If you are managing a single Exchange server or your Active Directory environment has just one site, your worries are over. When you deploy the first Exchange 2007 server that has the Hub Transport server role installed, a routing group connector is established between the servers that are running different versions of Exchange Server so mail continues to flow while you move mailboxes and transfer any connectors to external domains from servers that are running earlier versions of Exchange Server to Exchange 2007. If your Exchange organization is running multiple servers, you can modify the default routing group connector to add source servers and target servers. Making those configuration changes provides fault tolerance and load balancing.
If your Active Directory forest contains multiple sites, make sure that you take some time to plan your transition. Because two different administrators may manage Exchange Server and Active Directory in your organization, you might not be sure that the topology created by the Active Directory administrator is suitable for Exchange Server. However, the reasons for defining Active Directory sites are the very same reasons that you defined Exchange routing groups! Both are engineered to optimize traffic over the underlying network. You may be pleasantly surprised to discover that your current routing group configuration actually mirrors the Active Directory site configuration. Chances are that your routing group connectors are also following a similar path as the IP site links.
You can find out all about the Active Directory site and IP site link configuration by using commands in the Exchange Management Shell. For example, to see a list of all the Active Directory sites in the forest, type the following command:
To see a list of all the IP site links configured in the forest together with the Active Directory sites with which they are associated, run this cmdlet:
For more information about the Exchange Management Shell, see Using the Exchange Management Shell.
There are some big differences between the way that Exchange 2003 and Exchange 2007 perform message routing, and also there are some similarities. Think for a minute about why you created routing groups and routing group connectors. When you created these objects, you defined how Exchange 2003 servers communicate. Exchange 2003 servers in the same routing group can communicate directly with one another. Exchange 2003 servers in different routing groups have to use routing group connectors to communicate, and each routing group connector defines a point-to-point connection between routing groups. When no point-to-point connection between routing groups exists, SMTP traffic has to relay from routing group to routing group to get where it is going.
In Exchange 2007, Active Directory site membership determines which Exchange 2007 servers can communicate directly with one another. Exchange 2007 Hub Transport servers use the intra-organizational Send connector (implicit and invisible!) to relay messages to other Hub Transport servers, whether they are located in the local Active Directory site or in a remote Active Directory site.
Every time that a message leaves the confines of the routing group or Active Directory site where it originates, it must select a route to its destination. The algorithms used to determine routing paths in Exchange 2003 and Exchange 2007 are very similar. The server versions simply consider different configuration objects.
For more information about how Exchange 2007 uses site membership for routing messages and server discovery, see Planning to Use Active Directory Sites for Routing Mail.
The following analogy demonstrates the efficiency of the Exchange 2007 routing system compared to the Exchange 2003 routing system.
Imagine that your entire Exchange organization is a country with a transportation system based on toll roads. Because every road has a toll, you always plan the cheapest route. In Exchange 2003, each routing group represents a city in that country, and the routing group connectors are the roads between the cities. In Exchange 2003, message routing is like driving to your destination and stopping at every city along the way. If at some point during the journey, you encounter an obstruction, like a bridge that's out, road construction, or a road crew taking a long break, you have to stop to ask directions and hope that a suitable detour is available. What's more, the server that gives you the new directions must broadcast the detour route country-wide. All the maps must be updated to reflect the new route, and when the obstruction is removed, the maps are updated again. In the meantime, the detour can take you far from your destination.
Exchange 2007 doesn't work that way. In Exchange 2007, the Active Directory sites represent the cities and the IP site links are the roads, but you get to fly to where you're going, instead of drive. Once you know your destination, you hop on an airplane and fly over all the cities along the way. If for some reason you can't land at your destination city because of heavy fog, a blizzard, or baggage handlers on strike, the plane simply changes direction and lands in the closest possible city to your destination. Then it waits for conditions at your destination to change and resumes the flight when conditions allow. The flight path parallels the roadways, and each road still imposes a toll, so you select the cheapest route before you embark on the journey. This helps determine which city your flight diverts to if there are problems.
If there isn't a direct flight path between two given locations, you can specify that some or all flights must stop in a hub city before the journey can continue. When more than one person is on your flight, just like when a message is addressed to more than one recipient, and each person is going to a different destination, you all travel together until you reach a fork in the individual routes to your destinations. Then there's a short layover and passengers change planes as needed to reach their own destination.
Even better, if you don't agree with the tolls being charged to travel the roads between cities (i.e., the costs assigned to IP site links by the Active Directory administrator), you can change the rate that is charged to Exchange 2007 servers. Adjusting the tolls can change which flight path is the cheapest and may determine whether your flight is routed through a hub.
In Exchange 2007, these "transportation" efficiencies benefit your organization in the following ways:
-
Sticking with a single, deterministic route even when failures are encountered eases troubleshooting. You can easily determine the point in the routing path where problems occurred and begin investigations there. That's not so easy to do when messages take a detour route.
-
Fewer servers handle messages. Exchange 2007 takes advantage of the underlying IP network to eliminate interim hops between source servers and target servers.
-
The server-to-server communication overhead that exists in Exchange 2003 to keep detour routes up to date is eliminated.