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The TCP/IP Guide

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Table Of Contents  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

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DNS Name Server Data Storage: Resource Records and Classes
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DNS Zone Management, Contacts and Zone Transfers
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DNS Name Server Types and Roles: Primary/Master, Secondary/Slave and Caching-Only Servers
(Page 3 of 3)

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?

Key Concept: The master DNS server for a zone is its primary server, which maintains the master copy of DNS information. Most DNS zones also have at least one slave or secondary DNS server. These are important because they serve as backups for the primary server, and they can also help share the load of responding to requests in busy zones. Secondary name servers get their information from primary servers on a routine basis. Both master and slave servers are considered authoritative for the zones whose data they maintain.

Caching-Only Name Servers

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.

Key Concept: There are DNS servers that do not maintain DNS resource records of their own but solely hold recently-used information from other zones. These are called caching-only name servers and are not authoritative for any zone.

Previous Topic/Section
DNS Name Server Data Storage: Resource Records and Classes
Previous Page
Pages in Current Topic/Section
Next Page
DNS Zone Management, Contacts and Zone Transfers
Next Topic/Section

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Version 3.0 - Version Date: September 20, 2005

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