From: Brian Candler <b.candler@...>
Date: 2009-03-02T17:53:53+09:00
Subject: Re: DNS MX lookup issue: local machine returned as MX for an  non-existant domain!

Yves-Eric wrote:
> Problem solved. Executive summary: it is a documentation bug. DNS
> name queries need a final dot.

I disagree. DNS queries in normal use should *not* need a trailing dot, 
and indeed in E-mail addresses the final dot is forbidden.

If your system is appending a default domain, then it should be doing so 
according to an explicit configuration. In the case of nslookup / dig 
(libbind), this configuration is in /etc/resolv.conf

If Resolv::DNS is making up its own default domains from some other 
source, e.g. by hacking up your system hostname and guessing the domain 
from that, that's a bug in my opinion.

A quick source scan suggests this is exactly what's happening, and the 
offending code is here:

              hostname = Socket.gethostname
              if /\./ =~ hostname
                @search = [Label.split($')]
              else
                @search = [[]]
              end

However looking at the source also suggests you can fix this problem by 
setting :search=>[] as an argument to Resolv::DNS.new

> Where should I fill a bug report?

redmine.ruby-lang.org

I'd argue it's a case of dangerous defaults - but it may be rejected on 
the grounds that users (who know what they are doing) can override the 
default.

> For the record, I
> also learned that "[|proto]" means that the packet was truncated at
> the "proto" protocol level

Oh yes, sorry I forgot that. My prototypical use:

  tcpdump -ieth0 -s0 -nX ...

Regards,

Brian.
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