Which criterion in BGP route selection causes EBGP routes to be preferred over IBGP routes?

• A. Prefer EBGP route over IBGP
• B. Shortest AS path
• C. Highest weight
• D. Lowest MED

Answer: (A)

BGP’s route selection explicitly prioritizes routes learned from external neighbors over those learned from internal peers when comparing two paths to the same prefix. This rule, often referred to as eBGP over iBGP, means that if one route is learned via an external BGP session and another via an internal BGP session, the EBGP route is chosen. The purpose is to favor paths that leave the AS for interdomain routing, providing stability and alignment with external routing policies. After this preference is resolved, other factors like AS path length, origin, and MED come into play, but they do not override the explicit preference for EBGP routes over IBGP.