Unable to reverse lookup 1 PTR from a zone?

[James K. McConnell]

Hello..

I have a situation where I am, from one specific host, unable to lookup
one record from a reverse-lookup zone.  This host is running Red Hat 5.2,
and I'm using nslookup from the 8.1.2 rpm to query a 8.2.2p5 nameserver,
which is running on Red Hat 6.2.

Specifically, I am able to lookup every record in the zone
21.168.192.in-addr.arpa,
with the exception of the host with the IP address of 192.168.21.2.  I've
enabled tracing with ndc, and seen the following in the logs when I try
to lookup 192.168.21.2:

Jun  5 12:31:47 ns2 named[6442]: datagram from [198.190.167.2].18892, fd 22,
len 43
Jun  5 12:31:47 ns2 named[6442]: req: nlookup(2.21.168.192.in-addr.arpa) id
23669 type=12 class=1
Jun  5 12:31:47 ns2 named[6442]: req: found '2.21.168.192.in-addr.arpa' as
'2.21.168.192.in-addr.arpa' (cname=0)
Jun  5 12:31:47 ns2 named[6442]: ns_req: answer -> [198.190.167.2].18892
fd=22 id=23669 size=173 rc=0
Jun  5 12:31:52 ns2 named[6442]: datagram from [198.190.167.2].18892, fd 22,
len 43
Jun  5 12:31:52 ns2 named[6442]: req: nlookup(2.21.168.192.in-addr.arpa) id
23669 type=12 class=1
Jun  5 12:31:52 ns2 named[6442]: req: found '2.21.168.192.in-addr.arpa' as
'2.21.168.192.in-addr.arpa' (cname=0)
Jun  5 12:31:52 ns2 named[6442]: ns_req: answer -> [198.190.167.2].18892
fd=22 id=23669 size=173 rc=0
Jun  5 12:32:02 ns2 named[6442]: datagram from [198.190.167.2].18892, fd 22,
len 43
Jun  5 12:32:02 ns2 named[6442]: req: nlookup(2.21.168.192.in-addr.arpa) id
23669 type=12 class=1
Jun  5 12:32:02 ns2 named[6442]: req: found '2.21.168.192.in-addr.arpa' as
'2.21.168.192.in-addr.arpa' (cname=0)
Jun  5 12:32:02 ns2 named[6442]: ns_req: answer -> [198.190.167.2].18892
fd=22 id=23669 size=173 rc=0
Jun  5 12:32:22 ns2 named[6442]: datagram from [198.190.167.2].18892, fd 22,
len 43
Jun  5 12:32:22 ns2 named[6442]: req: nlookup(2.21.168.192.in-addr.arpa) id
23669 type=12 class=1
Jun  5 12:32:22 ns2 named[6442]: req: found '2.21.168.192.in-addr.arpa' as
'2.21.168.192.in-addr.arpa' (cname=0)
Jun  5 12:32:22 ns2 named[6442]: ns_req: answer -> [198.190.167.2].18892
fd=22 id=23669 size=173 rc=0

The nslookup looks like this (including the result):

> 192.168.21.2
Server:  ns2.tbred.com
Address:  198.190.167.17

*** ns2.tbred.com can't find 192.168.21.2: No response from server


Just to verify, I then lookup 192.168.21.3, and get the following result:

Jun  5 12:36:01 ns2 named[6442]: datagram from [198.190.167.2].19480, fd 22,
len 43
Jun  5 12:36:01 ns2 named[6442]: req: nlookup(3.21.168.192.in-addr.arpa) id
23670 type=12 class=1
Jun  5 12:36:01 ns2 named[6442]: req: found '3.21.168.192.in-addr.arpa' as
'3.21.168.192.in-addr.arpa' (cname=0)
Jun  5 12:36:01 ns2 named[6442]: ns_req: answer -> [198.190.167.2].19480
fd=22 id=23670 size=173 rc=0

Looking up this, and all other records, works with no problem.

It appears to me that I have one of two problems.  First, the 8.1.2
resolver may have a bug, and I should upgrade it to 8.2.2p5.  I plan to
do this, but I'd prefer to track down this problem first.  Second, it
may be possible that the response never makes it back to the host
that is requesting information.  I've strace'd the nslookup, and it
simply tells me I'm getting a timeout.  When I dumpdb on the server,
I can clearly see this record is loaded, and I receive a response for
this record from every other host I've tried.

What can I do to track down this problem?  Why should this affect only
one record?  Any assistance is appreciated.  I can provide any information
that may be necessary to track down this problem.

Thanks,

Jim McConnell