What is the risk of not filtering eBGP sessions properly?

• A. Not filtering eBGP sessions has no security impact.
• B. Exposure to bogus routes, leaks, and potential hijacks.
• C. Increased bandwidth efficiency.
• D. Faster convergence.

Answer: (B)

Not filtering eBGP sessions properly allows you to accept and propagate routes you shouldn’t trust. In BGP, routers rely on policies from peers to decide which routes to accept and advertise, but there isn’t automatic verification of the route's legitimacy. If you don’t filter, a peer could advertise prefixes it doesn’t own or routes that don’t belong in your routing table. That can lead to bogus routes being accepted, leaked to other peers, or even hijacked where traffic is misdirected or intercepted. The consequences include loss of reachability, traffic redirection through adversaries, and potential disruption for customers. Filtering, origin validation (like RPKI/ROA), and careful route policies help prevent these problems. Filtering does not increase bandwidth or speed up convergence; in fact, it protects against misrouting and instability that can cause outages or churn.