diff --git a/addr.go b/addr.go
new file mode 100644
index 0000000..4fefe58
--- /dev/null
+++ b/addr.go
@@ -0,0 +1,105 @@
+package stun
+
+import (
+	"fmt"
+	"net"
+	"strconv"
+)
+
+// MappedAddress represents MAPPED-ADDRESS attribute.
+//
+// This attribute is used only by servers for achieving backwards
+// compatibility with RFC 3489 clients.
+// https://tools.ietf.org/html/rfc5389#section-15.4
+type MappedAddress struct {
+	IP   net.IP
+	Port int
+}
+
+// AlternateServer represents ALTERNATE-SERVER attribute.
+//
+// https://tools.ietf.org/html/rfc5389#section-15.4
+type AlternateServer struct {
+	IP   net.IP
+	Port int
+}
+
+// AddTo adds ALTERNATE-SERVER attribute to message.
+func (s *AlternateServer) AddTo(m *Message) error {
+	a := (*MappedAddress)(s)
+	return a.addAs(m, AttrAlternateServer)
+}
+
+// GetFrom decodes ALTERNATE-SERVER from message.
+func (s *AlternateServer) GetFrom(m *Message) error {
+	a := (*MappedAddress)(s)
+	return a.getAs(m, AttrAlternateServer)
+}
+
+func (a MappedAddress) String() string {
+	return net.JoinHostPort(a.IP.String(), strconv.Itoa(a.Port))
+}
+
+func (a *MappedAddress) getAs(m *Message, t AttrType) error {
+	v, err := m.Get(t)
+	if err != nil {
+		return err
+	}
+	family := bin.Uint16(v[0:2])
+	if family != familyIPv6 && family != familyIPv4 {
+		return newDecodeErr("xor-mapped address", "family",
+			fmt.Sprintf("bad value %d", family),
+		)
+	}
+	ipLen := net.IPv4len
+	if family == familyIPv6 {
+		ipLen = net.IPv6len
+	}
+	// Ensuring len(a.IP) == ipLen and reusing a.IP.
+	if len(a.IP) < ipLen {
+		a.IP = a.IP[:cap(a.IP)]
+		for len(a.IP) < ipLen {
+			a.IP = append(a.IP, 0)
+		}
+	}
+	a.IP = a.IP[:ipLen]
+	for i := range a.IP {
+		a.IP[i] = 0
+	}
+	a.Port = int(bin.Uint16(v[2:4]))
+	copy(a.IP, v[4:])
+	return nil
+}
+
+func (a *MappedAddress) addAs(m *Message, t AttrType) error {
+	var (
+		family = familyIPv4
+		ip     = a.IP
+	)
+	if len(a.IP) == net.IPv6len {
+		if isIPv4(ip) {
+			ip = ip[12:16] // like in ip.To4()
+		} else {
+			family = familyIPv6
+		}
+	} else if len(ip) != net.IPv4len {
+		return ErrBadIPLength
+	}
+	value := make([]byte, 128)
+	value[0] = 0 // first 8 bits are zeroes
+	bin.PutUint16(value[0:2], family)
+	bin.PutUint16(value[2:4], uint16(a.Port))
+	copy(value[4:], ip)
+	m.Add(t, value[:4+len(ip)])
+	return nil
+}
+
+// AddTo adds MAPPED-ADDRESS to message.
+func (a *MappedAddress) AddTo(m *Message) error {
+	return a.addAs(m, AttrMappedAddress)
+}
+
+// GetFrom decodes MAPPED-ADDRESS from message.
+func (a *MappedAddress) GetFrom(m *Message) error {
+	return a.getAs(m, AttrMappedAddress)
+}
diff --git a/addr_test.go b/addr_test.go
new file mode 100644
index 0000000..3ce9be6
--- /dev/null
+++ b/addr_test.go
@@ -0,0 +1,92 @@
+package stun
+
+import (
+	"net"
+	"testing"
+)
+
+func TestMappedAddress(t *testing.T) {
+	m := new(Message)
+	addr := &MappedAddress{
+		IP:   net.ParseIP("122.12.34.5"),
+		Port: 5412,
+	}
+	t.Run("AddTo", func(t *testing.T) {
+		if err := addr.AddTo(m); err != nil {
+			t.Error(err)
+		}
+		t.Run("GetFrom", func(t *testing.T) {
+			got := new(MappedAddress)
+			if err := got.GetFrom(m); err != nil {
+				t.Error(err)
+			}
+			if !got.IP.Equal(addr.IP) {
+				t.Error("got bad IP: ", got.IP)
+			}
+			t.Run("Not found", func(t *testing.T) {
+				message := new(Message)
+				if err := got.GetFrom(message); err != ErrAttributeNotFound {
+					t.Error("should be not found: ", err)
+				}
+			})
+		})
+	})
+}
+
+func TestAlternateServer(t *testing.T) {
+	m := new(Message)
+	addr := &AlternateServer{
+		IP:   net.ParseIP("122.12.34.5"),
+		Port: 5412,
+	}
+	t.Run("AddTo", func(t *testing.T) {
+		if err := addr.AddTo(m); err != nil {
+			t.Error(err)
+		}
+		t.Run("GetFrom", func(t *testing.T) {
+			got := new(AlternateServer)
+			if err := got.GetFrom(m); err != nil {
+				t.Error(err)
+			}
+			if !got.IP.Equal(addr.IP) {
+				t.Error("got bad IP: ", got.IP)
+			}
+			t.Run("Not found", func(t *testing.T) {
+				message := new(Message)
+				if err := got.GetFrom(message); err != ErrAttributeNotFound {
+					t.Error("should be not found: ", err)
+				}
+			})
+		})
+	})
+}
+
+func BenchmarkMappedAddress_AddTo(b *testing.B) {
+	m := new(Message)
+	b.ReportAllocs()
+	addr := &MappedAddress{
+		IP:   net.ParseIP("122.12.34.5"),
+		Port: 5412,
+	}
+	for i := 0; i < b.N; i++ {
+		if err := addr.AddTo(m); err != nil {
+			b.Fatal(err)
+		}
+		m.Reset()
+	}
+}
+
+func BenchmarkAlternateServer_AddTo(b *testing.B) {
+	m := new(Message)
+	b.ReportAllocs()
+	addr := &AlternateServer{
+		IP:   net.ParseIP("122.12.34.5"),
+		Port: 5412,
+	}
+	for i := 0; i < b.N; i++ {
+		if err := addr.AddTo(m); err != nil {
+			b.Fatal(err)
+		}
+		m.Reset()
+	}
+}
diff --git a/xoraddr.go b/xoraddr.go
index 112685d..eeda31f 100644
--- a/xoraddr.go
+++ b/xoraddr.go
@@ -8,8 +8,8 @@ import (
 )
 
 const (
-	familyIPv4 byte = 0x01
-	familyIPv6 byte = 0x02
+	familyIPv4 uint16 = 0x01
+	familyIPv6 uint16 = 0x02
 )
 
 // XORMappedAddress implements XOR-MAPPED-ADDRESS attribute.
@@ -62,7 +62,7 @@ func (a *XORMappedAddress) AddTo(m *Message) error {
 	xorValue := make([]byte, net.IPv6len)
 	copy(xorValue[4:], m.TransactionID[:])
 	bin.PutUint32(xorValue[0:4], magicCookie)
-	bin.PutUint16(value[0:2], uint16(family))
+	bin.PutUint16(value[0:2], family)
 	bin.PutUint16(value[2:4], uint16(a.Port^magicCookie>>16))
 	xorBytes(value[4:4+len(ip)], ip, xorValue)
 	m.Add(AttrXORMappedAddress, value[:4+len(ip)])
@@ -95,7 +95,7 @@ func (a *XORMappedAddress) GetFrom(m *Message) error {
 	if err != nil {
 		return err
 	}
-	family := byte(bin.Uint16(v[0:2]))
+	family := bin.Uint16(v[0:2])
 	if family != familyIPv6 && family != familyIPv4 {
 		return newDecodeErr("xor-mapped address", "family",
 			fmt.Sprintf("bad value %d", family),