Networking - Routing: The Basics

Routing is the process of determining the path that data packets take from a source device to a destination device across networks. Routers make these decisions using routing tables, which list available paths. Routing can be classified into static and dynamic methods.

1. Static Routing

Definition:
Static routing is a routing method in which network administrators manually configure routes in a router’s routing table. These routes do not change unless the administrator modifies them.

Key Features:

• Routes are manually entered using router configuration commands.

• Best for small or stable networks where paths rarely change.

• No automatic adaptation to network failures or topology changes.

Advantages:

1. Simplicity: Easy to configure in small networks.

2. Predictability: The path taken by packets is fixed and known.

3. Low Resource Usage: Does not require CPU or memory for routing algorithms.

Disadvantages:

1. Lack of Scalability: Difficult to maintain in large networks with frequent changes.

2. No Fault Tolerance: If a link fails, packets cannot be rerouted automatically.

3. Manual Updates Required: Network changes must be manually reflected in the routing table.

Example Scenario:
A small office network with a single router connecting to the internet may use a static route:

• ip route 0.0.0.0 0.0.0.0 192.168.1.1
  Here, all unknown traffic is sent to the ISP router at 192.168.1.1.

2. Dynamic Routing

Definition:
Dynamic routing uses protocols to automatically discover network paths and maintain up-to-date routing tables. Routers exchange information about network topology and adapt to changes in real time.

Key Features:

• Uses routing protocols like RIP, OSPF, EIGRP, BGP.

• Automatically recalculates routes when network changes occur (link failure, new networks, etc.).

• Maintains multiple possible paths to optimize routing.

Advantages:

1. Automatic Updates: Changes in the network topology are detected and routing tables updated automatically.

2. Scalability: Works well in large, complex networks.

3. Fault Tolerance: If a path fails, routers find alternative routes without manual intervention.

Disadvantages:

1. Complexity: Requires knowledge of routing protocols and configurations.

2. Resource Usage: Consumes more CPU, memory, and bandwidth for routing updates.

3. Possible Instability: Incorrect configurations or rapid changes can cause routing loops or convergence delays.

Example Scenario:
In a large enterprise with multiple offices connected via WAN links:

• Routers use OSPF to automatically share topology information.

• If a link between two offices fails, traffic is dynamically rerouted over an alternate path without administrator intervention.

Comparison Table: Static vs. Dynamic Routing

Summary

• Static routing is simple, predictable, and resource-efficient, but inflexible and not fault-tolerant.

• Dynamic routing is adaptive, scalable, and fault-tolerant, making it ideal for modern networks, though it requires more resources and configuration expertise.

In practice, many networks use a hybrid approach, with static routes for fixed paths (like default gateways) and dynamic routing for complex, changing networks.