Message Routing Architecture
When a message is routed, it moves from sender to recipient according to a set of message routing rules. A message route can include multiple hops. A hop is a node along the routing path. In the routing architecture of a Microsoft Exchange Server 2003 organization, the nodes along the message route are represented by routing groups. Messaging connectors connect the nodes, or routing groups, to each other in the internal messaging environment. An Exchange organization might also be connected to an external messaging environment, such as the Internet, using messaging connectors that enable messages to enter or leave the Exchange organization.
This section discusses the following concepts:
Key elements of the Exchange Server 2003 routing topology You must be able to identify the components that comprise the message routing topology of an Exchange organization in order to understand the fundamentals of message routing in Exchange Server 2003.
Exchange Server 2003 message handling Before examining the actual routing mechanisms in Exchange Server 2003, you must understand how Exchange 2003 routes messages that are addressed to recipients who reside on the same Exchange server as the sender and recipients who reside on other Exchange servers in the same routing group, in other routing groups, or on external messaging systems.
Exchange Server 2003 message routing Exchange Server 2003 uses link state information to make dynamic routing decisions, rather than routing decisions based on a static routing table. To understand dynamic message routing in Exchange Server 2003, you must understand how Exchange Server 2003 selects message routes and how changes to the routing topology influence the message routing process.
Propagation of link state information Procedures must exist to replicate link state information between Exchange servers. These procedures ensure that each server has accurate information about the whole organization. With this information, the server can recalculate the optimal path to any destination in the messaging environment according to the current state of the routing topology. You must understand how servers propagate changes to the message routing topology across an Exchange Server 2003 organization. In addition, you must understand the details of the link state table (the table that contains the routing information) and the algorithm that is used to replicate link state information between Exchange servers.
Backward Compatibility with Exchange Server 5.5 Several routing issues arise when you integrate Exchange Server 2003 into an Exchange Server 5.5 organization. You must understand these issues to understand how Exchange Server 5.5 can use Exchange Server 2003 connectors and vice versa.
This section assumes that you are familiar with routing group topology design and the configuration of messaging connectors. For more information on transport and routing, see the Exchange Server 2003 Transport and Routing Guide.