A core router is a type of very powerful computer router used in large computer networks. It is the fastest, most powerful, and most expensive class of router available. A core router sits at the heart of a network and manages the flow of data packets within the network, often relying on lesser routers for connectivity.
In the world of routers, not all machines are created equal. While all types of routers have the same basic function of directing the flow of data packets, the number of packets any one router needs to process at once depends on where and how the device is being used. Consumer-level routers used to connect many homes and small offices to the Internet need to deal with only a fraction of the data a router in a large corporation or Internet Service Provider (ISP) has to manage. As a result, routers vary widely in size, power, and cost.
Very large computer networks commonly use a hierarchy of routers. At the top of this hierarchy are core routers, the fastest and most powerful class. A single core router can cost as much as a high-end sports car and is capable of processing millions of packets every second. It generally sits in the “center” of very large networks and sends and receives packets to lower classes of routers, such as edge routers, which sit on the edge of a network and transfer packets to other networks. These routers can communicate with one another using the Border Gateway Protocol (BGP) and may share information about the best routes to take or network destinations that have become unreachable.
Early incarnations of the core router contained a “global routing table,” a database containing virtually every possible route a given packet could take to reach its destination. These routers, therefore, were considered to be in the core or backbone of the Internet and were an essential component of early Internet architecture. As the Internet grew, however, even the most advanced router couldn’t keep up with the number of possible routes. Large networks were subdivided into smaller units known as autonomous systems (AS). The modern core router still maintains a large routing table; the scope of this table is confined to the AS rather than the Internet as a whole, however, making the concept of a “core” Internet largely obsolete.
Due to their cost, the market for core routers is largely limited to ISPs and some large institutions such as universities. There were once several companies providing core routers, but the end of the dot-com boom coupled with a number of Cisco Systems® acquisitions has narrowed the market to just two: Cisco®, which controls the majority of the market, and Juniper Networks®. The two companies have played a constant game of leapfrog since the early 2000s, and both now produce routers capable of handling enormous amounts of data.