openVPN - Split-tunneling DNS priority

I have commented out the (push "redirect-gateway def1") to turn our openVPN appliance into a split-tunneling mode.

#push "redirect-gateway def1"
push "route 172.21.1.0 255.255.248.0"
push "route 10.61.255.0 255.255.240.0"

However, seems I'm not able to control which DNS resolution goes to which. (as in whether servers sent inquiries to 8.8.8.8 vs internal dns 10.2.1.1 in our case)

I know in Windows, users can set DNS preference.

Is there some universal option across Mac/Win/Linux?

Thanks.

[Update: looking at comments, this seems not possible. Then shall I set internal 1st and public 2nd? What's the best practice within split-tunnel? In terms of DNS resolution in simplest way possible]

Solution 1:

workaround on "abc.ovpn" file on client side and NOT on server side fixed the problem.

Add "--block-outside-dns" and your internal DNS will be overruled by the one given by OpenVPN's TAP adapter.