What is the single type of Exterior Gateway Protocol (EGP)?

The correct answer is Path Vector because this is the only formal type of Exterior Gateway Protocol (EGP) used specifically for routing between different autonomous systems on the Internet. The Path Vector protocol provides a method for maintaining the path information that gets updated dynamically as the network topology changes. The most well-known implementation of the Path Vector protocol is the Border Gateway Protocol (BGP), which is essential for exchanging routing information among different autonomous systems on the Internet.

Path Vector protocols work by maintaining a path that a routing update has taken through the network, which allows routers to make better decisions about the best routes while avoiding routing loops. This feature is especially important in a large, decentralized environment like the Internet, where various administrators manage different autonomous systems independently.

In contrast, the other options listed (Distance Vector, Link State, and Static Routing) refer to Interior Gateway Protocols (IGPs) that are used within a single autonomous system. Distance Vector and Link State protocols are methods for routing within a single administrative domain, while Static Routing represents routes that are manually configured and do not change dynamically. Dismissing these as EGPs is crucial for understanding the role of Path Vector protocols in the wider Internet routing ecosystem.