Configure Windows Network Load Balancing for Hub Transport Servers


Applies to: Exchange Server 2010 SP3, Exchange Server 2010 SP2

You can configure Windows Network Load Balancing (NLB) to distribute non-Exchange messages among your Hub Transport or Edge Transport servers. To learn more about load balancing SMTP traffic, see Understanding SMTP Failover and Load Balancing in Transport.


Using a load balancing solution to handle message traffic between the Exchange servers in your organization isn't supported. You must exclude message traffic between Exchange servers from any load balancing solution you deploy in your environment.

Looking for other management tasks related to handling SMTP traffic? Check out Managing Message Routing.


Step 1: Use DNS Manager to create the SMTP namespace

You first need to create an SMTP namespace that will be used for Windows NLB. The following steps apply to the Active Directory-integrated Windows Domain Name System (DNS). If you use a third-party DNS server, refer to that documentation to create the necessary DNS records with the attributes shown in this procedure.

To perform this step, the account you use must be delegated membership in the DNS Admins group or the Domain Admins group.

  1. Log on to a computer that has the DNS management console installed, click Start, point to Administrative Tools, and then click DNS to open DNS Manager.

  2. If you aren't connected to the DNS server of your domain, use the following steps to connect to a DNS server. If you are connected to the correct server, go to step 3.

    1. On the Action menu, select Connect to DNS Server.

    2. Click The following computer, type the name of the DNS server to which you want to connect, and then click OK.

  3. On the menu, click View, and then select Advanced mode unless it's already selected.

  4. Expand the server name, and then expand the Forward Lookup Zones node.

  5. Right-click the zone in which you want to create the SMTP namespace, and then select New Host (A).

  6. Specify the host name for the SMTP namespace and the associated IP address, and then set Time to live (TTL) to 5 minutes. For example:

    • Name   mail

    • IP Address


      You will notice that when you type the host name, the FQDN box is automatically updated. Make sure that the FQDN box shows the exact name you want to use for your SMTP namespace.

  7. Click Add Host.

  8. Click OK in the confirmation window, and then click Done.

  9. Close DNS Manager.

Step 2: Use Windows to install and configure NLB

The Windows NLB cluster must be created and configured before you can create additional Receive connectors on your Hub Transport servers, and all Hub Transport servers must be added to the Windows NLB cluster.

Create your Windows NLB cluster by following the guidance in Implementing a New Network Load Balancing Cluster in the Windows Server 2008 documentation. Use the DNS record for the SMTP namespace you created in step 1 as the name and IP address of your Windows NLB cluster.

After the Windows NLB cluster has been created and configured, an extra IP address is added to each Hub Transport server. This IP address is known as the virtual IP address.

Step 3: Use the EMC to create a Receive connector

This step should be completed for each Hub Transport server participating in Windows NLB.

You need to be assigned permissions before you can perform this procedure. To see what permissions you need, see the "Receive connectors" or "Receive connectors - Edge Transport" entry in the Transport Permissions topic.

  1. In the console tree, navigate to Server Configuration > Hub Transport.

  2. In the result pane, select the server on which you want to create the connector, and then click the Receive Connectors tab.

  3. In the action pane, click New Receive Connector. The New SMTP Receive Connector wizard opens.

  4. On the Introduction page, enter a name for the connector, and then select Custom in the Select the intended use for this Receive connector box. Click Next.

  5. On the Local network settings page, select (All Available IPv4), and then click Edit.

  6. In the Edit Receive Connector Binding window, select Specify an IP address, and then enter the virtual IP address of the Hub Transport server created when you configured Windows NLB. Click OK.

  7. On the Local network settings page, enter the SMTP namespace you created in step 1 in the Specify the FQDN this connector will provide in response to HELO or EHLO box, and then click Next.

  8. On the Remote network settings page, leave the default values, and then click Next.

  9. On the New connector page, click New.

  10. Click Finish to exit the wizard.

Other Tasks

After you configure Windows NLB for Hub Transport servers, you may also want to do the following:

  • If the Hub Transport server needs to accept messages from non-authenticated sources, make sure Anonymous users is enabled on the new Receive connector. For more information, see step 6 in Configure Receive Connector Properties.

  • If the Receive connector also needs to be used for relaying purposes, you need to perform additional configuration. For example, you may have line-of-business (LOB) applications that need to relay messages through the local Exchange organization for delivery to external recipients. For more information, see Allow Anonymous Relay on a Receive Connector. Also, review the Exchange Server Team Blog article Allowing application servers to relay off Exchange Server.


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