Redundancy and Diversity
The root DNS servers are essential to the function of the Internet, as most Internet services, such as the World-Wide Web and electronic mail, are based on domain names. The DNS servers are potential points of failure for the entire Internet. For this reason, there are multiple root servers worldwide. The number has been limited to 13 in DNS responses because DNS was limited to 512-byte packets until protocol extensions (EDNS) were designed to lift this restriction. While it is possible to fit more entries into a packet of this size when using "label compression", 13 was chosen as a reliable limit. Since the introduction of IPv6, the next-generation Internet Protocol, previous practices are being modified and extra space is filled with IPv6 name servers.
The root name servers are hosted in multiple secure sites with high-bandwidth access to accommodate the traffic load. At first, all of these installations were located in the United States. However, the distribution has shifted and this is no longer the case. Usually each DNS server installation at a given site is physically a cluster of machines with load-balancing routers. A comprehensive list of servers, their locations, and properties is available at http://root-servers.org. As of November 2012 there were 345 root servers worldwide.
The modern trend is to use anycast addressing and routing to provide resilience and load balancing across a wide geographic area. For example, the j.root-servers.net root server, maintained by VeriSign, is represented by 41 (as of July 2008) individual server systems located around the world, which can be queried using anycast addressing.
Read more about this topic: DNS Root Zone
Famous quotes containing the word diversity:
“We call the intention good which is right in itself, but the action is good, not because it contains within it some good, but because it issues from a good intention. The same act may be done by the same man at different times. According to the diversity of his intention, however, this act may be at one time good, at another bad.”
—Peter Abelard (1079–1142)