Now that you have a textbook understanding of how to deploy Exchange 2000, the real work begins. How do you get from your existing Exchange Server 5.5 organization running on Windows NT 4.0 to Exchange 2000 running Windows 2000 with Active Directory? That is the task at hand. In this section we will try to arm you with the information and tools necessary to answer that question with a reasonable degree of certainty.

There are two components that need to be addressed in upgrading an Exchange Server 5.5 to Exchange 2000: upgrading the directory and upgrading the messaging infrastructure. The directory upgrade is more difficult to manage, because two directories with duplicate accounts need to be melded into a single Active Directory. The messaging system upgrade is heavy lifting because of the sheer volumes of data that need to be migrated or upgraded. With enough information, planning, and testing, your upgrade will be a challenging and successful project.

Upgrading the Directories to Active Directory

Understanding how your Windows NT 4.0 directory and Exchange Server 5.5 directory will come together to make up your Windows 2000 Active Directory is very important to the success of your migration project. The goal is to consolidate two different directories with similar object types into a third directory, maintaining dependencies along the way (Figure 6.6).

Figure 6.6 Merging Two Directories into Active Directory

For most companies that have multiple Exchange sites and/or NT 4.0 domains there will be a period of coexistence between Windows NT 4.0, Exchange Server 5.5, and Active Directory. To make coexistence between these messaging systems possible, certain restrictions had to be placed on how you can configure Exchange 2000 during coexistence. Like Windows 2000, which has a mixed mode to support coexistence with Windows NT, Exchange 2000 has a mixed mode to support coexistence with Exchange Server 5.5. When the first Exchange 2000 server is installed, the organization is in mixed mode. Once there is no longer any need to support Exchange Server 5.5 servers or services, the Exchange 2000 organization can be configured for native mode. Make certain you no longer need to coexist however, because once you flip this switch there's no going back.

For Exchange Server 5.5 to coexist with Exchange 2000, the Exchange 2000 servers must look and feel like another Exchange Server 5.5 server. To accomplish this, certain restrictions are placed on the flexibility of Exchange 2000 Administrative Groups and routing groups (see the sidebar titled Making Exchange 2000 look like Exchange Server 5.5). In mixed mode, the Exchange 2000 Administrative Group and the routing group are directly associated, so that they look to Exchange Server 5.5 like another Exchange Server 5.5 site. The restrictions on how Administrative Groups and routing groups can be configured while in mixed mode are as follows.

Routing groups cannot span Administrative Groups.

A server in a routing group cannot belong to a different Administrative Group.

Mailboxes cannot be moved between Administrative Groups.

Administrative Groups can contain multiple routing groups, but Exchange 5.5 servers will not recognize more than one routing group and will treat all Exchange servers in the Administrative Group as if it were a single site.

When you install your first Exchange 2000 server, after running forestprep and domainprep, coexistence between the Exchange Server 5.5 directory and Active Directory will be established. From the Exchange Server 5.5 directory, Exchange configuration information will replicate to Active Directory, and you will see Administrative Groups starting to appear that will mirror the sites defined in Exchange Server 5.5. During coexistence, therefore, your Administrative Groups will mirror your Exchange Server 5.5 sites, locking your administrative model into something similar to what you had with Exchange Server 5.5.

Making Exchange 2000 look like Exchange Server 5.5

When planning your Exchange 2000 deployment, it's important to understand the basic components of an Exchange 2000 organization. This is important because, as the person responsible for planning the deployment, you need to be familiar with how Exchange Server 5.5 and Exchange 2000 fit together. In previous versions of Exchange, the Exchange organization was made up of sites. Exchange sites defined the administrative model, how messages flowed through the organization, and the X.500 namespace. Each of these aspects of an Exchange site would likely have a unique set of design considerations. The ideal Exchange 5.5 administrative model was different from the ideal routing model. However, since these two design points are folded into a single object-the site-this often leads to compromises during the site design process. Usually, Exchange Server 5.5 sites were designed on the basis of available network bandwidth, with the administrative model taking a back seat. The consequence is that most Exchange organizations have a loose administrative model where users who are defined as Exchange Administrators within a site have full control over all objects in that site.

In Exchange 2000 sites no longer exist. They have been dismantled into three independently configurable components: Administrative Groups, Routing Groups, and the Active Directory namespace (Figure 6.7).

Figure 6.7 Exchange 2000

Each of these Exchange 2000 components can be designed independently of the others to meet specific design considerations. This is only true when Exchange 2000 is in native mode. When in mixed mode, to support coexistence, Administrative Groups and Routing Groups are dependent.

An administrative model that meets your organization's requirements can be implemented without affecting the routing topology, and vice versa.

Administrative groups

Objects in Exchange 2000 are contained in manageable groups named Administrative Groups. The objects in an Administrative Group inherit the permissions assigned the Administrative Groups. Administrative Groups can, but don't have to, contain any Exchange 2000 object. This means that all your routing groups and public folder hierarchies can be contained in one centralized Administrative Group, while your Exchange 2000 server objects are contained in regional Administrative Groups. This type of flexibility allows for new administrative models not previously available with Exchange.

Routing groups

Message flow within and between routing groups is similar to previous versions of Exchange. Messages are delivered between servers within a routing group in a single hop, or point-to-point. Between routing groups, messages are routed through bridgehead servers and across connectors. Despite similarities in how messages flow, there are vast differences between the inner workings of Exchange Server 5.5 and Exchange 2000 message transfer. Some of the major changes to message transfer in Exchange 2000 include SMTP being the primary protocol used to deliver messages within a routing group and the preferred protocol between routing groups. Also, Exchange 2000 is much smarter about how to route a message between routing groups. The state of all connectors that connect routing groups is contained in a database on all servers. Once a connector fails, all servers are notified, and that connector will not be used again until it becomes available.

Those who are responsible for your Exchange 2000 deployment should have a working knowledge of Exchange 2000. Too often those who design the Exchange 2000 topology get all the training while those who do the deployment, it is assumed, will be able to get by on their Exchange Server 5.5 skill set. This may not be the case. After reading this chapter, I think you'll agree.

When to Consolidate before Deploying

When you coexist with Exchange Server 5.5, you inherit the Exchange Server 5.5 site topology into your Exchange 2000 organization. What's more, you can't move servers between Exchange 2000 Administrative Groups to reorganize once the coexistence phase of your deployment is complete. This means that if your Exchange 2000 design or functional specification has a different Administrative Group structure than your Exchange Server 5.5 site topology, you're in a bind (but not alone). There are two approaches to overcoming this problem.

After your upgrade to Exchange 2000 is complete, you can go to native mode and move mailboxes between Administrative Groups (not servers, mind you, just mailboxes). You could then create additional Administrative Groups that contain Exchange 2000 servers, and move users out of unwanted Exchange Server 5.5 sites, then retire those sites.

With Exchange Server 5.5 service pack 1 you can move servers between Exchange Server 5.5 sites using the Move Server Wizard. This presents the other option. You could reorganize your Exchange Server 5.5 site structure to look like your Exchange 2000 Administrative Group structure using the Move Server Wizard, then upgrade from Exchange Server 5.5 to Exchange 2000, resulting in the Administrative Group structure defined in your Exchange 2000 design.

Neither of these options are inviting. Each would require a great deal of effort and resources in addition to extending the deployment process and causing more end-user downtime. However, until Microsoft releases an Exchange 2000 version of the Move Mailbox Wizard, there are not many other choices.

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