iBGP’s full mesh requirement refers to logical BGP session establishment, not physical network design. As long as reachability exists between iBGP peers (through an IGP like OSPF or IS-IS), iBGP sessions can be established regardless of physical topology (ring, star, partial mesh, etc.).
Key CCDE v3.1 design principles:
Logical iBGP mesh ≠ physical mesh requirement.
Physical topologies can be optimized independently of iBGP peering structure.
Control plane designs like route reflectors or confederations further optimize scalability without changing physical topology.
Why other options are incorrect:
B: iBGP works on any topology where IP reachability exists.
C: Physical full mesh is unnecessary for iBGP.
D: iBGP functions over any IGP-provided reachability domain, including rings.
