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Date:      Sun, 30 Jul 2000 12:17:26 +0100 (BST)
From:      =?iso-8859-1?q?Dan=20Fairs?= <danfairs@yahoo.co.uk>
To:        Roelof Osinga <roelof@eboa.com>, Evren Yurtesen <yurtesen@ispro.net.tr>
Cc:        freebsd-questions@FreeBSD.ORG
Subject:   Re: reverse dns
Message-ID:  <20000730111726.13738.qmail@web3202.mail.yahoo.com>

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> But they also are in a position to steer you in the direction of
> the one they provided the blocks to. Most likely their NS will
> either hold the reverse data or in turn knows where to steer
> you next.
> 
> Roelof

Hi,

There is a system for doing this. In a nutshell, when you put an
address into the DNS system, you enter a mapping that looks like this:

foo.bar.com. IN A 123.456.789.123

This will allow you to look up the IP for foo.bah.com. When this
mapping is entered into the DNS, it is common to also enter another
mapping:

123.789.456.123.in-addr.arpa. IN PTR foo.bar.com.

This permits reverse lookups, as the resolver doing the reverse lookup
simply reverses the address it wants to look up, bungs the
in-addr.arpa. domain on the end, and queries the nameserver for the
appropriate PTR record. This would return, in this case, foo.bar.com.

I've skimmed over a lot of the detail here - I'd recommend the O'Reilly
book, 'DNS and BIND', by Paul Albitz and Cricket Liu, which will tell
you everything you could ever want to know about DNS.

Hope this helps,
Dan

=====
Daniel Fairs		dan@spiderplant.no-spam.net
System Administrator
spiderplant.net

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