Final answer:
BGP, or Border Gateway Protocol, is the correct answer for an Exterior Gateway Protocol among the options provided. IS-IS and RIP are Interior Gateway Protocols, and IPv6 is a version of Internet Protocol, not a routing protocol.
Step-by-step explanation:
The correct answer to which of the following is an Exterior Gateway Protocol (EGP) is a. BGP. BGP stands for Border Gateway Protocol, and it is indeed an Exterior Gateway Protocol used to exchange routing information between different autonomous systems on the internet. Unlike BGP, options b. IS-IS (Intermediate System to Intermediate System) and c. RIP (Routing Information Protocol) are both Interior Gateway Protocols (IGPs), which are used within a single autonomous system. Option d. IPv6 is actually a version of the Internet Protocol and is not a routing protocol at all.