diff --git a/examples/tcp_daytime_service.py b/examples/tcp_daytime_service.py
index 982b195a..f32895e6 100755
--- a/examples/tcp_daytime_service.py
+++ b/examples/tcp_daytime_service.py
@@ -56,8 +56,8 @@ class TcpDaytimeService(TcpService):
     def __init__(
         self,
         *,
-        local_ip_address: str = "0.0.0.0",
-        local_port: int = 13,
+        local_ip_address: str,
+        local_port: int,
         message_count: int = -1,
         message_delay: int = 1,
     ):
@@ -113,14 +113,24 @@ def service(self, *, connected_socket: Socket) -> None:
 
 @click.command()
 @click.option("--interface", default="tap7")
-def cli(*, interface: str) -> None:
+@click.option("--local-ip-address", default="0.0.0.0")
+@click.option("--local-port", default=13, type=int)
+def cli(
+    *,
+    interface: str,
+    local_ip_address: str,
+    local_port: int,
+) -> None:
     """
     Start PyTCP stack and stop it when user presses Ctrl-C.
     Run the TCP Daytime service.
     """
 
     stack = TcpIpStack(fd=initialize_tap(tap_name=interface))
-    service = TcpDaytimeService()
+    service = TcpDaytimeService(
+        local_ip_address=local_ip_address,
+        local_port=local_port,
+    )
 
     try:
         stack.start()
diff --git a/examples/tcp_discard_service.py b/examples/tcp_discard_service.py
index 959b2ee8..64a2849f 100755
--- a/examples/tcp_discard_service.py
+++ b/examples/tcp_discard_service.py
@@ -53,7 +53,10 @@ class TcpDiscardService(TcpService):
     """
 
     def __init__(
-        self, *, local_ip_address: str = "0.0.0.0", local_port: int = 9
+        self,
+        *,
+        local_ip_address: str,
+        local_port: int,
     ):
         """
         Class constructor.
@@ -120,14 +123,24 @@ def service(self, *, connected_socket: Socket) -> None:
 
 @click.command()
 @click.option("--interface", default="tap7")
-def cli(*, interface: str) -> None:
+@click.option("--local-ip-address", default="0.0.0.0")
+@click.option("--local-port", default=9, type=int)
+def cli(
+    *,
+    interface: str,
+    local_ip_address: str,
+    local_port: int,
+) -> None:
     """
     Start PyTCP stack and stop it when user presses Ctrl-C.
     Run the TCP Discard service.
     """
 
     stack = TcpIpStack(fd=initialize_tap(tap_name=interface))
-    service = TcpDiscardService()
+    service = TcpDiscardService(
+        local_ip_address=local_ip_address,
+        local_port=local_port,
+    )
 
     try:
         stack.start()
diff --git a/examples/tcp_echo_service.py b/examples/tcp_echo_service.py
index d1f6f479..ee7dbc80 100755
--- a/examples/tcp_echo_service.py
+++ b/examples/tcp_echo_service.py
@@ -54,7 +54,10 @@ class TcpEchoService(TcpService):
     """
 
     def __init__(
-        self, *, local_ip_address: str = "0.0.0.0", local_port: int = 7
+        self,
+        *,
+        local_ip_address: str,
+        local_port: int,
     ):
         """
         Class constructor.
@@ -131,14 +134,24 @@ def service(self, *, connected_socket: Socket) -> None:
 
 @click.command()
 @click.option("--interface", default="tap7")
-def cli(*, interface: str) -> None:
+@click.option("--local-ip-address", default="0.0.0.0")
+@click.option("--local-port", default=7, type=int)
+def cli(
+    *,
+    interface: str,
+    local_ip_address: str,
+    local_port: int,
+) -> None:
     """
     Start PyTCP stack and stop it when user presses Ctrl-C.
     Run the TCP Echo service.
     """
 
     stack = TcpIpStack(fd=initialize_tap(tap_name=interface))
-    service = TcpEchoService()
+    service = TcpEchoService(
+        local_ip_address=local_ip_address,
+        local_port=local_port,
+    )
 
     try:
         stack.start()
diff --git a/examples/udp_daytime_service.py b/examples/udp_daytime_service.py
index 35ef4a17..905835d8 100755
--- a/examples/udp_daytime_service.py
+++ b/examples/udp_daytime_service.py
@@ -54,7 +54,10 @@ class UdpDaytimeService(UdpService):
     """
 
     def __init__(
-        self, *, local_ip_address: str = "0.0.0.0", local_port: int = 13
+        self,
+        *,
+        local_ip_address: str,
+        local_port: int,
     ):
         """
         Class constructor.
@@ -83,14 +86,24 @@ def service(self, *, listening_socket: Socket) -> None:
 
 @click.command()
 @click.option("--interface", default="tap7")
-def cli(*, interface: str) -> None:
+@click.option("--local-ip-address", default="0.0.0.0")
+@click.option("--local-port", default=13, type=int)
+def cli(
+    *,
+    interface: str,
+    local_ip_address: str,
+    local_port: int,
+) -> None:
     """
     Start PyTCP stack and stop it when user presses Ctrl-C.
     Run the UDP Daytime service.
     """
 
     stack = TcpIpStack(fd=initialize_tap(tap_name=interface))
-    service = UdpDaytimeService()
+    service = UdpDaytimeService(
+        local_ip_address=local_ip_address,
+        local_port=local_port,
+    )
 
     try:
         stack.start()
diff --git a/examples/udp_discard_service.py b/examples/udp_discard_service.py
index ccf098cd..c0591d95 100755
--- a/examples/udp_discard_service.py
+++ b/examples/udp_discard_service.py
@@ -53,7 +53,10 @@ class UdpDiscardService(UdpService):
     """
 
     def __init__(
-        self, *, local_ip_address: str = "0.0.0.0", local_port: int = 9
+        self,
+        *,
+        local_ip_address: str,
+        local_port: int,
     ):
         """
         Class constructor.
@@ -80,14 +83,24 @@ def service(self, *, listening_socket: Socket) -> None:
 
 @click.command()
 @click.option("--interface", default="tap7")
-def cli(*, interface: str) -> None:
+@click.option("--local-ip-address", default="0.0.0.0")
+@click.option("--local-port", default=9, type=int)
+def cli(
+    *,
+    interface: str,
+    local_ip_address: str,
+    local_port: int,
+) -> None:
     """
     Start PyTCP stack and stop it when user presses Ctrl-C.
     Run the UDP Discard service.
     """
 
     stack = TcpIpStack(fd=initialize_tap(tap_name=interface))
-    service = UdpDiscardService()
+    service = UdpDiscardService(
+        local_ip_address=local_ip_address,
+        local_port=local_port,
+    )
 
     try:
         stack.start()
diff --git a/examples/udp_echo_service.py b/examples/udp_echo_service.py
index 02a2aa13..8565a539 100755
--- a/examples/udp_echo_service.py
+++ b/examples/udp_echo_service.py
@@ -53,9 +53,7 @@ class UdpEchoService(UdpService):
     UDP Echo service support class.
     """
 
-    def __init__(
-        self, *, local_ip_address: str = "0.0.0.0", local_port: int = 7
-    ):
+    def __init__(self, *, local_ip_address: str = "::", local_port: int = 7):
         """
         Class constructor.
         """
@@ -96,14 +94,19 @@ def service(self, *, listening_socket: Socket) -> None:
 
 @click.command()
 @click.option("--interface", default="tap7")
-def cli(*, interface: str) -> None:
+@click.option("--local-ip-address", default="0.0.0.0")
+@click.option("--local-port", default=7, type=int)
+def cli(*, interface: str, local_ip_address: str, local_port: int) -> None:
     """
     Start PyTCP stack and stop it when user presses Ctrl-C.
     Run the UDP Echo service.
     """
 
     stack = TcpIpStack(fd=initialize_tap(tap_name=interface))
-    service = UdpEchoService()
+    service = UdpEchoService(
+        local_ip_address=local_ip_address,
+        local_port=local_port,
+    )
 
     try:
         stack.start()
diff --git a/pytcp/protocols/udp/fpa.py b/pytcp/protocols/udp/fpa.py
index 3be17278..328efbf3 100755
--- a/pytcp/protocols/udp/fpa.py
+++ b/pytcp/protocols/udp/fpa.py
@@ -76,6 +76,7 @@ def __init__(
         self._plen = UDP_HEADER_LEN + len(self._data)
         self._hlen = UDP_HEADER_LEN
         self._dlen = len(self._data)
+        self._cksum = 0
 
     def __len__(self) -> int:
         """