https://tools.ietf.org/html/rfc2796
Currently in the Internet, BGP deployments are configured such that all BGP speakers within a single AS must be fully meshed and any external routing information must be re-distributed to all other routers within that AS. For n BGP speakers within an AS that requires to maintain n*(n-1)/2 unique IBGP sessions. This "full mesh" requirement clearly does not scale when there are a large number of IBGP speakers each exchanging a large volume of routing information, as is common in many of todays internet networks.
This scaling problem has been well documented and a number of proposals have been made to alleviate this [2,3]. This document represents another alternative in alleviating the need for a "full mesh" and is known as "Route Reflection". This approach allows a BGP speaker (known as "Route Reflector") to advertise IBGP learned routes to certain IBGP peers. It represents a change in the commonly understood concept of IBGP, and the addition of two new optional transitive BGP attributes to prevent loops in routing updates.
