DNS root zone

A DNS root zone is the top level of the DNS hierarchy for a given DNS system. The term, when not otherwise qualified, is generally used to refer to the root zone of the largest global DNS system deployed on the Internet. This "official" DNS system is by far the largest deployment of DNS in the world.

The combination of limits in the DNS and IP protocols means that there is a limit of thirteen root server names that can be accommodated within a root zone.

Table of contents

1 Technical details of root server lookup
2 Redundancy and diversity
3 Politics of the DNS root zone
4 Alternative DNS root proposals
5 Proposed alternative systems to DNS
6 External links

Technical details of root server lookup

There are thirteen root server names that are authoritative for queries to the global DNS root zone, the maximum number possible. The root servers hold the list of addresses for the authoritative servers for the top-level domains. Every name lookup must either start with an access to a root server, or use information that was once obtained from a root server.

The root servers have the official names a.root-servers.net to m.root-servers.net. However, to look up the IP address of a root server from these names, you must first be able to look up a root server, to find the address of an authoritative server for the .net DNS zone. Clearly this creates a paradox, so the address of at least one root server needs to be known by a host in order to bootstrap access to the DNS system.

Once the address of a single functioning root server is known, the rest of the DNS information can be discovered recursively, and the address of any machine on the Internet can be looked up in this way.

An additional level of redundancy is provided by the fact that a single root server name, and its corresponding IP address, may correspond with many physical servers around the world, using a method called anycast.