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<H3 align="left"><img src="../../gx/dennis/qbubble.gif"
height="50" width="60" alt="(?) " border="0"
>reverse dns</H3>
<p><strong>From Iskandar Awall
</strong></p>
<p align="right"><strong>Answered By Mike Orr
<br></strong></p>
<P><STRONG>
Do you know a step by step guide in doing reverse dns lookup in unix. I
have done a reverse dns lookup but it doesn't seem to be able to resolve.
</STRONG></P>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
> [Mike]
You've got a choice of several commands. 'dig' seems to provide the
most information.
</BLOCKQUOTE>
<blockquote><pre>$ host 1.2.3.4
$ host domain.com
$ dig 1.2.3.4
$ dig domain.com
$ dig 1.2.3.4 ANY
$ dig domain.com ANY
$ nslookup
&gt; set type=any
&gt; 1.2.3.4
&gt; domain.com
&gt; [ctrl-d]
$
</pre></blockquote>
<BLOCKQUOTE>
If a reverse lookup fails, it probably means there is no reverse record
for that IP. There's no technical connection between forward and
reverse records. Indeed, they may even be maintained by different
organizations, so keeping them in sync may be impossible. The forward
record (name -&gt; number) is maintained by whoever hosts your domain
name--your ISP, another company, or you on your own server. The reverse
record (number -&gt; name) is maintained by whoever maintains your IP
number; i.e., your ISP. My ISP, For instance, refuses to change my
reverse record from a long ugly DSL name because they say their billing
system depends on that name. I have my own domain which I host myself
(to avoid the $5-$20/month the ISP would charge, which is an outrageous
rip-off for one minute's worth of labor when it changes, and no cost in
months it doesn't change--except the cost to run their DNS server, which
they'd have to do anyway), but since I cannot get the reverse record
changed, the forward and reverse records don't match. There are also
some ISPs out there who don't have reverse records at all, because they
think that setting reverse records for their customers' IPs is not worth
the time.
</BLOCKQUOTE>
<BLOCKQUOTE>
Users are caught in the middle of a debate over whether reverse records
should be used for identification. The pro argument is that it helps
identify spammers and abusers. The con argument (which I believe) is
that the purpose of domain names is convenience: so you don't have to
remember a number, and so that a site can maintain a "permanent"
identifier even if they move to another server or a different ISP.
You shouldn't <EM>have</EM> to have a domain name, much less have it set to
any particular value. And to identify scRipT kIddyZ, just do a simple
traceroute. The second-last hop is their ISP (or part of their own
network), and ISPs always have their own domain name showing. And
what if a computer has several domain names, each hosted at a different
organization? There can be only one reverse record, so all the other
names will be left out in the cold.
</BLOCKQUOTE>
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