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| 9.5 |  | The BGP Routing Process |
| 9.5.1 |  | An overview of the BGP routing process |

This section describes the process that BGP uses to make routing decisions. Routes are exchanged between BGP peers by way of update messages. BGP routers receive the update messages, perform some policies or filters on the updates, and then pass the routes on to other BGP peers.

The Cisco implementation of BGP keeps track of all BGP updates in a BGP table separate from the IP routing table. In case multiple routes to the same destination exist, BGP does not flood its peers with all those routes. Instead, BGP picks only the best route and sends it to the peers. In addition to passing along routes from peers, a BGP router may originate routing updates to advertise networks that belong to its own AS. Valid local routes originated in the system and the best routes learned from BGP peers are then installed in the IP routing table. The IP routing table is used for the final routing decision.

The following sections detail the BGP routing process, implementing BGP routing policy, controlling BGP routing with attributes, and handling the BGP decision process.