After upgrading a Windows 2000 Server computer to Windows Server 2003, most Web applications will run normally. Although IIS 6 includes ASP.NET, it also includes the so-called Classic ASP, which is included with IIS 5. Both ASP.NET and Classic ASP can run side by side with no problems because they differentiate between each other by using different filename extensions: ASP for Classic ASP and ASPX for ASP.NET.
One of the biggest problems in moving from IIS 5 to IIS 6 is that IIS 5 enables session state by default and IIS 6 does not. On a server upgrade, IIS 6 should retain the equivalent IIS 5 settings. However, if you're moving your Web site from an IIS 5 server to a new IIS 6 server, you might need to enable session state maintenance in the IIS 6 server properties, as shown in Figure 7.15.
Other than session state issues, most ASP and ASP.NET Web applications will migrate with no modification. Certain types of applications, as we've already discussed, can require IIS 5.0 Isolation Mode to be enabled in the server's properties. Your Web developers should be able to advise you if this will be necessary in your environment.