BGP can be likened to the GPS system of the internet, overseeing the transmission of data across the vast digital landscape. It serves as a guiding force, directing information through the most efficient pathways, much like how a GPS navigates the best route for a vehicle. For instance, when you send a text message with images to a friend abroad through a messaging app, the data traverses various countries before reaching its intended recipient. BGP plays a pivotal role in orchestrating this intricate journey, ensuring that your data takes the most effective route across diverse networks.
In this article, we delve into the inner workings of BGP, shedding light on its mechanisms and functionalities. By understanding the nuances of BGP, you’ll gain insight into how your data can seamlessly and reliably navigate the intricate network of the internet.
Despite the seamless nature of our daily interactions with the internet, its functionality hinges on a sophisticated infrastructure that enables the swift transfer of data. This infrastructure encompasses a complex mesh of fiber optic cables spanning countries and continents, complemented by cellular towers and, in remote regions, satellite transmission.
Below this tangible foundation, diverse industries coordinate complex procedures to leverage the complete capabilities of this infrastructure. Among these procedures, routing emerges as a pivotal and fundamental function, enabled by routing protocols. Routing entails the systematic transfer of data packets from their origin to their designated endpoint. At the crux of internet routing resides the Border Gateway Protocol (BGP), which serves as the focal point of discussion in this article.
When applying the aforementioned attributes to incoming routes from BGP neighbors, a clear routing policy emerges. This process involves the consideration of multiple attributes in a sequential manner, based on their respective numeric values. Within a routing policy, distinct numerical values can be allocated to different sets of routes, guided by various BGP attributes. For instance, one set of routes might be assigned a Local Preference value of 150 to indicate high priority, while another set could be designated with a Weight value of 200. These numerical values serve as criteria for the routing algorithm to determine the path that data packets should traverse.
If multiple routes possess different Weight values, the route with the highest Weight is chosen, and the process terminates there. Local Preference, AS Path Length, and other attributes are not taken into consideration for these routes.
However, if all routes share the same Weight value or if Weight is unset (which might occur with routers from vendors other than Cisco, as Weight is specific to Cisco,) the routing decision proceeds to the next attribute in the hierarchy, which is Local Preference. At this stage, the route with the highest Local Preference is selected, and the lower-priority attributes are disregarded.
Hence, when the routing policy assigns a Local Preference value of 150 and a Weight value of 200, it’s not about one being inherently superior to the other. Instead, it hinges on which attribute will be prioritized based on the hierarchical order. Weight takes precedence over Local Preference, and if Weight alone can determine the best route, Local Preference doesn’t come into play.
Throughout this article, we have explored the indispensable role of the Border Gateway Protocol (BGP) in orchestrating the routes and packets across the internet. From its initial inception with just a few thousand routes in public networks to the present day with over 930,000 routes, BGP’s extraordinary scalability mirrors the expansive growth of the internet and our global interconnectedness. As technology continues to advance and the world becomes more interconnected, BGP remains a steadfast, efficient, and reliable component of our digital infrastructure.