Interior Gateway Protocol (IGP) works by allowing routers within an autonomous system (AS) to exchange routing information and determine the best paths for forwarding packets. IGPs operate within a single administrative domain and are responsible for maintaining routing tables that specify how to reach various network destinations. They use algorithms to calculate routes based on metrics like hop count, bandwidth, or delay. IGPs ensure efficient and reliable packet delivery by adapting to changes in network topology and updating routing tables dynamically. Examples of IGPs include RIP (Routing Information Protocol), OSPF (Open Shortest Path First), and EIGRP (Enhanced Interior Gateway Routing Protocol), each suited for different network sizes and configurations.
IGRP (Interior Gateway Routing Protocol) was a Cisco proprietary routing protocol designed for use within autonomous systems (ASs). It utilized a combination of distance vector and link-state routing algorithms to determine optimal routes to network destinations. IGRP routers exchanged routing updates containing information about reachable networks and associated metrics, such as bandwidth and delay. IGRP supported features like equal-cost load balancing across multiple paths and convergence mechanisms to quickly adapt to network changes. However, IGRP has largely been replaced by more advanced and scalable routing protocols like EIGRP (Enhanced Interior Gateway Routing Protocol) in modern network environments.
The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols used within local area networks and smaller networks. RIP routers periodically broadcast their entire routing tables to neighboring routers, sharing information about available routes and associated hop counts. Upon receiving these updates, routers compare the advertised routes with their own routing table entries. If a shorter path to a destination is found, the router updates its routing table accordingly. RIP operates with a maximum hop count limit of 15, meaning it cannot support networks larger than this limit effectively. RIP routers use split horizon, triggered updates, and route poisoning mechanisms to prevent routing loops and ensure convergence to stable routing tables. However, due to its limitations in handling larger networks and slower convergence times compared to more modern protocols, RIP is less commonly used in larger and more complex network environments, where protocols like OSPF and BGP are preferred.