[Dnsmasq-discuss] Different behaviour with "interface=" on two almost identical systems

[Chris Green]

I've been doing a bit of clearing up of loose ends on systems on my
LAN and decided that dnsmasq really only needs to listen on the
loopback address on all my systems except the actual DNS server for
the LAN.

So I changed the dnsmasq.conf file to the following on all systems
except the DNS server:-

    #
    #
    # Default dnsmasq configuration file, with this configuration file dnsmasq
    # provides only local DNS caching and no DHCP.  This file is used on nearly
    # all my systems which are ever on the home LAN.
    #
    #
    # Set to listen only on localhost.
    #
    interface=
    #
    #
    # This sets the upstream server[s] to the one[s] set by Network Manager,
    # usually automatically using DHCP from the ISP's (or my) DHCP/DNS server.
    # If we're on the home LAN the resolv-file will set the nameserver to
    # 192.168.1.1, if away from home it will be the ISP's nameserver[s].
    # 
    resolv-file=/run/NetworkManager/no-stub-resolv.conf

On my desktop system (192.168.1.3) this works as expected:-

    chris$ nmap localhost | grep 53
    53/tcp   open  domain
    chris$ nmap 192.168.1.3 | grep 53
    chris$ 


But on 192.168.1.4 it doesn't:-
    chris$ nmap 192.168.1.4 | grep 53
    53/tcp  open  domain
    chris$ 

Both systems are running xubuntu with dnsmasq version 2.90.


... and another system, also running dnsmasq version 2.90:-

    chris at t470$ nmap 192.168.1.128 | grep 53
    53/tcp    open  domain
    chris at t470


So why are they acting differently and, possibly more to the point,
how do I make dnsmasq listen only on the loopback address?


... and the /run/NetworkManager/no-stub-resolv.conf file is the same
on all the systems:-

    # Generated by NetworkManager
    search zbmc.eu
    nameserver 192.168.1.1


-- 
Chris Green