An Interior Gateway Protocol (IGP) is a type of routing protocol used within an autonomous system (AS) to facilitate the exchange of routing information between routers. An AS is essentially a network or a group of networks under the control of a single administrative entity, such as a company, organization, or Internet Service Provider (ISP). IGPs are designed to enable routers within the same AS to share information about IP routes efficiently, thereby optimizing the routing of data packets within the AS.
IGPs can be categorized into two main types: distance-vector routing protocols and link-state routing protocols. Distance-vector protocols determine the best path to a destination based on the distance to that destination, where the distance is typically measured in terms of hops. Link-state protocols, on the other hand, build a complete map of the network’s topology to route packets based on the state of the links (connections) between routers. Some IGPs also exhibit characteristics of both distance-vector and link-state protocols and are referred to as advanced distance vector or hybrid protocols.
Examples of IGP Protocols
- Routing Information Protocol (RIP): A distance-vector protocol that uses hop count as its metric.
- Open Shortest Path First (OSPF): A link-state protocol that uses the Shortest Path First (SPF) algorithm to determine the most efficient route.
- Intermediate System to Intermediate System (IS-IS): A link-state protocol similar to OSPF, used mainly in large networks.
- Enhanced Interior Gateway Routing Protocol (EIGRP): A Cisco proprietary protocol that combines features of both distance-vector and link-state protocols.
Key Characteristics of IGPs
- Operate within a single AS: IGPs are used for routing within an autonomous system, which is under the control of a single administrative entity.
- Dynamic route update: IGPs dynamically update routing information to adapt to changes in the network topology, ensuring efficient data routing.
- Examples include RIP, OSPF, IS-IS, and EIGRP: These protocols are among the most commonly used IGPs, each with its own set of features and operational characteristics.
Contrast with Exterior Gateway Protocols (EGPs)
While IGPs are used for routing within an autonomous system, Exterior Gateway Protocols (EGPs) are used for routing between different autonomous systems. The most widely used EGP is the Border Gateway Protocol (BGP), which is essential for routing data across the internet, connecting different ASes.
In summary, IGPs play a crucial role in the internal routing of data within an autonomous system, optimizing the path that data packets take to reach their destination. By dynamically updating routing information, IGPs help maintain efficient and reliable network operations within an AS.