Bug#343140: libc6: resolver always checks search list in /etc/resolv.conf

[Gabor Gombas <gombasg@sztaki.hu>]

On Mon, Dec 12, 2005 at 09:13:13PM -0800, Edward Buck wrote:

> In a nutshell, when using 'search' lines in /etc/resolv.conf, the
> resolver always appends listed search domains to a hostname lookup even
> when the host being searched is fully-qualified (contains one or more dots).

No, a host name containing a dot is _not_ a FQDN. A host name _ending_
with a dot is a FQDN.

Using "host.subdomain" while search is set to "some.domain" to access
"host.subdomain.some.domain" is a common and frequently used feature.

> This results in a LOT of needless DNS traffic.  On a busy mail server,
> it makes using the 'search' lines extremely expensive (because DNS traffic
> increases exponentially).
>
> Here's an strace of 'telnet mx1.hotmail.com 25'.  Oddly, it seems to do
> the right thing initially but the fully-qualified lookup must always
> fail, resulting in subsequent lookups using the search list.

Then use a _real_ FQDN and try 'telnet mx1.hotmail.com. 25' (note the
terminating dot).

Gabor

-- 
     ---------------------------------------------------------
     MTA SZTAKI Computer and Automation Research Institute
                Hungarian Academy of Sciences
     ---------------------------------------------------------