Current Configuration All below servers are running Exchange 2007, SP1. We don't have any legacy 2003 or 2000 Exchange Servers. Mailbox Services We are running CCR for our mailbox services. The Active Node is located in our central office, and the Passive Node is located at our DR Site, which is a separate AD Site. Hub Transport and CAS We currently only have one CAS and Hub Transport Server, which is located at our central office. This is clearly a concern, as it represents a single point of failure. Edge We are not running any edge servers. We utilize third party solutions for our anti-spam solution. My main objective at this point is to increase our availability in regards to the CAS and Hub Transport Servers. My initial thought was to just install one Hub Transport and CAS server at the DR Site, which is also home to the Passive Node of the CCR. I have read that it is good design to have two Hub Transport and CAS Servers for every AD Site that has an Exchange Mailbox. While this is certainly desirable, I am not sure it is within our budget. I figure I would be far better off adding an additional Hub Transport server at our DR Site, as again, we have only the one right now. Also, once I get an additional Hub / CAS server setup - which would be located at our DR site - could I configure that Hub / CAS server to point to another SMTP gateway which would also be located at the DR site? The objective being if the central site were unavailable, then the DR site would allow mailbox access, and still function in regards to mail transport. Thanks in Advance. Martin

Hi, Base on your scenario, DR(Disaster recovery) site is not the same location as AD site, but machine there should has been added to the same AD, is that right? Be sure theres high speed link between these two sites. You cannot install the Hub Transport server role on the same hardware as the Mailbox server role when the Mailbox server role is deployed in a cluster. However, we support deployment of the Hub Transport server role on the same hardware as the Client Access server role. NLB is a good high availability option for both the Hub Transport server role and the Client Access server role when the Mailbox server role is deployed in a cluster. You can try to deploy a hub transport server in DR site using Windows Network Load Balancing technology. Also you can use DNS round robin load balancing determines the routing path. Fault tolerance is achieved by connecting to the next available server in aprioritized list of serverswhen the selected server is unavailable. Besides, you can create a SMTP Send connector(smart host) to relay email to your SMTP gateway. Note:NLB only can be donewith Exchange 2007 with sp1. You can refer to the below article: How you can load balance Exchange Server 2007 Service Pack 1 Hub Transport Servers using Windows Network Load Balancing technology. http://www.msexchange.org/articles_tutorials/exchange-server-2007/planning-architecture/load-balancing-exchange-2007-sp1-hub-transport-servers-windows-network-load-balancing-technology-part2.html Configuring round robin http://technet2.microsoft.com/windowsserver/f/?en/library/e0f49958-f290-49fc-adb4-71ed8deefd621033.mspx?wt.svl=highavail Load Balancing and Fault Tolerance for Transport Servers http://technet.microsoft.com/en-us/library/bb267003(EXCHG.80).aspx How to Configure the Availability Service for Network Load Balanced Computers http://technet.microsoft.com/en-us/library/aa997237(EXCHG.80).aspx Cluster Continuous Replication Recovery Behavior http://technet.microsoft.com/en-us/library/aa995938(EXCHG.80).aspx Understanding Active Directory Site-Based Routing http://technet.microsoft.com/en-us/library/aa998825(EXCHG.80).aspx Hope it helps. Xiu

Xiu, Thank you for the detailed info and links. We are running Exchange 2007 SP1 so I will continue to plan adding an additional Hub Transport server at our DR location. There is a 100 mb link between the two sites so we decent bandwidth between the two locations. I will read up on NLB as I haven't implemented that before. Thanks again.

Hi, About NLB you can refer to another thread where I give the detail information about NLB. Questions about NLB on CAS/HUB server http://forums.microsoft.com/TechNet/ShowPost.aspx?PostID=3365667&SiteID=17 Good luck. Xiu