Thursday, September 1, 2011

Authoritative vs Non-Authoritative DNS Server

 
What is Authoritative DNS Server?

An authoritative name server is a name server that gives answers that have been configured by an original source, for example, the domain administrator or by dynamic DNS methods. An authoritative-only name server only returns answers to queries about domain names that have been specifically configured by the administrator.

An authoritative server indicates its status of supplying definitive answers, deemed authoritative, by setting a flag (a protocol structure bit), called the Authoritative Answer (AA) bit in its responses. This flag is usually to indicate that the responding name server is an authority for the domain name in question

 An authoritative name server can either be a master server or a slave server. A master server is a server that stores the original (master) copies of all zone records. A slave server uses an automatic updating mechanism of the DNS protocol in communication with its master to maintain an identical copy of the master records.



What is Non-Authoritative DNS server?

Non authoritative name servers do not contain copies of any domains. Instead they have a cache file that is constructed from all the DNS lookups it has performed in the past for which it has gotten an authoritative response. When a non-authoritative server queries an authoritative server and receives an authoritative answer, it passes that answer along to the querier as an authoritative answer.

Thus, non-authoritative servers can answer authoritatively for a given resolution request. However, non-authoritative servers are not authoritative for any domain they do not contain specific zone files for. Most often, a non-authoritative server answers with a previous lookup from its lookup cache. Any answer retrieved from the cache of any server is deemed non-authoritative because it did not come from an authoritative server.



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