BGP
BGP is the EGP protocol that is mostly used between the two
autonomous system and the preference scenario when we have to apply that protocol
is multihoming. Border gateway protocol is the protocol that is known as the
path vector protocol and this protocol is also called the advanced distance
vector routing protocol. Border gateway protocol has the two flavors EBGP and
IBGP. The flavor that is configure between the two different autonomous system
is known as EBGP and other flavor IBGP that is configure in same autonomous system.
So, this protocol is work on the basis of the attributes and this protocol select
the route on the base of multiple points.
BGP Process of Route Selection
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| Fig 1: BGP Process of Route Selection |
The process of the selection of the route in the border
gateway protocol is called the BGP route selection process and that process is
based on the multiple factors that are very important to calculate best and
valid path. Border gateway protocol is the protocol that has the multiples
attributes and all the routing is based on those attributes for the calculation
of the best path. Border gateway protocol best path selection is based on the value
of the BGP’s attributes that update consists and the other border gateway
protocol configurable factors. Border gateway protocol is the protocol that considers
the only synchronized routes with no Autonomous system loops and next hops
address that is the valid.
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| Fig 2: BGP Process of Route Selection |
Following are the points that are include in the process of
the route selection:
- Favor the route with the highest weight.
- Favor the route with the highest local preference.
- Favor the aggregates routes that are also known as the locally generated routes.
- Favor the routes with the shortest Autonomous system path.
- Favor the route with lowest origin attribute.
- Favor the route with lowest MED attribute.
- Favor the routes that is EBGP as compared to the IBGP route.
- Favor the route by the nearer IGP peer.
- Favor the oldest Exterior border gateway protocol route.
- Favor the route with the lowest neighbor Border gateway protocol router ID value.
- Favor the route with the lowest neighbor IP address.
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