. The Internet Peering Site with Connections between Carriers' Routers Racks with multiple carriers' routers Backup generators Windowless, hurricane-proof building with high levels of security and duplicate power sources Fiber-optic cables to carriers and power sources Figure 6-2 Traffic at peering points is routed between the facilities of multiple network operators. Address Structures Two universal addressing schemes, Internet Protocol versions 4 and 6 (IPv4 and IPv6), are used to transmit messages from computers, smartphones, and tablet computers worldwide. The system of routing messages based on IP addresses is managed by 12 organizations that administer 13 clusters of servers, called root servers. The Criticality of Root Servers The root name server system was implemented in the 1990s. The Internet cannot function without root servers, which route messages to the correct organization. Root servers are critical for the sustainability, capacity, and survivability of the Internet. To lessen the system's vulnerability to malicious actions such as Denial-of-Service (DoS) attacks, wherein millions of fake messages bombard a site, root servers balance incom- ing messages among multiple servers within each root. If one server within the root is brought down, other servers within the root handle the traffic. Ensuring protection against hackers is an ongoing endeavor. The Structure of the Internet The 13 Root Servers Worldwide The Domain Name System (DNS) is the umbrella name of the Internet's capability to translate alpha characters to numeric IP addresses within root servers. Carriers and organizations send traffic addressed to locations outside their networks to one of the 13 sets of root servers, usually the one nearest to them, to determine where to route these messages. The root servers, which are massive databases, translate alphabetic host- names (gmail.com) into numeric IP addresses (193.22.1.126), and vice versa. Of the 12 organizations that operate the root servers, eight of them have root servers located i