DNS root servers

Posted on 2011-09-29
Last Modified: 2012-08-14
Hi experts,

I'm not a DNS experts but I am studying a concept of load balancing DNS.

If someone said:

"The Root DNS servers provide the nameservers for as the NetScalers ADNS servers namely: ( or ("

Are they saying that the root DNS server are authoratative for
And that the Root DNS has an A-record for that point to two IPs and
Question by:trojan81
  • 2
LVL 33

Expert Comment

ID: 36818561
No actually, they are saying the the Root DNS server's found to authorative Name Servers for the a-record

In this case the authorative servers: and are both authorative for the domain and each one has an a record for the host address


Author Comment

ID: 36850585

First, thank you.
Just to confirm,

The public Root servers see that and are authoratative for Both those name servers have an A-record for

In an example like this, how does the Root server know which Name server to send the request to? Is it load balancing or will it send the DNS request to both NS1 and NS2?
LVL 33

Accepted Solution

it_saige earned 500 total points
ID: 36890048
This should answer most of your questions:

To quote:

"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.
Every DNS zone must be assigned a set of authoritative name servers that are installed in NS records in the parent zone.
When domain names are registered with a domain name registrar their installation at the domain registry of a top level domain requires the assignment of a primary name server and at least one secondary name server. The requirement of multiple name servers aims to make the domain still functional even if one name server becomes inaccessible or inoperable.[12] The designation of a primary name server is solely determined by the priority given to the domain name registrar. For this purpose generally only the fully qualified domain name of the name server is required, unless the servers are contained in the registered domain, in which case the corresponding IP address is needed as well.
Primary name servers are often master name servers, while secondary name server may be implemented as slave servers.
An authoritative server indicates its status of supplying definitive answers, deemed authoritative, by setting a software flag (a protocol structure bit), called the Authoritative Answer (AA) bit in its responses.[5] This flag is usually reproduced prominently in the output of DNS administration query tools (such as dig) to indicate that the responding name server is an authority for the domain name in question.[5]"

The master server responds first with slave server(s) responding if the master is offline.

Here is another resource:




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