Understanding the AD Forest
If an AD structure is not already in place, a new AD forest must be established. Designing the AD forest infrastructure can be complex, and can require nearly as much thought into design as the actual Exchange Server configuration itself. Therefore, it is important to fully understand the concepts behind AD before beginning an Exchange Server 2010 design.
In short, a single “instance” of AD consists of a single AD forest. A forest is composed of AD trees, which are contiguous domain namespaces in the forest. Each tree is composed of one or more domains.
The simplest designs often work the best. The same principle applies to AD design. The designer should start with the assumption that a simple forest and domain structure will work for the environment. However, when factors create constraints, multiple forests can be established to satisfy the requirements of the constraints.
Determining Exchange Server 2010 Placement
Previous versions of Exchange Server essentially forced many organizations into deploying servers in sites with greater than a dozen or so users. With the concept of site consolidation in Exchange Server 2010, however, smaller numbers of Exchange servers can service clients in multiple locations, even if they are separated by slow WAN links. For small and medium-sized organizations, this essentially means that a small handful of servers is required, depending on availability needs. Larger organizations require a larger number of Exchange servers, depending on the number of sites and users. In addition, Exchange Server 2010 introduces new server role concepts, which should be understood so that the right server can be deployed in the right location.
Understanding Exchange Server 2010 Server Roles
Exchange Server 2010 firmed up the server role concept outlined with Exchange Server 2007. Before Exchange Server 2007/2010, server functionality was loosely termed, such as referring to an Exchange server as an OWA or front-end server, bridgehead server, or a mailbox or back-end server. In reality, there was no set terminology that was used for Exchange server roles. Exchange Server 2010, on the other hand, distinctly defines specific roles that a server can hold. Multiple roles can reside on a single server, or multiple servers can have the same role. By standardizing on these roles, it becomes easier to design an Exchange Server environment by designating specific roles for servers in specific locations.
Client access server (CAS)
The CAS role allows for client connections via nonstandard methods such as Outlook Web App (OWA), Exchange ActiveSync, Post Office Protocol 3 (POP3), and Internet Message Access Protocol (IMAP). Exchange Server 2010 also forces MAPI traffic and effectively all client traffic through the CAS layer. CAS servers are the replacement for Exchange 2000/2003 front-end servers and can be load balanced for redundancy purposes. As with the other server roles, the CAS role can coexist with other roles for smaller organizations with a single server, for example.
Edge Transport server
The Edge Transport server role was introduced with Exchange Server 2007, and consists of a standalone server that typically resides in the demilitarized zone (DMZ) of a firewall. This server filters inbound SMTP mail traffic from the Internet for viruses and spam, and then forwards it to internal Hub Transport servers. Edge Transport servers keep a local AD Application Mode (ADAM) instance that is synchronized with the internal AD structure via a mechanism called EdgeSync. This helps to reduce the surface attack area of Exchange Server. The Edge Transport role can only exist by itself on a server, it cannot be combined with other roles.
Hub Transport server
The Hub Transport server role acts as a mail bridgehead for mail sent between servers in one AD site and mail sent to other AD sites. There needs to be at least one Hub Transport server within an AD site that contains a server with the mailbox role, but there can also be multiple Hub Transport servers to provide for redundancy and load balancing. HT roles are also responsible for message compliance and rules. The HT role can be combined with other roles on a server, and is often combined with the CAS role.
Mailbox server
The mailbox server role is intuitive; it acts as the storehouse for mail data in users’ mailboxes and down-level public folders if required. All connections to the mailbox servers are proxied through the CAS servers.
. Unified Messaging server
The Unified Messaging server role allows a user’s Inbox to be used for voice messaging and fax capabilities.
Any or all of these roles can be installed on a single server or on multiple servers. For smaller organizations, a single server holding all Exchange Server roles is sufficient. For larger organizations, a more complex configuration might be required.
In some cases with very small organizations, the number of users is small enough to warrant the installation of all AD and Exchange Server 2010 components on a single server. This scenario is possible, as long as all necessary components—DNS, a global catalog domain controller, and Exchange Server 2010—are installed on the same hardware.
In general, however, it is best to separate AD and Exchange Server onto separate hardware wherever possible.
Windows Management and Scripting 