Name the three well-known mandatory attributes.

• A. AS path, Next Hop, Origin
• B. Local Preference, Atomic Aggregate, Community
• C. Aggregator, Community, Next Hop
• D. Origin, Local Preference, AS Path

Answer: (A)

In BGP, three attributes are required in every route update because they provide essential, universally-needed information about how the route arrived and how to reach it. The AS_PATH lists the sequence of autonomous systems the route has traversed. This helps prevent routing loops and supports policy decisions because you can see the path the update took across the Internet. The NEXT_HOP tells you the IP address of the next router to reach the destination; without this, a router wouldn’t know where to forward the packets. The ORIGIN attribute indicates how the route was learned—whether from an internal IGP, an external EGP, or if the origin is incomplete—so a router can make informed decisions when comparing multiple paths.

The other attributes mentioned—Local Preference, Atomic Aggregate, Community, and Aggregator—are useful for shaping routing policies and route handling, but they’re not required to be present on every update. Local Preference is a local policy knob within an AS, Atomic Aggregate and Aggregator relate to how routes are summarized or who performed aggregation, and Community is a tagging mechanism for policy purposes.