Reverse DNS

Reverse DNS is used to convert IP addresses to host name by querying a DNS serveur. So you need to get an Internet access working.
If your logfile have only IP addresses, you can choose to activate this option to get countries stats or you could choose to convert your IP logfile before running W3Perl with a tool like fastresolve.

An alternate way is to use the GeoIP or GeoIP_free module which can do the job locally (but you'll need first to install one of these two perl module). But based on a local file, this is not as accurate than querying a DNS server.