On Thu, 19 Nov 2009, stan wrote:
>On Thu, Nov 19, 2009 at 11:24:44AM -0500, Dave Anderson wrote:
>> On Thu, 19 Nov 2009, stan wrote:
>>
>> >On Wed, Nov 18, 2009 at 11:03:27PM -0500, Dave Anderson wrote:
>> >> On Wed, 18 Nov 2009, stan wrote:
>> >>
>> >> >On Wed, Nov 18, 2009 at 05:00:02PM -0500, Dave Anderson wrote:
>> >> >> On Wed, 18 Nov 2009, stan wrote:
>> >> >>
>> >> >> >Can anyone xplain this behavior to me?
>> >> >>
>> >> >> Without access to your nameservers it's not possible to be sure, but
>> >> >> see
>> >> >> below -- this looks normal to me.
>> >> >>
>> >> >> >Given the following resolv.conf file:
>> >> >> >
>> >> >> >r...@pm3fw:root# cat /etc/resolv.conf
>> >> >> >lookup file bind
>> >> >> >search mcn.chs kapstonepaper.com pm3.charleston.meadwestvaco.com
>> >> >> >nameserver 127.0.0.1
>> >> >> >nameserver 10.209.128.20
>> >> >> >nameserver 10.209.128.26
>> >> >> >nameserver 10.209.142.158
>> >> >> >
>> >> >> >And:
>> >> >> >
>> >> >> >r...@pm3fw:root# nslookup
>> >> >> >> cvsup
>> >> >> >Server: 127.0.0.1
>> >> >> >Address: 127.0.0.1#53
>> >> >> >
>> >> >> >Non-authoritative answer:
>> >> >> >Name: cvsup.mcn.chs
>> >> >> >Address: 10.209.142.151
>> >> >> >> 10.209.142.151
>> >> >> >Server: 127.0.0.1
>> >> >> >Address: 127.0.0.1#53
>> >> >> >
>> >> >> >151.142.209.10.in-addr.arpa name = cvsup.meadwestvaco.com.
>> >> >> >> exit
>> >> >> >
>> >> >> >Why does this happen ? And how?
>> >> >>
>> >> >> You apparently have a system with multiple names and a single IP
>> >> >> address. Both cvsup.mch.chs and cvsup.meadwestvaco.com are assigned
>> >> >> address 10.209.142.151, but the reverse-lookup entry can't return both
>> >> >> names. Given the order of domains in your 'search' directive,
>> >> >> cvsup.mcn.chs is looked up first and so is the name that nslookup
>> >> >> reports, but cvsup.meadwestvaco.com was chosen as the 'official' name
>> >> >> for the reverse lookup by whoever set up your DNS.
>> >> >>
>> >> >Your analysis is correct, in that thier are multiple names (don't ask
>> >> >:-().
>> >> >I have control of some of the nameservers. They are bind 9 on OpenBSD,
>> >> >can
>> >> >you clarify what you mean by "offical name" are you talking about a A
>> >> >entry, as oposed to a CNAME entry?
>> >>
>> >> Sorry I wasn't clear. I was referring to the *.in-addr.arpa 'PTR' DNS
>> >> entry which provides the translation from IPv4 address to host name.
>> >
>> >K, I am starting to understand this now, thequestion is how to fix it. I do
>> >have a PTR record in my 10.in-addr.arpa db. If I wan this NOT to be the
>> >authortative entry for this IP -> name tarnsaltion, so that an authortative
>> >eoll 'pass on by" this Bind instnace and go on to one further down, how can
>> >I acomplis htis?
>>
>> If I'm understanding you correctly, you can't. The only control which I
>> recall offhand that you have over whether a nameserver responds with
>> data from its cache is to set the 'authoritative' flag in your request,
>> which will cause a nameserver with only cached data to pass the request
>> on -- but you don't want to do this routinely since it defeats the
>> distributed nature of DNS and so results in overloading the
>> authoritative servers.
>>
>> All that the 'authoritative' flag tells you is whether the response came
>> from a server with the entry in its cache (not authoritative) or from
>> one which has that information manually configured on it
>> (authoritative) -- so I'm not at all sure what you mean by 'fix it'.
>>
>> What exactly is the behavior that you want?
>>
>I would like to have all programs get the same results as nslookup, that is
>get *.mcn.chs for the reverese lookup from this machine. I have other
>machines configureddiferently in resolv.conf that I want to get the
>*.meadwestvaco.com resolution. This has been a long a painful taril, and I
>thoguht I had what I wanted based upon using nslookup as a test. When I saw
>diffeent software (nmap in this case) getting diferent resolutin, it was
>verry disapointiing.
Um, nslookup doesn't get e.g. cvsup.mcn.chs as the reverse lookup -- it
just finds that name first when looking up 'cvsup' because of the order
in which you specified domains in the 'search' directive in your
resolv.conf. When you asked nslookup for a reverse lookup of
10.209.142.151 it returned cvsup.meadwestvaco.com just like everything
else did.
The 'reverse lookup' for a.b.c.d by definition returns the value of the
PTR record(s) with label d.c.b.a.in-addr.arpa. Barring DNS spazzes,
this will be the same no matter which machine issues the request. Well,
normally. There is one special case I'm aware of -- if you configure
your nameservers with 'split-horizon' DNS, they can return different
information depending on the IP address range from which the request
originates.
Dave
--
Dave Anderson
<d...@daveanderson.com>
