Border Gateway Protocol (BGP)

Border Gateway Protocol (BGP) is used to Exchange routing information for the internet and is the protocol used between ISP which are different ASes.

The protocol can connect together any internetwork of autonomous system using an arbitrary topology. The only requirement is that each AS have at least one router that is able to run BGP and that is router connect to at least one other AS’s BGP router. BGP’s main function is to exchange network reach-ability information with other BGP systems. Border Gateway Protocol constructs an autonomous systems’ graph based on the information exchanged between BGP routers.

Characteristics of Border Gateway Protocol (BGP):

  • Inter-Autonomous System Configuration: The main role of BGP is to provide communication between two autonomous systems.
  • BGP supports Next-Hop Paradigm.
  • Coordination among multiple BGP speakers within the AS (Autonomous System).
  • Path Information: BGP advertisement also include path information, along with the reachable destination and next destination pair.
  • Policy Support: BGP can implement policies that can be configured by the administrator. For ex:- a router running BGP can be configured to distinguish between the routes that are known within the AS and that which are known from outside the AS.
  • Runs Over TCP.
  • BGP conserve network Bandwidth.
  • BGP supports CIDR.
  • BGP also supports Security.

Functionality of Border Gateway Protocol (BGP):
BGP peers performs 3 functions, which are given below.

  1. The first function consist of initial peer acquisition and authentication. both the peers established a TCP connection and perform message exchange that guarantees both sides have agreed to communicate.
  2. The second function mainly focus on sending of negative or positive reach-ability information.
  3. The third function verifies that the peers and the network connection between them are functioning correctly.

BGP Route Information Management Functions:

  • Route Storage:
    Each BGP stores information about how to reach other networks.
  • Route Update:
    In this task, Special techniques are used to determine when and how to use the information received from peers to properly update the routes.
  • Route Selection:
    Each BGP uses the information in its route databases to select good routes to each network on the internet network.
  • Route advertisement:
    Each BGP speaker regularly tells its peer what is knows about various networks and methods to reach them.


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