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BGP Routes
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 software 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.
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