Draytek VIGOR2925 SERIES User Manual page 232

If both the Primary IP and Secondary IP Address fields are
left empty, the router will assign its own IP address to local
users as a DNS proxy server and maintain a DNS cache.
If the IP address of a domain name is already in the DNS
cache, the router will resolve the domain name immediately.
Otherwise, the router forwards the DNS query packet to the
external DNS server by establishing a WAN (e.g.
DSL/Cable) connection.
When you finish the configuration, please click OK to save and exit this page.
Vigor2925 Series User's Guide
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