Planning Your Exchange Server Routing Design


Topic Last Modified: 2005-04-29

Your routing topology is the basis of your messaging system. You must plan your routing topology with network, bandwidth, and geographical considerations in mind. This topic explains how routing works in Microsoft® Exchange Server 2003 to create a routing topology that works with your existing systems and network and shows you how to design connectors for communicating with recipients outside your organization.

Routing describes how Exchange transfers messages from one server to another. When planning your routing topology, you need to understand how messages are transferred within Exchange and plan a topology for the most efficient transfer of messages. You also need to plan the locations of connectors to messaging systems outside your Exchange organization. Careful planning can reduce the volume of network traffic and optimize Exchange and Windows services.

If any of the following factors apply, multiple routing groups may be necessary:

  • Network connections don't provide the connectivity required.

  • Problems often afflict the underlying network.

  • There are multiple Exchange 5.5 sites.

  • Message transmission must be scheduled or controlled between different locations.

  • You need to set up administrative restrictions around message flow.

The topic Assessing Your Exchange Server 2003 Design Requirements describes the process of conducting a thorough assessment of your existing network infrastructure. Before you begin planning your routing design, use the information you gather about your existing network to answer the following questions:

  • What is the current network topology?

  • What are the connections between locations, including available bandwidth and latency?

  • What other applications use bandwidth, and what applications are planned for the future?

  • How many users are at each location?

  • Where are the users located, and what are their usage patterns? With which groups do they communicate?

  • What type of business does your company conduct? Consider tools that are already using bandwidth (for example, point-of-sale systems).

  • Where are the data centers?

  • Where are your Internet access points?

  • Do you need access to public folders across locations? Do you have applications or public folder usage across different locations?

  • Do you need to share free/busy information across locations? (Remember that free/busy information is handled in the same way as public folder referrals.)

  • What is the current Active Directory design, and where are global catalog servers and domain controllers placed? How are the Windows sites designed (in other words, do they correlate to routing groups)?

Connectors between routing groups are ways to funnel mail; in fact, too many connectors can have a negative impact on message flow. For this reason, try to avoid creating too many routing groups; it is recommended that you not exceed 150 routing groups. However, in situations where you have multiple connections to a possible destination, you can define connectors between routing groups to control message flow. Within a routing group, communication between servers is point-to-point, so you cannot determine paths and costs to ensure the least expensive route between two servers is chosen. However, by creating routing groups, you can assign costs to various paths to ensure the most efficient route is used.

In addition to planning routing groups internal to your organization, you also need to plan the locations of connectors to messaging systems outside your Exchange organization.