Lecture Notes on Networking Protocols

Overview

• Emphasis on hands-on practice over passive learning.
• Download Packet Tracer and engage with the scenarios.
• Understanding concepts through practical application (e.g., riding a bicycle).

Network Topology

• Focus on an internal PC and an Internet router.
• Example setup includes:
  • Multiple devices interconnected.
  • An Internet router connecting to the external network.
  • Servers in the internal network.

Communication Concepts

• IP Addressing:
  • An IP address allows devices to communicate via protocols (specifically IPv4 in this example).
• Example Devices:
  • BT Home Hub as the Internet router.
  • Internal servers to connect via IP.

Packet Communication Steps

1. Opening a Web Browser on PC:

   • Change Packet Tracer mode to simulation mode.
   • Connect via HTTP to 10.1.1.100 (server IP).

2. Address Resolution Protocol (ARP):

   • PC requests the MAC address of the server using ARP.
   • ARP sends a broadcast frame to find the MAC address.
   • Server responds with its MAC address.

3. TCP Connection Establishment:

   • A three-way handshake occurs before data transfer.
   • TCP packet encapsulated in HTTP packets.

4. Understanding Layer Structure:

   • Layer 1: Physical (Ethernet)
   • Layer 2: Data Link (MAC addressing)
   • Layer 3: Network (IP addressing)
   • Layer 4: Transport (TCP/UDP)
   • Layer 7: Application (HTTP)

Packet Analysis

• Inbound and Outbound PDU:
  • MAC addresses, IP addresses, and port numbers change between requests/responses.
  • Source and destination information is crucial for communications.

Protocol and Port Numbers

• Common Protocols:

  • HTTP – Port 80
  • FTP – Port 21
  • TFTP – Port 69
  • SSH – Port 22
  • Telnet – Port 23

• Ephemeral Ports:

  • Randomly assigned source ports for outgoing connections (e.g., 1025).
  • Dynamic port numbers allow multiple sessions to different ports.

Summary of Protocol Interaction

• When a PC connects to a server:
  • Source MAC/IP and port are swapped with destination MAC/IP and port upon response.
  • Identifying the appropriate protocol and application involves checking port numbers.

Importance of Protocol Understanding

• Understanding how protocols interact at different layers improves network troubleshooting and design.
• Emphasizes the need to study well-known port numbers and protocols for exams and practical applications.