Types of DNS servers

The Authoritative DNS Name Server and The Non-Authoritative DNS Name Caching Server are the two most common types of DNS servers.

Depending on the network size and topology, either of these DNS servers can be implemented, and the services required for maintaining DNS names.

An ‘Authoritative’ DNS server

An Authoritative DNS server is the authoritative source for all DNS requests made for a designated zone or domain. Authoritative servers can be a Primary or Secondary (slave) name server.

The secondary server serves as a fault tolerance backup for the primary authoritative DNS server. It carries a copy of the primary server's DNS database.

The secondary DNS server can respond to other authoritative requests with an authoritative response which allows for load balancing between the Primary and Secondary, and provides system fault tolerance in case of critical failure.

Authoritative servers also do caching of information learned during queries and responses.

(Caching is where a client host requests information from a server that the server may not have. The server goes out and retrieves this information for the client and holds it in a temporary file called a cache, in case another host requests the same information.)

This data has a Time To Live (TTL) period to keep data from getting outdated. This type of server becomes part of the tree seen in Figure 1.0, so it becomes a mission critical box for your domain if you choose to run one.

A ‘Non-Authoritative’ or ‘Caching Only’ DNS server

A Non-Authoritative or Caching Only DNS server is not the delegated server for its existing zone or domain. It cannot respond to requests in an authoritative manor such as authoritative queries from other authoritative servers.

It is the easiest DNS server to set up, requires no dependence on other authoritative servers, and can save time and bandwidth with little effort.

The non-authoritative server first requests the data from an authoritative server and caches it for a period of time (standard=24 hours). An administrator can set the TTL, but too long may result in stale data.

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