What is a recommended approach to implement prefix filtering to block bogon prefixes?

• A. Block all prefixes to everyone.
• B. Only use outbound filters.
• C. Disable filtering.
• D. Create dedicated prefix-lists or route-maps for bogons; apply inbound; monitor and adjust; tie with RPKI for validation.

Answer: (D)

Filtering bogon prefixes works best when you actively control what you accept from peers, using inbound checks to drop unallocated or otherwise invalid prefixes before they enter your routing table. The recommended approach is to create dedicated filters—prefix-lists or route-maps—that enumerate bogon prefixes, then apply them inbound on your BGP sessions with peers. This setup prevents you from learning and installing bogus routes. Keep the filters under active maintenance: monitor announcements and bogon lists, adjust as needed, and respond to changes in legitimate allocations. Strengthen this with RPKI validation, which provides cryptographic proof of prefix origination; combining bogon filtering with RPKI helps reject routes that don’t have valid origin validation, reducing hijacks and misconfiguration risks. In contrast, blocking all prefixes would cut connectivity, filtering only outbound won’t protect you from what you receive, and disabling filtering leaves you exposed to bogus routes.