Networking and Internet Protocols Lecture Notes

Moving Box Metaphor

• Transporting Boxes: Common method is using a moving truck.
  • Network Comparison: The road represents the network (wireless, DSL, cable, Ethernet).
  • Truck as IP: Internet Protocol (IP) likened to the moving truck.
  • Box as Data: Encapsulated data traveling inside the truck.

Network Structure

• Devices: Include workstations, clients, laptops (senders) and servers (receivers).
• Ethernet Frame Structure:
  • Payload: Contains IP data, which includes TCP data, and further HTTP data.
  • Headers and Trailers: Ethernet header and trailer surround the payload.

IP and Protocols

• IP (Internet Protocol): The main protocol for moving data across networks.
• TCP (Transmission Control Protocol):
  • Connection-oriented, ensures reliable delivery, and has flow control.
  • Features: Acknowledgment of data receipt, retransmission of lost data, message reordering.
• UDP (User Datagram Protocol):
  • Connectionless, no acknowledgment of receipt, no flow control.
  • Use Cases: Ideal for real-time applications like VoIP, DHCP, TFTP.

Protocol Layers

• OSI Model: TCP/UDP operate at Transport Layer (Layer 4 of OSI).
• Encapsulation: TCP and UDP are encapsulated within IP packets.

Addressing and Multiplexing

• IP Addressing: Unique identifiers for devices in a network (like house addresses).
• Port Numbers: Direct data to the correct application or "room" (e.g., Port 80 for HTTP).
  • Non-Ephemeral Ports: Well-known and permanent (e.g., Port 80, 443).
  • Ephemeral Ports: Temporary, assigned in real-time by the OS.

TCP vs UDP

• TCP Characteristics:
  • Reliable, connection-oriented, flow control.
  • Used in applications like HTTPS, SSH.
• UDP Characteristics:
  • Unreliable, connectionless, no flow control.
  • Used in applications like VoIP, DHCP.

Port Numbers and Security

• Standardization: Same port numbers across servers for simplicity (e.g., Port 80 for web traffic).
• Security Implications:
  • Port numbers are not a security feature.
  • Easy to scan and find open ports.

Example of Traffic Flow

• Scenario: Client with IP 10.0.0.1 communicates with server IP 10.0.0.2.
• Traffic Types: HTTP (Port 80), VoIP (Port 5004), Email (Port 143).
• Port Assignments:
  • Source ports are random for outgoing traffic.
  • Destination ports are well-known for incoming traffic.