Which of the following is an example of a non-transit AS?

• A. A data center
• B. An Internet Exchange Point
• C. A large ISP
• D. An organization that is multihoming with two ISPs

Answer: (D)

In BGP, an Autonomous System is classified by whether it forwards traffic for other networks. A non-transit AS does not provide transit services to third parties; it carries traffic only for its own networks and for customers it directly connects to, using upstream providers for reachability but not as a transit path for others. An organization that is multihomed to two ISPs fits this perfectly: it connects to multiple providers for redundancy and access, but it does not act as a route for traffic between other networks. The other options don’t fit as clearly: a data center may host networks and could be involved in transit if it offers such services; an Internet Exchange Point mainly enables peering rather than providing transit; a large ISP is typically a transit provider, not a non-transit AS.