Solaris DNS Reference : Types of DNS Servers

1. Root Servers:

Root servers are positioned at the top or root of the DNS hierarchy, and maintain data about each of the top-level zones. The root servers are maintained by the NIC and have been moved to a common domain for consistent naming purposes. The root servers are named as,, and so on.

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2. Primary(Master) Servers:

Each domain must have a primary server. Primary server has the following features.

  • There is generally only one primary server per domain.
  • They are the system where all the changes are made to the domain.
  • They are the authoritative for all domains they serve.
  • They periodically update and synchronize secondary servers of the domain.
  • In BIND 8.1.2, they are defined by the type master argument to the zone statement in the configuration file /etc/named.conf.

3. Secondary servers:

Each domain should have at least one secondary server. In fact,the NIC will not allow a domain to become officially registered as a subdomain of a top-level domain until a site demonstrates two working DNS servers. Secondary servers have the following features.

  • There is one or more secondary server per domain.
  • They obtain copy of the domain information for all domains they serve from the appropriate primary server or another secondary server for the domain.
  • They are authoritative for all the domains they serve.
  • They periodically receive updates from the primary servers of the domain.
  • They provide load sharing with the primary servers and other servers of the domain.
  • They provide redundancy in case one or more other servers are temporarily unavailable.
  • They provide more local access to name resolution if placed appropriately.
  • In BIND 8.1.2, they are defined by the type slave argument to the zone statement in the /etc/named.conf file.

4. Caching-Only servers

These servers only cache information for any DNS domain. They are not authoritative for any domain. Caching-only servers provide the following features.

  • They provide local cache of looked up names.
  • They have lower administrative overhead.
  • They are never authoritative for any domain
  • They reduce overhead associated with secondary servers performing zone transfers from primary servers.
  • They allow DNS client access to local cached naming information without the expense of setting up a DNS primary or secondary server.

5. Forwarding servers:

Forwarding servers are a variation on a primary or secondary server and act as focal points for all off-site DNS queries. Designating a server as a forwarding server causes all off-site requests to go through that server first. Forwarding servers have the following features.

  • They are used to centralize off-site requests
  • The server being used as a forwarder builds up a rich cache of information.
  • All off-site queries go through forwarders first.
  • They reduce the number of redundant off-site requests
  • No special setup on forwarders is required
  • If forwarders fail to respond to queries, the local server can still contact a remote site, DNS servers itself.



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1 Response

  1. September 16, 2015

    […] Read – Types of DNS Servers […]

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