Route reflection adds hierarchy to IBGP. The basic way this works is that some routers in an AS readvertise their routes within the same AS so that all routers within the AS know about all routes on the network. A route reflector is a router whose BGP configuration enables readvertising of routes between IBGP neighbors. A route reflector client is a device that uses a route reflector to readvertise its routes to the entire AS. It also relies on that route reflector to learn about routes from the rest of the network.