After preparing your Active Directory you're ready to install Microsoft Exchange Server 2007 to bring the new Microsoft Exchange features to your enterprise environment. There are however a few things you need to take into account when you plan Microsoft Exchange Server 2007 Roles in your Active Directory.

As you might have picked up somewhere Microsoft Exchange Server 2007 doesn't utilize Routing Groups and Administrative Groups like Microsoft Exchange 2000 Server and Microsoft Exchange Server 2003 did: Microsoft Exchange Server 2007 maps to Active Directory Sites for it's routing configuration.

I'll discuss the way Microsoft Exchange Server 2007 interacts with Active Directory Sites for routing from two points of view:

• Newly deployed Microsoft Exchange 2007 Organization (new deployments);
• Microsoft Exchange Server 2007 in a previous Microsoft Exchange Organization (coexistence).

New deployments

No more routing groups

What Microsoft Exchange Server 2007 basically does is that it maps a Routing Group to a group of TCP/IP-based subnets connected by fast and reliable connections, which is what Microsoft in Active Directory terms considers to be an Active Directory Site. Furthermore in Active Directory world Sites are used to logically represent the physical network topology, to route replication traffic efficiently and to route queries and authentication requests.

To make use of Active Directory Sites topology for Exchange routing makes perfect sense, doesn't it?

Microsoft conducted a survey to understand the use of Routing Groups and learned that when organizations used Routing Groups they mapped to Active Directory Sites most of the time. Instead of boring you with tediously setting up connectors Microsoft Exchange Server 2007 does the work for you when you deploy a new Microsoft Exchange 2007 Organization!

Not ideal for everyone

Of course not everyone wants to map it's Microsoft Exchange Organization directly to Active Directory Sites, so there's a way to change the default behavior a little bit. But not in the Graphical User Interface! (GUI) The guys from the Exchange team must have known we're real men, so they put the real Active Directory connector fiddling stuff in the commandlets. (the Graphical User Interface is for women only, right Paul?)

Something else that might have lead to the cmdlets-only strategy is the fact that you won't be changing Active Directory site links every day. Why clutter the new Microsoft Exchange Management Console with it?

The Hub Transport Role

The Hub Transport role is responsible for all internal mail flow so message routing in Microsoft Exchange 2007 Organizations is performed by servers equipped with the Hub Transport Role. All Microsoft Exchange 2007 roles are Active Directory site-ware, so servers look into Active Directory to lookup other Microsoft Exchange roles.

A Microsoft Exchange Server 2007 box with the Hub Transport Role (a "Hub Transport Server") will deliver messages to a Microsoft Exchange Server 2007 box with the Mailbox Role (a "Mailbox Server") within it's Active Directory Site or it relays the message to the Hub Transport Server in the Active Directory Site for the Mailbox Server on which the recipient mailbox resides.

If there are no Hub Transport Servers in the same Active Directory site as a Mailbox server, mail can't flow to that Mailbox server. The same is true for the Unified Messaging role, which also needs a Hub Transport Server in the same Active Directory Site.

Coexistence

When you have Microsoft Exchange 2000 Servers and Microsoft Exchange Server 2003 running next to your Microsoft Exchange Server 2007 however you will see a hardcoded routing group, but it's only there for transition and coexistency purposes. If you want to know why the routing and administrative groups are formatted the way they are, check this blogpost by Ross TenEyk.

The Hub Transport Role

The Hub Transport role is responsible for all internal mail flow. This role is similar to the bridgehead server in an Exchange 2000/2003 organization. In fact it originally was called the Bridgehead Role until it was changed.

When the first Exchange 2007 server is installed in an existing Exchange organization, you are prompted to select a bridgehead server in the existing organization with which to establish the initial routing group connector. Exchange 2007 only uses routing group connectors when it communicates with Exchange 2003 or Exchange 2000 servers in the same Exchange organization.

Exchange Routing Group (DWBGZMFD01QNBJR)

All Exchange 2007 servers are automatically put in a single routing group that is called Exchange Routing Group (DWBGZMFD01QNBJR). The initial routing group connector is assigned a cost of 1. The Hub Transport Server that you installed and the Exchange 2003 or 2000 bridgehead server that you selected are set as the source and target servers. Permissions are granted to the bridgehead server to send e-mail to and receive e-mail from Exchange 2007 Hub Transport servers.

Transitioning

Scott Landry of the Microsoft Exchange team made an excellent explanation on the teams blog on coexistence between previous versions of Microsoft Exchange Server and Microsoft Exchange Server 2007 and how to make the transition to Microsoft Exchange Server 2007 without any hick-ups. If you want to know more about the routing groups and need some pictures to understand the whole story I suggest you check it out!

Set-AdSite and Set-AdSiteLink

In Microsoft Exchange Server 2007, computers that have the Hub Transport server role installed use Active Directory sites and the costs that are assigned to the Active Directory IP site links to determine the least cost routing path from each Hub Transport server in the organization to every other Hub Transport server in the organization. After the least cost routing path is determined, the source Hub Transport servers relay messages to the target Hub Transport servers. By default, the Hub Transport servers that are located in Active Directory sites along the path between the source server and the target server do not process or relay the messages in any way.

Partners in crime

The Set-AdSite and Set-AdSiteLink cmdlets are the tools to change the way your Microsoft Exchange 2007 servers with the Hub Transport Role function.

You can use Set-AdSite to make an Active Directory Site act as a hub site. Hub Transport Servers in an Active Directory Hub Site will process messages when they flow through the Active Directory site. This allows for new routing rules, journalling options, etc. Set-AdSiteLink can be used to configure an Exchange-specific cost to the Active Directory IP site link.

Conclusion

In regards to routing your Microsoft Exchange Server 2007 boxes will always use Active Directory Sites. Routing is performed by Microsoft Exchange Server 2007 Hub Transport Servers. You need to place a Hub Transport Server in every Active Directory Site where you have a Microsoft Exchange Server 2007 Mailbox Server or a Microsoft Exchange Server 2007 Unified Messaging Server. You can change the default routing behavior of your Hub Transport Servers by using the Set-AdSite and Set-AdSiteLink Cmdlets.

Further Reading

New Transport and Routing Functionality
Planning to Use Active Directory Sites for Routing Mail
Set-AdSite
Set-AdSiteLink
Dedicated Active Directory Sites for Exchange
Best Practices for Transitioning an Exchange Organization
How to smoothly survive the transition from Linkstate to Exchange 2007 routing

Disclaimer Beta Software

The information on this webpage applies to software from Microsoft that was in testing phase but utilizable by experienced users by the time the webpage was written. This software has not been released for sale, distribution or usage for the general public. The information on this webpage and the beta software are provided "as is" without warranty of any kind, either expressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose.