DNS Round Robin

[Barry Margolin]

In article <92vimc$18s at pub3.rc.vix.com>, Tony Teo  <tony.teo at f5.com> wrote:
>
>Hi,
>
>I need some tips to clarify some DNS issue I got.
>
>A primary and a secondary name server's ip address will be required to
>register in the internet root servers for a certain domain.
>
>Qns 1 : So when a query is send from a LDNS to the root servers, are
>both the name servers being return back to the LDNS for subsequent query
>?

Yes.  Why don't you send a query using dig or nslookup and see what you get.

>Assuming that both address are returned to the LDNS.
>
>Qns 2 : Does the LDNS always query the primary name server ? When will
>the secondary name server be query ? Is it under the event when the
>primary become unavailable or unreachable ?

All NS records look alike.  There's nothing in an NS record that indicates
which is the primary or secondary name server.  Caching nameservers
remember server response times, and query the server that has the best
record.  If none of the servers are currently in its memory, it will pick
one at random.

If the preferred server doesn't respond, another server will be tried, and
the originally preferred server's response time will be set very high (so
it won't be used again).  Periodically the response times are reset so that
it can discover if the server has come back to life.

>Qns 3 : Does the LDNS uses round robin algorithm  between the primary
>and secondary name servers ?

No, see above.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Burlington, MA
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