The internet is vast and complex, and so we use simplifying metaphors to describe it. They cut the internet down to a size that fits in our heads. The internet is a place we visit. It’s a web. It’s a cloud. It used to be an information superhighway. The true nature of the internet is in its name: the internet. The internet is an interconnected network, a network of networks. As it moves from point to point across the internet, information may traverse many networks.
BGP, the Border Gateway Protocol, determines the route information takes through these networks. Most organizations needn’t concern themselves with the BGP protocol or the infrastructure it runs on. They have a single connection to the internet — usually an ISP — and their bandwidth provider takes care of the routing. But BGP is important to data center operators and server hosting providers. It can affect network latencies, the time it takes for data to travel between points on the internet. Hosting providers want to optimize BGP routing to provide better service to their customers.
The networks that constitute the internet are called Autonomous Systems. They are often under the control of an Internet Service Provider or telecoms company, but large businesses may also manage an AS. Each AS is given an Autonomous System Number. ASNs are used to route traffic between networks. ASNs are comparable to the IP addresses that route packets around the web, but they don’t work in quite the same way.
When you travel to a city to visit the home of a friend, the airline pilot needs to know which airport to fly to. She doesn’t need to know your friend’s home address. But when you catch a taxi outside the airport, the driver needs a house number and street name. An ASN is like the airport location and an IP number is like your friend’s address.
On a long air journey, you might have several layovers before reaching the destination. The airline tries to get you there in the fewest hops. It’s faster and less expensive. But, if the weather is so bad that the plane can’t land at one of the scheduled layovers, the flight may take an alternate route with different layovers.
BGP is similar. There are often many routes between networks on the internet. Data centers have multiple connections to bandwidth providers. The BGP system decides which route is the fastest, which has the fewest layovers, and sends data through the best route. BGP routing considers other factors too, including reliability. Faster is better, but a supersonic airliner that can’t fly half of the time is better avoided. Data center operators optimize the routes in advance so that the data’s journey is predictable and fast.
BGP is less well-known than other protocols, but it is just as important. To see how important, consider what happens when BGP goes wrong. This November, a small ISP in Nigeria accidentally updated its BGP routing table to include hundreds of IPs owned by Google. A Chinese telecoms company accepted the erroneous data, causing other network providers to accept it too. For a couple of hours, data intended for and sent by Google ended up in Nigeria, causing downtime for Google services. Small mistakes in the BGP system can cause big headaches to businesses and users.
Server hosting clients don’t need to know about BGP, but they should take comfort in the knowledge that their hosting provider uses the BGP system to provide reliable and low-latency connectivity to any network in the world.