What mechanism is commonly used to prevent route leaks within an AS?

• A. Disabling all iBGP sessions.
• B. Using only eBGP sessions.
• C. Implementing a full iBGP mesh or using route reflectors.
• D. Relying on manual config without filters.

Answer: (C)

Within an AS, iBGP has a rule that routes learned via iBGP are not re-advertised to other iBGP peers. This helps prevent routing loops, but it also means you must ensure every iBGP speaker learns the same routes. The common ways to achieve this without creating an unwieldy mesh are to deploy a full iBGP mesh (every iBGP speaker peers with every other) or to use route reflectors. A full mesh guarantees that a route learned on one iBGP peer is directly shared with all others, eliminating leaks. Route reflectors reduce the number of required iBGP sessions by letting a central reflector receive routes from one or more clients and reflect them to other clients, while still preserving loop-free propagation. This combination is the standard approach to prevent internal route leaks within an AS.