[Dnsmasq-discuss] multiple upstream servers

Dan Schaper dan.schaper at pi-hole.net
Thu Jul 30 15:36:28 BST 2020


wkitty42 at gmail.com wrote on 7/30/2020 5:09 AM:
> On 7/29/20 7:59 PM, Dan Schaper wrote:
>> You've told dnsmasq to send a lease with option 6 (DNS) set to
>> 10.88.13.3. Where dnsmasq forwards the queries to is not relevant to
>> your issue, you only have one upstream server configured.
>
> are you saying that this
>
>>> dhcp-option=tag:red,option:dns-server,10.88.13.3
>>> dhcp-option=tag:green,option:dns-server,10.88.13.4
>
> is not defining two upstream servers?

It's defining the contents of the lease sent to the client(s). It's not
defining what DNS servers that dnsmasq will use to resolve queries.

So, for a client, that defines resolvers, not 'upstream' servers. The
--server directive defines what servers dnsmasq will use. dnsmasq will
use the resolvers on the hosts /etc/resolv.conf unless --no-resolv is
configured, and then --server configuration modifications.

If this is an attempt to have dnsmasq pick what server to query as it's
upstream depending on what client is requesting then that's not going to
work in my understanding. dnsmasq can only use the actual query contents
to chose different 'upstream' resolvers, things like the query domain or
DNS zone.

If this is an attempt to have a client send all of it's requests to two
different dnsmasq instances then you have to make sure the clients are
only configured to use that specific dnsmasq instance. If it's a linux
client then /etc/resolv.conf must contain that single IP for that
specific dnsmasq server and only that IP address. If there are multiple
IP addresses in /etc/resolv.conf then they will all be used, there is no
such thing as primary and secondary DNS servers.

>>> dhcp-option=option:dns-server,10.88.13.4
>>> server=10.88.13.4#53
>
> or is one of both of these overriding that?

See above for the difference between --server and --dhcp-option
configurations. It's likely that the combined --dhcp-option lines are
giving red clients both .3 and .4 for option 6. After understanding how
--dhcp-option affects clients you may decide that the better
configuration is to set red to .3 and set NOT red to .4, if only red
should use .3 and everyone else should use .4. But that would need to be
checked by actually looking at the configuration on the clients to see
what resolvers they have in their final configuration(s).


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