#asus
#proxmox
#pi-hole
Pi-hole on LAN doesn't work with "Guest Network Pro". You can enable "intranet access" for guests, but that defeats the point of a separate network.
I didn't find any solutions here, so I figured out a setup that works for me. I'm sharing it in case it helps someone else.
The Asus router will force a random ip address if your device requests one outside the main DHCP range, so you need to configure the main net range to overlap the guest range. For example, I set my Asus router DNS subnet to 192.168.1.1/16 and the guest network to 192.168.2.1/24. The guest network has VLAN ID 52 according to the router. I just left it at the default.
In Proxmox, I installed Pi-hole LXC using tteck's Proxmox VE Helper-Scripts and gave it a static ip address 192.168.9.9/16 for the main LAN.
For the guest network, I added a new network adapter eth1, gave it 192.168.2.9/24 and added the VLAN Tag 52.
And in the Router, under the guest network's "Advanced Settings" I configure the DNS ip from eth1 above:
Now it works. One Pi-hole, two networks. 