Exchange Server: How to use the InterOrg Replication Tool to Replicate Free/Busy Between Exchange 2003 & 2007

Recently, the company I work for acquired another large enterprise. In order to facilitate the integration of the two companies, I was required to get the Free/Busy calendar information flowing between the two organizations Exchange Servers. In our situation we were running Exchange 2003 Front-End and Back End servers with Exchange 2007 Edge Transports. The acquired company was running Exchange 2007 with separate mailbox, client access, and hub transport servers.

For us, this was a short term thing as we were migrating to Exchange 2010 anyway. Nevertheless, it was exceedingly important we get this running quickly.

Microsoft actually has three excellent articles on deploying the InterOrg Replication Tool:

InterOrganization Replication Tool

Installing, configuring and using the InterOrganization Replication Tool

How to Use the Exchange 2003 Version of the Inter-Organizational Replication Tool with Exchange 2007

Between those three articles, you can easily get the InterOrganizational Replication Tool set up and configured… but not necessarily operational.
; )

There are three important bits of information those three articles neglect to mention.

In our situation, we purchased another company and needed to replicate Free/Busy information.

However, since the purchased company was in another country and hadn’t been secured to our standards yet, we had strict firewall policies in place between our organizations (even though we were connected via a private VPN at this point).

Obviously RPC (utilizing TCP port 135 and a random port between 1024 & 65535) had to be opened up between our two Exchange servers in order for the Replication Tool to do its magic. However, we also happened upon another interesting fact while watching the traffic flow through the firewall. We kept having issues with it working, and it turns out that RPC needs to be open to the relevant domain controllers in the sites for both sides of the connector.

Effectively, when trying to authenticate to Active Directory, the Replication Tool is trying to authenticate directly against the domain controller and not the Exchange server it is actually connecting to.

Seems obvious now, but there is nothing in the Microsoft documentation that discusses that… it just references the ports to the Exchange servers.

Additionally, we had another little hiccup. We had prepped our Exchange 2003 organization already for the Exchange 2010 migration. Even though we had no actual Exchange 2010 servers in the organization yet, the legacyExchangeDN attribute for all new contact records (utilized for the Replication Tool) was being set to the Exchange 2010 Organization (which was non-existent), not the Exchange 2003 Organization.

This prevented the InterOrg Replication Tool from functioning. We ended up using ADModify.net from Microsoft (an awesome tool) to bulk modify all of the contact records (hundreds) we had imported into Active Directory. We looked at an old account to get the proper format for the Exchange 2003 legacyExchangeDN setting and changed all of the new contact records.

Finally, it’s important to note that the Exchange servers you connect to from the InterOrg Replication Tool need to be the backend servers if you have a split role environment (which we did on both sides).

Once that was done, coupled with the Firewall rules and the legacyExchangeDN modification, we were up and running with the precious Free/Busy data being freely replicated between our organizations.

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