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To prevent inter-server communications from robbing the network of valuable bandwidth, Exchange uses the concept of routing groups. Typically, routing groups will follow the geographic layout of the network. Each physical location is often designated as a routing group. Routing group connectors parallel the WAN links used to connect the various facilities to each other.
The idea behind routing groups is reduction of replication related traffic. For example, if you had a satellite office, you wouldn't want your main office servers to replicate data to 10 remote servers individually, because that would create a lot of network traffic. Instead, routing groups allow the main office to send updates to a single server in the remote office; then that server can distribute the updates to the remaining servers. This way, replication traffic only has to flow across the WAN link once, rather than once for each server.
The server that's receiving the updates is called the routing group master (sometimes referred to as a bridgehead server). Each routing group has its own routing group master.
Exchange routing groups use something called Link State Algorithm (LSA) to maintain link state information. What a lot of people don't realize is that LSA is almost identical to the OSPF (Open Shortest Path First) protocol.
If you find yourself having outing group problems, the first thing you need to know is that Exchange server uses TCP port 691 to swap link state information between servers. Therefore, I recommend beginning your troubleshooting process by verifying that your firewalls aren't blocking this port.
Just like traditional routers, in an Exchange environment, each routing group master maintains a copy of a routing table, known as a link state table. Any time the link state changes on an Exchange server, the change is sent to the server's routing group master over TCP port 691. The routing group master updates its link state table and then propagates the change to other Exchange servers as necessary.
One interesting thing about the link state table is that it is never committed to the hard disk; it is maintained exclusively in RAM. So if your routing groups start to malfunction and you suspect the problem stems from a link state table, you can clear the link state table just by rebooting the server.
Of course we all know that, while rebooting tends to fix a lot of problems, it isn't a magic cure-all. Sometimes you simply need to have more information regarding the problem before you can fix it. It can be pretty tough to extract routing group status information manually though. The reason is because link state information is sent though TCP port 691 in the form of an Orginfo packet. The information contained in this packet is presented in Globally Unique Identifier (GUID) format. It can be a really big job matching GUIDs up to servers, routing groups and connectors.
Fortunately, there is a tool that can accomplish this task for you. Microsoft has created a version of WinRoute that is specifically intended for use in troubleshooting Exchange routing groups. WinRoute extracts the necessary information from the link state table and then displays the information in a readable format rather than in GUID format.
Using WinRoute is simple. After launching WinRoute, select the New Query command from the File menu. Next, enter the server name and bind options that you wish to use. WinRoute will display the routing information in tree format. Information about each of your organization's routing groups may be found beneath the tree's General Info container.
There are two main things that you should be looking for while troubleshooting routing groups. First, you will want to check out the status of each routing group connector. Second, you will want to look at is the Major Version attribute for each routing group. The major version is actually a sequence number that gets assigned upon synchronization. If a routing group's major version number is set to zero, it means the link state information has never been received from the routing group master.
Hopefully, I have given you enough information to help you start to troubleshoot any routing group problems that you might run into. If you need additional help, check out Microsoft KB article 281382, How to use the WinRoute tool.
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