Which two mechanisms remove the iBGP full-mesh requirement for scaling?

Confederations and Route Reflectors are the two primary mechanisms used to scale iBGP and eliminate the full-mesh requirement. Confederations divide a large Autonomous System (AS) into smaller sub-ASs. Each sub-AS maintains a full mesh of iBGP peers internally, but appears as a single AS to external ASs. This reduces the number of iBGP connections required. Route Reflectors allow BGP routers to forward iBGP-learned routes to other iBGP peers within the same AS, breaking the full-mesh rule that all iBGP speakers must peer with each other. Clients peer with the route reflector, and the reflector propagates routes. iBGP-to-eBGP route redistribution is not a scaling mechanism for iBGP; it's about route exchange between different BGP types. BGP peer filtering is for controlling advertised or received routes, not for reducing the number of iBGP peerings.