Configuring Message Routing

Routing Groups and Message Routing

Reliable, permanent connections between computers running Exchange are not always feasible; for example, servers in a company's European offices may be connected to their North American subsidiary by an unreliable, slow link. A full-mesh topology is not effective when a slower, less reliable, or non-permanent network link exists in the routing topology.

In this case, an administrator can place servers in Europe in one group and servers in North America in a separate group. Within each group, servers are connected by high-speed, permanent connections. Between each group, however, there might be a single, slower connection. Groups of servers linked together in this way are called routing groups. This is shown in the following illustration.

Enlarge figure

When you have a single group of servers in a full-mesh topology, no special routing group configuration or administration is required. Routing group configuration and administration becomes necessary only when you need to connect two or more routing groups or when you install connectors to foreign messaging systems in your Exchange Server installation.

Connecting Routing Groups

Communication between two routing groups is handled by Exchange connectors. You can use SMTP, X.400, or Routing Group connectors to connect two routing groups. You can configure multiple connectors of different kinds between two routing groups.

All message traffic leaving a routing group leaves through one or more of the servers in that group, which are known as bridgehead servers. Similarly, all message traffic coming into a routing group enters through a bridgehead server.

If the first bridgehead server to which Exchange transmits message information is down, Exchange uses another bridgehead server, which is defined on the connector within the routing group, to transmit the message.

In addition to message traffic, routing information is also sent through bridgehead servers to other routing groups. This information is called link state information, and other routing groups use it to determine the optimal route from one routing group to another.

Using Public Folders

When a client must use an alternate server to access public folder content, Exchange uses routing groups to determine the closest available server. This allows the client to access public folder content from the closest available server by using a single cost database that also contains e-mail routing calculations. Redundant cost tables maintained in previous versions of Exchange are eliminated.

Related Topics

Link States