Exchange 2003 organization
You should install the first Exchange 2007 server in VANCOUVER Site.
All Exchange 2007 servers belong to Exchange Routing Group (DWBGZMFD01QNBJR). When you install the first Exchange 2007 in VANCOUVER SITE, the routing group connector (two-way) between Exchange Routing Group (DWBGZMFD01QNBJR) and VANCOUVER routing group is created.
All messages that are relayed between Exchange 2007 and Exchange 2003 are routed through the initial routing group connector.
An Exchange 2007 is introduced into Burnaby Site. Tim's mailbox is hosted in Exchange 2003 of burnaby site. Chris's mailbox is hosted in Exchange 2007 of Burnaby Site.
When Tim sends mail to Chris, it will be routed through VANCOUVER Site and come back.
To avoid such excessive routing hops, you can create another routing group connector that connects the single Exchange 2007 routing group to the Burnaby routing group.
To avoid routing loop, modify the registry to suppress link state. Routing loop is a potential situation. It only occurs in a complex environment.
To suppress link state updates on Exchange 2003 or Exchange 2000
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\RESvc\Parameters.
Right-click Parameters and select New DWORD value. Name the new DWORD value SuppressStateChanges--value:1
Restart computer
New-RoutingGroupConnector -Name "RGC Burnaby Vancouver" -SourceTransportServers "Ex2007Burnaby.contoso.com" -TargetTransportServers "Ex2003Burnaby.contoso.com" -Cost 1 -bidirectional $true -PublicFolderReferralsEnabled $true
After a new routing group connector is created between Burnaby Routing Group and Exchange Routing Group, Tim sends mail directly to Chris without going through VANCOUVER SITE. However, if you want that message sent by Chris to TIM is routed without going through VANCOUVER SITE, you are better to assign the same cost for both routing group connectors.
The lowest cost routing path across routing group connectors is always used, and the Active Directory IP site link cost to reach the first routing group connector is only considered when two routing paths across routing group connectors have the same cost.
In the following diagram, all exchange 2007 servers are in same Exchange Routing Group, even though they are in different site.
All Exchange 2007 servers are in the same routing group: Exchange Routing Group.
Logical diagram of the routing groups communication:
Messages among Exchange 2007 servers are based on AD sites.
Messages from Exchange 2003 servers to Exchange 2007 and messages from Exchange 2007 to Exchange 2003 are based on Routing Group Connectors (RGC).
Example: A hub transport server in Site A delivers a message to Routing Group B.
Three possible routing paths exist.
Option 1:
RGC-1 and RGC 1-2 (10+10)
Option 2:
RGC-2 (10). The source mailbox is in Site A. Best routing path based on Routing Group Connector cost does not count the AD IP Site Link cost. The message travels from HUB Transport server in Site A to Hub Transport Server in Site B. Site B delivers the message to Routing Group B.
Option 3:
RGC-3 and RGC 2-3 (10+10)
The source mailbox is in Site A. Best routing path based on Routing Group Connector cost does not count the AD IP Site Link cost. The message travels from HUB Transport server in Site A to Hub Transport Server in Site C. Site C delivers the message to Routing Group C and then to Routing Group B.
Best route: option 2.
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Routing loop
There are two reasons. If there are 2 or more connectors between two routing groups and primary connector is down, Exchange 2003 will pick the alternate connector (route). Exchange 2003 uses the minor link state method to notify each other about a down link. However, Exchange 2007 does not use the link state. Without knowing a routing group connector down, Exchange 2007 continues to route messages to the down connector.
Let me modify the cost of Routing Group Connectors.
Messages from Site A to routing group B.
Best route is RGC-3 (cost 5) + RGC 2-3 (cost 10).
However, RGC 2-3 is down. Because of the minor link state update, all Exchange 2003 servers know the RGC 2-3 down. However, Exchange 2007 servers don't have any knowledge of down link. Exchange 2007 servers still use the RGC-3 and RGC 2-3 route. When messages reach the Routing Group C, Routing Group C selects the RGC 1-3 path because the RGC 2-3 path down. When Routing Group A gets the messages, it routes them through RGC-1 connector because it has the lower cost.
Looping:
