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Re: Needless DNS queries

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On 6/7/22, Tim Woodall <debianuser@woodall.me.uk> wrote:
> On Tue, 7 Jun 2022, Greg Wooledge wrote:
>
>> On Tue, Jun 07, 2022 at 11:22:34AM -0400, Dan Ritter wrote:
>>>
>>> search		Search list for host-name lookup.  By default, the search
>>>  [...]
>>> 	This may be changed by listing the desired domain search
>>> path following the search keyword with spaces or tabs separating the
>>> names.  Resolver queries having fewer than ndots dots (default is
>>> 1) in them will be attempted using each component of the search path in
>>> turn until a match is found.
>>
>> I've read this paragraph a few times, and as far as I can tell, it's
>> simply wrong.
>>
> Seems right to me:
>
> $ cat /etc/resolv.conf
> search home.woodall.me.uk
> options ndots:3
> nameserver 2001:8b0:bfcd:100:216:3eff:fee0:7102
> nameserver 2001:8b0:bfcd:8100:216:3eff:fee1:7102
>
> $ host ipv4.wlan.dirac
> ipv4.wlan.dirac.home.woodall.me.uk has address 192.168.3.16
> ipv4.wlan.dirac.home.woodall.me.uk has address 192.168.4.16
>
> Change that 3 to a 2 and:
>
> $ host ipv4.wlan.dirac
> Host ipv4.wlan.dirac not found: 3(NXDOMAIN)
>
>
>> If you go down farther in the page and look at:
>>
>>              ndots:n
>>                     Sets a threshold for the number of dots which must
>> appear
>>                     in a name given to res_query(3) (see resolver(3))
>> before
>>                     an  initial absolute query will be made.  The default
>> for
>>                     n is 1, meaning that if there are any dots in a name,
>> the
>>                     name  will  be tried first as an absolute name before
>> any
>>                     search list elements are appended to it.  The  value
>> for
>>                     this option is silently capped to 15.
>>
>> This one says that it simply determines whether the name will be tried
>> as is *before* appending the search domain(s) to it, or whether it just
>> skips straight to appending the search domains.
>>
>
> Doesn't that say that, in my second example it will try ipv4.wlan.dirac.,
> get NXDOMAIN, and pass that up the stack.

host and dig are non-standard.  or use non-standard name lookups? library??
In any case, try your example with ping or ssh - the search list will
be applied after the initial NXDOMAIN

Lee

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Needless DNS queries Dieter Rohlfing <dr-erc@gmx.net> - 2022-06-07 17:10 +0200
  Re: Needless DNS queries David Wright <deblis@lionunicorn.co.uk> - 2022-06-07 17:30 +0200
  Re: Needless DNS queries Dan Ritter <dsr@randomstring.org> - 2022-06-07 17:40 +0200
    Re: Needless DNS queries Tim Woodall <debianuser@woodall.me.uk> - 2022-06-07 18:10 +0200
    Re: Needless DNS queries Greg Wooledge <greg@wooledge.org> - 2022-06-07 19:00 +0200
      Re: Needless DNS queries Darac Marjal <mailinglist@darac.org.uk> - 2022-06-07 19:40 +0200
        Re: Needless DNS queries Lee <ler762@gmail.com> - 2022-06-08 00:10 +0200
      Re: Needless DNS queries Tim Woodall <debianuser@woodall.me.uk> - 2022-06-08 00:20 +0200
        Re: Needless DNS queries Lee <ler762@gmail.com> - 2022-06-08 03:00 +0200
          Re: Needless DNS queries Greg Wooledge <greg@wooledge.org> - 2022-06-08 03:10 +0200
            Re: Needless DNS queries Lee <ler762@gmail.com> - 2022-06-08 07:30 +0200
  Re: Needless DNS queries Dieter Rohlfing <dr-erc@gmx.net> - 2022-06-14 15:10 +0200

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