[ale] nslookup problems

[Omar Loggiodice]

Matthew Avery Writes :
:
:So as not to keep you all in the dark here is something new
:I discovered when playing with nslookup.
:
:Here are the results from several nslookup sessions I ran.
:It looks to me like the nameserver is working OK:
:
:>From miranda (Linux machine at my desk):
:
:miranda 38# nslookup - 192.92.183.13
:*** Can't find server name for address 192.92.183.13: No response from server
:*** Default servers are not available
:miranda 39# nslookup - 129.99.35.1
:Default Server:  fs01.nas.nasa.gov
:Address:  129.99.35.1
:
:> amelia.nas.nasa.gov
:Server:  fs01.nas.nasa.gov
:Address:  129.99.35.1
:                         
:For some reason I can't *start* nslookup with the default
:nameserver for miranda but if I start it with another 
:nameserver and then switch it works fine.  Very strange.
:
:-Matt-

Actually this is the proper behaviour.

When you start nslookup with "- 192.92.183.13"  the
following happens:

a. 192.92.183.13 is added to the list of available name servers
b. A PTR query is sent to the list of available name servers to find the 
   FQDN for 192.92.183.13
c. 192.92.183.13 doesn't have a PTR record for itself. nslookup doesn't
   have any more nameservers to use.
d. Terminates with an error saying it can't find the FQDN for 192.92.183.13

So, you are probably missing a PTR (IP adress to name mapping) record for
192.92.183.13...you need to add something like:

13.183.92.192.in-addr.arpa.	IN PTR nameserver.asetech.com 

Now you are probably asking yourself why does it work when you switch 
to the server *after* starting nslookup with the other server.

The reason is that nslookup is a little bit more permissive when you already
have entered interactive mode (it doesn't require the PTR record for the
nameserver).  I agree this is inconsistent, but this is useful when
debugging nameservers.

Forgetting  PTR records is one of the most common errors when setting up
nameservers. Usually they are not caught, unless people try to ftp to a
"smart" ftp server (like ftp.funet.fi) which double-checks and makes sure
the reverse-mapping (IP to name) matches the direct-mapping (name to IP). 

Don't forget to contact interNic to register your reverse-address mapping if
you own your set of IP addresses.

Hmm....I take that back........judging by whois 192.92.183.0 looks like your
inverse mapping is provided by internal servers at NASA....you probably
don't need to contact InterNIC. Just make sure your inverse mapping is
registered in your master nameservers.


-- 
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  Omar R.  /__ /_/ /_/ /_/ / /_/ /_/ / /_  /-_  CIS: 74040,1543
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