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 Name Server Functions, Name Server Architecture and General Operation 1 2 3 4 DNS Name Server Types and Roles: Primary/Master, Secondary/Slave and Caching-Only Servers

One of the most important jobs performed by name servers is the storage of name data. Since the authority for registering names is distributed across the internetwork using DNS, the database of name information is likewise distributed. An authoritative server is responsible for storing and managing all the information for the zones of authority it is assigned.

Each DNS server is, in essence, a type of database server. The database contains many kinds of information about the subdomains and individual devices within the domain or zone for which the server is responsible. In DNS, the database entries that contain this name information are called resource records (RRs). A specific set of RRs is associated with each node within the zone.

The entire point of DNS is to allow humans to work with names and computers to work with numbers, and we see this principle further reflected in the two very different representations that exist for the DNS resource records themselves:

• Resource Record Field Format (Binary) Representation: Name servers are required to respond to queries for name information by sending resource records within DNS messages. Obviously, we want to do this in as efficient a way as possible, so each resource record is internally stored using a special field format that is similar to the many field formats we have seen used for messages in other protocols. All resource records use a general field format for some of their fields, and then have a unique portion that is specific to the resource record type.
  
  
• Master File (Text) Representation: Computers are happy to exchange binary-encoded field formats and have no problem remembering that, for example, resource record type 15 corresponds to a mail exchange (MX) record. However, human administrators want to be able to quickly and easily maintain DNS information without having to remember cryptic codes or work with binary values. For this reason, DNS uses a master file format for its user-machine interface, which allows resource records to be specified in text form for easier maintenance.

DNS Name Server Functions, Name Server Architecture and General Operation 1 2 3 4 DNS Name Server Types and Roles: Primary/Master, Secondary/Slave and Caching-Only Servers