Reverse mapping question

[Joseph S D Yao]

> if you don't mind.  In a forward lookup (ie, resolving name -> IP address), would
> it matter if they had delegated the reverse block to me?  ...

Not for a forward lookup, no.

> Let's say someone wants to connect to www.domain.com.  Their DNS is queried, and
> since it has no listings for domain.com, it queries one of the root servers to find
> out who controls the "com." top level domains.  It then queries that server to see
> who controls the domain.com zone.  And finally, it queries that nameserver (who
> incidently controls the domain.com zone) and receives an IP address.  Now the user
> connects to that IP address.  The root server knows which name server is in charge
> of the domain.com zone because that's how it was registered with Network
> Solutions.  Does this sound correct?

Bingo.

> While I'm at it, let me test my understanding of reverse mappings.  Say my IP
> address is 1.2.3.4.  If someone wanted to find out the hostname for that IP
> address, their DNS would query in-addr.arpa, to find out the name server who is in
> charge of the "4" zone.  ...

Whoops.  You've got it backwards.  Actually, no, the problem is, you
DON'T have it backwards.  The "reverse" domain is 4.3.2.1.in-addr.arpa.
So you start with looking up 1.in-addr.arpa.  And, as you said, the
rest is just the same as looking up the forward address.  Why reverse
the IP?  So that the owner of, e.g., 2.1.in-addr.arpa (1.2.*.*) can
delegate 3.2.1.in-addr.arpa etc.

> Is reverse mapping really necessary?  Would it be feasible for me to host a domain,
> without having the IP address delegated to my name server's control?

As my wife has been heard to say, "necessary" is so relative.  But I
feel it is wrong not to have it.  Many sites are using reverse-DNS
lookups as a basic test of whether you are spoofing or not.  To not
have the reverse DNS would be a disservice to your users.

Besides, what's worse, it's inelegant.

--
Joe Yao				jsdy at cospo.osis.gov - Joseph S. D. Yao
COSPO/OSIS Computer Support					EMT-B
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