An Introduction to Exchange 2013 Load Balancing

By Michael Van Hornebeeck,

Ever since Exchange 2010, load balancing has become an essential part of highly available Exchange Server infrastructures. While the new Exchange 2013 architecture allows for other, perhaps easier, ways to support load balancing requirements, there are still various options to choose from…

As with most IT topics, it's best to start with the basics. This is no different with load balancing for Exchange 2013. When setting up load balancing for your Exchange infrastructure, the following concepts will always be involved:

  1. A virtual service (VS) -- also often called a virtual IP -- which is configured on the load balancer. The VS is usually a unique combination of an IP address and a TCP port, like and port 443.
  2. Each VS contains a set of rules that defines the load balancing logic that it will use. Along with the set of rules, each VS also contains two or more "real" servers. Traffic that hits the load balancers is forwarded there.
  3. Each VS also contains what is known as a health check. The load balancer executes this health check against the underlying servers in order to determine whether they are available to route traffic to.

For example, if a server is down, it is removed from the pool of servers and will not receive traffic until it is available. Depending on the make and model of your load balancer, a health check may be anything from a simple ping to an advanced script that checks end-to-end functionality of the VS on the real servers.

Load balancing typically operates at two different layers: Layer 4 (L4) and Layer 7 (L7). When talking about load balancing, we're really talking about network, right? Try hard and I’m sure you'll remember some -- if not all -- of the layers of the famous OSI model.


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