In a full-mesh iBGP design, every router must establish and maintain a BGP session with every other router. As the number of routers increases, the number of BGP sessions and the amount of BGP processing increases exponentially. This leads to high CPU utilization, especially in devices with limited processing capabilities, such as distribution routers.

Themost cost-effectiveandscalablesolution in this scenario is toimplement route reflectors (RRs)on the two core routers. Route reflectors significantly reduce the number of iBGP peerings required, eliminating the full mesh requirement by allowing the distribution routers (RR clients) to establish a single iBGP session with the route reflector. The route reflector handles route advertisement to other RR clients, thereby reducing overhead on the distribution routers.

This solution adheres to CCDE v3.1 design principles for:

Optimizing control plane scalability

Reducing unnecessary CPU load from control protocols

Ensuring a maintainable and scalable enterprise BGP deployment

Why the other options are incorrect:

BandD(Increasing memory): Addresses only hardware capacity without solving the root cause (BGP scaling issue).

C(Using eBGP): Misaligned with enterprise internal network design; eBGP adds complexity in route policy and administrative boundaries.

E(Increasing bandwidth): Bandwidth does not alleviate CPU overhead caused by BGP processing.

Implementing route reflectors aligns with both scalability and cost-efficiency goals as prescribed in the CCDE v3.1 methodology.