I configure the DHCP lease settings to use a different primary DNS server to point my clients to an AdGuard Home server (similar to PiHole) so I can block ads and cache requests. I also use this setup to do conditional forwarding to a Lancache server to download and cache games my kids download from Epic/Steam/Xbox, etc. This setup works great on the main network but causes issues for clients on the guest vlan since they can't reach the DNS server. Most devices timeout trying to reach the primary DNS server but fall back to the secondary (which is the main Deco). However, some devices either have extremly long timeouts or refuse to work at all. This is especially a problem with the Xbox One since it will complain there is no inernet when it can't resolve names using the primary DNS server. As a result I have to manually enter the gateway address as the primary resolver in the Xbox network config.
I've tried putting a Raspberry Pi on the guest network vlan and giving it the same IP as my AdGuard server, but as soon as it talks on the guest vlan I can no longer talk to the AdGuard server on the main network. I don't think it's an ARP issue since the devices have unique MAC addresses, but I think it messes with the routing table since the default route is the same for both networks.
Would it be possible to have a future firmware release configure the guest network to be on a different subnet so they don't overlap? Or, maybe (not sure how this would be possible) have the option to provide different DHCP lease options for the guest network.
My local subnet is 192.168.0.0/24, the main Deco is 192.168.0.1 and my AdGuard server is 192.168.0.2 My lease settings are setup so I only specify the primary DNS server as 192.168.0.2 and I leave the secondary field empty. Wit this setup, clients are assigned 192.168.0.2 as the primary resolver and 192.168.0.1 as the secondary.