What is the difference between interior gateway protocols and exterior gateway protocols?

The main difference between interior gateway protocols (IGPs) and exterior gateway protocols (EGPs) lies in the scope and purpose of their routing operations within a network.

Interior Gateway Protocols (IGPs)

IGPs are used for routing within an autonomous system (AS) or an internal network. They help routers exchange routing information and make routing decisions within the boundaries of the AS. Some common IGPs include Routing Information Protocol (RIP), Open Shortest Path First (OSPF), and Intermediate System to Intermediate System (IS-IS). IGPs are typically used to facilitate communication and routing between routers within a single organization or network.

Key characteristics of IGPs:

1. Used for routing within a single autonomous system or internal network.
2. Exchange routing information between routers within the same network domain.
3. Typically focus on factors such as shortest path or link cost when making routing decisions.
4. Examples include RIP, OSPF, IS-IS.

Exterior Gateway Protocols (EGPs):

EGPs, on the other hand, are used for routing between autonomous systems (ASes) or different networks operated by separate organizations. Their primary purpose is to exchange routing information between different ASes on the internet. The most widely used EGP is the Border Gateway Protocol (BGP), which enables routers to exchange routing information across multiple networks and make routing decisions that span across AS boundaries.

Key characteristics of EGPs:

1. Used for routing between autonomous systems or different networks.
2. Exchange routing information between routers in different ASes.
3. Focus on factors such as AS path, policies, and external reachability when making routing decisions.
4. Examples include Border Gateway Protocol (BGP).

In summary, IGPs are employed for internal routing within a network or autonomous system, while EGPs are used for routing between autonomous systems or different networks. The scope, routing decision factors, and the protocols used are the primary distinctions between these two types of gateway protocols.