[Dnsmasq-discuss] dnsmasq not working as DNS server for client machines

[Chris Green]

On Thu, May 22, 2014 at 08:11:24PM -0700, Dave Taht wrote:
>    On May 22, 2014 3:37 PM, "Chris Green" <[1]cl at isbd.net> wrote:
>    >
>    >
>    > A  A  IP Address: A  A  A  A  192.168.1.125
>    > A  A  Broadcast Address: A 192.168.1.255
>    > A  A  Subnet Mask: A  A  A  A 255.255.255.0
>    > A  A  Default Route: A  A  A 192.168.1.1
>    > A  A  Primary DNS: A  A  A  A 192.168.1.4
>    >
>    > The default route is an ADSL router and the primary DNS is my desktop
>    > server machine running dnsmasq. A So it would appear that dnsmasq isn't
>    > answering DNS queries rather than it's not doing DHCP correctly.
>    >
>    > It's almost certainly a trivial configuration problem but I can't see
>    > it at the moment.
> 
>    Tcpdump is your friend.
> 
Maybe it is but what do I do with it?  :-)

If I run tcpdump on the (supposed to be) dnsmasq server machine
listening for packets on port 53, e.g. I do:-

    tcpdump host 192.168.1.4 and port 53

Then I see incoming packets when systems make DNS requests, e.g.:-

    10:01:26.252358 IP acer-aspire.zbmc.eu.60680 > chris.zbmc.eu.domain:
    59352+ A? chris.zbmc.eu. (31)
    10:01:26.252533 IP acer-aspire.zbmc.eu.30826 > chris.zbmc.eu.domain:
    24757+ AAAA? chris.zbmc.eu. (31)
    10:01:31.257784 IP acer-aspire.zbmc.eu.60680 > chris.zbmc.eu.domain:
    59352+ A? chris.zbmc.eu. (31)
    10:01:31.258104 IP acer-aspire.zbmc.eu.30826 > chris.zbmc.eu.domain:
    24757+ AAAA? chris.zbmc.eu. (31)

So the requests are coming in, it's just that dnsmasq isn't answering.
It sounds as if something, somewhere is preventing responses to
external DNS requests, in other words I still have the 'dnsmasq run by
network manager' mode of operation.  However I can't see where this is
done nowadays, there's no portmapper or similar thing any more.  So
what configures dnsmasq (or anything) to get and act upon packets from
the outside?



-- 
Chris Green