Re: DNS Resolution and Short Names with Dots

["Karl E. Jorgensen" <karl@jorgensen.org.uk>]

Hi

On Tue, Sep 23, 2014 at 05:46:29PM -0400, Mark Kamichoff wrote:
> Hi -
> 
> I've been running into somewhat inconsistent behavior with DNS short
> name resolution in Debian across a few systems.
> 
> Here's the behavior that I've occasionally relied on over the years:
> 
> % cat /etc/resolv.conf
> search example.com
> nameserver 192.0.2.10
> % host foo.bar.baz.example.com.
> foo.bar.baz.example.com has address 192.0.2.1
> foo.bar.baz.example.com has IPv6 address 2001:db8::1
> % host foo.bar.baz
> foo.bar.baz.example.com has address 192.0.2.1
> foo.bar.baz.example.com has IPv6 address 2001:db8::1
> 
> Basically, I expect the search suffix to always be appended to the label
> unless a trailing "." (ie, fully-qualified) is the last character.
> 
> I don't know if it was a glibc upgrade or something else but on a few of
> my Debian systems (combination of i386 and x86_64) I now cannot resolve
> any short names that have a dot in them.  So, the above example now
> returns:
> 
> % cat /etc/resolv.conf
> search example.com
> nameserver 192.0.2.10
> % host foo.bar.baz.example.com.
> foo.bar.baz.example.com has address 192.0.2.1
> foo.bar.baz.example.com has IPv6 address 2001:db8::1
> % host foo.bar.baz
> Host foo.bar.baz not found: 3(NXDOMAIN)
> 
> However, something this will still succeed:
> 
> % host www
> www.example.com has address 192.0.2.2
> www.example.com has IPv6 address 2001:db8::2

So... it looks like the number of dots in the query matter....

Perhaps one of the recent libc upgrades have changed the default for
'ndots' ?

If so, according to a quick scan of the resolv.conf(5) manual page you
should be able add this to /etc/resolv.conf to get your old behaviour back:

       options ndots:3

Hope this helps

-- 
Karl E. Jorgensen