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Reverse DNS |
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Reverse DNS turns an IP address into a hostname --
for example, it might turn 192.0.2.25 into
host.example.com.
For your domains, standard DNS (turning a hostname
into an IP address, such turning host.example.com
into 192.0.2.25) starts with the company (registrar)
that you registered your domains with. You let them
know what DNS servers are responsible for your
domain names, and the registrar sends this
information to the root servers (technically, the
parent servers for your TLD). Then, anyone in the
world can access your domains, and you can send them
to any IP addresses you want. You have full control
over your domains, and can send people to any IPs
(whether or not you have control over those IPs,
although you should have permission to send them to
IPs that are not yours).
Reverse DNS works in a similar method. For your IPs,
reverse DNS (turning 192.0.2.25 back into
host.example.com) starts with your ISP (or whoever
told you what your IP addresses are). You let them
know what DNS servers are responsible for the
reverse DNS entries for your IPs (or, they can enter
the reverse DNS entries on their DNS servers), and
your ISP gives this information out when their DNS
servers get queried for your reverse DNS entries.
Then, anyone in the world can look up the reverse
DNS entries for your IPs, and you can return any
hostnames you want (whether or not you have control
over those domains, although you should have
permission to point them to hostnames that are not
on your domains).
So for both standard DNS and reverse DNS, there are
two steps: [1] You need DNS servers, and [2] You
need to tell the right company (your registrar for
standard DNS lookups, or your ISP for reverse DNS
lookups) where your DNS servers are located. Without
Step 2, nobody will be able to reach your DNS
servers.
If you can comprehend the above paragraphs (which
takes some time), you'll understand the biggest
problem that people have with reverse DNS entries.
The biggest problem people have is that they have
DNS servers that work fine with their domains
(standard DNS), they add reverse DNS entries to
those servers, and it doesn't work. If you
understand the above paragraphs, you'll see the
problem: If your ISP doesn't know that you have DNS
servers to handle the reverse DNS for your IPs, they
won't send that information to the root servers, and
nobody will even get to your DNS servers for reverse
DNS lookups. |
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