How to create windows Network Load Balance (NLB) for Microsoft Exchange.

What is NLB?

NLB configuration is intended for application with relatively small data sets that does not change frequently such as Web, FTP, VPN to provide high availability, high scalability of client request.

For Exchange services, Load balancing helps distribute incoming client connections over a variety of endpoints to ensure that no one endpoint takes on a disproportional share of the load. Load balancing can also provide fail-over redundancy in case one or more endpoints fails. By using load balancing with Exchange Server 2013, you ensure that your users continue to receive Exchange service in case of a computer failure. Load balancing also enables your deployment to handle more traffic than one server can process while offering a single host name for your clients.

Configuration Steps:-

In my test environment, I have two CAS servers on Windows 2012 R2 using Virtualized environment.



Install ‘Network Load Balance’ feature from ‘Add roles and Features wizard’.




NIC card properties on first CAS (EX2013-CAS2.LAB.LOCAL)



NIC card properties on second CAS (EX2013-CAS3.LAB.LOCAL)



Change NIC ordering. Production NIC should be at top in both the servers.



Open Network Load Balancing console and click on ‘New Cluster’.




Select NLB network interface and click on ‘Next’.



By default, only one default IP will use. If you wish then add multiple IP.



Now click ‘Add’ give IP address of cluster where will be used by client request.



Give the full internet name of cluster OR CAS endpoint, in my example it will be ‘mail.lab.local’. select ‘Unicast’ cluster operation mode.



Let the default option as it is and click on ‘Finish’.



You may see spinning hour glass and the configuration will log at the bottom of the page. Double click on line in case of error during configuration to get detailed error message.



Once the wizard completes successfully, server will be shown in green color.



Now add second CAS server into NLB cluster, the step will most likely be the same.



A successful NLB configuration will show both node (CAS) in green status.



Now create a host record in DNS server pointing to IP address of NLB cluster.


You will notice now, the MAC address of NLB NIC on both NIC is same.



On Exchange shell, run following power shell to force client to use ‘mail.lab.local’.

Get-OutlookAnywhere | Set-OutlookAnywhere -InternalHostname mail.lab.local -InternalClientsRequireSsl $false

You can verify if cluster is reachable using ping command on IP address OR hostname.



Another way to confirm by opening OWA page using cluster name.


Additional consideration if you are using virtualized environment.

Go to NLB Manager \ Cluster Properties \ Clusters Parameters Tab and write down the Network address for the NLB cluster.

Shut down the NLB cluster VMs one by one (make sure you don’t shutdown both CAS at a time) then configure the network adapters in ESX/VMware/HyperV that you added to the VMs for the NLB cluster to use a static MAC address that matches the NLB network address: 02-BF-0A-0A-0A-28.


Please note:-
All content provided on this blog is for informational purposes only. The reason for this blog is to document the things that I have learned reading blogs/books/self about Windows Server. We do not own any responsibility for the events that may happen because of using/applying the code/concepts mentioned in this blog.
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#cas, #exchange, #high-availalablity, #nlb