Configuring Message Routing

Working with a Mixed Topology

If you already have a messaging system in place, or if you need to send messages to and share directory information with other messaging systems, Exchange includes tools that support the following scenarios:

Maintaining messaging connectivity between Exchange and other messaging systems is important to any coexistence strategy. Through the use of connectors, Exchange provides messaging connectivity over LAN, WAN, asynchronous, or X.25 connections. These connectors include the following:

When a computer running Exchange 5.5 communicates with a computer running Exchange 2000 within the same site or in another site in the same organization through a Routing Group connector (a site connector in Exchange 5.5), RPC is used for the message transfer. This is the only time Exchange 2000 Server uses the RPC protocol. Any intra-site directory replication between Exchange 5.5 and Exchange 2000 Server occurs through ADC rather than RPC.

You can install Exchange 2000 Server in existing Exchange 4.0 and Exchange 5.x sites. Installing Exchange 2000 Server does not prevent you from adding computers running earlier versions of Exchange to the site. When you install Exchange 2000 Server on additional computers, you can specify whether the server should join the existing site. Existing site information is obtained from Microsoft Windows 2000 Server Active Directory.

It is also possible for an Exchange 5.5 server to be introduced to a mixed-mode Exchange routing group. This scenario could arise during migration to enable the use of old connectors.

Exchange 5.x uses the site concept to define both administration and routing. Exchange 2000 splits these two functions into administrative groups and routing groups for greater flexibility. When Exchange 2000 is in mixed mode, in which Exchange 2000 Server coexists with Exchange 5.x, this same relationship between administration and routing exists. The Exchange 2000 administrative group and routing group are coupled, and there is only one routing group for each administrative group.

When mixed versions of Exchange coexist, it is important for all Exchange servers to have information about the entire organization. To enable all servers to have information about the entire organization, the following mappings are performed between Exchange Directory and Active Directory:

Mapping and replication of data is accomplished by ADC.

Routing coexistence is also provided by ADC, which provides replication for user objects in the domain naming context and the configuration context. Exchange 2000 reads connected sites and address space information available from computers running earlier versions of Exchange and places the data in its link state table and Gateway Address Resolution Table (GWART). This allows Exchange to use any existing native or third-party connectors.

Similarly, any routes available in Exchange 2000 are replicated by ADC to computers running earlier versions of Exchange through the Exchange 2000 Server GWART, allowing them to use connectors specific to Exchange 2000 Server.

For additional information about planning mixed-mode organizations, see Microsoft Exchange 2000 Server Planning and Installation.

This section contains the following topics: