Networking Fundamentals Course - Summary Lesson

Introduction

• Final lesson in the free module of the Networking Fundamentals course.
• Purpose: Teach the core of networking and how data flows through a network.

Key Topics Covered

1. OSI Model

   • Discussed the functions of each layer in communication.

2. Host Communication

   • How hosts on the same network communicate regardless of connection.

3. Switches

   • Facilitate communication within a network.

4. Routers

   • Manage communication between different networks and learn routes.

Essential Tables for Data Flow

• Understanding data flow relies on three tables:
  • MAC Address Table: Maps switch ports to MAC addresses.
  • ARP Table (ARP Cache): Maps IP addresses to MAC addresses.
  • Routing Table: Maps IP networks to interfaces or next hop IP addresses.

Network Topology Example

• Components:

  • Three routers (R1, R2, R3) and three hosts (A, B, C).
  • Each has IP addresses, connected via NICs with unique MAC addresses.

• Switch:

  • Will only have a MAC Address Table; IP addresses are irrelevant for switches in this context.

Packet Sending Process

1. Sending Data from Host A to Host B:

   • Host A adds Layer 3 header (source IP: 11.8.8.11, destination IP: 22.7.7.22).
   • Host A checks ARP table for Router 1's MAC address.
   • ARP Request sent (broadcast) to resolve MAC address.
   • Switch learns MAC mapping from ARP request and floods to all ports.
   • Router 1 replies with ARP response to Host A.
   • Host A now knows Router 1’s MAC address and sends data packet.
   • Packet travels through the network, processed by switches and routers.
   • Router 2 receives the packet and checks its routing table.
   • Router 2 sends an ARP request to find Host B’s MAC address.
   • Host B responds, Router 2 sends the packet to Host B.

2. Response from Host B to Host A:

   • Host B sends packet back to Host A using established MAC and IP information.
   • Process involves similar steps as sending from Host A to Host B, including routing through Router 2 and Router 1.

3. Sending Data from Host A to Host C:

   • Similar process, but Host A now communicates with Host C.
   • Involves ARP requests and responses to resolve MAC addresses at Router 3.
   • Finally, Host C sends a response back to Host A through the established routing.

Conclusion

• Understanding packet flow and the role of MAC, ARP, and routing tables is crucial for a networking engineer.
• Key interview question: "What happens when you type www.google.com?"
  • Involves DNS resolution followed by HTTP requests.

Final Thoughts

• Mastering this material is essential for anyone pursuing a career in networking.
• Encouragement to share experiences and insights gained from the course.