An overview of key interior and exterior gateway routing protocols.
Dynamic routing protocols are classified into two main categories: Interior Gateway Protocols (IGPs) and Exterior Gateway Protocols (EGPs). IGPs are used for routing within a single autonomous system (AS), which is a network under a single administrative control (like a corporation or a university). EGPs are used for routing between different autonomous systems. Routing Information Protocol (RIP) is one of the oldest IGPs. It's a distance-vector protocol that uses hop count (the number of routers a packet must pass through) as its metric. It's simple to configure but suffers from slow convergence and is limited to small networks (maximum of 15 hops). Open Shortest Path First (OSPF) is a much more modern and widely used IGP. It's a link-state protocol. Each router running OSPF builds a complete map of the network topology and then uses the Shortest Path First (SPF) algorithm to calculate the best, loop-free paths. OSPF is efficient, scalable, and converges quickly after a network change, making it suitable for large enterprise networks. Border Gateway Protocol (BGP) is the one and only EGP used on the global internet. Its job is to exchange routing and reachability information between different autonomous systems. Unlike IGPs that focus on finding the fastest path, BGP makes routing decisions based on complex path attributes and policies defined by network administrators. BGP is what holds the internet together, ensuring that traffic can be routed from an AS in one country to an AS in another.