```mermaid graph TB; Upstream["dns.google (8.8.8.8; 8.8.4.4)"] Clients["Clients [192.168.1.0/24]"] Router["VyOS Router [192.168.1.1]"] PiHole["PiHole [192.168.1.22]"] PiHole2["PiHole [192.168.1.21]"] BlackHole["Black Hole"] Router --"Sends DHCP with DNS=192.168.1.1"--> Clients Clients --"DNS Requests"--> Router Router --"Primary"--> PiHole Router --"Fallback"--> PiHole2 PiHole --"Blacklisted domains"--> BlackHole PiHole2 --"Blacklisted domains"--> BlackHole PiHole --"Valid requests"--> Upstream PiHole2 --"Valid requests"--> Upstream ``` Clients connecting to the local network for the first time will receive as part of the DHCP negotiation ([code 6](https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol#Information)) the domain name server's address. This address will correspond to the IP address of the router (`192.168.1.1`). From that point, the client's DNS requests will go directly to the router. This means the PiHole will not be able to track requests per-client. However, a client can be manually configured to request DNS resolution directly from the Pihole. DNS requests to the PiHole will be checked against the [configured adlists](https://pihole.jafner.net/groups-adlists.php). If matched, the request will be blocked. If a user is attempting to access a website that is blocked, the request should quickly resolve to a Domain Not Found error. It will look like this: [Chrome](/docs/img/pihole_domain_blocked_chrome.png) [Firefox](/docs/img/pihole_domain_blocked_firefox.png) If the request does not match any adlists, it will be passed upstream to Google `8.8.8.8` (or backup `8.8.4.4`). Presently, the PiHole does not cache any requests.