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How did you get here? BGP explained

The Border Gateway Protocol, or BGP in short, is the foundation of Internet routing. Routing defines the path of Internet traffic in a network and between networks. Like GPS – helping you to find the best route to get from A to B – BGP is instrumental finding the most suitable route for traffic and data, for example, how you got from your device to this article on our website.  

The network of networks 

The Internet is a network of networks, so called Autonomous Systems (AS) which are connected to each other. These networks are run by thousands of commercial and non-commercial entities such as Internet Service Providers (ISPs), Content Delivery Networks, corporations, universities etc. Every Autonomous System is uniquely identified and represented by an Autonomous System Number (ASN).  

Each AS has rules and policies for how traffic is handed within network. The public IP addresses of your device are part of the AS of your ISP, and the ISP handles the traffic to and from any other device within their network. But if you are trying to access a site beyond the AS, then it is probably BGP that gets involved. 

BGP makes the Internet operate efficiently 

When there were only a few networks, connecting them was quite simple. But with more and more networks – as of April 2021, there are about 800,000 ASNs – and more and more Internet traffic, there needs to be a system for how the traffic is being exchanged. Enter BGP which manages how data gets delivered between networks and makes it possible for the Internet to operate efficiently. 

AS networks have routers running BGP that advertise or announce to their neighbors (or peers) the prefixes of IP addresses that they can deliver traffic to. These routers then use decision-making algorithms and policies established in AS-peering agreements to analyze the attributes they receive via the prefix announcements and choose which peer is best to send each packet of data to at any given time. Generally speaking, the path with the fewest number of network hops – number ASes the data has to go through before reaching its destination – is selected. Once the data moves across an AS and reaches another BGP router connected to a different AS, the process repeats itself until the data reaches the AS where the destination site is located. 

Learn more about BGP in our webinar series 

The above explanation is very a simplified way of describing BGP. For a network engineer this might help you to explain people what you do for a living, but if you want to learn more about BGP, check out the DE-CIX Academy webinar series hosted by Wolfgang Tremmel. Each of the about half an hour-long webinar concentrates on a particular BGP topic with experiments to give you hands-on examples.  

Wolfgang also does the BGP webinars live both in English and in German, check out our event listings for the upcoming ones.