diff --git a/squinnondation/squinnondation.py b/squinnondation/squinnondation.py
index 7946ef8..3ef127c 100644
--- a/squinnondation/squinnondation.py
+++ b/squinnondation/squinnondation.py
@@ -3,7 +3,8 @@
 
 import socket
 from argparse import ArgumentParser
-from typing import Any, Tuple
+from enum import Enum
+from typing import Any, Optional, Tuple
 
 
 class Squinnondation:
@@ -47,15 +48,18 @@ class Squinnondation:
             pkt = Packet()
             pkt.magic = 95
             pkt.version = 0
-            pkt.body = TLV()
+            pkt.body = DataTLV()
             msg = f"Hello world, my name is {squirrel.nickname}!"
-            pkt.body.raw_data = msg.encode("UTF-8")
-            pkt.body_length = len(pkt.body.raw_data)
+            pkt.body.data = msg.encode("UTF-8")
+            pkt.body.sender_id = 42
+            pkt.body.nonce = 18
+            pkt.body.length = len(msg) + 1 + 1 + 8 + 4
+            pkt.body_length = pkt.body.length + 2
             squirrel.send_packet(hazelnut, pkt)
 
         while True:
             pkt, addr = squirrel.receive_packet()
-            print(f"received message: {pkt.body.raw_data.decode('UTF-8')}")
+            print(f"received message: {pkt.body.data.decode('UTF-8')}")
 
 
 class TLV:
@@ -64,7 +68,18 @@ class TLV:
     TODO: add subclasses for each type of TLV
     """
     type: int
-    raw_data: bytes
+
+    def unmarshal(self, raw_data: bytes) -> None:
+        """
+        Parse data and construct TLV.
+        """
+        raise NotImplementedError
+
+    def marshal(self) -> bytes:
+        """
+        Translate the TLV into a byte array.
+        """
+        raise NotImplementedError
 
     def validate_data(self) -> bool:
         """
@@ -74,6 +89,184 @@ class TLV:
         """
         return True
 
+    @staticmethod
+    def tlv_classes():
+        return [Pad1TLV, PadNTLV, HelloTLV, NeighbourTLV, DataTLV, AckTLV, GoAwayTLV, WarningTLV]
+
+
+class Pad1TLV(TLV):
+    """
+    This TLV is simply ignored.
+    """
+    type: int = 0
+
+    def unmarshal(self, raw_data: bytes) -> None:
+        """
+        There is nothing to do. We ignore the packet.
+        """
+        self.type = raw_data[0]
+
+    def marshal(self) -> bytes:
+        """
+        The TLV is empty.
+        """
+        return self.type.to_bytes(1, "big")
+
+
+class PadNTLV(TLV):
+    """
+    This TLV is filled with zeros. It is ignored.
+    """
+    type: int = 1
+    length: int
+    mbz: bytes
+
+    def validate_data(self) -> bool:
+        if self.mbz != int(0).to_bytes(self.length, "big"):
+            raise ValueError("The body of a PadN TLV is not filled with zeros.")
+        return True
+
+    def unmarshal(self, raw_data: bytes) -> None:
+        """
+        Store the zero-array, then ignore the packet.
+        """
+        self.type = raw_data[0]
+        self.length = raw_data[1]
+        self.mbz = raw_data[2:2 + self.length]
+
+    def marshal(self) -> bytes:
+        """
+        Construct the byte array filled by zeros.
+        """
+        return self.type.to_bytes(1, "big") + self.length.to_bytes(1, "big") + self.mbz[:self.length]
+
+
+class HelloTLV(TLV):
+    type: int = 2
+    length: int
+    source_id: int
+    dest_id: Optional[int]
+
+    def validate_data(self) -> bool:
+        if self.length != 8 and self.length != 16:
+            raise ValueError("The length of a Hello TLV must be 8 for a short Hello, or 16 for a long Hello,"
+                             f"found {self.length}")
+        return True
+
+    def unmarshal(self, raw_data: bytes) -> None:
+        self.type = raw_data[0]
+        self.length = raw_data[1]
+        self.source_id = int.from_bytes(raw_data[2:10], "big")
+        if self.length == 16:
+            self.dest_id = int.from_bytes(raw_data[10:18], "big")
+
+    def marshal(self) -> bytes:
+        data = self.type.to_bytes(1, "big") + self.length.to_bytes(1, "big") + self.source_id.to_bytes(8, "big")
+        if self.dest_id:
+            data += self.dest_id.to_bytes(8, "big")
+        return data
+
+
+class NeighbourTLV(TLV):
+    type: int = 3
+    length: int
+    ip_address: int
+    port: int
+
+    def unmarshal(self, raw_data: bytes) -> None:
+        self.type = raw_data[0]
+        self.length = raw_data[1]
+        self.ip_address = raw_data[2:18]
+        self.port = int.from_bytes(raw_data[18:20], "big")
+
+    def marshal(self) -> bytes:
+        return self.type.to_bytes(1, "big") + \
+               self.length.to_bytes(1, "big") + \
+               self.ip_address.to_bytes(16, "big") + \
+               self.port.to_bytes(2, "big")
+
+
+class DataTLV(TLV):
+    type: int = 4
+    length: int
+    sender_id: int
+    nonce: int
+    data: bytes
+
+    def unmarshal(self, raw_data: bytes) -> None:
+        self.type = raw_data[0]
+        self.length = raw_data[1]
+        self.sender_id = int.from_bytes(raw_data[2:10], "big")
+        self.nonce = int.from_bytes(raw_data[10:14], "big")
+        self.data = raw_data[14:2 + self.length]
+
+    def marshal(self) -> bytes:
+        return self.type.to_bytes(1, "big") + \
+               self.length.to_bytes(1, "big") + \
+               self.sender_id.to_bytes(8, "big") + \
+               self.nonce.to_bytes(4, "big") + \
+               self.data
+
+
+class AckTLV(TLV):
+    type: int = 5
+    length: int
+    sender_id: int
+    nonce: int
+
+    def unmarshal(self, raw_data: bytes) -> None:
+        self.type = raw_data[0]
+        self.length = raw_data[1]
+        self.sender_id = int.from_bytes(raw_data[2:10], "big")
+        self.nonce = int.from_bytes(raw_data[10:14], "big")
+
+    def marshal(self) -> bytes:
+        return self.type.to_bytes(1, "big") + \
+               self.length.to_bytes(1, "big") + \
+               self.sender_id.to_bytes(8, "big") + \
+               self.nonce.to_bytes(4, "big")
+
+
+class GoAwayTLV(TLV):
+    class GoAwayType(Enum):
+        UNKNOWN = 0
+        EXIT = 1
+        TIMEOUT = 2
+        PROTOCOL_VIOLATION = 3
+
+    type: int = 6
+    length: int
+    code: GoAwayType
+    message: str
+
+    def unmarshal(self, raw_data: bytes) -> None:
+        self.type = raw_data[0]
+        self.length = raw_data[1]
+        self.code = GoAwayTLV.GoAwayType(raw_data[2])
+        self.message = raw_data[3:self.length - 1].decode("UTF-8")
+
+    def marshal(self) -> bytes:
+        return self.type.to_bytes(1, "big") + \
+               self.length.to_bytes(1, "big") + \
+               self.code.value.to_bytes(1, "big") + \
+               self.message.encode("UTF-8")[:self.length - 1]
+
+
+class WarningTLV(TLV):
+    type: int = 7
+    length: int
+    message: str
+
+    def unmarshal(self, raw_data: bytes) -> None:
+        self.type = raw_data[0]
+        self.length = raw_data[1]
+        self.message = raw_data[2:self.length].decode("UTF-8")
+
+    def marshal(self) -> bytes:
+        return self.type.to_bytes(1, "big") + \
+               self.length.to_bytes(1, "big") + \
+               self.message.encode("UTF-8")[:self.length]
+
 
 class Packet:
     """
@@ -108,8 +301,11 @@ class Packet:
         pkt.magic = data[0]
         pkt.version = data[1]
         pkt.body_length = int.from_bytes(data[2:4], byteorder="big")
-        pkt.body = TLV()
-        pkt.body.raw_data = data[4:4+pkt.body_length]
+        tlv_type = data[4]
+        if not (0 <= tlv_type < len(TLV.tlv_classes())):
+            raise ValueError(f"TLV type is not supported: {tlv_type}")
+        pkt.body = TLV.tlv_classes()[tlv_type]()
+        pkt.body.unmarshal(data[4:4+pkt.body_length])
 
         pkt.validate_data()
 
@@ -122,7 +318,7 @@ class Packet:
         data = self.magic.to_bytes(1, "big")
         data += self.version.to_bytes(1, "big")
         data += self.body_length.to_bytes(2, "big")
-        data += self.body.raw_data
+        data += self.body.marshal()
         return data