How the BGP works

BGP (Border Gateway Protocol) is a routing protocol mainly used by Internet Service Providers (ISPs) to provide Internet access services. A key feature of BGP is its ability to scale to handle vast amounts of Internet route information, allowing for flexible control over optimal route decisions.

This section describes how BGP works and how to configure it on network devices such as Cisco routers.

BGP Basic Configuration and Verification Commands

The basic configuration process for BGP consists of the following three steps
1. Enable the BGP routing process
2. Configuring the Neighbor
3. Generating BGP routes

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BGP Neighbor Status

The states of BGP neighbors are Idle/Conect/Active/OpenSent/OpenConfirm/Established. This section describes the states of these BGP neighbors.

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BGP Neighbor Authentication

BGP neighbor authentication allows you to establish a neighbor only with a legitimate BGP router.
This section describes the configuration commands for neighbor authentication and a simple configuration example.

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BGP Well Known Mandatory Attributes

There are various path attributes added to the BGP route. Well Known Mandatory attributes are always added to a BGP route.

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BGP local-as

local-as allows you to establish a BGP neighbor for a specific EBGP neighbor with an AS other than the original AS number and exchange routes.
This section describes the operation of BGP local-as and the configuration commands.

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bgp fast-external-fallover

bgp fast-external-fallover is a feature that immediately drops the neighbor if the interface used for the BGP connection goes down.

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BGP Prefix Limitation

If a large amount of route information (prefix) is sent due to a neighbor's misconfiguration, for example, the load on the router may increase and have an adverse effect on the router. Therefore, the neighbor maximum-prefix command is used to limit the number of route information received from BGP neighbors.

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