nslookup oddities (Was: SRV record not working)

[Mark Andrews]

nslookup applies the search list by default and doesn’t stop on a NODATA response.

Some versions of nslookup have been modified by OS vendors to use /etc/hosts for address lookups.

nslookup doesn’t display the entire response by default.


> On 20 Aug 2018, at 12:28 pm, Lee <ler762 at gmail.com> wrote:
> 
> On 8/19/18, Doug Barton <dougb at dougbarton.us> wrote:
>> On 08/19/2018 12:11 PM, Lee wrote:
>>> On 8/18/18, Doug Barton <dougb at dougbarton.us> wrote:
>> 
>>>> nslookup uses the local resolver stub. That's fine, if that's what you
>>>> want/need to test. If you want to test specific servers, or what is
>>>> visible from the Internet, etc. dig is the right tool, as the answers
>>>> you get from nslookup cannot be guaranteed to be directly related to the
>>>> question you asked.
>>> 
>>> Could you expand on that a bit please?  I thought
>>>   nslookup <name> <server>
>>> was pretty much equivalent to
>>>  dig <name> @<server>
>>> 
>>> the exception being that nslookup looks for a & aaaa records and dig
>>> just looks for a records
>> 
>> Nope. Depending on what operating system you're on, what version of
>> nslookup you have, how you format your query, and how the system is
>> configured; even telling nslookup to query a specific server may not get
>> you the answer you're looking for.
> 
> That's still awfully vague.  Do you have any examples of
>    nslookup <name> <server>
> returning bad information?
> 
>> If you want to know what answer your stub resolver is going to return
>> for a given query, nslookup is a great tool. Although, if you just need
>> to know what address record you'll get back, ping works just as well.
> 
> ping just shows one address; "nslookup  www.yahoo.com" shows all of them
> 
>> If you want to really debug DNS you need to learn to use dig, and
>> understand the output.
> 
> Agreed.  If you're serious about debugging DNS you needs to learn dig.
> But the assertion is
>>>> ... the answers
>>>> you get from nslookup cannot be guaranteed to be directly related to the
>>>> question you asked.
> 
> so I'm wondering how, or under what circumstances, nslookup returns
> invalid information.
> 
> Thanks
> Lee
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Mark Andrews, ISC
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