Q. Can additional routing group connectors be installed between newly installed Exchange Server 2007 servers and Exchange Server 2003 or Exchange 2000 Server environments?

A. Yes. By default, all Exchange 2007 servers are placed in a single routing group, which should not change. One routing group connector is also created between one or more Exchange 2007 Hub Transport servers in one site, and one or more Exchange 2003 or Exchange 2000 bridgehead servers within a routing group.

In a widely distributed environment, it may not make sense for all of the mail flow between Exchange 2007 servers and Exchange 2003 or Exchange 2000 servers to pass through one particular Active Directory (AD) site and one particular Exchange 2003 or Exchange 2000 routing group.

For example, lets say I create a routing group connector between Exchange 2007 servers in Dallas and the Exchange 2003 or Exchange 2000 bridgehead servers in a Dallas routing group. This setup is great for the Exchange servers in Dallas, and probably the any other U.S. servers. But what if I have Exchange 2007 and Exchange 2003 or Exchange 2000 servers in London. For a London-based Exchange 2007 server to send a mail to a London-based Exchange 2003 or Exchange 2000 server, the message would probably be sent to the Dallas-based Exchange 2007 Hub Transport server, which would then send the message to the Dallas-based Exchange 2003 or Exchange 2000 bridgehead server, which would then send the message to the London-based Exchange 2003 or Exchange 2000 server.

The New-RoutingGroupConnector cmdlet can create a new routing group connector between the London-based Exchange 2007 servers and the London routing group Exchange 2003 bridgehead servers with the following code:

New-RoutingGroupConnector -Name 'Exchange 2007 RGC' -SourceTransportServers '<FQDN of Exchange 2007 Hub Transport Server>' -TargetTransportServers 'FQDN of Exchange 2003 Bridgehead Server' -Cost 100 -Bidirectional $true -PublicFolderReferralsEnabled $true

You would need to ensure the cost of the new London routing group connector cost is equal to the Dallas routing group connector cost. Otherwise, the routing group connector cost is the first factor used by Exchange to calculate the message route, even though the London routing group connector is in the same AD site as the Exchange 2003 or Exchange 2000 servers.

  • Examine all possible routing paths across routing group connectors and select the routing path that has the least total routing group cost (this ignores the AD site link costs).
  • If more than one routing path has the same cost, examine all possible routing paths across IP site links to reach the first routing group connector, and select the routing path that has the lowest total IP site link cost. In our example, if the Dallas routing group connector has the same cost as the London routing group connector, since the IP site link for the London-based Exchange 2007 server is less for a London Exchange 2007 server, the London routing group connector would be used.
  • If more than one routing path has the same routing group cost, and it has the same IP site link cost, select the routing path that includes the least number of hops.
  • If more than one routing path has the same routing group cost, the same IP site link cost, and the same number of hops, select the routing path where the name of the last AD site before the destination site has the lowest alphanumeric value.

Now, if the London routing group connector has a cost of 101, then the message would still go through the Dallas-based routing group connector, since the routing path for the routing group connectors would be cheaper.

It’s vital that you disable minor link state updates on all Exchange 2003 servers prior to creating additional routing group connectors between Exchange 2007 routing group and any other routing groups in the Exchange 2003 or Exchange 2000 infrastructure. If you don't, routing loops may occur. Exchange 2003 may make updates to its routing topology based connector-down situations, which the Exchange 2007 server would be unaware of. The Exchange 2003 server would send a message to a particular Exchange 2007 server to avoid a down connector, but the Exchange 2007 would send it back because it sees a cheaper route, and the message would keep bouncing between them.

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