Chapter 3: Understanding Exchange Server Routing Architecture

Overview

One of the most significant differences between Microsoft Exchange Server 5.5 and Microsoft Exchange Server 2003 lies in the basic architecture of an Exchange system. The message routing topology in Exchange Server 5.5 is based on sites. As you’ll recall, a site is a logical grouping of servers that enjoy permanent, high-bandwidth connectivity. Architecturally, each site defines three distinct boundaries: the boundary for single-hop routing, the administrative unit, and a namespace hierarchy in the directory structure.

In Microsoft Exchange 2000 and later, these three boundaries have been separated into individual elements. Single-hop routing is defined by a routing group, the unit of administration is defined by the administrative group, and the namespace hierarchy exists in the Active Directory directory service in the form of a domain. This architecture gives administrators much more flexibility in determining how Exchange Server 2003 is administered because administrative assignments can be divided along functions and activities rather than by geography.

This chapter focuses on the routing architecture used in Exchange Server 2003. It describes what routing groups are, how to plan and name them, how they connect, and how link state information works to provide better message routing than Exchange 5.5 Server. We’ll also look at the transport architecture and discuss some of the transport architectural features.