In What Scenarios Should I Use the DNS Relay Function?
The DNS proxy or relay function enables a DNS client on a LAN to connect to an external DNS server. After the external DNS server translates the domain name of the DNS client to an IP address, the DNS client can access the Internet.
After receiving DNS query packets from the DNS client, the device with DNS proxy enabled searches the local cache. The device with DNS relay enabled directly forwards the DNS query packets to the external DNS server, and does not search the local cache.
If the DNS client needs to obtain resource records on the DNS server in real time, enable the DNS relay function on the device.