When you publish Web servers or server farms, you can select whether the connection from Microsoft Internet Security and Acceleration (ISA) Server 2006 to the Web server or server farm is over HTTP or HTTPS. When the connection is over HTTP, data sent from ISA Server to the Web server, including client credentials needed for authentication delegation, may be sent over HTTP in plaintext, depending on the delegation method, and could be intercepted and read by a user on the same network as the Web server or server farm. When you select to use Secure Sockets Layer (SSL) for the connection, communication from ISA Server to the Web server or server farm will be encrypted and sent over HTTPS.
The use of SSL requires that you install a digital certificate on the Web server or server farm. The name on the certificate must match the internal site name in the Web publishing rule. For more information about certificates, see Digital Certificates for ISA Server at the Microsoft ISA Server TechCenter Web site (http://www.microsoft.com/).
We recommend that you select the SSL option, because this is a more secure configuration, particularly when you use a plaintext authentication delegation such as Basic delegation.