[Dnsmasq-discuss] dnsmasq to provide public DNS service

[T o n g]

If I'm to provide DNS service to the public (outside my local network) 
using dnsmasq, how to do it, e.g., how to set the listen-address? It 
didn't work out of the box after I installed it in my Ubuntu (16.04 LTS 
xenial) so I changed to the following, but it stops working:

    $ cat /etc/dnsmasq.d/public.conf
    # listen to public
    listen-address=0.0.0.0
    # provide only DNS service and disable DHCP and TFTP on it
    no-dhcp-interface=eth0

    $ dig +short docs.google.com
    ;; connection timed out; no servers could be reached

    $ netstat -ulnp | grep :53
    (Not all processes could be identified, non-owned process info
	 will not be shown, you would have to be root to see it all.)
    udp        0      0 0.0.0.0:53              
0.0.0.0:*                           -               
    udp6       0      0 :::53                   :::*


Please help. 
Thanks.