1. What is Routing in Networking?

Routing is the process of selecting a path for data packets to travel from the source device to the destination device across networks.

• Done by routers (network devices).

• Uses routing tables and routing protocols.

• Works at the Network Layer (Layer 3) of the OSI Model.

2. How Routing Works

When you send data to another device:

1. Your device creates a packet with the destination IP.

2. The packet goes to your default gateway (router).

3. The router checks its routing table.

4. The router forwards the packet toward the next hop (another router or destination).

5. The process repeats until the packet reaches the destination.

3. Example of Routing

Scenario:
You want to access www.example.com from your laptop.

• Laptop IP: 192.168.1.10

• Router IP: 192.168.1.1

• Website IP: 203.0.113.5

Step-by-Step Process

1. Laptop sends the packet to the router (default gateway).

2. Router checks its routing table.

3. If the destination (203.0.113.5) is outside the local network, the router forwards it to the ISP router.

4. ISP router forwards the packet across multiple routers on the internet.

5. Finally, the packet reaches the destination server and the response travels back the same way.

4. Types of Routing

A. Static Routing

• Manually configured by network administrators.

• Best for small networks.

• No automatic updates if the network changes.

Example Command (Cisco):

Router(config)# ip route 192.168.2.0 255.255.255.0 192.168.1.2

This means:
To reach 192.168.2.0, send packets to next hop 192.168.1.2.

B. Dynamic Routing

• Uses routing protocols to update routes automatically.

• Best for large, complex networks.

Popular Routing Protocols:

C. Default Routing

• Used when a router doesn’t know the route.

• Configures a default path for unknown destinations.

Example Command (Cisco):

Router(config)# ip route 0.0.0.0 0.0.0.0 192.168.1.1

Meaning:
If the destination is unknown, send all packets to 192.168.1.1.

5. Routing Table

Routers store routes in a routing table, which contains:

• Destination network

• Subnet mask

• Next hop (gateway)

• Interface

• Metric (cost)

Example Routing Table

6. Diagram of Routing

 [Laptop]
 192.168.1.10
      |
      | (Private Network)
      |
 [Router A]
 192.168.1.1
 Public IP: 103.45.21.5
      |
      | Internet
      |
 [Router B - ISP]
      |
      | -----> Routing via multiple routers
      |
 [Web Server]
 203.0.113.5

7. Summary of Routing