Most web servers can be configured do DNS lookups on the IP address of incoming requests, but is more efficient to not have the web server do it. Either the web server or Summary can do the lookups. Someone must do the lookups if you want the Top Level Domain and Domains reports to work. If the Domains report is empty, it could be that DNS lookups are turned off both in the server and in Summary. In Summary the domain name is considered to be the rightmost two or three segments of the name.
Summary uses three segments when it suspects that two segments are indicating a country.
Download - A request for a file that is stored or decoded into a file in the visitor's file system, as opposed to being displayed on the screen as part of a web page. Summary uses the file name extension to determine if a request is a download. The set of extensions used to make this determination can be configured . Duration - Used in Summary to denote the length of a period of time in seconds. The first non-graphic requested as part of a visit.