Routing Fundamentals

Routing Table

A routing table is a database in a router that holds information on possible network paths and how to reach each destination. The table contains routing entries that provide details about the destination network, the next hop (next router on the path), and the route metric, which ranks each path by efficiency.

Routing Protocols

Routing protocols are rules that routers use to communicate routing information with each other, allowing dynamic route updates.

Interior Gateway Protocols (IGP): Used within a single autonomous system (AS), examples include RIP, OSPF, and EIGRP.

Exterior Gateway Protocols (EGP): Used between different autonomous systems, with BGP being the most common example.

Routing protocols enable routers to automatically adjust to changes in the network, such as new devices, broken links, or changed topologies.

Static Routing:

Static routing is manually configured by a network administrator. It’s typically used for simple networks where paths don’t change frequently. While stable, it lacks flexibility and scalability.

Dynamic Routing:

Dynamic routing automatically adjusts paths based on real-time network conditions.

It uses protocols (like RIP, OSPF, BGP) to detect and respond to network changes, making it better for complex or large networks.

Hop

A hop refers to each stop or node a packet makes as it travels from the source to the destination.

Each router a packet passes through is counted as a hop, and the total number of hops can influence path selection, as shorter paths are generally preferred.

Next Hop

The next hop is the immediate next router in the path to the destination.

When a router determines a path, it doesn’t necessarily know the entire route but only the next hop. The next router will repeat this process until the destination is reached.

Autonomous System (AS)

An autonomous system is a network or group of networks under a single administrative domain. ASs are assigned unique AS numbers (ASNs) and can contain numerous routers and networks. Routing within an AS uses IGPs, while routing between ASs uses EGPs like BGP.

Convergence

Convergence is the process of all routers in a network updating their routing tables and reaching a consistent view of the network.

Fast convergence is crucial for network stability and ensures that data packets are routed effectively despite changes, such as a link going down. Some protocols converge faster than others (e.g., OSPF converges faster than RIP).

Responsibilities

✅ Network Engineering

✅ Network Design

✅ Router Configuration

✅ Access Control

✅ Compliance