BGP Routes Overview
A BGP route consists of the following:
- A destination, described as an IP address prefix.
- Information that describes the path to the destination,
including the following:
- AS path, which is a list of numbers of the ASs that a route passes through to reach the local router. The first number in the path is that of the last AS in the path—the AS closest to the local router. The last number in the path is the AS farthest from the local router, which is generally the origin of the path.
- Path attributes, which contain additional information about the AS path that is used in routing policy.
BGP peers advertise routes to each other in update messages.
BGP stores its routes in the Junos OS routing table. The routing table stores the following information about BGP routes:
- Routing information learned from update messages received from peers
- Local routing information that the BGP system selects by applying local policies to routes received in update messages
- Information that the BGP system selects to advertise to its BGP peers in the update messages it sends
For each prefix in the routing table, the routing protocol process selects a single best path, called the active path. The algorithm for determining the active path is described in How the Active Route Is Determined.
