Jafner.net/homelab/docs/DNS Resolution.md

```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.