Where do software query reverse IP ?

Barry Margolin barmar at bbnplanet.com
Tue Nov 9 17:56:21 UTC 1999

In article <38281D94.E0FEAD18 at club-internet.fr>,
ECO  <eco at club-internet.fr> wrote:
>  Let's suppose we have :
>- a nameserver, ns1, authoritative for the domain example.com.
>- www.example.com. A   ; And the reverse also...
>  Some software after an A lookup do a reverse query to verify whether the
>IP address matches the name or not.

Very little software does this.  Reverse queries are usually done by
servers when they get a connection from a client, either so that they can
check the client against a hostname in an access list, or so that they can
log the client hostname.

>  My question is : Will the software do a reverse query on ns1 for the IP
> as it found ns1 to be the master DNS server of
>(www.)example.com ?

It will do the reverse query using whatever server the reverse domain is
delegated to.  There's no reason for a client machine to assume that the
forward and reverse DNS are on the same machine, since often they aren't;
for instance if www.company.com is at a web hosting center, but the rest of
the company.com domain is on the company's LAN, the forward entry will be
on the company's on DNS server but the reverse entry will be on the web
hosting company's DNS server.

Barry Margolin, barmar at bbnplanet.com
GTE Internetworking, Powered by BBN, Burlington, MA
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.

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