Reverse DNS, IP addr -> name via PTR

[Brian {Hamilton Kelly}]

On 5 Aug, in article <199908051727.NAA10127 at fw1-b.osis.gov>
     jsdy at cospo.osis.gov "Joseph S D Yao" wrote:

> OK, one more time, since there has been a spate of questions about this
> again ...

'Sfunny that: it's not just individuals that seem never to have heard of
the in-addr.arpa domain but a LOT of clueless so-called ISPs too :-(

[snip]

> and then you must put your pointers from the host numbers back to the
> names, e.g.:
> 
>         1       IN  PTR         router.foo.com.
>         2       IN  PTR         firewall.foo.com.
>         3       IN  PTR         host.foo.com.
>         ...
>         42      IN  PTR         answer.foo.com.
                                  ^^^^^^
>         ...

You set up the scenario for a good joke there: why didn't you make it?

[snip]

> Now, giving your local name server all of this information, it will
> return any reverse-DNS query with the proper information.  E.g.,
> queries of the form:
> 
>         nslookup  1.2.3.42    ns.foo.com
>         nslookup  -type=ptr  42.3.2.1.in-addr.arpa   ns.foo.com
>         dig   @ns.foo.com   42.3.2.1.in-addr.arpa  ptr
> 
> will return the host name as part of the answer.

... and in this particular scenario, "answer" as part of the host name.

Boom, boom!

Seriously, there's one important point that I think you failed to make,
and oh boy do a lot of novices make it.  You ought to have pointed out
that he really *needs* the "." after "foo.com" in each of those pointer
records; otherwise, of course, the nslookup will return the spectacularly
useless result "answer.foo.com.3.2.1.in-addr.arpa"
                                    
-- 
Brian {Hamilton Kelly}                                         bhk at dsl.co.uk
    "But we're a university.  We /have/ to have a library!..."said Ridcully,
         "What sort of people would we be if we didn't go into the library?"
    "Students", said the Senior Wrangler, morosely. [TP: The Last Continent]