diff --git a/icmp/diag_test.go b/icmp/diag_test.go
index 6a87a60..2ecd465 100644
--- a/icmp/diag_test.go
+++ b/icmp/diag_test.go
@@ -71,8 +71,7 @@
 	})
 	t.Run("Ping/Privileged", func(t *testing.T) {
 		if m, ok := nettest.SupportsRawIPSocket(); !ok {
-			t.Log(m)
-			return
+			t.Skip(m)
 		}
 		for i, dt := range []diagTest{
 			{
@@ -102,6 +101,50 @@
 			}
 		}
 	})
+	t.Run("Probe/Privileged", func(t *testing.T) {
+		if m, ok := nettest.SupportsRawIPSocket(); !ok {
+			t.Skip(m)
+		}
+		for i, dt := range []diagTest{
+			{
+				"ip4:icmp", "0.0.0.0", iana.ProtocolICMP,
+				icmp.Message{
+					Type: ipv4.ICMPTypeExtendedEchoRequest, Code: 0,
+					Body: &icmp.ExtendedEchoRequest{
+						ID:    os.Getpid() & 0xffff,
+						Local: true,
+						Extensions: []icmp.Extension{
+							&icmp.InterfaceIdent{
+								Class: 3, Type: 1,
+								Name: "doesnotexist",
+							},
+						},
+					},
+				},
+			},
+
+			{
+				"ip6:ipv6-icmp", "::", iana.ProtocolIPv6ICMP,
+				icmp.Message{
+					Type: ipv6.ICMPTypeExtendedEchoRequest, Code: 0,
+					Body: &icmp.ExtendedEchoRequest{
+						ID:    os.Getpid() & 0xffff,
+						Local: true,
+						Extensions: []icmp.Extension{
+							&icmp.InterfaceIdent{
+								Class: 3, Type: 1,
+								Name: "doesnotexist",
+							},
+						},
+					},
+				},
+			},
+		} {
+			if err := doDiag(dt, i); err != nil {
+				t.Error(err)
+			}
+		}
+	})
 }
 
 func doDiag(dt diagTest, seq int) error {
@@ -124,6 +167,7 @@
 		f.Accept(ipv6.ICMPTypeTimeExceeded)
 		f.Accept(ipv6.ICMPTypeParameterProblem)
 		f.Accept(ipv6.ICMPTypeEchoReply)
+		f.Accept(ipv6.ICMPTypeExtendedEchoReply)
 		if err := c.IPv6PacketConn().SetICMPFilter(&f); err != nil {
 			return err
 		}
@@ -132,6 +176,8 @@
 	switch m := dt.m.Body.(type) {
 	case *icmp.Echo:
 		m.Seq = 1 << uint(seq)
+	case *icmp.ExtendedEchoRequest:
+		m.Seq = 1 << uint(seq)
 	}
 	wb, err := dt.m.Marshal(nil)
 	if err != nil {
@@ -159,9 +205,13 @@
 	case dt.m.Type == ipv4.ICMPTypeEcho && rm.Type == ipv4.ICMPTypeEchoReply:
 		fallthrough
 	case dt.m.Type == ipv6.ICMPTypeEchoRequest && rm.Type == ipv6.ICMPTypeEchoReply:
+		fallthrough
+	case dt.m.Type == ipv4.ICMPTypeExtendedEchoRequest && rm.Type == ipv4.ICMPTypeExtendedEchoReply:
+		fallthrough
+	case dt.m.Type == ipv6.ICMPTypeExtendedEchoRequest && rm.Type == ipv6.ICMPTypeExtendedEchoReply:
 		return nil
 	default:
-		return fmt.Errorf("got %+v from %v; want echo reply", rm, peer)
+		return fmt.Errorf("got %+v from %v; want echo reply or extended echo reply", rm, peer)
 	}
 }
 
diff --git a/icmp/dstunreach.go b/icmp/dstunreach.go
index 75db991..7464bf7 100644
--- a/icmp/dstunreach.go
+++ b/icmp/dstunreach.go
@@ -16,24 +16,24 @@
 	if p == nil {
 		return 0
 	}
-	l, _ := multipartMessageBodyDataLen(proto, p.Data, p.Extensions)
+	l, _ := multipartMessageBodyDataLen(proto, true, p.Data, p.Extensions)
 	return 4 + l
 }
 
 // Marshal implements the Marshal method of MessageBody interface.
 func (p *DstUnreach) Marshal(proto int) ([]byte, error) {
-	return marshalMultipartMessageBody(proto, p.Data, p.Extensions)
+	return marshalMultipartMessageBody(proto, true, p.Data, p.Extensions)
 }
 
 // parseDstUnreach parses b as an ICMP destination unreachable message
 // body.
-func parseDstUnreach(proto int, b []byte) (MessageBody, error) {
+func parseDstUnreach(proto int, typ Type, b []byte) (MessageBody, error) {
 	if len(b) < 4 {
 		return nil, errMessageTooShort
 	}
 	p := &DstUnreach{}
 	var err error
-	p.Data, p.Extensions, err = parseMultipartMessageBody(proto, b)
+	p.Data, p.Extensions, err = parseMultipartMessageBody(proto, typ, b)
 	if err != nil {
 		return nil, err
 	}
diff --git a/icmp/echo.go b/icmp/echo.go
index e6f15ef..c611f65 100644
--- a/icmp/echo.go
+++ b/icmp/echo.go
@@ -31,7 +31,7 @@
 }
 
 // parseEcho parses b as an ICMP echo request or reply message body.
-func parseEcho(proto int, b []byte) (MessageBody, error) {
+func parseEcho(proto int, _ Type, b []byte) (MessageBody, error) {
 	bodyLen := len(b)
 	if bodyLen < 4 {
 		return nil, errMessageTooShort
@@ -43,3 +43,115 @@
 	}
 	return p, nil
 }
+
+// An ExtendedEchoRequest represents an ICMP extended echo request
+// message body.
+type ExtendedEchoRequest struct {
+	ID         int         // identifier
+	Seq        int         // sequence number
+	Local      bool        // must be true when identifying by name or index
+	Extensions []Extension // extensions
+}
+
+// Len implements the Len method of MessageBody interface.
+func (p *ExtendedEchoRequest) Len(proto int) int {
+	if p == nil {
+		return 0
+	}
+	l, _ := multipartMessageBodyDataLen(proto, false, nil, p.Extensions)
+	return 4 + l
+}
+
+// Marshal implements the Marshal method of MessageBody interface.
+func (p *ExtendedEchoRequest) Marshal(proto int) ([]byte, error) {
+	b, err := marshalMultipartMessageBody(proto, false, nil, p.Extensions)
+	if err != nil {
+		return nil, err
+	}
+	bb := make([]byte, 4)
+	binary.BigEndian.PutUint16(bb[:2], uint16(p.ID))
+	bb[2] = byte(p.Seq)
+	if p.Local {
+		bb[3] |= 0x01
+	}
+	bb = append(bb, b...)
+	return bb, nil
+}
+
+// parseExtendedEchoRequest parses b as an ICMP extended echo request
+// message body.
+func parseExtendedEchoRequest(proto int, typ Type, b []byte) (MessageBody, error) {
+	if len(b) < 4+4 {
+		return nil, errMessageTooShort
+	}
+	p := &ExtendedEchoRequest{ID: int(binary.BigEndian.Uint16(b[:2])), Seq: int(b[2])}
+	if b[3]&0x01 != 0 {
+		p.Local = true
+	}
+	var err error
+	_, p.Extensions, err = parseMultipartMessageBody(proto, typ, b[4:])
+	if err != nil {
+		return nil, err
+	}
+	return p, nil
+}
+
+// An ExtendedEchoReply represents an ICMP extended echo reply message
+// body.
+type ExtendedEchoReply struct {
+	ID     int  // identifier
+	Seq    int  // sequence number
+	State  int  // 3-bit state working together with Message.Code
+	Active bool // probed interface is active
+	IPv4   bool // probed interface runs IPv4
+	IPv6   bool // probed interface runs IPv6
+}
+
+// Len implements the Len method of MessageBody interface.
+func (p *ExtendedEchoReply) Len(proto int) int {
+	if p == nil {
+		return 0
+	}
+	return 4
+}
+
+// Marshal implements the Marshal method of MessageBody interface.
+func (p *ExtendedEchoReply) Marshal(proto int) ([]byte, error) {
+	b := make([]byte, 4)
+	binary.BigEndian.PutUint16(b[:2], uint16(p.ID))
+	b[2] = byte(p.Seq)
+	b[3] = byte(p.State<<5) & 0xe0
+	if p.Active {
+		b[3] |= 0x04
+	}
+	if p.IPv4 {
+		b[3] |= 0x02
+	}
+	if p.IPv6 {
+		b[3] |= 0x01
+	}
+	return b, nil
+}
+
+// parseExtendedEchoReply parses b as an ICMP extended echo reply
+// message body.
+func parseExtendedEchoReply(proto int, _ Type, b []byte) (MessageBody, error) {
+	if len(b) < 4 {
+		return nil, errMessageTooShort
+	}
+	p := &ExtendedEchoReply{
+		ID:    int(binary.BigEndian.Uint16(b[:2])),
+		Seq:   int(b[2]),
+		State: int(b[3]) >> 5,
+	}
+	if b[3]&0x04 != 0 {
+		p.Active = true
+	}
+	if b[3]&0x02 != 0 {
+		p.IPv4 = true
+	}
+	if b[3]&0x01 != 0 {
+		p.IPv6 = true
+	}
+	return p, nil
+}
diff --git a/icmp/extension.go b/icmp/extension.go
index 402a751..2005068 100644
--- a/icmp/extension.go
+++ b/icmp/extension.go
@@ -4,7 +4,12 @@
 
 package icmp
 
-import "encoding/binary"
+import (
+	"encoding/binary"
+
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
+)
 
 // An Extension represents an ICMP extension.
 type Extension interface {
@@ -38,7 +43,7 @@
 // It will return a list of ICMP extensions and an adjusted length
 // attribute that represents the length of the padded original
 // datagram field. Otherwise, it returns an error.
-func parseExtensions(b []byte, l int) ([]Extension, int, error) {
+func parseExtensions(typ Type, b []byte, l int) ([]Extension, int, error) {
 	// Still a lot of non-RFC 4884 compliant implementations are
 	// out there. Set the length attribute l to 128 when it looks
 	// inappropriate for backwards compatibility.
@@ -48,20 +53,28 @@
 	// header.
 	//
 	// See RFC 4884 for further information.
-	if 128 > l || l+8 > len(b) {
-		l = 128
-	}
-	if l+8 > len(b) {
-		return nil, -1, errNoExtension
-	}
-	if !validExtensionHeader(b[l:]) {
-		if l == 128 {
+	switch typ {
+	case ipv4.ICMPTypeExtendedEchoRequest, ipv6.ICMPTypeExtendedEchoRequest:
+		if len(b) < 8 || !validExtensionHeader(b) {
 			return nil, -1, errNoExtension
 		}
-		l = 128
-		if !validExtensionHeader(b[l:]) {
+		l = 0
+	default:
+		if 128 > l || l+8 > len(b) {
+			l = 128
+		}
+		if l+8 > len(b) {
 			return nil, -1, errNoExtension
 		}
+		if !validExtensionHeader(b[l:]) {
+			if l == 128 {
+				return nil, -1, errNoExtension
+			}
+			l = 128
+			if !validExtensionHeader(b[l:]) {
+				return nil, -1, errNoExtension
+			}
+		}
 	}
 	var exts []Extension
 	for b = b[l+4:]; len(b) >= 4; {
@@ -82,6 +95,12 @@
 				return nil, -1, err
 			}
 			exts = append(exts, ext)
+		case classInterfaceIdent:
+			ext, err := parseInterfaceIdent(b[:ol])
+			if err != nil {
+				return nil, -1, err
+			}
+			exts = append(exts, ext)
 		}
 		b = b[ol:]
 	}
diff --git a/icmp/extension_test.go b/icmp/extension_test.go
index 193859e..a7669da 100644
--- a/icmp/extension_test.go
+++ b/icmp/extension_test.go
@@ -11,10 +11,12 @@
 	"testing"
 
 	"golang.org/x/net/internal/iana"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
 )
 
 func TestMarshalAndParseExtension(t *testing.T) {
-	fn := func(t *testing.T, proto int, hdr, obj []byte, te Extension) error {
+	fn := func(t *testing.T, proto int, typ Type, hdr, obj []byte, te Extension) error {
 		b, err := te.Marshal(proto)
 		if err != nil {
 			return err
@@ -22,39 +24,53 @@
 		if !reflect.DeepEqual(b, obj) {
 			return fmt.Errorf("got %#v; want %#v", b, obj)
 		}
-		for i, wire := range []struct {
-			data     []byte // original datagram
-			inlattr  int    // length of padded original datagram, a hint
-			outlattr int    // length of padded original datagram, a want
-			err      error
-		}{
-			{nil, 0, -1, errNoExtension},
-			{make([]byte, 127), 128, -1, errNoExtension},
-
-			{make([]byte, 128), 127, -1, errNoExtension},
-			{make([]byte, 128), 128, -1, errNoExtension},
-			{make([]byte, 128), 129, -1, errNoExtension},
-
-			{append(make([]byte, 128), append(hdr, obj...)...), 127, 128, nil},
-			{append(make([]byte, 128), append(hdr, obj...)...), 128, 128, nil},
-			{append(make([]byte, 128), append(hdr, obj...)...), 129, 128, nil},
-
-			{append(make([]byte, 512), append(hdr, obj...)...), 511, -1, errNoExtension},
-			{append(make([]byte, 512), append(hdr, obj...)...), 512, 512, nil},
-			{append(make([]byte, 512), append(hdr, obj...)...), 513, -1, errNoExtension},
-		} {
-			exts, l, err := parseExtensions(wire.data, wire.inlattr)
-			if err != wire.err {
-				return fmt.Errorf("#%d: got %v; want %v", i, err, wire.err)
+		switch typ {
+		case ipv4.ICMPTypeExtendedEchoRequest, ipv6.ICMPTypeExtendedEchoRequest:
+			exts, l, err := parseExtensions(typ, append(hdr, obj...), 0)
+			if err != nil {
+				return err
 			}
-			if wire.err != nil {
-				continue
-			}
-			if l != wire.outlattr {
-				return fmt.Errorf("#%d: got %d; want %d", i, l, wire.outlattr)
+			if l != 0 {
+				return fmt.Errorf("got %d; want 0", l)
 			}
 			if !reflect.DeepEqual(exts, []Extension{te}) {
-				return fmt.Errorf("#%d: got %#v; want %#v", i, exts[0], te)
+				return fmt.Errorf("got %#v; want %#v", exts[0], te)
+			}
+		default:
+			for i, wire := range []struct {
+				data     []byte // original datagram
+				inlattr  int    // length of padded original datagram, a hint
+				outlattr int    // length of padded original datagram, a want
+				err      error
+			}{
+				{nil, 0, -1, errNoExtension},
+				{make([]byte, 127), 128, -1, errNoExtension},
+
+				{make([]byte, 128), 127, -1, errNoExtension},
+				{make([]byte, 128), 128, -1, errNoExtension},
+				{make([]byte, 128), 129, -1, errNoExtension},
+
+				{append(make([]byte, 128), append(hdr, obj...)...), 127, 128, nil},
+				{append(make([]byte, 128), append(hdr, obj...)...), 128, 128, nil},
+				{append(make([]byte, 128), append(hdr, obj...)...), 129, 128, nil},
+
+				{append(make([]byte, 512), append(hdr, obj...)...), 511, -1, errNoExtension},
+				{append(make([]byte, 512), append(hdr, obj...)...), 512, 512, nil},
+				{append(make([]byte, 512), append(hdr, obj...)...), 513, -1, errNoExtension},
+			} {
+				exts, l, err := parseExtensions(typ, wire.data, wire.inlattr)
+				if err != wire.err {
+					return fmt.Errorf("#%d: got %v; want %v", i, err, wire.err)
+				}
+				if wire.err != nil {
+					continue
+				}
+				if l != wire.outlattr {
+					return fmt.Errorf("#%d: got %d; want %d", i, l, wire.outlattr)
+				}
+				if !reflect.DeepEqual(exts, []Extension{te}) {
+					return fmt.Errorf("#%d: got %#v; want %#v", i, exts[0], te)
+				}
 			}
 		}
 		return nil
@@ -63,6 +79,7 @@
 	t.Run("MPLSLabelStack", func(t *testing.T) {
 		for _, et := range []struct {
 			proto int
+			typ   Type
 			hdr   []byte
 			obj   []byte
 			ext   Extension
@@ -70,6 +87,7 @@
 			// MPLS label stack with no label
 			{
 				proto: iana.ProtocolICMP,
+				typ:   ipv4.ICMPTypeDestinationUnreachable,
 				hdr: []byte{
 					0x20, 0x00, 0x00, 0x00,
 				},
@@ -84,6 +102,7 @@
 			// MPLS label stack with a single label
 			{
 				proto: iana.ProtocolIPv6ICMP,
+				typ:   ipv6.ICMPTypeDestinationUnreachable,
 				hdr: []byte{
 					0x20, 0x00, 0x00, 0x00,
 				},
@@ -107,6 +126,7 @@
 			// MPLS label stack with multiple labels
 			{
 				proto: iana.ProtocolICMP,
+				typ:   ipv4.ICMPTypeDestinationUnreachable,
 				hdr: []byte{
 					0x20, 0x00, 0x00, 0x00,
 				},
@@ -135,7 +155,7 @@
 				},
 			},
 		} {
-			if err := fn(t, et.proto, et.hdr, et.obj, et.ext); err != nil {
+			if err := fn(t, et.proto, et.typ, et.hdr, et.obj, et.ext); err != nil {
 				t.Error(err)
 			}
 		}
@@ -143,6 +163,7 @@
 	t.Run("InterfaceInfo", func(t *testing.T) {
 		for _, et := range []struct {
 			proto int
+			typ   Type
 			hdr   []byte
 			obj   []byte
 			ext   Extension
@@ -150,6 +171,7 @@
 			// Interface information with no attribute
 			{
 				proto: iana.ProtocolICMP,
+				typ:   ipv4.ICMPTypeDestinationUnreachable,
 				hdr: []byte{
 					0x20, 0x00, 0x00, 0x00,
 				},
@@ -163,6 +185,7 @@
 			// Interface information with ifIndex and name
 			{
 				proto: iana.ProtocolICMP,
+				typ:   ipv4.ICMPTypeDestinationUnreachable,
 				hdr: []byte{
 					0x20, 0x00, 0x00, 0x00,
 				},
@@ -184,6 +207,7 @@
 			// Interface information with ifIndex, IPAddr, name and MTU
 			{
 				proto: iana.ProtocolIPv6ICMP,
+				typ:   ipv6.ICMPTypeDestinationUnreachable,
 				hdr: []byte{
 					0x20, 0x00, 0x00, 0x00,
 				},
@@ -214,7 +238,77 @@
 				},
 			},
 		} {
-			if err := fn(t, et.proto, et.hdr, et.obj, et.ext); err != nil {
+			if err := fn(t, et.proto, et.typ, et.hdr, et.obj, et.ext); err != nil {
+				t.Error(err)
+			}
+		}
+	})
+	t.Run("InterfaceIdent", func(t *testing.T) {
+		for _, et := range []struct {
+			proto int
+			typ   Type
+			hdr   []byte
+			obj   []byte
+			ext   Extension
+		}{
+			// Interface identification by name
+			{
+				proto: iana.ProtocolICMP,
+				typ:   ipv4.ICMPTypeExtendedEchoRequest,
+				hdr: []byte{
+					0x20, 0x00, 0x00, 0x00,
+				},
+				obj: []byte{
+					0x00, 0x0c, 0x03, 0x01,
+					byte('e'), byte('n'), byte('1'), byte('0'),
+					byte('1'), 0x00, 0x00, 0x00,
+				},
+				ext: &InterfaceIdent{
+					Class: classInterfaceIdent,
+					Type:  typeInterfaceByName,
+					Name:  "en101",
+				},
+			},
+			// Interface identification by index
+			{
+				proto: iana.ProtocolIPv6ICMP,
+				typ:   ipv6.ICMPTypeExtendedEchoRequest,
+				hdr: []byte{
+					0x20, 0x00, 0x00, 0x00,
+				},
+				obj: []byte{
+					0x00, 0x0c, 0x03, 0x02,
+					0x00, 0x00, 0x00, 0x00,
+					0x00, 0x00, 0x03, 0x8f,
+				},
+				ext: &InterfaceIdent{
+					Class: classInterfaceIdent,
+					Type:  typeInterfaceByIndex,
+					Index: 911,
+				},
+			},
+			// Interface identification by address
+			{
+				proto: iana.ProtocolICMP,
+				typ:   ipv4.ICMPTypeExtendedEchoRequest,
+				hdr: []byte{
+					0x20, 0x00, 0x00, 0x00,
+				},
+				obj: []byte{
+					0x00, 0x10, 0x03, 0x03,
+					byte(iana.AddrFamily48bitMAC >> 8), byte(iana.AddrFamily48bitMAC & 0x0f), 0x06, 0x00,
+					0x01, 0x23, 0x45, 0x67,
+					0x89, 0xab, 0x00, 0x00,
+				},
+				ext: &InterfaceIdent{
+					Class: classInterfaceIdent,
+					Type:  typeInterfaceByAddress,
+					AFI:   iana.AddrFamily48bitMAC,
+					Addr:  []byte{0x01, 0x23, 0x45, 0x67, 0x89, 0xab},
+				},
+			},
+		} {
+			if err := fn(t, et.proto, et.typ, et.hdr, et.obj, et.ext); err != nil {
 				t.Error(err)
 			}
 		}
diff --git a/icmp/interface.go b/icmp/interface.go
index 78b5b98..617f757 100644
--- a/icmp/interface.go
+++ b/icmp/interface.go
@@ -14,9 +14,6 @@
 
 const (
 	classInterfaceInfo = 2
-
-	afiIPv4 = 1
-	afiIPv6 = 2
 )
 
 const (
@@ -127,11 +124,11 @@
 func (ifi *InterfaceInfo) marshalIPAddr(proto int, b []byte) []byte {
 	switch proto {
 	case iana.ProtocolICMP:
-		binary.BigEndian.PutUint16(b[:2], uint16(afiIPv4))
+		binary.BigEndian.PutUint16(b[:2], uint16(iana.AddrFamilyIPv4))
 		copy(b[4:4+net.IPv4len], ifi.Addr.IP.To4())
 		b = b[4+net.IPv4len:]
 	case iana.ProtocolIPv6ICMP:
-		binary.BigEndian.PutUint16(b[:2], uint16(afiIPv6))
+		binary.BigEndian.PutUint16(b[:2], uint16(iana.AddrFamilyIPv6))
 		copy(b[4:4+net.IPv6len], ifi.Addr.IP.To16())
 		b = b[4+net.IPv6len:]
 	}
@@ -145,14 +142,14 @@
 	afi := int(binary.BigEndian.Uint16(b[:2]))
 	b = b[4:]
 	switch afi {
-	case afiIPv4:
+	case iana.AddrFamilyIPv4:
 		if len(b) < net.IPv4len {
 			return nil, errMessageTooShort
 		}
 		ifi.Addr.IP = make(net.IP, net.IPv4len)
 		copy(ifi.Addr.IP, b[:net.IPv4len])
 		b = b[net.IPv4len:]
-	case afiIPv6:
+	case iana.AddrFamilyIPv6:
 		if len(b) < net.IPv6len {
 			return nil, errMessageTooShort
 		}
@@ -234,3 +231,92 @@
 	}
 	return ifi, nil
 }
+
+const (
+	classInterfaceIdent    = 3
+	typeInterfaceByName    = 1
+	typeInterfaceByIndex   = 2
+	typeInterfaceByAddress = 3
+)
+
+// An InterfaceIdent represents interface identification.
+type InterfaceIdent struct {
+	Class int    // extension object class number
+	Type  int    // extension object sub-type
+	Name  string // interface name
+	Index int    // interface index
+	AFI   int    // address family identifier; see address family numbers in IANA registry
+	Addr  []byte // address
+}
+
+// Len implements the Len method of Extension interface.
+func (ifi *InterfaceIdent) Len(_ int) int {
+	switch ifi.Type {
+	case typeInterfaceByName:
+		l := len(ifi.Name)
+		if l > 255 {
+			l = 255
+		}
+		return 4 + (l+3)&^3
+	case typeInterfaceByIndex:
+		return 4 + 8
+	case typeInterfaceByAddress:
+		return 4 + 4 + (len(ifi.Addr)+3)&^3
+	default:
+		return 4
+	}
+}
+
+// Marshal implements the Marshal method of Extension interface.
+func (ifi *InterfaceIdent) Marshal(proto int) ([]byte, error) {
+	b := make([]byte, ifi.Len(proto))
+	if err := ifi.marshal(proto, b); err != nil {
+		return nil, err
+	}
+	return b, nil
+}
+
+func (ifi *InterfaceIdent) marshal(proto int, b []byte) error {
+	l := ifi.Len(proto)
+	binary.BigEndian.PutUint16(b[:2], uint16(l))
+	b[2], b[3] = classInterfaceIdent, byte(ifi.Type)
+	switch ifi.Type {
+	case typeInterfaceByName:
+		copy(b[4:], ifi.Name)
+	case typeInterfaceByIndex:
+		binary.BigEndian.PutUint64(b[4:4+8], uint64(ifi.Index))
+	case typeInterfaceByAddress:
+		binary.BigEndian.PutUint16(b[4:4+2], uint16(ifi.AFI))
+		b[4+2] = byte(len(ifi.Addr))
+		copy(b[4+4:], ifi.Addr)
+	}
+	return nil
+}
+
+func parseInterfaceIdent(b []byte) (Extension, error) {
+	ifi := &InterfaceIdent{
+		Class: int(b[2]),
+		Type:  int(b[3]),
+	}
+	switch ifi.Type {
+	case typeInterfaceByName:
+		ifi.Name = strings.Trim(string(b[4:]), string(0))
+	case typeInterfaceByIndex:
+		if len(b[4:]) < 8 {
+			return nil, errInvalidExtension
+		}
+		ifi.Index = int(binary.BigEndian.Uint64(b[4 : 4+8]))
+	case typeInterfaceByAddress:
+		if len(b[4:]) < 4 {
+			return nil, errInvalidExtension
+		}
+		ifi.AFI = int(binary.BigEndian.Uint16(b[4 : 4+2]))
+		l := int(b[4+2])
+		if len(b[4+4:]) < l {
+			return nil, errInvalidExtension
+		}
+		ifi.Addr = make([]byte, l)
+		copy(ifi.Addr, b[4+4:])
+	}
+	return ifi, nil
+}
diff --git a/icmp/message.go b/icmp/message.go
index 81140b0..46fe95a 100644
--- a/icmp/message.go
+++ b/icmp/message.go
@@ -11,6 +11,7 @@
 // ICMP extensions for MPLS are defined in RFC 4950.
 // ICMP extensions for interface and next-hop identification are
 // defined in RFC 5837.
+// PROBE: A utility for probing interfaces is defined in RFC 8335.
 package icmp // import "golang.org/x/net/icmp"
 
 import (
@@ -107,21 +108,25 @@
 	return b[len(psh):], nil
 }
 
-var parseFns = map[Type]func(int, []byte) (MessageBody, error){
+var parseFns = map[Type]func(int, Type, []byte) (MessageBody, error){
 	ipv4.ICMPTypeDestinationUnreachable: parseDstUnreach,
 	ipv4.ICMPTypeTimeExceeded:           parseTimeExceeded,
 	ipv4.ICMPTypeParameterProblem:       parseParamProb,
 
-	ipv4.ICMPTypeEcho:      parseEcho,
-	ipv4.ICMPTypeEchoReply: parseEcho,
+	ipv4.ICMPTypeEcho:                parseEcho,
+	ipv4.ICMPTypeEchoReply:           parseEcho,
+	ipv4.ICMPTypeExtendedEchoRequest: parseExtendedEchoRequest,
+	ipv4.ICMPTypeExtendedEchoReply:   parseExtendedEchoReply,
 
 	ipv6.ICMPTypeDestinationUnreachable: parseDstUnreach,
 	ipv6.ICMPTypePacketTooBig:           parsePacketTooBig,
 	ipv6.ICMPTypeTimeExceeded:           parseTimeExceeded,
 	ipv6.ICMPTypeParameterProblem:       parseParamProb,
 
-	ipv6.ICMPTypeEchoRequest: parseEcho,
-	ipv6.ICMPTypeEchoReply:   parseEcho,
+	ipv6.ICMPTypeEchoRequest:         parseEcho,
+	ipv6.ICMPTypeEchoReply:           parseEcho,
+	ipv6.ICMPTypeExtendedEchoRequest: parseExtendedEchoRequest,
+	ipv6.ICMPTypeExtendedEchoReply:   parseExtendedEchoReply,
 }
 
 // ParseMessage parses b as an ICMP message.
@@ -143,7 +148,7 @@
 	if fn, ok := parseFns[m.Type]; !ok {
 		m.Body, err = parseDefaultMessageBody(proto, b[4:])
 	} else {
-		m.Body, err = fn(proto, b[4:])
+		m.Body, err = fn(proto, m.Type, b[4:])
 	}
 	if err != nil {
 		return nil, err
diff --git a/icmp/message_test.go b/icmp/message_test.go
index 95f6c37..c278b8b 100644
--- a/icmp/message_test.go
+++ b/icmp/message_test.go
@@ -77,6 +77,18 @@
 					},
 				},
 				{
+					Type: ipv4.ICMPTypeExtendedEchoRequest, Code: 0,
+					Body: &icmp.ExtendedEchoRequest{
+						ID: 1, Seq: 2,
+					},
+				},
+				{
+					Type: ipv4.ICMPTypeExtendedEchoReply, Code: 0,
+					Body: &icmp.ExtendedEchoReply{
+						State: 4 /* Delay */, Active: true, IPv4: true,
+					},
+				},
+				{
 					Type: ipv4.ICMPTypePhoturis,
 					Body: &icmp.DefaultMessageBody{
 						Data: []byte{0x80, 0x40, 0x20, 0x10},
@@ -121,6 +133,18 @@
 					},
 				},
 				{
+					Type: ipv6.ICMPTypeExtendedEchoRequest, Code: 0,
+					Body: &icmp.ExtendedEchoRequest{
+						ID: 1, Seq: 2,
+					},
+				},
+				{
+					Type: ipv6.ICMPTypeExtendedEchoReply, Code: 0,
+					Body: &icmp.ExtendedEchoReply{
+						State: 5 /* Probe */, Active: true, IPv6: true,
+					},
+				},
+				{
 					Type: ipv6.ICMPTypeDuplicateAddressConfirmation,
 					Body: &icmp.DefaultMessageBody{
 						Data: []byte{0x80, 0x40, 0x20, 0x10},
diff --git a/icmp/multipart.go b/icmp/multipart.go
index f271356..9ebbbaf 100644
--- a/icmp/multipart.go
+++ b/icmp/multipart.go
@@ -10,12 +10,14 @@
 // exts as extensions, and returns a required length for message body
 // and a required length for a padded original datagram in wire
 // format.
-func multipartMessageBodyDataLen(proto int, b []byte, exts []Extension) (bodyLen, dataLen int) {
+func multipartMessageBodyDataLen(proto int, withOrigDgram bool, b []byte, exts []Extension) (bodyLen, dataLen int) {
 	for _, ext := range exts {
 		bodyLen += ext.Len(proto)
 	}
 	if bodyLen > 0 {
-		dataLen = multipartMessageOrigDatagramLen(proto, b)
+		if withOrigDgram {
+			dataLen = multipartMessageOrigDatagramLen(proto, b)
+		}
 		bodyLen += 4 // length of extension header
 	} else {
 		dataLen = len(b)
@@ -50,8 +52,8 @@
 // marshalMultipartMessageBody takes data as an original datagram and
 // exts as extesnsions, and returns a binary encoding of message body.
 // It can be used for non-multipart message bodies when exts is nil.
-func marshalMultipartMessageBody(proto int, data []byte, exts []Extension) ([]byte, error) {
-	bodyLen, dataLen := multipartMessageBodyDataLen(proto, data, exts)
+func marshalMultipartMessageBody(proto int, withOrigDgram bool, data []byte, exts []Extension) ([]byte, error) {
+	bodyLen, dataLen := multipartMessageBodyDataLen(proto, withOrigDgram, data, exts)
 	b := make([]byte, 4+bodyLen)
 	copy(b[4:], data)
 	off := dataLen + 4
@@ -71,16 +73,23 @@
 					return nil, err
 				}
 				off += ext.Len(proto)
+			case *InterfaceIdent:
+				if err := ext.marshal(proto, b[off:]); err != nil {
+					return nil, err
+				}
+				off += ext.Len(proto)
 			}
 		}
 		s := checksum(b[dataLen+4:])
 		b[dataLen+4+2] ^= byte(s)
 		b[dataLen+4+3] ^= byte(s >> 8)
-		switch proto {
-		case iana.ProtocolICMP:
-			b[1] = byte(dataLen / 4)
-		case iana.ProtocolIPv6ICMP:
-			b[0] = byte(dataLen / 8)
+		if withOrigDgram {
+			switch proto {
+			case iana.ProtocolICMP:
+				b[1] = byte(dataLen / 4)
+			case iana.ProtocolIPv6ICMP:
+				b[0] = byte(dataLen / 8)
+			}
 		}
 	}
 	return b, nil
@@ -88,7 +97,7 @@
 
 // parseMultipartMessageBody parses b as either a non-multipart
 // message body or a multipart message body.
-func parseMultipartMessageBody(proto int, b []byte) ([]byte, []Extension, error) {
+func parseMultipartMessageBody(proto int, typ Type, b []byte) ([]byte, []Extension, error) {
 	var l int
 	switch proto {
 	case iana.ProtocolICMP:
@@ -99,11 +108,14 @@
 	if len(b) == 4 {
 		return nil, nil, nil
 	}
-	exts, l, err := parseExtensions(b[4:], l)
+	exts, l, err := parseExtensions(typ, b[4:], l)
 	if err != nil {
 		l = len(b) - 4
 	}
-	data := make([]byte, l)
-	copy(data, b[4:])
+	var data []byte
+	if l > 0 {
+		data = make([]byte, l)
+		copy(data, b[4:])
+	}
 	return data, exts, nil
 }
diff --git a/icmp/multipart_test.go b/icmp/multipart_test.go
index 611fecf..7440882 100644
--- a/icmp/multipart_test.go
+++ b/icmp/multipart_test.go
@@ -23,17 +23,21 @@
 		if err != nil {
 			return err
 		}
-		switch proto {
-		case iana.ProtocolICMP:
-			if b[5] != 32 {
-				return fmt.Errorf("got %d; want 32", b[5])
-			}
-		case iana.ProtocolIPv6ICMP:
-			if b[4] != 16 {
-				return fmt.Errorf("got %d; want 16", b[4])
-			}
+		switch tm.Type {
+		case ipv4.ICMPTypeExtendedEchoRequest, ipv6.ICMPTypeExtendedEchoRequest:
 		default:
-			return fmt.Errorf("unknown protocol: %d", proto)
+			switch proto {
+			case iana.ProtocolICMP:
+				if b[5] != 32 {
+					return fmt.Errorf("got %d; want 32", b[5])
+				}
+			case iana.ProtocolIPv6ICMP:
+				if b[4] != 16 {
+					return fmt.Errorf("got %d; want 16", b[4])
+				}
+			default:
+				return fmt.Errorf("unknown protocol: %d", proto)
+			}
 		}
 		m, err := icmp.ParseMessage(proto, b)
 		if err != nil {
@@ -43,6 +47,11 @@
 			return fmt.Errorf("got %v; want %v", m, &tm)
 		}
 		switch m.Type {
+		case ipv4.ICMPTypeExtendedEchoRequest, ipv6.ICMPTypeExtendedEchoRequest:
+			got, want := m.Body.(*icmp.ExtendedEchoRequest), tm.Body.(*icmp.ExtendedEchoRequest)
+			if !reflect.DeepEqual(got.Extensions, want.Extensions) {
+				return errors.New(dumpExtensions(got.Extensions, want.Extensions))
+			}
 		case ipv4.ICMPTypeDestinationUnreachable:
 			got, want := m.Body.(*icmp.DstUnreach), tm.Body.(*icmp.DstUnreach)
 			if !reflect.DeepEqual(got.Extensions, want.Extensions) {
@@ -200,6 +209,51 @@
 					},
 				},
 			},
+			{
+				Type: ipv4.ICMPTypeExtendedEchoRequest, Code: 0,
+				Body: &icmp.ExtendedEchoRequest{
+					ID: 1, Seq: 2, Local: true,
+					Extensions: []icmp.Extension{
+						&icmp.InterfaceIdent{
+							Class: 3,
+							Type:  1,
+							Name:  "en101",
+						},
+					},
+				},
+			},
+			{
+				Type: ipv4.ICMPTypeExtendedEchoRequest, Code: 0,
+				Body: &icmp.ExtendedEchoRequest{
+					ID: 1, Seq: 2, Local: true,
+					Extensions: []icmp.Extension{
+						&icmp.InterfaceIdent{
+							Class: 3,
+							Type:  2,
+							Index: 911,
+						},
+						&icmp.InterfaceIdent{
+							Class: 3,
+							Type:  1,
+							Name:  "en101",
+						},
+					},
+				},
+			},
+			{
+				Type: ipv4.ICMPTypeExtendedEchoRequest, Code: 0,
+				Body: &icmp.ExtendedEchoRequest{
+					ID: 1, Seq: 2,
+					Extensions: []icmp.Extension{
+						&icmp.InterfaceIdent{
+							Class: 3,
+							Type:  3,
+							AFI:   iana.AddrFamily48bitMAC,
+							Addr:  []byte{0x01, 0x23, 0x45, 0x67, 0x89, 0xab},
+						},
+					},
+				},
+			},
 		} {
 			if err := fn(t, iana.ProtocolICMP, tm); err != nil {
 				t.Errorf("#%d: %v", i, err)
@@ -287,6 +341,51 @@
 					},
 				},
 			},
+			{
+				Type: ipv6.ICMPTypeExtendedEchoRequest, Code: 0,
+				Body: &icmp.ExtendedEchoRequest{
+					ID: 1, Seq: 2, Local: true,
+					Extensions: []icmp.Extension{
+						&icmp.InterfaceIdent{
+							Class: 3,
+							Type:  1,
+							Name:  "en101",
+						},
+					},
+				},
+			},
+			{
+				Type: ipv6.ICMPTypeExtendedEchoRequest, Code: 0,
+				Body: &icmp.ExtendedEchoRequest{
+					ID: 1, Seq: 2, Local: true,
+					Extensions: []icmp.Extension{
+						&icmp.InterfaceIdent{
+							Class: 3,
+							Type:  1,
+							Name:  "en101",
+						},
+						&icmp.InterfaceIdent{
+							Class: 3,
+							Type:  2,
+							Index: 911,
+						},
+					},
+				},
+			},
+			{
+				Type: ipv6.ICMPTypeExtendedEchoRequest, Code: 0,
+				Body: &icmp.ExtendedEchoRequest{
+					ID: 1, Seq: 2,
+					Extensions: []icmp.Extension{
+						&icmp.InterfaceIdent{
+							Class: 3,
+							Type:  3,
+							AFI:   iana.AddrFamilyIPv4,
+							Addr:  []byte{192, 0, 2, 1},
+						},
+					},
+				},
+			},
 		} {
 			if err := fn(t, iana.ProtocolIPv6ICMP, tm); err != nil {
 				t.Errorf("#%d: %v", i, err)
@@ -309,6 +408,11 @@
 			if !reflect.DeepEqual(got, want) {
 				s += fmt.Sprintf("#%d: got %#v, %#v, %#v; want %#v, %#v, %#v\n", i, got, got.Interface, got.Addr, want, want.Interface, want.Addr)
 			}
+		case *icmp.InterfaceIdent:
+			want := wantExts[i].(*icmp.InterfaceIdent)
+			if !reflect.DeepEqual(got, want) {
+				s += fmt.Sprintf("#%d: got %#v; want %#v\n", i, got, want)
+			}
 		}
 	}
 	if len(s) == 0 {
@@ -435,6 +539,34 @@
 			},
 			4 + 4 + 4 + 0 + 136, // [length, unused], extension header, object header, object payload and original datagram
 		},
+
+		{
+			iana.ProtocolICMP,
+			&icmp.ExtendedEchoRequest{},
+			4, // [id, seq, l-bit]
+		},
+		{
+			iana.ProtocolICMP,
+			&icmp.ExtendedEchoRequest{
+				Extensions: []icmp.Extension{
+					&icmp.InterfaceIdent{},
+				},
+			},
+			4 + 4 + 4, // [id, seq, l-bit], extension header, object header
+		},
+		{
+			iana.ProtocolIPv6ICMP,
+			&icmp.ExtendedEchoRequest{
+				Extensions: []icmp.Extension{
+					&icmp.InterfaceIdent{
+						Type: 3,
+						AFI:  iana.AddrFamilyNSAP,
+						Addr: []byte{0x49, 0x00, 0x01, 0xaa, 0xaa, 0xbb, 0xbb, 0xcc, 0xcc, 0x00},
+					},
+				},
+			},
+			4 + 4 + 4 + 16, // [id, seq, l-bit], extension header, object header, object payload
+		},
 	} {
 		if out := tt.in.Len(tt.proto); out != tt.out {
 			t.Errorf("#%d: got %d; want %d", i, out, tt.out)
diff --git a/icmp/packettoobig.go b/icmp/packettoobig.go
index a1c9df7..afbf24f 100644
--- a/icmp/packettoobig.go
+++ b/icmp/packettoobig.go
@@ -29,7 +29,7 @@
 }
 
 // parsePacketTooBig parses b as an ICMP packet too big message body.
-func parsePacketTooBig(proto int, b []byte) (MessageBody, error) {
+func parsePacketTooBig(proto int, _ Type, b []byte) (MessageBody, error) {
 	bodyLen := len(b)
 	if bodyLen < 4 {
 		return nil, errMessageTooShort
diff --git a/icmp/paramprob.go b/icmp/paramprob.go
index 0a2548d..8587255 100644
--- a/icmp/paramprob.go
+++ b/icmp/paramprob.go
@@ -21,7 +21,7 @@
 	if p == nil {
 		return 0
 	}
-	l, _ := multipartMessageBodyDataLen(proto, p.Data, p.Extensions)
+	l, _ := multipartMessageBodyDataLen(proto, true, p.Data, p.Extensions)
 	return 4 + l
 }
 
@@ -33,7 +33,7 @@
 		copy(b[4:], p.Data)
 		return b, nil
 	}
-	b, err := marshalMultipartMessageBody(proto, p.Data, p.Extensions)
+	b, err := marshalMultipartMessageBody(proto, true, p.Data, p.Extensions)
 	if err != nil {
 		return nil, err
 	}
@@ -42,7 +42,7 @@
 }
 
 // parseParamProb parses b as an ICMP parameter problem message body.
-func parseParamProb(proto int, b []byte) (MessageBody, error) {
+func parseParamProb(proto int, typ Type, b []byte) (MessageBody, error) {
 	if len(b) < 4 {
 		return nil, errMessageTooShort
 	}
@@ -55,7 +55,7 @@
 	}
 	p.Pointer = uintptr(b[0])
 	var err error
-	p.Data, p.Extensions, err = parseMultipartMessageBody(proto, b)
+	p.Data, p.Extensions, err = parseMultipartMessageBody(proto, typ, b)
 	if err != nil {
 		return nil, err
 	}
diff --git a/icmp/timeexceeded.go b/icmp/timeexceeded.go
index 344e158..14e9e23 100644
--- a/icmp/timeexceeded.go
+++ b/icmp/timeexceeded.go
@@ -15,23 +15,23 @@
 	if p == nil {
 		return 0
 	}
-	l, _ := multipartMessageBodyDataLen(proto, p.Data, p.Extensions)
+	l, _ := multipartMessageBodyDataLen(proto, true, p.Data, p.Extensions)
 	return 4 + l
 }
 
 // Marshal implements the Marshal method of MessageBody interface.
 func (p *TimeExceeded) Marshal(proto int) ([]byte, error) {
-	return marshalMultipartMessageBody(proto, p.Data, p.Extensions)
+	return marshalMultipartMessageBody(proto, true, p.Data, p.Extensions)
 }
 
 // parseTimeExceeded parses b as an ICMP time exceeded message body.
-func parseTimeExceeded(proto int, b []byte) (MessageBody, error) {
+func parseTimeExceeded(proto int, typ Type, b []byte) (MessageBody, error) {
 	if len(b) < 4 {
 		return nil, errMessageTooShort
 	}
 	p := &TimeExceeded{}
 	var err error
-	p.Data, p.Extensions, err = parseMultipartMessageBody(proto, b)
+	p.Data, p.Extensions, err = parseMultipartMessageBody(proto, typ, b)
 	if err != nil {
 		return nil, err
 	}