(Isaserver2006 is the most widely used isa version in enterprises. This version enhances the support for OWA publishing and multiple web sites publishing, and adds support for sharepointportalserver publishing; The single sign on feature is added to support single sign on for all web services published through a web listener; A new server farm function is added to support server clustering through multiple web servers to achieve load balancing, and this feature does not need windows NLB or cluster support; It strengthens the DDoS Defense Function and greatly enhances the ability to prevent DDoS attacks.)