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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 Data Storage: Resource Records and Classes 1 2 3 DNS Zone Management, Contacts and Zone Transfers

Name Server Roles

The “master” and “slave” roles for a zone are logical and do not always correspond to individual physical hardware devices. A single physical name server can play multiple roles in the following cases:

• It can be the master name server for more than one zone. Each zone in this case has a distinct set of resource records maintained in separate master files.
  
  
• It can be a slave name server for more than one zone.
  
  
• It can be a slave name server for certain zones as well as a primary for others.

Note however that a single physical name server cannot be a primary and a secondary server for the same zone, since… well, what would be the point?

We'll see later in this section that for efficiency reasons, all DNS servers perform caching of DNS information so it can be used again if requested in the near future. This includes both master and slave name servers. The importance of caching is so significant that there are some servers that are set up only to cache information from other DNS servers. Unsurprisingly, these are called caching-only name servers.

These name servers are not authoritative for any zone or domain, and don't maintain any resource records of their own. They can only answer name resolution requests by contacting other name servers that are authoritative and then relaying the information. They then store the information for future requests. Why bother? The reason is performance. Through strategic placement, a caching-only server can increase DNS resolution performance substantially in some networks by cutting down on requests to authoritative servers.

DNS Name Server Data Storage: Resource Records and Classes 1 2 3 DNS Zone Management, Contacts and Zone Transfers