I did some tests running WireGuard on my GL-MV1000W Brume with DNS set manually on the client device and dnsleaktest.com shows that manual DNS is being used, overriding other DNS settings on the router.

I do not have a public AdGuardHome site, so I tested with public DNS servers from Quad9, OpenDNS, CleanBrowsing, Alternate DNS and AdGuard DNS, none of which I already use, nor used by the VPN provider (NordVPN).

With WireGuard running on the Brume, the DNS requests goes through the VPN tunnel, resulting in DNS servers near the endpoint location. With WireGuard not running, the DNS servers are near my own location.

EDIT:
Note that AdGuardHome is a DNS forwarder, not a true DNS server. Hence, dnsleaktest.com may not show the AdGuardHome IP address, but shows the upstream DNS servers that you have configured in AdGuardHome (e.g., Cloudflare, Quad9).

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