[sf-lug] resolver problem

[Daniel Gimpelevich]

On Tue, 2016-04-05 at 07:36 -0700, Michael Paoli wrote:
> So ...
> 
> > From: "Alex Kleider" <akleider at sonic.net>
> > Subject: Re: [sf-lug] resolver problem
> > Date: Mon, 04 Apr 2016 18:44:31 -0700
> 
> > I checked resolv.conf but clearly the way Ubuntu is configured
> they  
> > don't want me messing with it:
> > nameserver 10.0.0.2
> > search sonic.net
> >
> > As for nsswitch.conf, it's Greek to me but here it is:
> > hosts:          files mdns4_minimal [NOTFOUND=return] dns mdns4
> 
> The resolver libraries first check files (/etc/hosts),
> then mdns4_minimal (whatever that is - likely some DNS or
> nameservice  
> caching thingy)
> if that gives a NOTFOUND by that point - I'm presuming an  
> authoritative not found
> (NXDOMAIN or similar) at that point, rather than a failure, at that  
> point it returns
> those results.  But if it got some other result - other than answer,  
> it continues
> to DNS - where you haev 10.0.0.2 per /etc/resolv.conf, and then it may
> also
> use mdns4 after that.  So ... depending what results are received
> from  
> files and
> mdns4_minimal, it may not even try DNS.

There is a reply from mDNS only when the query is in the .local TLD,
that is, NOTFOUND means it's for a bogus .local hostname, which should
then also be shielded from being put through real DNS servers.