June 8, 2021
Border Gateway Protocol (BGP) is a main dynamic application layer protocol used for packet routing between autonomous systems on the Internet.

How it works

BGP routers exchange information on routing availability with each other. They also advertise different network attributes. This data helps to generate the most optimal routing paths and to configure routing rules.

BGP sends data based on IP addresses. With BGP it is impossible to create routing rules which would take into account applications’ data or a packet sending network. Therefore, a special policy-based routing (PBR) is needed to direct packets based on additional criteria.

Routing process

The routing process is a step-by-step process within autonomous systems. All protocol policies apply to external autonomous systems. When choosing, companies usually give priority to corporate instructions over technical specifications for certain routers. For example, using one of them might be more reasonable. That is why policies configured with modified attributes, advertised routes, and applied filters are important for BGP operation.

Transmitted data and information

Routing data is transmitted with important information—the list of autonomous systems through which the packets have been routed. This information allows BGP to understand where a router is located with respect to the systems and to eliminate routing loops. This data might be used to configure BGP policies.

When choosing path routers that use interior dynamic routing protocols usually compare certain technical characteristics, for example, link bandwidth capacity.

It’s worth noting that BGP’s main purpose is only routing. The packet delivery as such is ensured by the TCP.

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