Root Server Definition

Root servers are an important, albeit small, part of how the internet works. The current Domain Name System would not work the way it does without them. Unlike other servers that host files for websites, databases, archiving, and downloading, root servers host a single small file through which no internet traffic directly passes. This file is known as the root zone file, and, as of December 2004, contained o­nly 5335 lines of text for a total file size of 119 KB. The root zone file is updated approximately twice per week: sometimes more, sometimes less.

The function of the root zone file is to translate unique worldwide web names into other identifying codes for use o­n the web, in email, and other internet services. The root zone file also contains a list of names and IP addresses of top-level domain servers, such as .com, .org, .net, and country-specific top-level domains. In 2004, there were 773 such authoritative servers for 258 top-level domains. The root servers, however, do not contain all DNS information, and they are not queried for each packet sent through the internet. They are o­nly queried periodically by other name servers for information which they do not already have.

Root servers are operated by o­nly 12 different organizations, and each o­ne is identified by a unique letter code. Note that VeriSign is assigned two codes.

A – VeriSign, Inc.
B – Information Sciences Institute
C – Cogent Communications
D – University of Maryland
E – NASA Ames Research Center
F – Internet Systems Consortium, Inc.
G – U.S. DOD Network Information Center
H – U.S. Army Research Lab
I – Autonomica
J – VeriSign, Inc.
M – WIDE Project

Each letter code represents o­ne of the 13 IPv4 addresses that provide root server service. The operators are obliged to carry current DNS information to the public. Some of the operators offer the service from o­nly a single location, while others use multiple locations.