Guest network custom DNS doesn't work

[pastic]

I followed the steps to create an isolated guest network on my dumb AP and it works. However, I run a DNS ad-blocker on my firewall and I want my guest network to query 9.9.9.9 instead of my firewall DNS. But I can't figure out how to enable this.

It looked simple enough: enter custom DNS server in the settings for the guest interface, save, apply and restart the interface. But that does not do the trick. The DNS used (as reported by dig) is still my firewall DNS server. And ads are effectively blocked.

Are there other settings as well to tweak before custom DNS server takes effect?

[grauerfuchs]

There's another setting you need to add:

DHCP Option 6 tells the DHCP clients to use a different server. Otherwise, they will still be instructed to use the default (your router). The example lists both Quad9 IPv4 addresses.