3.2 Routing Information Bases

The Routing Information Base (RIB) within a BGP speaker consists of three distinct parts:

1. Adj-RIBs-In: The Adj-RIBs-In store routing information that has been learned from inbound UPDATE messages. Their contents represent routes that are available as an input to the Decision Process.

2. Loc-RIB: The Loc-RIB contains the local routing information that the BGP speaker has selected by applying its local policies to the routing information contained in its Adj-RIBs-In.

3. Adj-RIBs-Out: The Adj-RIBs-Out store the information that the local BGP speaker has selected for advertisement to its peers. The routing information stored in the Adj-RIBs-Out will be carried in the local BGP speaker's UPDATE messages and advertised to its peers.

In summary, the Adj-RIBs-In contain unprocessed routing information that has been advertised to the local BGP speaker by its peers; the Loc-RIB contains the routes that have been selected by the local BGP speaker's Decision Process; and the Adj-RIBs-Out organize the routes for advertisement to specific peers by means of the local speaker's UPDATE messages.

Although the conceptual model distinguishes between Adj-RIBs-In, Loc-RIB, and Adj-RIBs-Out, this neither implies nor requires that an implementation must maintain three separate copies of the routing information. The choice of implementation (for example, 3 copies of the information vs 1 copy with pointers) is not constrained by the protocol.