Virtual servers are different from virtual directories. On IIS, virtual servers are a mechanism by which several Web sites can be hosted on a single IIS 5.0 server. In effect, the IIS server behaves as if it were actually multiple IIS servers, each with its own properties, content, and assigned Web site operators. IIS 5.0 allows an unlimited number of virtual servers to be created. Virtual servers, in turn, may have one or more virtual directories contained in them. A virtual directory is always created within a virtual server or on the default Web site.

Virtual servers are created by defining a new Web site and mapping this site to the home directory of the Web content for the site. The home directory for the virtual server may be mapped to:

• A directory on the local machine
• A share on a remote server

http://mis

http://marketing

http://sales

could all refer to the same physical intranet server. As another example, the URLs:

http://www.mtit.com

http://www.santry.com

could likewise refer to the same physical Internet server. In this case, each Web site or virtual server belongs to a separate company.

NOTE: Another name for a virtual server is a Web site. These two terms will be used interchangeably in this book.

What Characterizes a Virtual Server?

Virtual servers (that is, Web sites) are uniquely identified by the following three parameters:

• IP address
• TCP port number
• Host header name

http://server6

http://server6:7200

http://server6:25803

In the first URL above, the port number is not specified, causing the server to respond to the default HTTP port, which is port 80. In the other two URLs, a port number has been randomly chosen from the numbers 1023 to 65535, excluding the well-known port numbers defined in the text file

C:\winnt\system32\drivers\etc\services.

Similarly, multiple Web sites could be created on IIS 5--each with a different IP address, but the same (default) TCP port number (port 80).

The feature of Windows 2000 that makes virtual servers possible is the assignment of multiple IP addresses to a single server, a process known as multihoming. In order to host multiple domain names on a single IIS server, you can assign as many IP addresses to your server as you have Web sites to host. When you create each Web site, you assign it one of the IP addresses bound to your IIS server.

Multiple Web sites can also have the same IP address and TCP port number by using a feature called host header names, which is explained later in this chapter.

NOTE: When you have multiple IP addresses assigned to an IIS server, each time you create a new virtual server, you must assign it an IP address. If you do not assign the virtual server an IP address but instead leave the IP address as "all unassigned" on the virtual server's property sheet, the virtual server responds to any IP addresses that are bound to the server but are not assigned to any other virtual server, making this virtual server the default Web site.

Why Use Virtual Servers?

• Virtual servers are useful for many of the same reasons as virtual directories: security, easy backups and upgrades, content segregation and administration, and so on. However, virtual servers offer even more features than virtual directories do.
• Virtual servers are completely configurable. Each virtual server behaves as if it is a separate IIS server, and all the configuration options for the default Web site are available for any other Web site.
• Virtual servers may be stopped, started, and paused just like a real IIS server. For example, you may want to stop a virtual server while updating it with new content or changing its access permissions.
• Virtual servers may be assigned separate Web site operators. Each department could have its own virtual server and assign users who can fully administer its site. Note: From an administrator's point of view, this is probably the main benefit of using virtual servers--you can delegate administration of virtual servers to their Web site operators!
• Bandwidth-throttling and performance-tuning settings may be established for each virtual server.
• Virtual servers may contain any number of virtual directories. For example, the Marketing Web site could contain a home directory and several subdirectories whose content can be located in noncontiguous locations on various servers in the network, such as:

  http://marketing.mtit.com/

  http://marketing.mtit.com/proposals/

  http://marketing.mtit.com/contacts/