Re: fallback DNS server

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Beniamino Galvani schreef op 21-07-2016 10:10:
> On Thu, Jul 21, 2016 at 09:54:03AM +0200, Nicolas Bock wrote:
> > How do I check that dnsmasq is using the server? NetworkManager 
> > started
> > dnsmasq with
> >
> > /usr/sbin/dnsmasq --no-resolv --keep-in-foreground --no-hosts
> > --bind-interfaces --pid-file=/run/NetworkManager/dnsmasq.pid
> > --listen-address=127.0.0.1 --cache-size=400 --conf-file=/dev/null
> > --proxy-dnssec --enable-dbus=org.freedesktop.NetworkManager.dnsmasq
> > --conf-dir=/etc/NetworkManager/dnsmasq.d
> >
> > and in /etc/NetworkManager/dnsmasq.d is only the file I dropped in 
> > there
> > with the fallback DNS servers.
>
> NetworkManager logs should contain messages from dnsmasq and there
> should be lines as:
>
>   dnsmasq[7295]: using nameserver 192.168.1.1#53
>   dnsmasq[7295]: using nameserver 1.2.3.4#53
>
> telling you which servers are in use.
>
> If you want to be paranoid, you can temporarily add the "log-queries"
> option in a configuration snippet in /etc/NetworkManager/dnsmasq.d and
> restart NM. After that, NM logs will show all the queries sent by
> dnsmasq to each server.
>
> Beniamino


Is there a way to find out about the running configuration of DNSmasq?

The trouble I have is that with /etc/resolv.conf you can see clearly 
what the nameservers are but it is a mystery when it is getting used by 
NM. Apart from seeing some logs.

DNSmasq really doesn't have options for retrieving the current 
configuration. Stuff like the OpenVPN "learn" script uses an exernal 
file followed by -HUP to feed more stuff into DNSmasq. That in itself is 
more usable for a user not knowing what is going on than some DBus 
command. I really don't know how to use DBus, its syntax is too complex.

But DNSMasq was not designed around dbus in that sense, or being 
designed around giving state information on the command line. It puts 
leases in some file and updates that, it doesn't tell you when you ask 
for it.

I wish it could just read the stuff from a file instead of using DBus, 
but yeah.

(Actually, of course, it can, just fine).

This is the OpenVPN learn script, or part of it:

case "$1" in

   add|update)
     /usr/bin/awk '
         # update/uncomment address|FQDN with new record, drop any 
duplicates:
         $1 == "'"$IP"'" || $1 == "#'"$IP"'" || $2 == "'"$FQDN"'" \
             { if (!m) print "'"$IP"'\t'"$FQDN"'"; m=1; next }
         { print }
         END { if (!m) print "'"$IP"'\t'"$FQDN"'" }           # add new 
address to end
     ' "$HOSTS" > "$t" && cat "$t" > "$HOSTS"
   ;;

   delete)
     /usr/bin/awk '
         # no FQDN, comment out all matching addresses (should only be 
one)
         $1 == "'"$IP"'" { print "#" $0; next }
         { print }
     ' "$HOSTS" > "$t" && cat "$t" > "$HOSTS"
   ;;

esac

After which it just does:

# signal dnsmasq to reread hosts file
/bin/kill -HUP $(cat /var/run/dnsmasq.pid)


It's of course pleasant that you can use dnsmasq locally to have access 
to multiple sources (such as VPN and regular internet).


But I just don't know how to troubleshoot when something goes wrong 
because resolv.conf only shows 127.0.1.1 and nothing else.

Is there a command to get the list of nameservers actually getting used 
by the current system?