Routing Protocol Theory

Routing protocols are a family of network protocols that allow routers to exchange information about network topology and the best path to reach a destination network. Routing protocols play a crucial role in enabling communication between devices across networks, and they are essential in enabling the internet to function.

There are two main types of routing protocols: interior gateway protocols (IGPs) and exterior gateway protocols (EGPs).

IGPs are used to exchange routing information between routers within a single autonomous system (AS). An AS is a collection of networks that are under a common administrative domain. Examples of IGPs include Routing Information Protocol (RIP), Open Shortest Path First (OSPF), and Intermediate System to Intermediate System (IS-IS).

EGPs, on the other hand, are used to exchange routing information between routers in different autonomous systems. Examples of EGPs include Border Gateway Protocol (BGP) and Exterior Gateway Protocol (EGP).

Routing protocols use a variety of metrics to determine the best path to a destination network. The most common metrics used by routing protocols include hop count, bandwidth, delay, reliability, and load. Routing protocols can be classified based on their behavior as distance vector protocols, link state protocols, or hybrid protocols.

Distance vector protocols, such as RIP, advertise the entire routing table to their neighbors periodically. Each router maintains a distance vector, which is a list of the distances to all known networks. These protocols have a simple design and are easy to implement, but they are prone to routing loops and slow convergence times.

Link state protocols, such as OSPF and IS-IS, advertise information about the state of the links in the network. Each router constructs a complete map of the network topology and calculates the shortest path to each destination network. These protocols have faster convergence times and are more scalable than distance vector protocols, but they require more processing power and memory.

Hybrid protocols, such as Enhanced Interior Gateway Routing Protocol (EIGRP), combine the best features of distance vector and link state protocols. These protocols use distance vector algorithms to advertise information about their directly connected networks and link state algorithms to advertise information about the rest of the network. They are faster and more scalable than pure distance vector protocols, but they require more memory and processing power than pure link state protocols.