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Message routing in a coexistence environment
When you install the first Exchange 2007 in Surrey Routing Group, two routing group connectors (Ex20071-Paula and Paula-Ex20071) are created and Exchange Routing Group (DWBGZMFD01QNBJR) is created.
Get-RoutingGroupConnector | fl Name,Sour*,Target*
Later, both ex20072 and ex20073 join the Exchange Routing Group (DWBGZMFD01QNBJR).
The Ex20071,ex20072 and ex20073 belongs to the Exchange Routing Group (DWBGZMFD01QNBJR).
Scenario 1:
Mike2003 mailbox is in Exchange 2003 server in PrinceGeorge Routing Group.
Mike2007 mailbox is in Exchange 2007 server in PrinceGeorge Routing Group.
Mike2003 sends a message to Mike2007. Even though the exchange 2003 and exchange 2007 are nearby, the message path still goes a long way.
Scenario 2:
Mike2003 is on Exchange 2003 server in Burnaby Routing Group. Mike2003 sends messages to Mike2007 in PrinceGeorge Routing Group.
Best solution: install the first Exchange 2007 in Vancouver Routing Group?
Both the hosting Exchange servers for Mike2003 and Mike2007 are in the same Prince George Site (AD site). However, the message delivery takes a long way.
How about to create a new Routing Group Connector?
New-RoutingGroupConnector
Two RG connectors exist in the coexistence environment.
When Mike2007 sends a message to Mike2003, it will be delivered locally.
Problem arises when you introduce the extra Routing Groups. Exchange 2003 servers use the Link State mechanism to determine the route status and best route. Exchange 2007 servers rely on Active Directory topology and have no knowledge of the Link State knowledge exchange.
First thing, you must 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
If you don’t, the looping may occur.
Three RG connectors exist in the coexistence network.
How may the looping occur?
When John2003 sends mail toe Mike2003, the lowest cost route will be:
Ex20071 is in site Vancouver.
Ex20073 is in Site Surrey.
Ex20072 is in site princeGeorge.
Assuming the RG2-3 is down.
Because of the minor link state update, all Exchange 2003 servers know the RG2-3 is down. However, Exchange 2007 servers don't have any knowledge of down link. Exchange 2007 servers still use the RG2-3 route to make routing decision.
At Vancouver Routing Group, Exchange 2003 selects RG1-4 route for delivery (RG1-4+RG3-4=1+25).
Because Ex20071 does not have knowledge of RG2-3 down status, Ex20071 makes the decision (RG2-4+RG2-3=5+10; RG3-4=25). So, Ex20071 delivers the message to Ex20072. Ex20072 delivers it to Exchange 2003 server in PrinceGeorge Routing Group. The exchange 2003 server knows the RG2-3 is down. The exchange 2003 selects the RG1-2 route.
Looping occurs. Mike2003 cannot receive messages from John2003.
If there is physically no loop, the looping would happen.