DNS Server WAN vs LAN

Do the WAN DNS servers specified in “Use the following DNS server address(es)” always get used for external DNS when the LAN is set to “Assign DNS server automatically”, or should the desired external DNS servers get specified under LAN too? (My computer sees the DNS server as the Surf SOHO IP address.)

Surf SOHO (Frimware 7.0.0 build 1139)