At http://computer.howstuffworks.com/internet-infrastructure.htm, howstuffworks explains how the internet is physically connected, and we can relate the internet to some important ideas of graph theory. Say we have a computer in a corporate network (A) that wants to connect to a computer (B) across the country, on some other network. If we start with a simple corporate network of which A is a member, employee computers are connected to a local router. These computers are nodes, the methods of connections are edges, and the router is essentially a gatekeeper since it is the only way for nodes on the company network to talk to each other. This corporate network is connected by, for example, a T1 line to an ISP. This connection from company to ISP is a bridge, since it is the only path between the computers on the company network and the larger internet.

At this point, the ISP will connect to a regional network access point (another bridge, the only path for the computers on the company network to access networks across the country). Other ISPs and large corporations also agree to share information and connectivity at these network access points, which are connected to each other around the country. At this high level, there are no gatekeepers since there are multiple paths between the interconnected NAPs. But when we have reached the NAP which B’s ISP connects to, choices are fewer. From the NAP, we go to B’s ISP, then to B’s local network, then to B (following the reverse process of how A gets to the NAP). We can see that the internet is essentially made up of tons of nodes connected to gatekeepers, connected together by bridges, all essential elements of graph theory. It is fascinating to think that this process takes such a small amount of time, usually much less than a second.