Custom IP feature should be configurable (enable/disable)

[craSH]

It would be great if the new feature for custom IP interrogation (#94) could be enabled or disabled via a command line argument. In some cases, the host may be able to reveal potentially sensitive internal DNS information for private IP addresses depending on deployment/configuration.

[mpolden]

Good point. In any case we should deny lookups of private IPs, would that be sufficient?

[craSH]

I would welcome that as an option, but I actually have this deployed in my internal network and use it both internally and externally, so I don't want to entirely deny local IP lookups.