+			h, done, err := payloadIterator.Next()
+			if err != nil {
+				t.Errorf("payloadIterator.Next(): %s", err)
+				return
+			}
+			if done != wantDone {
+				t.Errorf("got payloadIterator.Next() = (%T, %t, _), want = (_, %t, _)", h, done, wantDone)
+				return
+			}
+			if done {
+				break
+			}
+			if _, ok := h.(header.IPv6RawPayloadHeader); !ok {
+				t.Errorf("got payloadIterator.Next() = (%T, _, _), want = (header.IPv6RawPayloadHeader, _, _)", h)
+				continue
+			}
+			wantDone = true
+		}
+	}
+}
+
+var _ header.Network = (*ipv6HeaderWithExtHdr)(nil)
+
+// ipv6HeaderWithExtHdr provides a header.Network implementation that takes
+// extension headers into consideration, which is not the case with vanilla
+// header.IPv6.
+type ipv6HeaderWithExtHdr struct {
+	header.IPv6
+	transport tcpip.TransportProtocolNumber
+	payload   []byte
+}
+
+// TransportProtocol implements header.Network.
+func (h *ipv6HeaderWithExtHdr) TransportProtocol() tcpip.TransportProtocolNumber {
+	return h.transport
+}
+
+// Payload implements header.Network.
+func (h *ipv6HeaderWithExtHdr) Payload() []byte {
+	return h.payload
+}
+
+// IPv6ExtHdrOptionChecker is a function to check an extension header option.
+type IPv6ExtHdrOptionChecker func(*testing.T, header.IPv6ExtHdrOption)
+
+// IPv6HopByHopExtensionHeader checks the extension header is a Hop by Hop
+// extension header and validates the containing options with checkers.
+//
+// checkers must exhaustively contain all the expected options.
+func IPv6HopByHopExtensionHeader(checkers ...IPv6ExtHdrOptionChecker) IPv6ExtHdrChecker {
+	return func(t *testing.T, payloadHeader header.IPv6PayloadHeader) {
+		t.Helper()
+
+		hbh, ok := payloadHeader.(header.IPv6HopByHopOptionsExtHdr)
+		if !ok {
+			t.Errorf("unexpected IPv6 payload header, got = %T, want = header.IPv6HopByHopOptionsExtHdr", payloadHeader)
+			return
+		}
+		optionsIterator := hbh.Iter()
+		for _, f := range checkers {
+			opt, done, err := optionsIterator.Next()
+			if err != nil {
+				t.Errorf("optionsIterator.Next(): %s", err)
+				return
+			}
+			if done {
+				t.Errorf("got optionsIterator.Next() = (%T, %t, _), want = (_, false, _)", opt, done)
+			}
+			f(t, opt)
+		}
+		// Validate all options were consumed.
+		for {
+			opt, done, err := optionsIterator.Next()
+			if err != nil {
+				t.Errorf("optionsIterator.Next(): %s", err)
+				return
+			}
+			if !done {
+				t.Errorf("got optionsIterator.Next() = (%T, %t, _), want = (_, true, _)", opt, done)
+			}
+			if done {
+				break
+			}
+		}
+	}
+}
+
+// IPv6RouterAlert validates that an extension header option is the RouterAlert
+// option and matches on its value.
+func IPv6RouterAlert(want header.IPv6RouterAlertValue) IPv6ExtHdrOptionChecker {
+	return func(t *testing.T, opt header.IPv6ExtHdrOption) {
+		routerAlert, ok := opt.(*header.IPv6RouterAlertOption)
+		if !ok {
+			t.Errorf("unexpected extension header option, got = %T, want = header.IPv6RouterAlertOption", opt)
+			return
+		}
+		if routerAlert.Value != want {
+			t.Errorf("got routerAlert.Value = %d, want = %d", routerAlert.Value, want)
+		}
+	}
+}
diff --git a/pkg/tcpip/header/ipv6.go b/pkg/tcpip/header/ipv6.go
index 55d09355a..d522e5f10 100644
--- a/pkg/tcpip/header/ipv6.go
+++ b/pkg/tcpip/header/ipv6.go
@@ -48,11 +48,13 @@ type IPv6Fields struct {
 	// FlowLabel is the "flow label" field of an IPv6 packet.
 	FlowLabel uint32
 
-	// PayloadLength is the "payload length" field of an IPv6 packet.
+	// PayloadLength is the "payload length" field of an IPv6 packet, including
+	// the length of all extension headers.
 	PayloadLength uint16
 
-	// NextHeader is the "next header" field of an IPv6 packet.
-	NextHeader uint8
+	// TransportProtocol is the transport layer protocol number. Serialized in the
+	// last "next header" field of the IPv6 header + extension headers.
+	TransportProtocol tcpip.TransportProtocolNumber
 
 	// HopLimit is the "Hop Limit" field of an IPv6 packet.
 	HopLimit uint8
@@ -62,6 +64,9 @@ type IPv6Fields struct {
 
 	// DstAddr is the "destination ip address" of an IPv6 packet.
 	DstAddr tcpip.Address
+
+	// ExtensionHeaders are the extension headers following the IPv6 header.
+	ExtensionHeaders IPv6ExtHdrSerializer
 }
 
 // IPv6 represents an ipv6 header stored in a byte array.
@@ -253,12 +258,14 @@ func (IPv6) SetChecksum(uint16) {
 
 // Encode encodes all the fields of the ipv6 header.
 func (b IPv6) Encode(i *IPv6Fields) {
+	extHdr := b[IPv6MinimumSize:]
 	b.SetTOS(i.TrafficClass, i.FlowLabel)
 	b.SetPayloadLength(i.PayloadLength)
-	b[IPv6NextHeaderOffset] = i.NextHeader
 	b[hopLimit] = i.HopLimit
 	b.SetSourceAddress(i.SrcAddr)
 	b.SetDestinationAddress(i.DstAddr)
+	nextHeader, _ := i.ExtensionHeaders.Serialize(i.TransportProtocol, extHdr)
+	b[IPv6NextHeaderOffset] = nextHeader
 }
 
 // IsValid performs basic validation on the packet.
diff --git a/pkg/tcpip/header/ipv6_extension_headers.go b/pkg/tcpip/header/ipv6_extension_headers.go
index 571eae233..1fbb2cc98 100644
--- a/pkg/tcpip/header/ipv6_extension_headers.go
+++ b/pkg/tcpip/header/ipv6_extension_headers.go
@@ -20,7 +20,9 @@ import (
 	"encoding/binary"
 	"fmt"
 	"io"
+	"math"
 
+	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 )
 
@@ -75,8 +77,8 @@ const (
 	// Fragment Offset field within an IPv6FragmentExtHdr.
 	ipv6FragmentExtHdrFragmentOffsetOffset = 0
 
-	// ipv6FragmentExtHdrFragmentOffsetShift is the least significant bits to
-	// discard from the Fragment Offset.
+	// ipv6FragmentExtHdrFragmentOffsetShift is the bit offset of the Fragment
+	// Offset field within an IPv6FragmentExtHdr.
 	ipv6FragmentExtHdrFragmentOffsetShift = 3
 
 	// ipv6FragmentExtHdrFlagsIdx is the index to the flags field within an
@@ -114,6 +116,37 @@ const (
 	IPv6FragmentExtHdrFragmentOffsetBytesPerUnit = 8
 )
 
+// padIPv6OptionsLength returns the total length for IPv6 options of length l
+// considering the 8-octet alignment as stated in RFC 8200 Section 4.2.
+func padIPv6OptionsLength(length int) int {
+	return (length + ipv6ExtHdrLenBytesPerUnit - 1) & ^(ipv6ExtHdrLenBytesPerUnit - 1)
+}
+
+// padIPv6Option fills b with the appropriate padding options depending on its
+// length.
+func padIPv6Option(b []byte) {
+	switch len(b) {
+	case 0: // No padding needed.
+	case 1: // Pad with Pad1.
+		b[ipv6ExtHdrOptionTypeOffset] = uint8(ipv6Pad1ExtHdrOptionIdentifier)
+	default: // Pad with PadN.
+		s := b[ipv6ExtHdrOptionPayloadOffset:]
+		for i := range s {
+			s[i] = 0
+		}
+		b[ipv6ExtHdrOptionTypeOffset] = uint8(ipv6PadNExtHdrOptionIdentifier)
+		b[ipv6ExtHdrOptionLengthOffset] = uint8(len(s))
+	}
+}
+
+// ipv6OptionsAlignmentPadding returns the number of padding bytes needed to
+// serialize an option at headerOffset with alignment requirements
+// [align]n + alignOffset.
+func ipv6OptionsAlignmentPadding(headerOffset int, align int, alignOffset int) int {
+	padLen := headerOffset - alignOffset
+	return ((padLen + align - 1) & ^(align - 1)) - padLen
+}
+
 // IPv6PayloadHeader is implemented by the various headers that can be found
 // in an IPv6 payload.
 //
@@ -206,29 +239,51 @@ type IPv6ExtHdrOption interface {
 	isIPv6ExtHdrOption()
 }
 
-// IPv6ExtHdrOptionIndentifier is an IPv6 extension header option identifier.
-type IPv6ExtHdrOptionIndentifier uint8
+// IPv6ExtHdrOptionIdentifier is an IPv6 extension header option identifier.
+type IPv6ExtHdrOptionIdentifier uint8
 
 const (
 	// ipv6Pad1ExtHdrOptionIdentifier is the identifier for a padding option that
 	// provides 1 byte padding, as outlined in RFC 8200 section 4.2.
-	ipv6Pad1ExtHdrOptionIdentifier IPv6ExtHdrOptionIndentifier = 0
+	ipv6Pad1ExtHdrOptionIdentifier IPv6ExtHdrOptionIdentifier = 0
 
 	// ipv6PadBExtHdrOptionIdentifier is the identifier for a padding option that
 	// provides variable length byte padding, as outlined in RFC 8200 section 4.2.
-	ipv6PadNExtHdrOptionIdentifier IPv6ExtHdrOptionIndentifier = 1
+	ipv6PadNExtHdrOptionIdentifier IPv6ExtHdrOptionIdentifier = 1
+
+	// ipv6RouterAlertHopByHopOptionIdentifier is the identifier for the Router
+	// Alert Hop by Hop option as defined in RFC 2711 section 2.1.
+	ipv6RouterAlertHopByHopOptionIdentifier IPv6ExtHdrOptionIdentifier = 5
+
+	// ipv6ExtHdrOptionTypeOffset is the option type offset in an extension header
+	// option as defined in RFC 8200 section 4.2.
+	ipv6ExtHdrOptionTypeOffset = 0
+
+	// ipv6ExtHdrOptionLengthOffset is the option length offset in an extension
+	// header option as defined in RFC 8200 section 4.2.
+	ipv6ExtHdrOptionLengthOffset = 1
+
+	// ipv6ExtHdrOptionPayloadOffset is the option payload offset in an extension
+	// header option as defined in RFC 8200 section 4.2.
+	ipv6ExtHdrOptionPayloadOffset = 2
 )
 
+// ipv6UnknownActionFromIdentifier maps an extension header option's
+// identifier's high  bits to the action to take when the identifier is unknown.
+func ipv6UnknownActionFromIdentifier(id IPv6ExtHdrOptionIdentifier) IPv6OptionUnknownAction {
+	return IPv6OptionUnknownAction((id & ipv6UnknownExtHdrOptionActionMask) >> ipv6UnknownExtHdrOptionActionShift)
+}
+
 // IPv6UnknownExtHdrOption holds the identifier and data for an IPv6 extension
 // header option that is unknown by the parsing utilities.
 type IPv6UnknownExtHdrOption struct {
-	Identifier IPv6ExtHdrOptionIndentifier
+	Identifier IPv6ExtHdrOptionIdentifier
 	Data       []byte
 }
 
 // UnknownAction implements IPv6OptionUnknownAction.UnknownAction.
 func (o *IPv6UnknownExtHdrOption) UnknownAction() IPv6OptionUnknownAction {
-	return IPv6OptionUnknownAction((o.Identifier & ipv6UnknownExtHdrOptionActionMask) >> ipv6UnknownExtHdrOptionActionShift)
+	return ipv6UnknownActionFromIdentifier(o.Identifier)
 }
 
 // isIPv6ExtHdrOption implements IPv6ExtHdrOption.isIPv6ExtHdrOption.
@@ -251,7 +306,7 @@ func (i *IPv6OptionsExtHdrOptionsIterator) Next() (IPv6ExtHdrOption, bool, error
 			// options buffer has been exhausted and we are done iterating.
 			return nil, true, nil
 		}
-		id := IPv6ExtHdrOptionIndentifier(temp)
+		id := IPv6ExtHdrOptionIdentifier(temp)
 
 		// If the option identifier indicates the option is a Pad1 option, then we
 		// know the option does not have Length and Data fields. End processing of
@@ -294,6 +349,14 @@ func (i *IPv6OptionsExtHdrOptionsIterator) Next() (IPv6ExtHdrOption, bool, error
 				panic(fmt.Sprintf("error when skipping PadN (N = %d) option's data bytes: %s", length, err))
 			}
 			continue
+		case ipv6RouterAlertHopByHopOptionIdentifier:
+			var routerAlertValue [ipv6RouterAlertPayloadLength]byte
+			if n, err := i.reader.Read(routerAlertValue[:]); err != nil {
+				panic(fmt.Sprintf("error when reading RouterAlert option's data bytes: %s", err))
+			} else if n != ipv6RouterAlertPayloadLength {
+				return nil, true, fmt.Errorf("read %d bytes for RouterAlert option, expected %d", n, ipv6RouterAlertPayloadLength)
+			}
+			return &IPv6RouterAlertOption{Value: IPv6RouterAlertValue(binary.BigEndian.Uint16(routerAlertValue[:]))}, false, nil
 		default:
 			bytes := make([]byte, length)
 			if n, err := io.ReadFull(&i.reader, bytes); err != nil {
@@ -609,3 +672,248 @@ func (i *IPv6PayloadIterator) nextHeaderData(fragmentHdr bool, bytes []byte) (IP
 
 	return IPv6ExtensionHeaderIdentifier(nextHdrIdentifier), bytes, nil
 }
+
+// IPv6SerializableExtHdr provides serialization for IPv6 extension
+// headers.
+type IPv6SerializableExtHdr interface {
+	// identifier returns the assigned IPv6 header identifier for this extension
+	// header.
+	identifier() IPv6ExtensionHeaderIdentifier
+
+	// length returns the total serialized length in bytes of this extension
+	// header, including the common next header and length fields.
+	length() int
+
+	// serializeInto serializes the receiver into the provided byte
+	// buffer and with the provided nextHeader value.
+	//
+	// Note, the caller MUST provide a byte buffer with size of at least
+	// length. Implementers of this function may assume that the byte buffer
+	// is of sufficient size. serializeInto MAY panic if the provided byte
+	// buffer is not of sufficient size.
+	//
+	// serializeInto returns the number of bytes that was used to 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(nextHeader uint8, b []byte) int
+}
+
+var _ IPv6SerializableExtHdr = (*IPv6SerializableHopByHopExtHdr)(nil)
+
+// IPv6SerializableHopByHopExtHdr implements serialization of the Hop by Hop
+// options extension header.
+type IPv6SerializableHopByHopExtHdr []IPv6SerializableHopByHopOption
+
+const (
+	// ipv6HopByHopExtHdrNextHeaderOffset is the offset of the next header field
+	// in a hop by hop extension header as defined in RFC 8200 section 4.3.
+	ipv6HopByHopExtHdrNextHeaderOffset = 0
+
+	// ipv6HopByHopExtHdrLengthOffset is the offset of the length field in a hop
+	// by hop extension header as defined in RFC 8200 section 4.3.
+	ipv6HopByHopExtHdrLengthOffset = 1
+
+	// ipv6HopByHopExtHdrPayloadOffset is the offset of the options in a hop by
+	// hop extension header as defined in RFC 8200 section 4.3.
+	ipv6HopByHopExtHdrOptionsOffset = 2
+
+	// ipv6HopByHopExtHdrUnaccountedLenWords is the implicit number of 8-octet
+	// words in a hop by hop extension header's length field, as stated in RFC
+	// 8200 section 4.3:
+	//   Length of the Hop-by-Hop Options header in 8-octet units,
+	//   not including the first 8 octets.
+	ipv6HopByHopExtHdrUnaccountedLenWords = 1
+)
+
+// identifier implements IPv6SerializableExtHdr.
+func (IPv6SerializableHopByHopExtHdr) identifier() IPv6ExtensionHeaderIdentifier {
+	return IPv6HopByHopOptionsExtHdrIdentifier
+}
+
+// length implements IPv6SerializableExtHdr.
+func (h IPv6SerializableHopByHopExtHdr) length() int {
+	var total int
+	for _, opt := range h {
+		align, alignOffset := opt.alignment()
+		total += ipv6OptionsAlignmentPadding(total, align, alignOffset)
+		total += ipv6ExtHdrOptionPayloadOffset + int(opt.length())
+	}
+	// Account for next header and total length fields and add padding.
+	return padIPv6OptionsLength(ipv6HopByHopExtHdrOptionsOffset + total)
+}
+
+// serializeInto implements IPv6SerializableExtHdr.
+func (h IPv6SerializableHopByHopExtHdr) serializeInto(nextHeader uint8, b []byte) int {
+	optBuffer := b[ipv6HopByHopExtHdrOptionsOffset:]
+	totalLength := ipv6HopByHopExtHdrOptionsOffset
+	for _, opt := range h {
+		// Calculate alignment requirements and pad buffer if necessary.
+		align, alignOffset := opt.alignment()
+		padLen := ipv6OptionsAlignmentPadding(totalLength, align, alignOffset)
+		if padLen != 0 {
+			padIPv6Option(optBuffer[:padLen])
+			totalLength += padLen
+			optBuffer = optBuffer[padLen:]
+		}
+
+		l := opt.serializeInto(optBuffer[ipv6ExtHdrOptionPayloadOffset:])
+		optBuffer[ipv6ExtHdrOptionTypeOffset] = uint8(opt.identifier())
+		optBuffer[ipv6ExtHdrOptionLengthOffset] = l
+		l += ipv6ExtHdrOptionPayloadOffset
+		totalLength += int(l)
+		optBuffer = optBuffer[l:]
+	}
+	padded := padIPv6OptionsLength(totalLength)
+	if padded != totalLength {
+		padIPv6Option(optBuffer[:padded-totalLength])
+		totalLength = padded
+	}
+	wordsLen := totalLength/ipv6ExtHdrLenBytesPerUnit - ipv6HopByHopExtHdrUnaccountedLenWords
+	if wordsLen > math.MaxUint8 {
+		panic(fmt.Sprintf("IPv6 hop by hop options too large: %d+1 64-bit words", wordsLen))
+	}
+	b[ipv6HopByHopExtHdrNextHeaderOffset] = nextHeader
+	b[ipv6HopByHopExtHdrLengthOffset] = uint8(wordsLen)
+	return totalLength
+}
+
+// IPv6SerializableHopByHopOption provides serialization for hop by hop options.
+type IPv6SerializableHopByHopOption interface {
+	// identifier returns the option identifier of this Hop by Hop option.
+	identifier() IPv6ExtHdrOptionIdentifier
+
+	// length returns the *payload* size of the option (not considering the type
+	// and length fields).
+	length() uint8
+
+	// alignment returns the alignment requirements from this option.
+	//
+	// Alignment requirements take the form [align]n + offset as specified in
+	// RFC 8200 section 4.2. The alignment requirement is on the offset between
+	// the option type byte and the start of the hop by hop header.
+	//
+	// align must be a power of 2.
+	alignment() (align int, offset int)
+
+	// serializeInto serializes the receiver into the provided byte
+	// buffer.
+	//
+	// Note, the caller MUST provide a byte buffer with size of at least
+	// length. Implementers of this function may assume that the byte buffer
+	// is of sufficient size. serializeInto MAY panic if the provided byte
+	// buffer is not of sufficient size.
+	//
+	// serializeInto will return the number of bytes that was used to
+	// 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) uint8
+}
+
+var _ IPv6SerializableHopByHopOption = (*IPv6RouterAlertOption)(nil)
+
+// IPv6RouterAlertOption is the IPv6 Router alert Hop by Hop option defined in
+// RFC 2711 section 2.1.
+type IPv6RouterAlertOption struct {
+	Value IPv6RouterAlertValue
+}
+
+// IPv6RouterAlertValue is the payload of an IPv6 Router Alert option.
+type IPv6RouterAlertValue uint16
+
+const (
+	// IPv6RouterAlertMLD indicates a datagram containing a Multicast Listener
+	// Discovery message as defined in RFC 2711 section 2.1.
+	IPv6RouterAlertMLD IPv6RouterAlertValue = 0
+	// IPv6RouterAlertRSVP indicates a datagram containing an RSVP message as
+	// defined in RFC 2711 section 2.1.
+	IPv6RouterAlertRSVP IPv6RouterAlertValue = 1
+	// IPv6RouterAlertActiveNetworks indicates a datagram containing an Active
+	// Networks message as defined in RFC 2711 section 2.1.
+	IPv6RouterAlertActiveNetworks IPv6RouterAlertValue = 2
+
+	// ipv6RouterAlertPayloadLength is the length of the Router Alert payload
+	// as defined in RFC 2711.
+	ipv6RouterAlertPayloadLength = 2
+
+	// ipv6RouterAlertAlignmentRequirement is the alignment requirement for the
+	// Router Alert option defined as 2n+0 in RFC 2711.
+	ipv6RouterAlertAlignmentRequirement = 2
+
+	// ipv6RouterAlertAlignmentOffsetRequirement is the alignment offset
+	// requirement for the Router Alert option defined as 2n+0 in RFC 2711 section
+	// 2.1.
+	ipv6RouterAlertAlignmentOffsetRequirement = 0
+)
+
+// UnknownAction implements IPv6ExtHdrOption.
+func (*IPv6RouterAlertOption) UnknownAction() IPv6OptionUnknownAction {
+	return ipv6UnknownActionFromIdentifier(ipv6RouterAlertHopByHopOptionIdentifier)
+}
+
+// isIPv6ExtHdrOption implements IPv6ExtHdrOption.
+func (*IPv6RouterAlertOption) isIPv6ExtHdrOption() {}
+
+// identifier implements IPv6SerializableHopByHopOption.
+func (*IPv6RouterAlertOption) identifier() IPv6ExtHdrOptionIdentifier {
+	return ipv6RouterAlertHopByHopOptionIdentifier
+}
+
+// length implements IPv6SerializableHopByHopOption.
+func (*IPv6RouterAlertOption) length() uint8 {
+	return ipv6RouterAlertPayloadLength
+}
+
+// alignment implements IPv6SerializableHopByHopOption.
+func (*IPv6RouterAlertOption) alignment() (int, int) {
+	// From RFC 2711 section 2.1:
+	//   Alignment requirement: 2n+0.
+	return ipv6RouterAlertAlignmentRequirement, ipv6RouterAlertAlignmentOffsetRequirement
+}
+
+// serializeInto implements IPv6SerializableHopByHopOption.
+func (o *IPv6RouterAlertOption) serializeInto(b []byte) uint8 {
+	binary.BigEndian.PutUint16(b, uint16(o.Value))
+	return ipv6RouterAlertPayloadLength
+}
+
+// IPv6ExtHdrSerializer provides serialization of IPv6 extension headers.
+type IPv6ExtHdrSerializer []IPv6SerializableExtHdr
+
+// Serialize serializes the provided list of IPv6 extension headers into b.
+//
+// Note, b must be of sufficient size to hold all the headers in s. See
+// IPv6ExtHdrSerializer.Length for details on the getting the total size of a
+// serialized IPv6ExtHdrSerializer.
+//
+// Serialize may panic if b is not of sufficient size to hold all the options
+// in s.
+//
+// Serialize takes the transportProtocol value to be used as the last extension
+// header's Next Header value and returns the header identifier of the first
+// serialized extension header and the total serialized length.
+func (s IPv6ExtHdrSerializer) Serialize(transportProtocol tcpip.TransportProtocolNumber, b []byte) (uint8, int) {
+	nextHeader := uint8(transportProtocol)
+	if len(s) == 0 {
+		return nextHeader, 0
+	}
+	var totalLength int
+	for i, h := range s[:len(s)-1] {
+		length := h.serializeInto(uint8(s[i+1].identifier()), b)
+		b = b[length:]
+		totalLength += length
+	}
+	totalLength += s[len(s)-1].serializeInto(nextHeader, b)
+	return uint8(s[0].identifier()), totalLength
+}
+
+// Length returns the total number of bytes required to serialize the extension
+// headers.
+func (s IPv6ExtHdrSerializer) Length() int {
+	var totalLength int
+	for _, h := range s {
+		totalLength += h.length()
+	}
+	return totalLength
+}
diff --git a/pkg/tcpip/header/ipv6_extension_headers_test.go b/pkg/tcpip/header/ipv6_extension_headers_test.go
index ab20c5f37..5d2296353 100644
--- a/pkg/tcpip/header/ipv6_extension_headers_test.go
+++ b/pkg/tcpip/header/ipv6_extension_headers_test.go
@@ -21,6 +21,7 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
+	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 )
 
@@ -59,7 +60,7 @@ func (a IPv6DestinationOptionsExtHdr) Equal(b IPv6DestinationOptionsExtHdr) bool
 func TestIPv6UnknownExtHdrOption(t *testing.T) {
 	tests := []struct {
 		name                  string
-		identifier            IPv6ExtHdrOptionIndentifier
+		identifier            IPv6ExtHdrOptionIdentifier
 		expectedUnknownAction IPv6OptionUnknownAction
 	}{
 		{
@@ -990,3 +991,331 @@ func TestIPv6ExtHdrIter(t *testing.T) {
 		})
 	}
 }
+
+var _ IPv6SerializableHopByHopOption = (*dummyHbHOptionSerializer)(nil)
+
+// dummyHbHOptionSerializer provides a generic implementation of
+// IPv6SerializableHopByHopOption for use in tests.
+type dummyHbHOptionSerializer struct {
+	id          IPv6ExtHdrOptionIdentifier
+	payload     []byte
+	align       int
+	alignOffset int
+}
+
+// identifier implements IPv6SerializableHopByHopOption.
+func (s *dummyHbHOptionSerializer) identifier() IPv6ExtHdrOptionIdentifier {
+	return s.id
+}
+
+// length implements IPv6SerializableHopByHopOption.
+func (s *dummyHbHOptionSerializer) length() uint8 {
+	return uint8(len(s.payload))
+}
+
+// alignment implements IPv6SerializableHopByHopOption.
+func (s *dummyHbHOptionSerializer) alignment() (int, int) {
+	align := 1
+	if s.align != 0 {
+		align = s.align
+	}
+	return align, s.alignOffset
+}
+
+// serializeInto implements IPv6SerializableHopByHopOption.
+func (s *dummyHbHOptionSerializer) serializeInto(b []byte) uint8 {
+	return uint8(copy(b, s.payload))
+}
+
+func TestIPv6HopByHopSerializer(t *testing.T) {
+	validateDummies := func(t *testing.T, serializable IPv6SerializableHopByHopOption, deserialized IPv6ExtHdrOption) {
+		t.Helper()
+		dummy, ok := serializable.(*dummyHbHOptionSerializer)
+		if !ok {
+			t.Fatalf("got serializable = %T, want = *dummyHbHOptionSerializer", serializable)
+		}
+		unknown, ok := deserialized.(*IPv6UnknownExtHdrOption)
+		if !ok {
+			t.Fatalf("got deserialized = %T, want = %T", deserialized, &IPv6UnknownExtHdrOption{})
+		}
+		if dummy.id != unknown.Identifier {
+			t.Errorf("got deserialized identifier = %d, want = %d", unknown.Identifier, dummy.id)
+		}
+		if diff := cmp.Diff(dummy.payload, unknown.Data); diff != "" {
+			t.Errorf("option payload deserialization mismatch (-want +got):\n%s", diff)
+		}
+	}
+	tests := []struct {
+		name       string
+		nextHeader uint8
+		options    []IPv6SerializableHopByHopOption
+		expect     []byte
+		validate   func(*testing.T, IPv6SerializableHopByHopOption, IPv6ExtHdrOption)
+	}{
+		{
+			name:       "single option",
+			nextHeader: 13,
+			options: []IPv6SerializableHopByHopOption{
+				&dummyHbHOptionSerializer{
+					id:      15,
+					payload: []byte{9, 8, 7, 6},
+				},
+			},
+			expect:   []byte{13, 0, 15, 4, 9, 8, 7, 6},
+			validate: validateDummies,
+		},
+		{
+			name:       "short option padN zero",
+			nextHeader: 88,
+			options: []IPv6SerializableHopByHopOption{
+				&dummyHbHOptionSerializer{
+					id:      22,
+					payload: []byte{4, 5},
+				},
+			},
+			expect:   []byte{88, 0, 22, 2, 4, 5, 1, 0},
+			validate: validateDummies,
+		},
+		{
+			name:       "short option pad1",
+			nextHeader: 11,
+			options: []IPv6SerializableHopByHopOption{
+				&dummyHbHOptionSerializer{
+					id:      33,
+					payload: []byte{1, 2, 3},
+				},
+			},
+			expect:   []byte{11, 0, 33, 3, 1, 2, 3, 0},
+			validate: validateDummies,
+		},
+		{
+			name:       "long option padN",
+			nextHeader: 55,
+			options: []IPv6SerializableHopByHopOption{
+				&dummyHbHOptionSerializer{
+					id:      77,
+					payload: []byte{1, 2, 3, 4, 5, 6, 7, 8},
+				},
+			},
+			expect:   []byte{55, 1, 77, 8, 1, 2, 3, 4, 5, 6, 7, 8, 1, 2, 0, 0},
+			validate: validateDummies,
+		},
+		{
+			name:       "two options",
+			nextHeader: 33,
+			options: []IPv6SerializableHopByHopOption{
+				&dummyHbHOptionSerializer{
+					id:      11,
+					payload: []byte{1, 2, 3},
+				},
+				&dummyHbHOptionSerializer{
+					id:      22,
+					payload: []byte{4, 5, 6},
+				},
+			},
+			expect:   []byte{33, 1, 11, 3, 1, 2, 3, 22, 3, 4, 5, 6, 1, 2, 0, 0},
+			validate: validateDummies,
+		},
+		{
+			name:       "two options align 2n",
+			nextHeader: 33,
+			options: []IPv6SerializableHopByHopOption{
+				&dummyHbHOptionSerializer{
+					id:      11,
+					payload: []byte{1, 2, 3},
+				},
+				&dummyHbHOptionSerializer{
+					id:      22,
+					payload: []byte{4, 5, 6},
+					align:   2,
+				},
+			},
+			expect:   []byte{33, 1, 11, 3, 1, 2, 3, 0, 22, 3, 4, 5, 6, 1, 1, 0},
+			validate: validateDummies,
+		},
+		{
+			name:       "two options align 8n+1",
+			nextHeader: 33,
+			options: []IPv6SerializableHopByHopOption{
+				&dummyHbHOptionSerializer{
+					id:      11,
+					payload: []byte{1, 2},
+				},
+				&dummyHbHOptionSerializer{
+					id:          22,
+					payload:     []byte{4, 5, 6},
+					align:       8,
+					alignOffset: 1,
+				},
+			},
+			expect:   []byte{33, 1, 11, 2, 1, 2, 1, 1, 0, 22, 3, 4, 5, 6, 1, 0},
+			validate: validateDummies,
+		},
+		{
+			name:       "no options",
+			nextHeader: 33,
+			options:    []IPv6SerializableHopByHopOption{},
+			expect:     []byte{33, 0, 1, 4, 0, 0, 0, 0},
+		},
+		{
+			name:       "Router Alert",
+			nextHeader: 33,
+			options:    []IPv6SerializableHopByHopOption{&IPv6RouterAlertOption{Value: IPv6RouterAlertMLD}},
+			expect:     []byte{33, 0, 5, 2, 0, 0, 1, 0},
+			validate: func(t *testing.T, _ IPv6SerializableHopByHopOption, deserialized IPv6ExtHdrOption) {
+				t.Helper()
+				routerAlert, ok := deserialized.(*IPv6RouterAlertOption)
+				if !ok {
+					t.Fatalf("got deserialized = %T, want = *IPv6RouterAlertOption", deserialized)
+				}
+				if routerAlert.Value != IPv6RouterAlertMLD {
+					t.Errorf("got routerAlert.Value = %d, want = %d", routerAlert.Value, IPv6RouterAlertMLD)
+				}
+			},
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			s := IPv6SerializableHopByHopExtHdr(test.options)
+			length := s.length()
+			if length != len(test.expect) {
+				t.Fatalf("got s.length() = %d, want = %d", length, len(test.expect))
+			}
+			b := make([]byte, length)
+			for i := range b {
+				// Fill the buffer with ones to ensure all padding is correctly set.
+				b[i] = 0xFF
+			}
+			if got := s.serializeInto(test.nextHeader, b); got != length {
+				t.Fatalf("got s.serializeInto(..) = %d, want = %d", got, length)
+			}
+			if diff := cmp.Diff(test.expect, b); diff != "" {
+				t.Fatalf("serialization mismatch (-want +got):\n%s", diff)
+			}
+
+			// Deserialize the options and verify them.
+			optLen := (b[ipv6HopByHopExtHdrLengthOffset] + ipv6HopByHopExtHdrUnaccountedLenWords) * ipv6ExtHdrLenBytesPerUnit
+			iter := ipv6OptionsExtHdr(b[ipv6HopByHopExtHdrOptionsOffset:optLen]).Iter()
+			for _, testOpt := range test.options {
+				opt, done, err := iter.Next()
+				if err != nil {
+					t.Fatalf("iter.Next(): %s", err)
+				}
+				if done {
+					t.Fatalf("got iter.Next() = (%T, %t, _), want = (_, false, _)", opt, done)
+				}
+				test.validate(t, testOpt, opt)
+			}
+			opt, done, err := iter.Next()
+			if err != nil {
+				t.Fatalf("iter.Next(): %s", err)
+			}
+			if !done {
+				t.Fatalf("got iter.Next() = (%T, %t, _), want = (_, true, _)", opt, done)
+			}
+		})
+	}
+}
+
+var _ IPv6SerializableExtHdr = (*dummyIPv6ExtHdrSerializer)(nil)
+
+// dummyIPv6ExtHdrSerializer provides a generic implementation of
+// IPv6SerializableExtHdr for use in tests.
+//
+// The dummy header always carries the nextHeader value in the first byte.
+type dummyIPv6ExtHdrSerializer struct {
+	id             IPv6ExtensionHeaderIdentifier
+	headerContents []byte
+}
+
+// identifier implements IPv6SerializableExtHdr.
+func (s *dummyIPv6ExtHdrSerializer) identifier() IPv6ExtensionHeaderIdentifier {
+	return s.id
+}
+
+// length implements IPv6SerializableExtHdr.
+func (s *dummyIPv6ExtHdrSerializer) length() int {
+	return len(s.headerContents) + 1
+}
+
+// serializeInto implements IPv6SerializableExtHdr.
+func (s *dummyIPv6ExtHdrSerializer) serializeInto(nextHeader uint8, b []byte) int {
+	b[0] = nextHeader
+	return copy(b[1:], s.headerContents) + 1
+}
+
+func TestIPv6ExtHdrSerializer(t *testing.T) {
+	tests := []struct {
+		name             string
+		headers          []IPv6SerializableExtHdr
+		nextHeader       tcpip.TransportProtocolNumber
+		expectSerialized []byte
+		expectNextHeader uint8
+	}{
+		{
+			name: "one header",
+			headers: []IPv6SerializableExtHdr{
+				&dummyIPv6ExtHdrSerializer{
+					id:             15,
+					headerContents: []byte{1, 2, 3, 4},
+				},
+			},
+			nextHeader:       TCPProtocolNumber,
+			expectSerialized: []byte{byte(TCPProtocolNumber), 1, 2, 3, 4},
+			expectNextHeader: 15,
+		},
+		{
+			name: "two headers",
+			headers: []IPv6SerializableExtHdr{
+				&dummyIPv6ExtHdrSerializer{
+					id:             22,
+					headerContents: []byte{1, 2, 3},
+				},
+				&dummyIPv6ExtHdrSerializer{
+					id:             23,
+					headerContents: []byte{4, 5, 6},
+				},
+			},
+			nextHeader: ICMPv6ProtocolNumber,
+			expectSerialized: []byte{
+				23, 1, 2, 3,
+				byte(ICMPv6ProtocolNumber), 4, 5, 6,
+			},
+			expectNextHeader: 22,
+		},
+		{
+			name:             "no headers",
+			headers:          []IPv6SerializableExtHdr{},
+			nextHeader:       UDPProtocolNumber,
+			expectSerialized: []byte{},
+			expectNextHeader: byte(UDPProtocolNumber),
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			s := IPv6ExtHdrSerializer(test.headers)
+			l := s.Length()
+			if got, want := l, len(test.expectSerialized); got != want {
+				t.Fatalf("got serialized length = %d, want = %d", got, want)
+			}
+			b := make([]byte, l)
+			for i := range b {
+				// Fill the buffer with garbage to make sure we're writing to all bytes.
+				b[i] = 0xFF
+			}
+			nextHeader, serializedLen := s.Serialize(test.nextHeader, b)
+			if serializedLen != len(test.expectSerialized) || nextHeader != test.expectNextHeader {
+				t.Errorf(
+					"got s.Serialize(..) = (%d, %d), want = (%d, %d)",
+					nextHeader,
+					serializedLen,
+					test.expectNextHeader,
+					len(test.expectSerialized),
+				)
+			}
+			if diff := cmp.Diff(test.expectSerialized, b); diff != "" {
+				t.Errorf("serialization mismatch (-want +got):\n%s", diff)
+			}
+		})
+	}
+}
diff --git a/pkg/tcpip/header/ipv6_fragment.go b/pkg/tcpip/header/ipv6_fragment.go
index 018555a26..9d09f32eb 100644
--- a/pkg/tcpip/header/ipv6_fragment.go
+++ b/pkg/tcpip/header/ipv6_fragment.go
@@ -27,12 +27,11 @@ const (
 	idV6        = 4
 )
 
-// IPv6FragmentFields contains the fields of an IPv6 fragment. It is used to describe the
-// fields of a packet that needs to be encoded.
-type IPv6FragmentFields struct {
-	// NextHeader is the "next header" field of an IPv6 fragment.
-	NextHeader uint8
+var _ IPv6SerializableExtHdr = (*IPv6SerializableFragmentExtHdr)(nil)
 
+// IPv6SerializableFragmentExtHdr is used to serialize an IPv6 fragment
+// extension header as defined in RFC 8200 section 4.5.
+type IPv6SerializableFragmentExtHdr struct {
 	// FragmentOffset is the "fragment offset" field of an IPv6 fragment.
 	FragmentOffset uint16
 
@@ -43,6 +42,29 @@ type IPv6FragmentFields struct {
 	Identification uint32
 }
 
+// identifier implements IPv6SerializableFragmentExtHdr.
+func (h *IPv6SerializableFragmentExtHdr) identifier() IPv6ExtensionHeaderIdentifier {
+	return IPv6FragmentHeader
+}
+
+// length implements IPv6SerializableFragmentExtHdr.
+func (h *IPv6SerializableFragmentExtHdr) length() int {
+	return IPv6FragmentHeaderSize
+}
+
+// serializeInto implements IPv6SerializableFragmentExtHdr.
+func (h *IPv6SerializableFragmentExtHdr) serializeInto(nextHeader uint8, b []byte) int {
+	// Prevent too many bounds checks.
+	_ = b[IPv6FragmentHeaderSize:]
+	binary.BigEndian.PutUint32(b[idV6:], h.Identification)
+	binary.BigEndian.PutUint16(b[fragOff:], h.FragmentOffset<<ipv6FragmentExtHdrFragmentOffsetShift)
+	b[nextHdrFrag] = nextHeader
+	if h.M {
+		b[more] |= ipv6FragmentExtHdrMFlagMask
+	}
+	return IPv6FragmentHeaderSize
+}
+
 // IPv6Fragment represents an ipv6 fragment header stored in a byte array.
 // Most of the methods of IPv6Fragment access to the underlying slice without
 // checking the boundaries and could panic because of 'index out of range'.
@@ -58,16 +80,6 @@ const (
 	IPv6FragmentHeaderSize = 8
 )
 
-// Encode encodes all the fields of the ipv6 fragment.
-func (b IPv6Fragment) Encode(i *IPv6FragmentFields) {
-	b[nextHdrFrag] = i.NextHeader
-	binary.BigEndian.PutUint16(b[fragOff:], i.FragmentOffset<<3)
-	if i.M {
-		b[more] |= 1
-	}
-	binary.BigEndian.PutUint32(b[idV6:], i.Identification)
-}
-
 // IsValid performs basic validation on the fragment header.
 func (b IPv6Fragment) IsValid() bool {
 	return len(b) >= IPv6FragmentHeaderSize
diff --git a/pkg/tcpip/network/ip_test.go b/pkg/tcpip/network/ip_test.go
index a314dd386..3005973d7 100644
--- a/pkg/tcpip/network/ip_test.go
+++ b/pkg/tcpip/network/ip_test.go
@@ -344,11 +344,11 @@ func TestSourceAddressValidation(t *testing.T) {
 		pkt.SetChecksum(header.ICMPv6Checksum(pkt, src, localIPv6Addr, buffer.VectorisedView{}))
 		ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 		ip.Encode(&header.IPv6Fields{
-			PayloadLength: header.ICMPv6MinimumSize,
-			NextHeader:    uint8(icmp.ProtocolNumber6),
-			HopLimit:      ipv6.DefaultTTL,
-			SrcAddr:       src,
-			DstAddr:       localIPv6Addr,
+			PayloadLength:     header.ICMPv6MinimumSize,
+			TransportProtocol: icmp.ProtocolNumber6,
+			HopLimit:          ipv6.DefaultTTL,
+			SrcAddr:           src,
+			DstAddr:           localIPv6Addr,
 		})
 		e.InjectInbound(header.IPv6ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
 			Data: hdr.View().ToVectorisedView(),
@@ -619,11 +619,11 @@ func TestReceive(t *testing.T) {
 				view := buffer.NewView(header.IPv6MinimumSize + payloadLen)
 				ip := header.IPv6(view)
 				ip.Encode(&header.IPv6Fields{
-					PayloadLength: payloadLen,
-					NextHeader:    10,
-					HopLimit:      ipv6.DefaultTTL,
-					SrcAddr:       remoteIPv6Addr,
-					DstAddr:       localIPv6Addr,
+					PayloadLength:     payloadLen,
+					TransportProtocol: 10,
+					HopLimit:          ipv6.DefaultTTL,
+					SrcAddr:           remoteIPv6Addr,
+					DstAddr:           localIPv6Addr,
 				})
 
 				// Make payload be non-zero.
@@ -993,11 +993,11 @@ func TestIPv6ReceiveControl(t *testing.T) {
 			// Create the outer IPv6 header.
 			ip := header.IPv6(view)
 			ip.Encode(&header.IPv6Fields{
-				PayloadLength: uint16(len(view) - header.IPv6MinimumSize - c.trunc),
-				NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-				HopLimit:      20,
-				SrcAddr:       outerSrcAddr,
-				DstAddr:       localIPv6Addr,
+				PayloadLength:     uint16(len(view) - header.IPv6MinimumSize - c.trunc),
+				TransportProtocol: header.ICMPv6ProtocolNumber,
+				HopLimit:          20,
+				SrcAddr:           outerSrcAddr,
+				DstAddr:           localIPv6Addr,
 			})
 
 			// Create the ICMP header.
@@ -1007,28 +1007,27 @@ func TestIPv6ReceiveControl(t *testing.T) {
 			icmp.SetIdent(0xdead)
 			icmp.SetSequence(0xbeef)
 
-			// Create the inner IPv6 header.
-			ip = header.IPv6(view[header.IPv6MinimumSize+header.ICMPv6PayloadOffset:])
-			ip.Encode(&header.IPv6Fields{
-				PayloadLength: 100,
-				NextHeader:    10,
-				HopLimit:      20,
-				SrcAddr:       localIPv6Addr,
-				DstAddr:       remoteIPv6Addr,
-			})
-
+			var extHdrs header.IPv6ExtHdrSerializer
 			// Build the fragmentation header if needed.
 			if c.fragmentOffset != nil {
-				ip.SetNextHeader(header.IPv6FragmentHeader)
-				frag := header.IPv6Fragment(view[2*header.IPv6MinimumSize+header.ICMPv6MinimumSize:])
-				frag.Encode(&header.IPv6FragmentFields{
-					NextHeader:     10,
+				extHdrs = append(extHdrs, &header.IPv6SerializableFragmentExtHdr{
 					FragmentOffset: *c.fragmentOffset,
 					M:              true,
 					Identification: 0x12345678,
 				})
 			}
 
+			// Create the inner IPv6 header.
+			ip = header.IPv6(view[header.IPv6MinimumSize+header.ICMPv6PayloadOffset:])
+			ip.Encode(&header.IPv6Fields{
+				PayloadLength:     100,
+				TransportProtocol: 10,
+				HopLimit:          20,
+				SrcAddr:           localIPv6Addr,
+				DstAddr:           remoteIPv6Addr,
+				ExtensionHeaders:  extHdrs,
+			})
+
 			// Make payload be non-zero.
 			for i := dataOffset; i < len(view); i++ {
 				view[i] = uint8(i)
@@ -1344,10 +1343,10 @@ func TestWriteHeaderIncludedPacket(t *testing.T) {
 				}
 				ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 				ip.Encode(&header.IPv6Fields{
-					NextHeader: transportProto,
-					HopLimit:   ipv6.DefaultTTL,
-					SrcAddr:    src,
-					DstAddr:    header.IPv4Any,
+					TransportProtocol: transportProto,
+					HopLimit:          ipv6.DefaultTTL,
+					SrcAddr:           src,
+					DstAddr:           header.IPv4Any,
 				})
 				return hdr.View().ToVectorisedView()
 			},
@@ -1387,10 +1386,12 @@ func TestWriteHeaderIncludedPacket(t *testing.T) {
 				}
 				ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 				ip.Encode(&header.IPv6Fields{
-					NextHeader: uint8(header.IPv6FragmentExtHdrIdentifier),
-					HopLimit:   ipv6.DefaultTTL,
-					SrcAddr:    src,
-					DstAddr:    header.IPv4Any,
+					// NB: we're lying about transport protocol here to verify the raw
+					// fragment header bytes.
+					TransportProtocol: tcpip.TransportProtocolNumber(header.IPv6FragmentExtHdrIdentifier),
+					HopLimit:          ipv6.DefaultTTL,
+					SrcAddr:           src,
+					DstAddr:           header.IPv4Any,
 				})
 				return hdr.View().ToVectorisedView()
 			},
@@ -1422,10 +1423,10 @@ func TestWriteHeaderIncludedPacket(t *testing.T) {
 			pktGen: func(t *testing.T, src tcpip.Address) buffer.VectorisedView {
 				ip := header.IPv6(make([]byte, header.IPv6MinimumSize))
 				ip.Encode(&header.IPv6Fields{
-					NextHeader: transportProto,
-					HopLimit:   ipv6.DefaultTTL,
-					SrcAddr:    src,
-					DstAddr:    header.IPv4Any,
+					TransportProtocol: transportProto,
+					HopLimit:          ipv6.DefaultTTL,
+					SrcAddr:           src,
+					DstAddr:           header.IPv4Any,
 				})
 				return buffer.View(ip).ToVectorisedView()
 			},
@@ -1457,10 +1458,10 @@ func TestWriteHeaderIncludedPacket(t *testing.T) {
 			pktGen: func(t *testing.T, src tcpip.Address) buffer.VectorisedView {
 				ip := header.IPv6(make([]byte, header.IPv6MinimumSize))
 				ip.Encode(&header.IPv6Fields{
-					NextHeader: transportProto,
-					HopLimit:   ipv6.DefaultTTL,
-					SrcAddr:    src,
-					DstAddr:    header.IPv4Any,
+					TransportProtocol: transportProto,
+					HopLimit:          ipv6.DefaultTTL,
+					SrcAddr:           src,
+					DstAddr:           header.IPv4Any,
 				})
 				return buffer.View(ip[:len(ip)-1]).ToVectorisedView()
 			},
diff --git a/pkg/tcpip/network/ipv6/icmp_test.go b/pkg/tcpip/network/ipv6/icmp_test.go
index 32adb5c83..02b18e9a5 100644
--- a/pkg/tcpip/network/ipv6/icmp_test.go
+++ b/pkg/tcpip/network/ipv6/icmp_test.go
@@ -296,11 +296,11 @@ func TestICMPCounts(t *testing.T) {
 				})
 				ip := header.IPv6(pkt.NetworkHeader().Push(header.IPv6MinimumSize))
 				ip.Encode(&header.IPv6Fields{
-					PayloadLength: uint16(len(icmp)),
-					NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-					HopLimit:      header.NDPHopLimit,
-					SrcAddr:       lladdr1,
-					DstAddr:       lladdr0,
+					PayloadLength:     uint16(len(icmp)),
+					TransportProtocol: header.ICMPv6ProtocolNumber,
+					HopLimit:          header.NDPHopLimit,
+					SrcAddr:           lladdr1,
+					DstAddr:           lladdr0,
 				})
 				ep.HandlePacket(pkt)
 			}
@@ -454,11 +454,11 @@ func TestICMPCountsWithNeighborCache(t *testing.T) {
 		})
 		ip := header.IPv6(pkt.NetworkHeader().Push(header.IPv6MinimumSize))
 		ip.Encode(&header.IPv6Fields{
-			PayloadLength: uint16(len(icmp)),
-			NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-			HopLimit:      header.NDPHopLimit,
-			SrcAddr:       lladdr1,
-			DstAddr:       lladdr0,
+			PayloadLength:     uint16(len(icmp)),
+			TransportProtocol: header.ICMPv6ProtocolNumber,
+			HopLimit:          header.NDPHopLimit,
+			SrcAddr:           lladdr1,
+			DstAddr:           lladdr0,
 		})
 		ep.HandlePacket(pkt)
 	}
@@ -853,11 +853,11 @@ func TestICMPChecksumValidationSimple(t *testing.T) {
 							}
 							ip := header.IPv6(buffer.NewView(header.IPv6MinimumSize))
 							ip.Encode(&header.IPv6Fields{
-								PayloadLength: uint16(len(icmp)),
-								NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-								HopLimit:      header.NDPHopLimit,
-								SrcAddr:       lladdr1,
-								DstAddr:       lladdr0,
+								PayloadLength:     uint16(len(icmp)),
+								TransportProtocol: header.ICMPv6ProtocolNumber,
+								HopLimit:          header.NDPHopLimit,
+								SrcAddr:           lladdr1,
+								DstAddr:           lladdr0,
 							})
 							pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
 								Data: buffer.NewVectorisedView(len(ip)+len(icmp), []buffer.View{buffer.View(ip), buffer.View(icmp)}),
@@ -930,11 +930,11 @@ func TestICMPChecksumValidationWithPayload(t *testing.T) {
 	errorICMPBody := func(view buffer.View) {
 		ip := header.IPv6(view)
 		ip.Encode(&header.IPv6Fields{
-			PayloadLength: simpleBodySize,
-			NextHeader:    10,
-			HopLimit:      20,
-			SrcAddr:       lladdr0,
-			DstAddr:       lladdr1,
+			PayloadLength:     simpleBodySize,
+			TransportProtocol: 10,
+			HopLimit:          20,
+			SrcAddr:           lladdr0,
+			DstAddr:           lladdr1,
 		})
 		simpleBody(view[header.IPv6MinimumSize:])
 	}
@@ -1048,11 +1048,11 @@ func TestICMPChecksumValidationWithPayload(t *testing.T) {
 
 				ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 				ip.Encode(&header.IPv6Fields{
-					PayloadLength: uint16(icmpSize),
-					NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-					HopLimit:      header.NDPHopLimit,
-					SrcAddr:       lladdr1,
-					DstAddr:       lladdr0,
+					PayloadLength:     uint16(icmpSize),
+					TransportProtocol: header.ICMPv6ProtocolNumber,
+					HopLimit:          header.NDPHopLimit,
+					SrcAddr:           lladdr1,
+					DstAddr:           lladdr0,
 				})
 				pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
 					Data: hdr.View().ToVectorisedView(),
@@ -1108,11 +1108,11 @@ func TestICMPChecksumValidationWithPayloadMultipleViews(t *testing.T) {
 	errorICMPBody := func(view buffer.View) {
 		ip := header.IPv6(view)
 		ip.Encode(&header.IPv6Fields{
-			PayloadLength: simpleBodySize,
-			NextHeader:    10,
-			HopLimit:      20,
-			SrcAddr:       lladdr0,
-			DstAddr:       lladdr1,
+			PayloadLength:     simpleBodySize,
+			TransportProtocol: 10,
+			HopLimit:          20,
+			SrcAddr:           lladdr0,
+			DstAddr:           lladdr1,
 		})
 		simpleBody(view[header.IPv6MinimumSize:])
 	}
@@ -1227,11 +1227,11 @@ func TestICMPChecksumValidationWithPayloadMultipleViews(t *testing.T) {
 
 				ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 				ip.Encode(&header.IPv6Fields{
-					PayloadLength: uint16(size + payloadSize),
-					NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-					HopLimit:      header.NDPHopLimit,
-					SrcAddr:       lladdr1,
-					DstAddr:       lladdr0,
+					PayloadLength:     uint16(size + payloadSize),
+					TransportProtocol: header.ICMPv6ProtocolNumber,
+					HopLimit:          header.NDPHopLimit,
+					SrcAddr:           lladdr1,
+					DstAddr:           lladdr0,
 				})
 				pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
 					Data: buffer.NewVectorisedView(header.IPv6MinimumSize+size+payloadSize, []buffer.View{hdr.View(), payload}),
@@ -1445,11 +1445,11 @@ func TestPacketQueing(t *testing.T) {
 				payloadLength := hdr.UsedLength()
 				ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 				ip.Encode(&header.IPv6Fields{
-					PayloadLength: uint16(payloadLength),
-					NextHeader:    uint8(udp.ProtocolNumber),
-					HopLimit:      DefaultTTL,
-					SrcAddr:       host2IPv6Addr.AddressWithPrefix.Address,
-					DstAddr:       host1IPv6Addr.AddressWithPrefix.Address,
+					PayloadLength:     uint16(payloadLength),
+					TransportProtocol: udp.ProtocolNumber,
+					HopLimit:          DefaultTTL,
+					SrcAddr:           host2IPv6Addr.AddressWithPrefix.Address,
+					DstAddr:           host1IPv6Addr.AddressWithPrefix.Address,
 				})
 				e.InjectInbound(ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
 					Data: hdr.View().ToVectorisedView(),
@@ -1487,11 +1487,11 @@ func TestPacketQueing(t *testing.T) {
 				pkt.SetChecksum(header.ICMPv6Checksum(pkt, host2IPv6Addr.AddressWithPrefix.Address, host1IPv6Addr.AddressWithPrefix.Address, buffer.VectorisedView{}))
 				ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 				ip.Encode(&header.IPv6Fields{
-					PayloadLength: header.ICMPv6MinimumSize,
-					NextHeader:    uint8(icmp.ProtocolNumber6),
-					HopLimit:      DefaultTTL,
-					SrcAddr:       host2IPv6Addr.AddressWithPrefix.Address,
-					DstAddr:       host1IPv6Addr.AddressWithPrefix.Address,
+					PayloadLength:     header.ICMPv6MinimumSize,
+					TransportProtocol: icmp.ProtocolNumber6,
+					HopLimit:          DefaultTTL,
+					SrcAddr:           host2IPv6Addr.AddressWithPrefix.Address,
+					DstAddr:           host1IPv6Addr.AddressWithPrefix.Address,
 				})
 				e.InjectInbound(header.IPv6ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
 					Data: hdr.View().ToVectorisedView(),
@@ -1586,11 +1586,11 @@ func TestPacketQueing(t *testing.T) {
 				payloadLength := hdr.UsedLength()
 				ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 				ip.Encode(&header.IPv6Fields{
-					PayloadLength: uint16(payloadLength),
-					NextHeader:    uint8(icmp.ProtocolNumber6),
-					HopLimit:      header.NDPHopLimit,
-					SrcAddr:       host2IPv6Addr.AddressWithPrefix.Address,
-					DstAddr:       host1IPv6Addr.AddressWithPrefix.Address,
+					PayloadLength:     uint16(payloadLength),
+					TransportProtocol: icmp.ProtocolNumber6,
+					HopLimit:          header.NDPHopLimit,
+					SrcAddr:           host2IPv6Addr.AddressWithPrefix.Address,
+					DstAddr:           host1IPv6Addr.AddressWithPrefix.Address,
 				})
 				e.InjectInbound(ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
 					Data: hdr.View().ToVectorisedView(),
@@ -1828,11 +1828,11 @@ func TestCallsToNeighborCache(t *testing.T) {
 			})
 			ip := header.IPv6(pkt.NetworkHeader().Push(header.IPv6MinimumSize))
 			ip.Encode(&header.IPv6Fields{
-				PayloadLength: uint16(len(icmp)),
-				NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-				HopLimit:      header.NDPHopLimit,
-				SrcAddr:       test.source,
-				DstAddr:       test.destination,
+				PayloadLength:     uint16(len(icmp)),
+				TransportProtocol: header.ICMPv6ProtocolNumber,
+				HopLimit:          header.NDPHopLimit,
+				SrcAddr:           test.source,
+				DstAddr:           test.destination,
 			})
 			ep.HandlePacket(pkt)
 
diff --git a/pkg/tcpip/network/ipv6/ipv6.go b/pkg/tcpip/network/ipv6/ipv6.go
index e506e99e9..a49b5ac77 100644
--- a/pkg/tcpip/network/ipv6/ipv6.go
+++ b/pkg/tcpip/network/ipv6/ipv6.go
@@ -19,6 +19,7 @@ import (
 	"encoding/binary"
 	"fmt"
 	"hash/fnv"
+	"math"
 	"sort"
 	"sync/atomic"
 	"time"
@@ -431,19 +432,27 @@ func (e *endpoint) MTU() uint32 {
 // MaxHeaderLength returns the maximum length needed by ipv6 headers (and
 // underlying protocols).
 func (e *endpoint) MaxHeaderLength() uint16 {
+	// TODO(gvisor.dev/issues/5035): The maximum header length returned here does
+	// not open the possibility for the caller to know about size required for
+	// extension headers.
 	return e.nic.MaxHeaderLength() + header.IPv6MinimumSize
 }
 
-func (e *endpoint) addIPHeader(srcAddr, dstAddr tcpip.Address, pkt *stack.PacketBuffer, params stack.NetworkHeaderParams) {
-	length := uint16(pkt.Size())
-	ip := header.IPv6(pkt.NetworkHeader().Push(header.IPv6MinimumSize))
+func (e *endpoint) addIPHeader(srcAddr, dstAddr tcpip.Address, pkt *stack.PacketBuffer, params stack.NetworkHeaderParams, extensionHeaders header.IPv6ExtHdrSerializer) {
+	extHdrsLen := extensionHeaders.Length()
+	length := pkt.Size() + extensionHeaders.Length()
+	if length > math.MaxUint16 {
+		panic(fmt.Sprintf("IPv6 payload too large: %d, must be <= %d", length, math.MaxUint16))
+	}
+	ip := header.IPv6(pkt.NetworkHeader().Push(header.IPv6MinimumSize + extHdrsLen))
 	ip.Encode(&header.IPv6Fields{
-		PayloadLength: length,
-		NextHeader:    uint8(params.Protocol),
-		HopLimit:      params.TTL,
-		TrafficClass:  params.TOS,
-		SrcAddr:       srcAddr,
-		DstAddr:       dstAddr,
+		PayloadLength:     uint16(length),
+		TransportProtocol: params.Protocol,
+		HopLimit:          params.TTL,
+		TrafficClass:      params.TOS,
+		SrcAddr:           srcAddr,
+		DstAddr:           dstAddr,
+		ExtensionHeaders:  extensionHeaders,
 	})
 	pkt.NetworkProtocolNumber = ProtocolNumber
 }
@@ -498,7 +507,7 @@ func (e *endpoint) handleFragments(r *stack.Route, gso *stack.GSO, networkMTU ui
 
 // WritePacket writes a packet to the given destination address and protocol.
 func (e *endpoint) WritePacket(r *stack.Route, gso *stack.GSO, params stack.NetworkHeaderParams, pkt *stack.PacketBuffer) *tcpip.Error {
-	e.addIPHeader(r.LocalAddress, r.RemoteAddress, pkt, params)
+	e.addIPHeader(r.LocalAddress, r.RemoteAddress, pkt, params, nil /* extensionHeaders */)
 
 	// iptables filtering. All packets that reach here are locally
 	// generated.
@@ -587,7 +596,7 @@ func (e *endpoint) WritePackets(r *stack.Route, gso *stack.GSO, pkts stack.Packe
 
 	linkMTU := e.nic.MTU()
 	for pb := pkts.Front(); pb != nil; pb = pb.Next() {
-		e.addIPHeader(r.LocalAddress, r.RemoteAddress, pb, params)
+		e.addIPHeader(r.LocalAddress, r.RemoteAddress, pb, params, nil /* extensionHeaders */)
 
 		networkMTU, err := calculateNetworkMTU(linkMTU, uint32(pb.NetworkHeader().View().Size()))
 		if err != nil {
@@ -1793,24 +1802,25 @@ func buildNextFragment(pf *fragmentation.PacketFragmenter, originalIPHeaders hea
 	fragPkt.NetworkProtocolNumber = ProtocolNumber
 
 	originalIPHeadersLength := len(originalIPHeaders)
-	fragmentIPHeadersLength := originalIPHeadersLength + header.IPv6FragmentHeaderSize
+
+	s := header.IPv6ExtHdrSerializer{&header.IPv6SerializableFragmentExtHdr{
+		FragmentOffset: uint16(offset / header.IPv6FragmentExtHdrFragmentOffsetBytesPerUnit),
+		M:              more,
+		Identification: id,
+	}}
+
+	fragmentIPHeadersLength := originalIPHeadersLength + s.Length()
 	fragmentIPHeaders := header.IPv6(fragPkt.NetworkHeader().Push(fragmentIPHeadersLength))
-	fragPkt.NetworkProtocolNumber = ProtocolNumber
 
 	// Copy the IPv6 header and any extension headers already populated.
 	if copied := copy(fragmentIPHeaders, originalIPHeaders); copied != originalIPHeadersLength {
 		panic(fmt.Sprintf("wrong number of bytes copied into fragmentIPHeaders: got %d, want %d", copied, originalIPHeadersLength))
 	}
-	fragmentIPHeaders.SetNextHeader(header.IPv6FragmentHeader)
-	fragmentIPHeaders.SetPayloadLength(uint16(copied + fragmentIPHeadersLength - header.IPv6MinimumSize))
 
-	fragmentHeader := header.IPv6Fragment(fragmentIPHeaders[originalIPHeadersLength:])
-	fragmentHeader.Encode(&header.IPv6FragmentFields{
-		M:              more,
-		FragmentOffset: uint16(offset / header.IPv6FragmentExtHdrFragmentOffsetBytesPerUnit),
-		Identification: id,
-		NextHeader:     uint8(transportProto),
-	})
+	nextHeader, _ := s.Serialize(transportProto, fragmentIPHeaders[originalIPHeadersLength:])
+
+	fragmentIPHeaders.SetNextHeader(nextHeader)
+	fragmentIPHeaders.SetPayloadLength(uint16(copied + fragmentIPHeadersLength - header.IPv6MinimumSize))
 
 	return fragPkt, more
 }
diff --git a/pkg/tcpip/network/ipv6/ipv6_test.go b/pkg/tcpip/network/ipv6/ipv6_test.go
index 1c01f17ab..5f07d3af8 100644
--- a/pkg/tcpip/network/ipv6/ipv6_test.go
+++ b/pkg/tcpip/network/ipv6/ipv6_test.go
@@ -69,11 +69,11 @@ func testReceiveICMP(t *testing.T, s *stack.Stack, e *channel.Endpoint, src, dst
 	payloadLength := hdr.UsedLength()
 	ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 	ip.Encode(&header.IPv6Fields{
-		PayloadLength: uint16(payloadLength),
-		NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-		HopLimit:      255,
-		SrcAddr:       src,
-		DstAddr:       dst,
+		PayloadLength:     uint16(payloadLength),
+		TransportProtocol: header.ICMPv6ProtocolNumber,
+		HopLimit:          255,
+		SrcAddr:           src,
+		DstAddr:           dst,
 	})
 
 	e.InjectInbound(ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
@@ -127,11 +127,11 @@ func testReceiveUDP(t *testing.T, s *stack.Stack, e *channel.Endpoint, src, dst
 	payloadLength := hdr.UsedLength()
 	ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 	ip.Encode(&header.IPv6Fields{
-		PayloadLength: uint16(payloadLength),
-		NextHeader:    uint8(udp.ProtocolNumber),
-		HopLimit:      255,
-		SrcAddr:       src,
-		DstAddr:       dst,
+		PayloadLength:     uint16(payloadLength),
+		TransportProtocol: udp.ProtocolNumber,
+		HopLimit:          255,
+		SrcAddr:           src,
+		DstAddr:           dst,
 	})
 
 	e.InjectInbound(ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
@@ -915,10 +915,12 @@ func TestReceiveIPv6ExtHdrs(t *testing.T) {
 			ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 			ip.Encode(&header.IPv6Fields{
 				PayloadLength: uint16(payloadLength),
-				NextHeader:    ipv6NextHdr,
-				HopLimit:      255,
-				SrcAddr:       addr1,
-				DstAddr:       dstAddr,
+				// We're lying about transport protocol here to be able to generate
+				// raw extension headers from the test definitions.
+				TransportProtocol: tcpip.TransportProtocolNumber(ipv6NextHdr),
+				HopLimit:          255,
+				SrcAddr:           addr1,
+				DstAddr:           dstAddr,
 			})
 
 			e.InjectInbound(ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
@@ -1947,10 +1949,12 @@ func TestReceiveIPv6Fragments(t *testing.T) {
 				ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 				ip.Encode(&header.IPv6Fields{
 					PayloadLength: uint16(f.data.Size()),
-					NextHeader:    f.nextHdr,
-					HopLimit:      255,
-					SrcAddr:       f.srcAddr,
-					DstAddr:       f.dstAddr,
+					// We're lying about transport protocol here so that we can generate
+					// raw extension headers for the tests.
+					TransportProtocol: tcpip.TransportProtocolNumber(f.nextHdr),
+					HopLimit:          255,
+					SrcAddr:           f.srcAddr,
+					DstAddr:           f.dstAddr,
 				})
 
 				vv := hdr.View().ToVectorisedView()
@@ -1995,7 +1999,7 @@ func TestInvalidIPv6Fragments(t *testing.T) {
 
 	type fragmentData struct {
 		ipv6Fields         header.IPv6Fields
-		ipv6FragmentFields header.IPv6FragmentFields
+		ipv6FragmentFields header.IPv6SerializableFragmentExtHdr
 		payload            []byte
 	}
 
@@ -2014,14 +2018,13 @@ func TestInvalidIPv6Fragments(t *testing.T) {
 			fragments: []fragmentData{
 				{
 					ipv6Fields: header.IPv6Fields{
-						PayloadLength: header.IPv6FragmentHeaderSize + 9,
-						NextHeader:    header.IPv6FragmentHeader,
-						HopLimit:      hoplimit,
-						SrcAddr:       addr1,
-						DstAddr:       addr2,
+						PayloadLength:     header.IPv6FragmentHeaderSize + 9,
+						TransportProtocol: header.UDPProtocolNumber,
+						HopLimit:          hoplimit,
+						SrcAddr:           addr1,
+						DstAddr:           addr2,
 					},
-					ipv6FragmentFields: header.IPv6FragmentFields{
-						NextHeader:     uint8(header.UDPProtocolNumber),
+					ipv6FragmentFields: header.IPv6SerializableFragmentExtHdr{
 						FragmentOffset: 0 >> 3,
 						M:              true,
 						Identification: ident,
@@ -2041,14 +2044,13 @@ func TestInvalidIPv6Fragments(t *testing.T) {
 			fragments: []fragmentData{
 				{
 					ipv6Fields: header.IPv6Fields{
-						PayloadLength: header.IPv6FragmentHeaderSize + 16,
-						NextHeader:    header.IPv6FragmentHeader,
-						HopLimit:      hoplimit,
-						SrcAddr:       addr1,
-						DstAddr:       addr2,
+						PayloadLength:     header.IPv6FragmentHeaderSize + 16,
+						TransportProtocol: header.UDPProtocolNumber,
+						HopLimit:          hoplimit,
+						SrcAddr:           addr1,
+						DstAddr:           addr2,
 					},
-					ipv6FragmentFields: header.IPv6FragmentFields{
-						NextHeader:     uint8(header.UDPProtocolNumber),
+					ipv6FragmentFields: header.IPv6SerializableFragmentExtHdr{
 						FragmentOffset: ((header.IPv6MaximumPayloadSize + 1) - 16) >> 3,
 						M:              false,
 						Identification: ident,
@@ -2089,10 +2091,9 @@ func TestInvalidIPv6Fragments(t *testing.T) {
 				hdr := buffer.NewPrependable(header.IPv6MinimumSize + header.IPv6FragmentHeaderSize)
 
 				ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize + header.IPv6FragmentHeaderSize))
-				ip.Encode(&f.ipv6Fields)
-
-				fragHDR := header.IPv6Fragment(hdr.View()[header.IPv6MinimumSize:])
-				fragHDR.Encode(&f.ipv6FragmentFields)
+				encodeArgs := f.ipv6Fields
+				encodeArgs.ExtensionHeaders = append(encodeArgs.ExtensionHeaders, &f.ipv6FragmentFields)
+				ip.Encode(&encodeArgs)
 
 				vv := hdr.View().ToVectorisedView()
 				vv.AppendView(f.payload)
@@ -2154,7 +2155,7 @@ func TestFragmentReassemblyTimeout(t *testing.T) {
 
 	type fragmentData struct {
 		ipv6Fields         header.IPv6Fields
-		ipv6FragmentFields header.IPv6FragmentFields
+		ipv6FragmentFields header.IPv6SerializableFragmentExtHdr
 		payload            []byte
 	}
 
@@ -2168,14 +2169,13 @@ func TestFragmentReassemblyTimeout(t *testing.T) {
 			fragments: []fragmentData{
 				{
 					ipv6Fields: header.IPv6Fields{
-						PayloadLength: header.IPv6FragmentHeaderSize + 16,
-						NextHeader:    header.IPv6FragmentHeader,
-						HopLimit:      hoplimit,
-						SrcAddr:       addr1,
-						DstAddr:       addr2,
+						PayloadLength:     header.IPv6FragmentHeaderSize + 16,
+						TransportProtocol: header.UDPProtocolNumber,
+						HopLimit:          hoplimit,
+						SrcAddr:           addr1,
+						DstAddr:           addr2,
 					},
-					ipv6FragmentFields: header.IPv6FragmentFields{
-						NextHeader:     uint8(header.UDPProtocolNumber),
+					ipv6FragmentFields: header.IPv6SerializableFragmentExtHdr{
 						FragmentOffset: 0,
 						M:              true,
 						Identification: ident,
@@ -2190,14 +2190,13 @@ func TestFragmentReassemblyTimeout(t *testing.T) {
 			fragments: []fragmentData{
 				{
 					ipv6Fields: header.IPv6Fields{
-						PayloadLength: header.IPv6FragmentHeaderSize + 16,
-						NextHeader:    header.IPv6FragmentHeader,
-						HopLimit:      hoplimit,
-						SrcAddr:       addr1,
-						DstAddr:       addr2,
+						PayloadLength:     header.IPv6FragmentHeaderSize + 16,
+						TransportProtocol: header.UDPProtocolNumber,
+						HopLimit:          hoplimit,
+						SrcAddr:           addr1,
+						DstAddr:           addr2,
 					},
-					ipv6FragmentFields: header.IPv6FragmentFields{
-						NextHeader:     uint8(header.UDPProtocolNumber),
+					ipv6FragmentFields: header.IPv6SerializableFragmentExtHdr{
 						FragmentOffset: 0,
 						M:              true,
 						Identification: ident,
@@ -2206,14 +2205,13 @@ func TestFragmentReassemblyTimeout(t *testing.T) {
 				},
 				{
 					ipv6Fields: header.IPv6Fields{
-						PayloadLength: header.IPv6FragmentHeaderSize + 16,
-						NextHeader:    header.IPv6FragmentHeader,
-						HopLimit:      hoplimit,
-						SrcAddr:       addr1,
-						DstAddr:       addr2,
+						PayloadLength:     header.IPv6FragmentHeaderSize + 16,
+						TransportProtocol: header.UDPProtocolNumber,
+						HopLimit:          hoplimit,
+						SrcAddr:           addr1,
+						DstAddr:           addr2,
 					},
-					ipv6FragmentFields: header.IPv6FragmentFields{
-						NextHeader:     uint8(header.UDPProtocolNumber),
+					ipv6FragmentFields: header.IPv6SerializableFragmentExtHdr{
 						FragmentOffset: 0,
 						M:              true,
 						Identification: ident,
@@ -2228,14 +2226,13 @@ func TestFragmentReassemblyTimeout(t *testing.T) {
 			fragments: []fragmentData{
 				{
 					ipv6Fields: header.IPv6Fields{
-						PayloadLength: uint16(header.IPv6FragmentHeaderSize + len(data) - 16),
-						NextHeader:    header.IPv6FragmentHeader,
-						HopLimit:      hoplimit,
-						SrcAddr:       addr1,
-						DstAddr:       addr2,
+						PayloadLength:     uint16(header.IPv6FragmentHeaderSize + len(data) - 16),
+						TransportProtocol: header.UDPProtocolNumber,
+						HopLimit:          hoplimit,
+						SrcAddr:           addr1,
+						DstAddr:           addr2,
 					},
-					ipv6FragmentFields: header.IPv6FragmentFields{
-						NextHeader:     uint8(header.UDPProtocolNumber),
+					ipv6FragmentFields: header.IPv6SerializableFragmentExtHdr{
 						FragmentOffset: 8,
 						M:              false,
 						Identification: ident,
@@ -2250,14 +2247,13 @@ func TestFragmentReassemblyTimeout(t *testing.T) {
 			fragments: []fragmentData{
 				{
 					ipv6Fields: header.IPv6Fields{
-						PayloadLength: header.IPv6FragmentHeaderSize + 16,
-						NextHeader:    header.IPv6FragmentHeader,
-						HopLimit:      hoplimit,
-						SrcAddr:       addr1,
-						DstAddr:       addr2,
+						PayloadLength:     header.IPv6FragmentHeaderSize + 16,
+						TransportProtocol: header.UDPProtocolNumber,
+						HopLimit:          hoplimit,
+						SrcAddr:           addr1,
+						DstAddr:           addr2,
 					},
-					ipv6FragmentFields: header.IPv6FragmentFields{
-						NextHeader:     uint8(header.UDPProtocolNumber),
+					ipv6FragmentFields: header.IPv6SerializableFragmentExtHdr{
 						FragmentOffset: 0,
 						M:              true,
 						Identification: ident,
@@ -2266,14 +2262,13 @@ func TestFragmentReassemblyTimeout(t *testing.T) {
 				},
 				{
 					ipv6Fields: header.IPv6Fields{
-						PayloadLength: uint16(header.IPv6FragmentHeaderSize + len(data) - 16),
-						NextHeader:    header.IPv6FragmentHeader,
-						HopLimit:      hoplimit,
-						SrcAddr:       addr1,
-						DstAddr:       addr2,
+						PayloadLength:     uint16(header.IPv6FragmentHeaderSize + len(data) - 16),
+						TransportProtocol: header.UDPProtocolNumber,
+						HopLimit:          hoplimit,
+						SrcAddr:           addr1,
+						DstAddr:           addr2,
 					},
-					ipv6FragmentFields: header.IPv6FragmentFields{
-						NextHeader:     uint8(header.UDPProtocolNumber),
+					ipv6FragmentFields: header.IPv6SerializableFragmentExtHdr{
 						FragmentOffset: 8,
 						M:              false,
 						Identification: ident,
@@ -2288,14 +2283,13 @@ func TestFragmentReassemblyTimeout(t *testing.T) {
 			fragments: []fragmentData{
 				{
 					ipv6Fields: header.IPv6Fields{
-						PayloadLength: uint16(header.IPv6FragmentHeaderSize + len(data) - 16),
-						NextHeader:    header.IPv6FragmentHeader,
-						HopLimit:      hoplimit,
-						SrcAddr:       addr1,
-						DstAddr:       addr2,
+						PayloadLength:     uint16(header.IPv6FragmentHeaderSize + len(data) - 16),
+						TransportProtocol: header.UDPProtocolNumber,
+						HopLimit:          hoplimit,
+						SrcAddr:           addr1,
+						DstAddr:           addr2,
 					},
-					ipv6FragmentFields: header.IPv6FragmentFields{
-						NextHeader:     uint8(header.UDPProtocolNumber),
+					ipv6FragmentFields: header.IPv6SerializableFragmentExtHdr{
 						FragmentOffset: 8,
 						M:              false,
 						Identification: ident,
@@ -2304,14 +2298,13 @@ func TestFragmentReassemblyTimeout(t *testing.T) {
 				},
 				{
 					ipv6Fields: header.IPv6Fields{
-						PayloadLength: header.IPv6FragmentHeaderSize + 16,
-						NextHeader:    header.IPv6FragmentHeader,
-						HopLimit:      hoplimit,
-						SrcAddr:       addr1,
-						DstAddr:       addr2,
+						PayloadLength:     header.IPv6FragmentHeaderSize + 16,
+						TransportProtocol: header.UDPProtocolNumber,
+						HopLimit:          hoplimit,
+						SrcAddr:           addr1,
+						DstAddr:           addr2,
 					},
-					ipv6FragmentFields: header.IPv6FragmentFields{
-						NextHeader:     uint8(header.UDPProtocolNumber),
+					ipv6FragmentFields: header.IPv6SerializableFragmentExtHdr{
 						FragmentOffset: 0,
 						M:              true,
 						Identification: ident,
@@ -2350,10 +2343,11 @@ func TestFragmentReassemblyTimeout(t *testing.T) {
 				hdr := buffer.NewPrependable(header.IPv6MinimumSize + header.IPv6FragmentHeaderSize)
 
 				ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize + header.IPv6FragmentHeaderSize))
-				ip.Encode(&f.ipv6Fields)
+				encodeArgs := f.ipv6Fields
+				encodeArgs.ExtensionHeaders = append(encodeArgs.ExtensionHeaders, &f.ipv6FragmentFields)
+				ip.Encode(&encodeArgs)
 
 				fragHDR := header.IPv6Fragment(hdr.View()[header.IPv6MinimumSize:])
-				fragHDR.Encode(&f.ipv6FragmentFields)
 
 				vv := hdr.View().ToVectorisedView()
 				vv.AppendView(f.payload)
@@ -2994,11 +2988,11 @@ func TestForwarding(t *testing.T) {
 			icmp.SetChecksum(header.ICMPv6Checksum(icmp, remoteIPv6Addr1, remoteIPv6Addr2, buffer.VectorisedView{}))
 			ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 			ip.Encode(&header.IPv6Fields{
-				PayloadLength: header.ICMPv6MinimumSize,
-				NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-				HopLimit:      test.TTL,
-				SrcAddr:       remoteIPv6Addr1,
-				DstAddr:       remoteIPv6Addr2,
+				PayloadLength:     header.ICMPv6MinimumSize,
+				TransportProtocol: header.ICMPv6ProtocolNumber,
+				HopLimit:          test.TTL,
+				SrcAddr:           remoteIPv6Addr1,
+				DstAddr:           remoteIPv6Addr2,
 			})
 			requestPkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
 				Data: hdr.View().ToVectorisedView(),
diff --git a/pkg/tcpip/network/ipv6/mld.go b/pkg/tcpip/network/ipv6/mld.go
index 48644d9c8..6f64b8462 100644
--- a/pkg/tcpip/network/ipv6/mld.go
+++ b/pkg/tcpip/network/ipv6/mld.go
@@ -234,17 +234,21 @@ func (mld *mldState) writePacket(destAddress, groupAddress tcpip.Address, mldTyp
 
 	icmp.SetChecksum(header.ICMPv6Checksum(icmp, localAddress, destAddress, buffer.VectorisedView{}))
 
+	extensionHeaders := header.IPv6ExtHdrSerializer{
+		header.IPv6SerializableHopByHopExtHdr{
+			&header.IPv6RouterAlertOption{Value: header.IPv6RouterAlertMLD},
+		},
+	}
+
 	pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
-		ReserveHeaderBytes: int(mld.ep.MaxHeaderLength()),
+		ReserveHeaderBytes: int(mld.ep.MaxHeaderLength()) + extensionHeaders.Length(),
 		Data:               buffer.View(icmp).ToVectorisedView(),
 	})
 
 	mld.ep.addIPHeader(localAddress, destAddress, pkt, stack.NetworkHeaderParams{
 		Protocol: header.ICMPv6ProtocolNumber,
 		TTL:      header.MLDHopLimit,
-	})
-	// TODO(b/162198658): set the ROUTER_ALERT option when sending Host
-	// Membership Reports.
+	}, extensionHeaders)
 	if err := mld.ep.nic.WritePacketToRemote(header.EthernetAddressFromMulticastIPv6Address(destAddress), nil /* gso */, ProtocolNumber, pkt); err != nil {
 		sentStats.Dropped.Increment()
 		return false, err
diff --git a/pkg/tcpip/network/ipv6/mld_test.go b/pkg/tcpip/network/ipv6/mld_test.go
index 93b8b3c5c..e2778b656 100644
--- a/pkg/tcpip/network/ipv6/mld_test.go
+++ b/pkg/tcpip/network/ipv6/mld_test.go
@@ -42,7 +42,10 @@ var (
 func validateMLDPacket(t *testing.T, p buffer.View, localAddress, remoteAddress tcpip.Address, mldType header.ICMPv6Type, groupAddress tcpip.Address) {
 	t.Helper()
 
-	checker.IPv6(t, p,
+	checker.IPv6WithExtHdr(t, p,
+		checker.IPv6ExtHdr(
+			checker.IPv6HopByHopExtensionHeader(checker.IPv6RouterAlert(header.IPv6RouterAlertMLD)),
+		),
 		checker.SrcAddr(localAddress),
 		checker.DstAddr(remoteAddress),
 		// Hop Limit for an MLD message must be 1 as per RFC 2710 section 3.
diff --git a/pkg/tcpip/network/ipv6/ndp.go b/pkg/tcpip/network/ipv6/ndp.go
index 3b892aeda..d515eb622 100644
--- a/pkg/tcpip/network/ipv6/ndp.go
+++ b/pkg/tcpip/network/ipv6/ndp.go
@@ -735,7 +735,7 @@ func (ndp *ndpState) sendDADPacket(addr tcpip.Address, addressEndpoint stack.Add
 	ndp.ep.addIPHeader(header.IPv6Any, snmc, pkt, stack.NetworkHeaderParams{
 		Protocol: header.ICMPv6ProtocolNumber,
 		TTL:      header.NDPHopLimit,
-	})
+	}, nil /* extensionHeaders */)
 
 	if err := ndp.ep.nic.WritePacketToRemote(header.EthernetAddressFromMulticastIPv6Address(snmc), nil /* gso */, ProtocolNumber, pkt); err != nil {
 		sent.Dropped.Increment()
@@ -1857,7 +1857,7 @@ func (ndp *ndpState) startSolicitingRouters() {
 		ndp.ep.addIPHeader(localAddr, header.IPv6AllRoutersMulticastAddress, pkt, stack.NetworkHeaderParams{
 			Protocol: header.ICMPv6ProtocolNumber,
 			TTL:      header.NDPHopLimit,
-		})
+		}, nil /* extensionHeaders */)
 
 		if err := ndp.ep.nic.WritePacketToRemote(header.EthernetAddressFromMulticastIPv6Address(header.IPv6AllRoutersMulticastAddress), nil /* gso */, ProtocolNumber, pkt); err != nil {
 			sent.Dropped.Increment()
diff --git a/pkg/tcpip/network/ipv6/ndp_test.go b/pkg/tcpip/network/ipv6/ndp_test.go
index 95c626bb8..05a0d95b2 100644
--- a/pkg/tcpip/network/ipv6/ndp_test.go
+++ b/pkg/tcpip/network/ipv6/ndp_test.go
@@ -213,11 +213,11 @@ func TestNeighorSolicitationWithSourceLinkLayerOption(t *testing.T) {
 			payloadLength := hdr.UsedLength()
 			ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 			ip.Encode(&header.IPv6Fields{
-				PayloadLength: uint16(payloadLength),
-				NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-				HopLimit:      255,
-				SrcAddr:       lladdr1,
-				DstAddr:       lladdr0,
+				PayloadLength:     uint16(payloadLength),
+				TransportProtocol: header.ICMPv6ProtocolNumber,
+				HopLimit:          255,
+				SrcAddr:           lladdr1,
+				DstAddr:           lladdr0,
 			})
 
 			invalid := s.Stats().ICMP.V6.PacketsReceived.Invalid
@@ -319,11 +319,11 @@ func TestNeighorSolicitationWithSourceLinkLayerOptionUsingNeighborCache(t *testi
 			payloadLength := hdr.UsedLength()
 			ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 			ip.Encode(&header.IPv6Fields{
-				PayloadLength: uint16(payloadLength),
-				NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-				HopLimit:      255,
-				SrcAddr:       lladdr1,
-				DstAddr:       lladdr0,
+				PayloadLength:     uint16(payloadLength),
+				TransportProtocol: header.ICMPv6ProtocolNumber,
+				HopLimit:          255,
+				SrcAddr:           lladdr1,
+				DstAddr:           lladdr0,
 			})
 
 			invalid := s.Stats().ICMP.V6.PacketsReceived.Invalid
@@ -599,11 +599,11 @@ func TestNeighorSolicitationResponse(t *testing.T) {
 					payloadLength := hdr.UsedLength()
 					ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 					ip.Encode(&header.IPv6Fields{
-						PayloadLength: uint16(payloadLength),
-						NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-						HopLimit:      255,
-						SrcAddr:       test.nsSrc,
-						DstAddr:       test.nsDst,
+						PayloadLength:     uint16(payloadLength),
+						TransportProtocol: header.ICMPv6ProtocolNumber,
+						HopLimit:          255,
+						SrcAddr:           test.nsSrc,
+						DstAddr:           test.nsDst,
 					})
 
 					invalid := s.Stats().ICMP.V6.PacketsReceived.Invalid
@@ -681,11 +681,11 @@ func TestNeighorSolicitationResponse(t *testing.T) {
 						payloadLength := hdr.UsedLength()
 						ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 						ip.Encode(&header.IPv6Fields{
-							PayloadLength: uint16(payloadLength),
-							NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-							HopLimit:      header.NDPHopLimit,
-							SrcAddr:       test.nsSrc,
-							DstAddr:       nicAddr,
+							PayloadLength:     uint16(payloadLength),
+							TransportProtocol: header.ICMPv6ProtocolNumber,
+							HopLimit:          header.NDPHopLimit,
+							SrcAddr:           test.nsSrc,
+							DstAddr:           nicAddr,
 						})
 						e.InjectLinkAddr(ProtocolNumber, "", stack.NewPacketBuffer(stack.PacketBufferOptions{
 							Data: hdr.View().ToVectorisedView(),
@@ -785,11 +785,11 @@ func TestNeighorAdvertisementWithTargetLinkLayerOption(t *testing.T) {
 			payloadLength := hdr.UsedLength()
 			ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 			ip.Encode(&header.IPv6Fields{
-				PayloadLength: uint16(payloadLength),
-				NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-				HopLimit:      255,
-				SrcAddr:       lladdr1,
-				DstAddr:       lladdr0,
+				PayloadLength:     uint16(payloadLength),
+				TransportProtocol: header.ICMPv6ProtocolNumber,
+				HopLimit:          255,
+				SrcAddr:           lladdr1,
+				DstAddr:           lladdr0,
 			})
 
 			invalid := s.Stats().ICMP.V6.PacketsReceived.Invalid
@@ -898,11 +898,11 @@ func TestNeighorAdvertisementWithTargetLinkLayerOptionUsingNeighborCache(t *test
 			payloadLength := hdr.UsedLength()
 			ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 			ip.Encode(&header.IPv6Fields{
-				PayloadLength: uint16(payloadLength),
-				NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-				HopLimit:      255,
-				SrcAddr:       lladdr1,
-				DstAddr:       lladdr0,
+				PayloadLength:     uint16(payloadLength),
+				TransportProtocol: header.ICMPv6ProtocolNumber,
+				HopLimit:          255,
+				SrcAddr:           lladdr1,
+				DstAddr:           lladdr0,
 			})
 
 			invalid := s.Stats().ICMP.V6.PacketsReceived.Invalid
@@ -979,29 +979,25 @@ func TestNDPValidation(t *testing.T) {
 			}
 
 			handleIPv6Payload := func(payload buffer.View, hopLimit uint8, atomicFragment bool, ep stack.NetworkEndpoint) {
-				nextHdr := uint8(header.ICMPv6ProtocolNumber)
-				var extensions buffer.View
+				var extHdrs header.IPv6ExtHdrSerializer
 				if atomicFragment {
-					extensions = buffer.NewView(header.IPv6FragmentExtHdrLength)
-					extensions[0] = nextHdr
-					nextHdr = uint8(header.IPv6FragmentExtHdrIdentifier)
+					extHdrs = append(extHdrs, &header.IPv6SerializableFragmentExtHdr{})
 				}
+				extHdrsLen := extHdrs.Length()
 
 				pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
-					ReserveHeaderBytes: header.IPv6MinimumSize + len(extensions),
+					ReserveHeaderBytes: header.IPv6MinimumSize + extHdrsLen,
 					Data:               payload.ToVectorisedView(),
 				})
-				ip := header.IPv6(pkt.NetworkHeader().Push(header.IPv6MinimumSize + len(extensions)))
+				ip := header.IPv6(pkt.NetworkHeader().Push(header.IPv6MinimumSize + extHdrsLen))
 				ip.Encode(&header.IPv6Fields{
-					PayloadLength: uint16(len(payload) + len(extensions)),
-					NextHeader:    nextHdr,
-					HopLimit:      hopLimit,
-					SrcAddr:       lladdr1,
-					DstAddr:       lladdr0,
+					PayloadLength:     uint16(len(payload) + extHdrsLen),
+					TransportProtocol: header.ICMPv6ProtocolNumber,
+					HopLimit:          hopLimit,
+					SrcAddr:           lladdr1,
+					DstAddr:           lladdr0,
+					ExtensionHeaders:  extHdrs,
 				})
-				if n := copy(ip[header.IPv6MinimumSize:], extensions); n != len(extensions) {
-					t.Fatalf("expected to write %d bytes of extensions, but wrote %d", len(extensions), n)
-				}
 				ep.HandlePacket(pkt)
 			}
 
@@ -1351,11 +1347,11 @@ func TestRouterAdvertValidation(t *testing.T) {
 					pkt.SetChecksum(header.ICMPv6Checksum(pkt, test.src, header.IPv6AllNodesMulticastAddress, buffer.VectorisedView{}))
 					ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 					ip.Encode(&header.IPv6Fields{
-						PayloadLength: uint16(payloadLength),
-						NextHeader:    uint8(icmp.ProtocolNumber6),
-						HopLimit:      test.hopLimit,
-						SrcAddr:       test.src,
-						DstAddr:       header.IPv6AllNodesMulticastAddress,
+						PayloadLength:     uint16(payloadLength),
+						TransportProtocol: icmp.ProtocolNumber6,
+						HopLimit:          test.hopLimit,
+						SrcAddr:           test.src,
+						DstAddr:           header.IPv6AllNodesMulticastAddress,
 					})
 
 					stats := s.Stats().ICMP.V6.PacketsReceived
diff --git a/pkg/tcpip/network/multicast_group_test.go b/pkg/tcpip/network/multicast_group_test.go
index 6579cd3c9..05d98a0a5 100644
--- a/pkg/tcpip/network/multicast_group_test.go
+++ b/pkg/tcpip/network/multicast_group_test.go
@@ -77,7 +77,10 @@ func validateMLDPacket(t *testing.T, p channel.PacketInfo, remoteAddress tcpip.A
 	t.Helper()
 
 	payload := header.IPv6(stack.PayloadSince(p.Pkt.NetworkHeader()))
-	checker.IPv6(t, payload,
+	checker.IPv6WithExtHdr(t, payload,
+		checker.IPv6ExtHdr(
+			checker.IPv6HopByHopExtensionHeader(checker.IPv6RouterAlert(header.IPv6RouterAlertMLD)),
+		),
 		checker.SrcAddr(ipv6Addr),
 		checker.DstAddr(remoteAddress),
 		// Hop Limit for an MLD message must be 1 as per RFC 2710 section 3.
@@ -239,11 +242,11 @@ func createAndInjectMLDPacket(e *channel.Endpoint, mldType uint8, maxRespDelay b
 
 	ip := header.IPv6(buf)
 	ip.Encode(&header.IPv6Fields{
-		PayloadLength: uint16(icmpSize),
-		HopLimit:      header.MLDHopLimit,
-		NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-		SrcAddr:       header.IPv4Any,
-		DstAddr:       header.IPv6AllNodesMulticastAddress,
+		PayloadLength:     uint16(icmpSize),
+		HopLimit:          header.MLDHopLimit,
+		TransportProtocol: header.ICMPv6ProtocolNumber,
+		SrcAddr:           header.IPv4Any,
+		DstAddr:           header.IPv6AllNodesMulticastAddress,
 	})
 
 	icmp := header.ICMPv6(buf[header.IPv6MinimumSize:])
@@ -1004,10 +1007,31 @@ func TestMGPWithNICLifecycle(t *testing.T) {
 				t.Helper()
 
 				ipv6 := header.IPv6(stack.PayloadSince(p.Pkt.NetworkHeader()))
-				if got := tcpip.TransportProtocolNumber(ipv6.NextHeader()); got != header.ICMPv6ProtocolNumber {
+
+				ipv6HeaderIter := header.MakeIPv6PayloadIterator(
+					header.IPv6ExtensionHeaderIdentifier(ipv6.NextHeader()),
+					buffer.View(ipv6.Payload()).ToVectorisedView(),
+				)
+
+				var transport header.IPv6RawPayloadHeader
+				for {
+					h, done, err := ipv6HeaderIter.Next()
+					if err != nil {
+						t.Fatalf("ipv6HeaderIter.Next(): %s", err)
+					}
+					if done {
+						t.Fatalf("ipv6HeaderIter.Next() = (%T, %t, _), want = (_, false, _)", h, done)
+					}
+					if t, ok := h.(header.IPv6RawPayloadHeader); ok {
+						transport = t
+						break
+					}
+				}
+
+				if got := tcpip.TransportProtocolNumber(transport.Identifier); got != header.ICMPv6ProtocolNumber {
 					t.Fatalf("got ipv6.NextHeader() = %d, want = %d", got, header.ICMPv6ProtocolNumber)
 				}
-				icmpv6 := header.ICMPv6(ipv6.Payload())
+				icmpv6 := header.ICMPv6(transport.Buf.ToView())
 				if got := icmpv6.Type(); got != header.ICMPv6MulticastListenerReport && got != header.ICMPv6MulticastListenerDone {
 					t.Fatalf("got icmpv6.Type() = %d, want = %d or %d", got, header.ICMPv6MulticastListenerReport, header.ICMPv6MulticastListenerDone)
 				}
diff --git a/pkg/tcpip/stack/ndp_test.go b/pkg/tcpip/stack/ndp_test.go
index 31b67b987..03d7b4e0d 100644
--- a/pkg/tcpip/stack/ndp_test.go
+++ b/pkg/tcpip/stack/ndp_test.go
@@ -577,11 +577,11 @@ func rxNDPSolicit(e *channel.Endpoint, tgt tcpip.Address) {
 	payloadLength := hdr.UsedLength()
 	ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 	ip.Encode(&header.IPv6Fields{
-		PayloadLength: uint16(payloadLength),
-		NextHeader:    uint8(icmp.ProtocolNumber6),
-		HopLimit:      255,
-		SrcAddr:       header.IPv6Any,
-		DstAddr:       snmc,
+		PayloadLength:     uint16(payloadLength),
+		TransportProtocol: icmp.ProtocolNumber6,
+		HopLimit:          255,
+		SrcAddr:           header.IPv6Any,
+		DstAddr:           snmc,
 	})
 	e.InjectInbound(header.IPv6ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{Data: hdr.View().ToVectorisedView()}))
 }
@@ -623,11 +623,11 @@ func TestDADFail(t *testing.T) {
 				payloadLength := hdr.UsedLength()
 				ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 				ip.Encode(&header.IPv6Fields{
-					PayloadLength: uint16(payloadLength),
-					NextHeader:    uint8(icmp.ProtocolNumber6),
-					HopLimit:      255,
-					SrcAddr:       tgt,
-					DstAddr:       header.IPv6AllNodesMulticastAddress,
+					PayloadLength:     uint16(payloadLength),
+					TransportProtocol: icmp.ProtocolNumber6,
+					HopLimit:          255,
+					SrcAddr:           tgt,
+					DstAddr:           header.IPv6AllNodesMulticastAddress,
 				})
 				e.InjectInbound(header.IPv6ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{Data: hdr.View().ToVectorisedView()}))
 			},
@@ -1011,11 +1011,11 @@ func raBufWithOptsAndDHCPv6(ip tcpip.Address, rl uint16, managedAddress, otherCo
 	payloadLength := hdr.UsedLength()
 	iph := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 	iph.Encode(&header.IPv6Fields{
-		PayloadLength: uint16(payloadLength),
-		NextHeader:    uint8(icmp.ProtocolNumber6),
-		HopLimit:      header.NDPHopLimit,
-		SrcAddr:       ip,
-		DstAddr:       header.IPv6AllNodesMulticastAddress,
+		PayloadLength:     uint16(payloadLength),
+		TransportProtocol: icmp.ProtocolNumber6,
+		HopLimit:          header.NDPHopLimit,
+		SrcAddr:           ip,
+		DstAddr:           header.IPv6AllNodesMulticastAddress,
 	})
 
 	return stack.NewPacketBuffer(stack.PacketBufferOptions{
diff --git a/pkg/tcpip/stack/transport_demuxer_test.go b/pkg/tcpip/stack/transport_demuxer_test.go
index 2cdb5ca79..a692af20b 100644
--- a/pkg/tcpip/stack/transport_demuxer_test.go
+++ b/pkg/tcpip/stack/transport_demuxer_test.go
@@ -141,11 +141,11 @@ func (c *testContext) sendV6Packet(payload []byte, h *headers, linkEpID tcpip.NI
 	// Initialize the IP header.
 	ip := header.IPv6(buf)
 	ip.Encode(&header.IPv6Fields{
-		PayloadLength: uint16(header.UDPMinimumSize + len(payload)),
-		NextHeader:    uint8(udp.ProtocolNumber),
-		HopLimit:      65,
-		SrcAddr:       testSrcAddrV6,
-		DstAddr:       testDstAddrV6,
+		PayloadLength:     uint16(header.UDPMinimumSize + len(payload)),
+		TransportProtocol: udp.ProtocolNumber,
+		HopLimit:          65,
+		SrcAddr:           testSrcAddrV6,
+		DstAddr:           testDstAddrV6,
 	})
 
 	// Initialize the UDP header.
diff --git a/pkg/tcpip/tests/integration/multicast_broadcast_test.go b/pkg/tcpip/tests/integration/multicast_broadcast_test.go
index 8be791a00..2e59f6a42 100644
--- a/pkg/tcpip/tests/integration/multicast_broadcast_test.go
+++ b/pkg/tcpip/tests/integration/multicast_broadcast_test.go
@@ -96,11 +96,11 @@ func TestPingMulticastBroadcast(t *testing.T) {
 		pkt.SetChecksum(header.ICMPv6Checksum(pkt, remoteIPv6Addr, dst, buffer.VectorisedView{}))
 		ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 		ip.Encode(&header.IPv6Fields{
-			PayloadLength: header.ICMPv6MinimumSize,
-			NextHeader:    uint8(icmp.ProtocolNumber6),
-			HopLimit:      ttl,
-			SrcAddr:       remoteIPv6Addr,
-			DstAddr:       dst,
+			PayloadLength:     header.ICMPv6MinimumSize,
+			TransportProtocol: icmp.ProtocolNumber6,
+			HopLimit:          ttl,
+			SrcAddr:           remoteIPv6Addr,
+			DstAddr:           dst,
 		})
 
 		e.InjectInbound(header.IPv6ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
@@ -272,11 +272,11 @@ func TestIncomingMulticastAndBroadcast(t *testing.T) {
 
 		ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
 		ip.Encode(&header.IPv6Fields{
-			PayloadLength: uint16(payloadLen),
-			NextHeader:    uint8(udp.ProtocolNumber),
-			HopLimit:      ttl,
-			SrcAddr:       remoteIPv6Addr,
-			DstAddr:       dst,
+			PayloadLength:     uint16(payloadLen),
+			TransportProtocol: udp.ProtocolNumber,
+			HopLimit:          ttl,
+			SrcAddr:           remoteIPv6Addr,
+			DstAddr:           dst,
 		})
 
 		e.InjectInbound(header.IPv6ProtocolNumber, stack.NewPacketBuffer(stack.PacketBufferOptions{
diff --git a/pkg/tcpip/transport/tcp/testing/context/context.go b/pkg/tcpip/transport/tcp/testing/context/context.go
index 010a23e45..ee55f030c 100644
--- a/pkg/tcpip/transport/tcp/testing/context/context.go
+++ b/pkg/tcpip/transport/tcp/testing/context/context.go
@@ -635,11 +635,11 @@ func (c *Context) SendV6PacketWithAddrs(payload []byte, h *Headers, src, dst tcp
 	// Initialize the IP header.
 	ip := header.IPv6(buf)
 	ip.Encode(&header.IPv6Fields{
-		PayloadLength: uint16(header.TCPMinimumSize + len(payload)),
-		NextHeader:    uint8(tcp.ProtocolNumber),
-		HopLimit:      65,
-		SrcAddr:       src,
-		DstAddr:       dst,
+		PayloadLength:     uint16(header.TCPMinimumSize + len(payload)),
+		TransportProtocol: tcp.ProtocolNumber,
+		HopLimit:          65,
+		SrcAddr:           src,
+		DstAddr:           dst,
 	})
 
 	// Initialize the TCP header.
diff --git a/pkg/tcpip/transport/udp/udp_test.go b/pkg/tcpip/transport/udp/udp_test.go
index cca865b34..08980c298 100644
--- a/pkg/tcpip/transport/udp/udp_test.go
+++ b/pkg/tcpip/transport/udp/udp_test.go
@@ -453,12 +453,12 @@ func (c *testContext) buildV6Packet(payload []byte, h *header4Tuple) buffer.View
 	// Initialize the IP header.
 	ip := header.IPv6(buf)
 	ip.Encode(&header.IPv6Fields{
-		TrafficClass:  testTOS,
-		PayloadLength: uint16(header.UDPMinimumSize + len(payload)),
-		NextHeader:    uint8(udp.ProtocolNumber),
-		HopLimit:      65,
-		SrcAddr:       h.srcAddr.Addr,
-		DstAddr:       h.dstAddr.Addr,
+		TrafficClass:      testTOS,
+		PayloadLength:     uint16(header.UDPMinimumSize + len(payload)),
+		TransportProtocol: udp.ProtocolNumber,
+		HopLimit:          65,
+		SrcAddr:           h.srcAddr.Addr,
+		DstAddr:           h.dstAddr.Addr,
 	})
 
 	// Initialize the UDP header.
@@ -1494,7 +1494,7 @@ func TestReadRecvOriginalDstAddr(t *testing.T) {
 
 			bindAddr := tcpip.FullAddress{Port: stackPort}
 			if err := c.ep.Bind(bindAddr); err != nil {
-				t.Fatalf("Bind(%+v): %s", bindAddr, err)
+				t.Fatalf("Bind(%#v): %s", bindAddr, err)
 			}
 
 			if test.flow.isMulticast() {
@@ -2029,8 +2029,8 @@ func TestV6UnknownDestination(t *testing.T) {
 			}
 			// Correct UDP length to access payload.
 			origDgram.SetLength(uint16(wantPayloadLen + header.UDPMinimumSize))
-			if got, want := origDgram.Payload(), payload[:wantPayloadLen]; !bytes.Equal(got, want) {
-				t.Fatalf("got origDgram.Payload() = %x, want = %x", got, want)
+			if diff := cmp.Diff(payload[:wantPayloadLen], origDgram.Payload()); diff != "" {
+				t.Fatalf("origDgram.Payload() mismatch (-want +got):\n%s", diff)
 			}
 		})
 	}
@@ -2089,12 +2089,12 @@ func TestShortHeader(t *testing.T) {
 	// Initialize the IP header.
 	ip := header.IPv6(buf)
 	ip.Encode(&header.IPv6Fields{
-		TrafficClass:  testTOS,
-		PayloadLength: uint16(udpSize),
-		NextHeader:    uint8(udp.ProtocolNumber),
-		HopLimit:      65,
-		SrcAddr:       h.srcAddr.Addr,
-		DstAddr:       h.dstAddr.Addr,
+		TrafficClass:      testTOS,
+		PayloadLength:     uint16(udpSize),
+		TransportProtocol: udp.ProtocolNumber,
+		HopLimit:          65,
+		SrcAddr:           h.srcAddr.Addr,
+		DstAddr:           h.dstAddr.Addr,
 	})
 
 	// Initialize the UDP header.
@@ -2597,12 +2597,12 @@ func TestReceiveShortLength(t *testing.T) {
 			// Try to receive the data.
 			v, _, err := c.ep.Read(nil)
 			if err != nil {
-				t.Fatalf("c.ep.Read(..): %s", err)
+				t.Fatalf("c.ep.Read(nil): %s", err)
 			}
 
 			// Check the payload is read back without extra bytes.
 			if diff := cmp.Diff(buffer.View(payload), v); diff != "" {
-				t.Errorf("c.ep.Read(..) mismatch (-want +got):\n%s", diff)
+				t.Errorf("c.ep.Read(nil) mismatch (-want +got):\n%s", diff)
 			}
 		})
 	}