@pennypacker 

Yeah, I've said it before but for anyone else in this boat who's just waiting to buy their next non-tplink router, in the meantime probably your cheapest and quickest way to get pi-hole working on the guest and main networks is just to run 2 instances of pi-hole. For me that means 2 pi zeros, but if you have a server you could probably just set it up in a docker container on each network. The router let's you set a primary and secondary DNS server. Set the primary to your main pi-hole's ip and the secondary to the guest pi-hole's ip. This way your clients will all always be using pi-hole, just the instance that they can access. Your guests will probably try and fail to reach your main instance but they will have access to the secondary pi-hole. 

  @richpriest I too want this separate DNS for the guest network feature. I have internal DNS that I want to use for my internal network, but I don't want Guest clients to be able to access it. If I set 8.8.8.8 as the primary option, then I can't resolve my internal systems names cause obviously Google doesn't have my info.

Anyway, the only fix I found that solves it for me is to add my DNS server first and then add Google (8.8.8.8) as a secondary. This seems to allow my guests to access the internet and still allow my internal connection to resolve internal DNS names.  It does mean that they are still trying to use my internal server first and then once it fails it uses google.

Jim

 I also want this separate DHCP/DNS for the guest network. Without this feature, the guest network is useless for me.

+1 to this feature request. I just bought the Deco WiFi 7 mesh system and everything has been great except for this issue. The guest network is useless with pi-hole on the main network.

I would argue that not being able to separately configure the DNS server for the guest network is a critical bug and not a feature request. It seems like an oversight that an isolated guest network depends on something outside of itself.

Completely agree with @Deco-Gecko. This is a bug, not a feature request. Why on earth would a separate vlan not have it's own DHCP/DNS config... either laziness or neglegence.

And the workaround you offer is laughable. Why would I have a guest network if I need to tell manually configure DNS for all my un-trusted devices (or worse, tell guests to do so when they connect)...

  @TP-Link 

As this has now been more than 3 years and most of the replies are either agreements or totally useless 'fixes', I'm now bowing out of the TPLink ecosystem.

I've been a long standing customer, even recommending your devices to many as part of my IT career, and assisting many on these forums (and Reddit), but the lack of support here is enough for me to jump ship.

  @richpriest same here, been waiting for 2 years for this to come but no proper actions are taken. Already moving to Unifi brand with all my wishlist already exists.