I've been writing a lot about Exchange 2000—that’s where the news is. However, most of us still run Exchange 5.5 servers on Windows NT 4.0 and wonder how we'll upgrade these servers to Windows 2000. For many, upgrading to Win2K will be the first or interim step before even considering Exchange 2000.
Upgrading and running Exchange 5.5 on a Win2K server has several prerequisites and considerations. The only version of Exchange supported on Win2K is Exchange 5.5 Service Pack 3 (SP3). If you're running pre-SP3 versions, you need to upgrade to SP3 before thinking about Win2K. You must also consider which version of Win2K you'll be upgrading to: Win2K Server, Win2K Advanced Server (Win2K AS), and Win2K Datacenter Server (Datacenter) editions will be available, so you must choose the option best suited to your installation. If you're interested in advanced Win2K features such as clustering, you might want to go with Win2K AS to avoid an additional upgrade in the future. And don’t forget that you can’t upgrade NT 4.0 Enterprise Edition to Win2K Server (it's considered a downgrade and not supported).
Next, you have to address items such as domains, Active Directory (AD), and DNS. If your existing Exchange 5.5 server is a domain controller (PDC or BDC), you must deal with this issue in the upgrade. Microsoft recommends that you upgrade the NT 4.0 domain controller to Win2K with AD, then remove the AD after the upgrade is complete. Of course, you need to ensure that other domain controllers are available (and have already been upgraded to Win2K and running in mixed mode) to provide authentication services. The bottom line here is a strong recommendation that when upgrading to Win2K, you set your Exchange 5.5 servers to function simply as domain member servers instead of domain controllers. Don’t forget about DNS: If your DNS infrastructure wasn’t working well with NT 4.0, you might have gotten by; however, with Win2K, you won’t have that luxury.
The final consideration relates to other services. If your Exchange 5.5 servers are running legacy connectors, you might want to keep those servers running NT 4.0 because of problems related to certain network protocols or third-party connectivity software. You must also consider services such as SMTP and Lightweight Directory Access Protocol (LDAP). If your Exchange 5.5 server is running the Internet Mail Service (IMS), you'll have conflicts with the SMTP service that is part of Win2K. LDAP is a similar case, and you need to take steps to avoid conflicts via IP port reassignment or other measures. Last, but not least, are third-party software and other Win2K services. Be sure to upgrade third-party software to versions that support Win2K. Clustering services are close to my heart, as I must upgrade my Exchange 5.5 server running in a
2-node cluster. This procedure is more complex than a standalone configuration and will take some additional planning and time. If you would like more information about running Exchange 5.5 with Win2K, Microsoft has a white paper available on its Web site.