Name three ways to filter BGP routing updates

• A. Access lists only
• B. Prefix lists only
• C. Route maps only
• D. Filter lists, prefix lists and route maps

Answer: (D)

Filtering BGP routing updates can be done in multiple ways, each giving different control over what updates you accept or advertise. Access lists (often used as filter lists or distribute-lists) let you permit or deny updates based on criteria like prefixes or AS paths. Prefix lists provide precise matching of specific prefixes or ranges, which is great for tightly controlling which routes are allowed. Route maps offer the most flexibility: they can match on several attributes (prefix, AS path, communities, etc.) and perform actions such as denying, permitting, or altering attributes on matched routes.

Because these methods exist and are used in combination to tailor BGP policies, the best answer includes all three categories: filter lists, prefix lists, and route maps. Each plays a different role, and using them together enables robust and granular BGP filtering.