SPWebApplication.ExternalUrlZone property
SharePoint 2013
Gets or sets the URL zone to be used for cross-firewall access. A URL zone is a location in the topology of the server farm.
Assembly: Microsoft.SharePoint (in Microsoft.SharePoint.dll)
Property value
Type: System.Nullable<SPUrlZone>An SPUrlZone object that provides the URL zone to be used for cross-firewall access, if there is one; otherwise, null.