[Dnsmasq-discuss] Upstream servers by host tag (or MAC)

Geoff Back geoff at demonlair.co.uk
Thu Sep 23 17:37:43 UTC 2021

On 23/09/2021 17:43, Michael wrote:
> On 9/23/21 04:35, Petr Menšík wrote:
>> Hi Hubert,
>> it may work, if you would run two dnsmasq instances. One for children
>> with OpenDNS as upstream servers, another for everyone else.
>> default instance:
>> bind-interfaces
>> listen-address=
>> server=
>> domain=home.arpa
>> dhcp-option=option:dns-server,,
>> dhcp-option=tag:child,option:dns-server:,
>> ...
>> children instance:
>> bind-interfaces
>> listen-address=
>> server=
>> server=/home.arpa/
>> Because the second instance would forward local domain to main instance,
>> which also registers dhcp, they should be able to resolve any local
>> names. But other names would be served by different server.
>> Children might have reserved different address range, but it might be
>> handy to be on shared broadcast link. Good for link-local address
>> resolution and easy local games setup. Not sure it is relevant anymore.
>> Not sure if can be on the same interface as It would
>> work fine with just DNS, but I think dhcp requires interface=eth0 or
>> similar. Which would block the second instance from working correctly. I
>> think alternative address would have to be on different interface.
> I do almost exactly this so I can confirm it works.
> I have one machine running docker.   On that machine, I run two 
> containers with their own IP addresses (macvlan).    .1 for the primary 
> including DHCP pointing to my main DNS.   Then the .2 version that 
> points to the safe DNS, but relays local name queries (and reverse) over 
> to the .1.
> Then in config as you highlighted above, I point the child machines to 
> the .2 and everything else to .1.
> It would be nice if you could use tags to point to different DNS 
> servers, but until that is an option, this works.
> Michael

I think using different upstream servers based on the requesting client
would be a problem because that would mean the same query would get
different results.  That would appear to be what you would like to see
(IIUC), but you then have all sorts of issues with the caches - there
would need to be separate caches for separate tag-selected servers, with
all the complexity involved in managing that.

Since running multiple copies of dnsmasq for DNS can be done on separate
IPs (I suggest with only one of them serving DHCP) I would tend to go
with that rather than adding multiple-cache complexity.



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Geoff Back
What if we're all just characters in someone's nightmares?

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