The Internet as we know it is the connection with websites and services hosted on other computers located around the globe. The internet is a network of networks supported by hardware devices such as routers and servers that exchange routing and location information. These routers connect via layers of ISP’s that interconnect through service provider exchanges such as LINX (London Internet Exchange) that route local and national traffic more efficiently and cost effectively. ISP in and exchange effective peer and exchange traffic over direct links or pass Inter-continental traffic to higher tier ISP’s for transmission across their vast bandwidth and low latency submarine cables.
Consumers see none of this as they are only using internet end-points such as PCF’s or Smartphones. They have no need to know how their browser finds and communicates with a website on the other side of the planet, and do so in milliseconds. However, a basic understanding of how ISP’s route traffic between end-points goes a long way to understand why the internet can be so unpredictable.
The language of the internet is BGP (Border Gateway Protocol) and it is a robust large scale routing protocol designed to handle the vast routing tables and constant changing states of routes on the internet. This is required because the Internet is an unmanaged malleable entity that is in a constant state of change. ISP routers exchange their routing tables with peers with whom they directly connect. Each router has a route table, which is populated with the best routes to destinations but from their own perspective. They share these routes with peers and add new routes they discover from peers hence building a larger vision of the internet. However, routes are not stable as they are in a constant state of flux with routers going offline or links dropping all around the globe. BGP must keep track of these routes and maintain only the best and most reliable summary routes to a destination. By doing so BGP assists ISPs around the world in interconnecting and finding a reliable route to a computer or website hosted on computers on another continent. To consider the size of this problem a BGP routing table contained in Aug 2014 more that 512,000 summary routes that have to be searched, maintained and exchanged with peers.