To filter reports by a specific rack you will first need to get the ID that the rack is assigned.
To get the ID open the Policy Manager Settings --> Policies tab and find the rack you wish to report on and the corresponding ID number. In this example below we will use the Default Rack with Policy ID 1.
Now that we know that the default racks Policy ID is 1 we can use this in the reports to show reporting data for just this rack.
At the bottom of the report you will see a "Conditions" section. This section is where we will tell the report that we only want to see information in the report selected with Policy Id [policy_id] = 1 ( Default Rack).
Now the report will only show reporting information of the Default rack since this is set as a condition for Policy ID 1.
More detailed section information can be found on the reports wiki page. http://wiki.untangle.com/index.php/Reports