Wisenet cameras ship with a default DNS setting of 188.8.131.52 & 184.108.40.206. These are public DNS servers from a Korean Telecom provider.
The standard configuration of a camera requires configuration of the appropriate DNS servers for your network.
The menu does not allow leaving these fields blank or entering an address of 0.0.0.0.
If you do not have a DNS server on your network, you can enter the loopback address of 127.0.0.1, which will prevent any external DNS inquiries from taking place.