The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  Name Systems and TCP/IP Name Registration and Name Resolution            9  TCP/IP Name Systems: Host Tables and Domain Name System (DNS)                 9  TCP/IP Domain Name System (DNS)                      9  DNS Name Servers and Name Resolution                           9  DNS Name Server Concepts and Operation

DNS Zone Management, Contacts and Zone Transfers 1 2 3 DNS Name Server Caching, Negative Caching and Data Persistence

The domain name system is strongly oriented around the notion of hierarchical structure: the name space, registration authorities and name servers are all arranged in a tree structure. Like these structures, the name resolution process is also hierarchical. As described in gory detail in the section on name resolution, a fully-qualified domain name is resolved by starting with the least-specific domain name element (label) and working towards the most-specific one.

Naturally, the least-specific portion of every name is the root node under which the entire DNS structure exists. This means that, absent caching and other performance enhancements, all name resolution begins with the root of the name tree. We find here a set of name servers that are responsible for name server functions for the DNS root: the DNS root name servers.

Like all name servers, they store information about, and provide name resolution services for, all the nodes within the “root zone”. This includes certain specific top-level domains and subdomains. Most top-level domains (TLDs), however, are in their own zones. The root name servers are used as the “go to” spot to obtain the names and addresses of the authoritative servers for each of these TLDs. For example, if we want to resolve the name “www.xyzindustries.co.uk”, the root name servers are where a resolver would find the identity of the name server that is responsible for “uk”.

DNS Zone Management, Contacts and Zone Transfers 1 2 3 DNS Name Server Caching, Negative Caching and Data Persistence