Inter- and Intra-Routing

An Exchange mail system consists of one or more computers, or servers, on which Exchange is installed. In larger installations, these servers are organized into two or more routing groups, which are then connected using Routing Group connectors.

After you install Exchange on the first computer in your messaging system, when you install Exchange on additional servers in the system, the installation program automatically configures the connection between these additional computers and the first computer.

Inter-Routing Group Communication

Inter-routing group communication is communication between servers in different routing groups. Inter-routing group communication usually, though not always, takes place over less reliable or intermittent links. Message transfer and communication is handled between routing groups using connectors. You can use Routing Group connectors, SMTP, TCP/IP X.400, or X25 X.400 connectors to connect two routing groups. In addition, to create adequate fault tolerance, you may want to create multiple connections.

When the recipient's mailbox is on a server in a different Exchange 2000 routing group, the server determines the recipient is on a server in a different routing group, identifies a route for the message to take, and routes the message to the appropriate connector. If the originating server is a bridgehead server, it can open a connection and transfer the message directly to a bridgehead server in the recipient's routing group. Each of the servers in a routing group maintains a table of link state information, which the servers use to determine whether connectors are up or down. The status of the connectors is transferred between servers within a routing group and to servers in connected routing groups, so servers can determine the optimal route from one routing group to another or can reroute messages if a connector is down. When a remote bridgehead server receives the message, the process is repeated until the message is delivered to the recipient's mailbox. Depending on the path a message takes to arrive at the recipient's mailbox, the message may travel through multiple servers and routing groups.

If a message is transferred to a recipient whose mailbox resides on a foreign messaging system or within another Exchange organization, the Exchange server receives the message and checks for the recipient in Active Directory. If the server can't locate the recipient, the server resolves the address by locating a connector over which the message can be transmitted. The server then routes the message to the bridgehead server, and the message travels through the connector. When the connector delivering the message is in a different routing group, the message is routed to that routing group. When the bridgehead server in the connector's routing group receives the message, it transfers the message to the Exchange server that hosts the connector. Depending on the destination mail system, the message may travel through one or more servers and connectors.

Intra-Routing Group Communication

Intra-routing group communication is communication between servers in the same routing group. Servers in the same routing group have reliable, full-mesh connectivity. You can add servers to routing groups only during installation. By default, every server in your organization is added to a routing group. After installation, you can move servers between routing groups to put servers that have reliable connections into the same routing group.

When a computer running Exchange 2000 Server determines that the recipient of a message is on the same server as the sender, it delivers the message to the recipient's mailbox. When the server determines the recipient's mailbox is on a different server in the same routing group, the routing process is slightly more complicated. If the recipient's server is an Exchange 2000 server, the message is routed through SMTP to the recipient's server. If the recipient's server uses an earlier version of Exchange, the message is routed through remote procedure call (RPC) to the recipient's server. Regardless of the protocol used, message transfer within a routing group is point to point, which means that the originating server communicates directly with the target server. When the recipient's server receives the message, it locates the recipient in Active Directory and transfers the message to the recipient's mailbox.

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