Which type of routing protocol is BGP best described as?

Border Gateway Protocol (BGP) is best described as a path vector protocol. This designation is critical because it illustrates how BGP operates. Unlike link state protocols, which use the state of network links to calculate the best path to a destination, or distance vector protocols that rely on the distance to the destination and direction (or vector) to reach that destination, BGP employs a different approach.

In path vector protocols, BGP maintains the complete path information that gets updated dynamically as the routing information is exchanged between routers. Each BGP router keeps track of the path that the routing information has traversed, which helps prevent routing loops and manage the complexities of paths taken across multiple autonomous systems (AS). This characteristic of tracking the entire path, rather than just a single metric like distance or link state, is what sets BGP apart and makes it particularly suited for inter-domain routing on the internet.

Understanding BGP as a path vector protocol also highlights its ability to provide policy-based routing decisions, allowing network administrators to determine the best path based on a series of attributes, including AS path, next-hop, and other metrics.