Lecture on Router Traffic Forwarding and Static Routing

Introduction to Router Traffic Forwarding

• Routers' Role: Forward traffic between one IP subnet and another.
• Simplified Process: The router performs a series of steps:
  • Identify destination IP address in incoming packets.
  • Determine the best route using tables.
  • Send packets directly if the subnet is connected, else determine the next hop.
  • Use routing tables to troubleshoot and validate packet paths.

Understanding Routing Tables

• Directly Connected Subnets: If a packet's destination is a directly connected subnet, it is sent there.
• Next Hop Determination: For non-local subnets, routers find the next hop.
• Routing Table Utilization: Essential for packet routing; packets with unknown destinations are discarded.

Network Diagram Example

• Three routers with different subnets.
  • Router 1:
    • Connected to subnets: 10.10.10.0/24, 10.10.40.0/24, 10.10.50.0/24.
    • Doesn't know about subnets on the other side of Router 2 and Router 3.
    • Example scenario: Sam can't reach Jack due to missing routes in Router 1's table.

Static Routing

• Definition: Manually creating a routing table.
• Advantages:
  • Quick to configure in small networks.
  • No overhead from dynamic routing protocols (CPU cycles, memory).
• Use Cases: Common in remote sites with a single internet connection (stub networks).
• Security: No dynamic changes make it more secure, but less adaptable.

Challenges with Static Routing

• Scalability: Impractical for large networks with many routers.
• Configuration Mistakes: Risk of routing loops and errors if misconfigured.
• Manual Updates Required: Network changes necessitate manual routing table updates.

Configuring Static Routes

• Router 1 Configuration Example:
  • Direct traffic for unknown subnets through specific routes.
  • Example Commands:
    • Route for 10.10.20.0/24 via 10.10.40.2 (Router 2).
    • Route for 10.10.30.0/24 via 10.10.50.2 (Router 3).
  • Result: Router 1 efficiently forwards packets to the correct subnet via configured static routes.