The Internet is basically made up of Internet service providers known as ISPs who connect each other's networks. How does an ISP in Kenya talk to an ISP in Japan? How does that ISP talk to customers of the ISP in Japan and get responses back? How is this any different from communication between two devices on local Ethernet? Remember that two-way packet flow is needed for communication between any two devices. The ISP in Kenya could buy a direct connection to the ISP in Japan; however, this would not scale. For it would mean that thousands of ISPs would have to buy connections to all other ISPs they need to talk to, thereby making the operational costs astronomical. Instead the ISP in Kenya tells his neighboring ISP what customers he has and the neighboring ISPs pass this information on to their neighbors and so on. This process repeats until the information reaches the ISP in Japan. This process is called routing. The mechanisms used are called routing protocols. Routing and routing protocols ensures that the Internet can scale and thousands of ISPs can provide connectivity to each other, thereby creating the Internet as we see it today. The ISP in Kenya does not actually tell his neighboring ISPs the names of the customers because the network equipment does not understand names. Instead he receives an IP address block as a member of the regional internet registry serving Kenya. His customers have received address space from this address block as part of their internet service and he announces this address block on his router to his neighboring ISPs. This is called "announcing a route".

© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.

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