The Sessions by Domain Report tabulates the number of unique sessions in the given time frame grouped by the domain where the request originated.  When tabulating, a prefix in front of the domain if found is ignored.  For example, the log entries of proxy2.aol.com and outbound6.hisoftware.com would be listed as aol.com and hisoftware.com respectively.  This report requires that the web server log files contain IP addresses that are resolved to host names.  If the log file does not contain domain host names, then the results of those IP address not resolved will be listed as unavailable.  Please refer to your web server documentation for more information on resolving IP addresses to domain host names.