So lets recap some of the issues discussed as they are somewhat spread out in this thread. Trying to make this as non technical as possible to avoid getting non technical folks confused with technical jargon/terms. This isn't a complete list, just some of the basics of what has been already discussed.
- Asus routers, using Asus firmware, will likely include the router's IP address as a LAN DNS address in addition to any manually input LAN DNS address a user may add. This means there is the potential LAN DNS requests could potentially bypass the Pi-Hole by going directly to the Asus router instead of the Pi-Hole.
- If using the Asus router DHCP server, one enters the Pi-Hole IP address into the LAN DNS field (LAN > DHCP Server > DNS and WINS Server Setting > DNS Server 1, and the DNS Server 2 if needed).
- If one flashes the Asus-Merlin firmware (https://www.asuswrt-merlin.net/) to their Asus router, one can disable the router's IP address from being included as a LAN DNS. In the Asus-Merlin configuration; LAN > DHCP set "Advertise router's IP in addition to user-specified DNS" to "No".
- The Pi-Hole documentation (Post-Install - Pi-hole documentation) does not mention or suggest using the Pi-Hole(s) IP address in the router's WAN DNS fields.
- Using Conditional Forwarding (on the Pi-Hole) may cause a loop which could potential cause issues depending on how one configures their router (using Pi-Hole as router WAN DNS for example).
- Several blog posts and other web pages that describe setting up Pi-Hole with Asus routers do make mention of using the Pi-Hole IP address for the router's WAN DNS. Doing so may present potential issues.
- Several blog posts and other web pages that describe setting up Pi-Hole with Asus routers do make mention of enabling Conditional Forwarding. Doing so may present potential issues.
- One can disable the router's DHCP server and enable the Pi-Hole embedded DHCP server if they so choose. One would have to manually re-create any static/reserved IP address mappings, that were present in the router, in the Pi-Hole DHCP server section/settings.
- Depending on one's configuration (both Pi-Hole and Asus router) the LAN client names may not be properly resolved by the Pi-Hole. One method, if using the router's DHCP server, that may or may not be recommended by Pi-Hole, is to edit the "host" file on the Pi-Hole to manually add IP addresses and client names. Then restart the Pi-Hole DNS. If one goes this route, use DHCP server static/reserved IP addresses. There are a number of ways to do this modification of the Pi-Hole host file option. One example: Adding a static host record to PiHole – Zewwy's Info Tech Talks EDIT TO ADD: See the post by deHakkelaar following this post that updates this particular issue and has a better way to deal with unresolved client names.
Couple of additional comments not previously mentioned.
- One issue some may run into when using Pi-Hole with a Asus router running stock Asus firmware or the Asus-Merlin firmware is Guest Network WiFi device DNS requests may not be routed through the Pi-Hole and certain IoT device features may fail to work on the Guest Network, especially when Guest Access Intranet is disabled. This due to the Asus guest network being blocked from accessing main LAN devices including the Pi-Hole. One workaround is to install the Asus Merlin firmware (https://www.asuswrt-merlin.net/), then install the YazFi script (https://github.com/jackyaz/YazFi). The YazFi script includes the ability to set guest WiFi network DNS servers. Make sure to read through the following thread on the YazFi to understand its limitations and additional configuration options: https://www.snbforums.com/threads/yazfi-enhanced-asuswrt-merlin-guest-wifi-inc-ssid-vpn-client.45924/. EDIT TO ADD: See the post by deHakkelaar following this post that updates this particular issue and has a alternate way to deal with the Guest Network WiFi clients when using the YazFi script.
- If using an Asus router one can power a Raspberry Pi Zero W (running Pi-Hole) off the router's USB 2.0 port. May not be recommended but is possible.
- One can setup a Pi Zero (running Pi-Hole) and Asus router with "Ethernet Gadget" connection to facilitate the use of a single USB cable to both power the Pi and provide "Ethernet" connection between the router and the Pi. Older thread with general directions on how to do so with an Asus router and Pi Zero W here: https://discourse.pi-hole.net/t/pi-zero-w-usb-ethernet-gadget-with-asus-router-fix/19352. However, one should test this Ethernet Gadget option extensively before using on a mission critical Asus router. There may be issues with router rebooting or Pi Zero rebooting causing the Ethernet Gadget connection to go offline and not recover.
As always; any modifications to either the router or the Pi or Pi-Hole is at the user's own risk! To make any non recommended modifications like flashing firmware or editing router/Pi/Pi-Hole files will require some additional knowledge including how to use SSH and issue some general Linux commands.