Friday 27 February 2015

Setting up Layer 4 and 7 Load Balancing with Exchange 2013

Typically you would have two layer 3 load balancers that create a virtual IP for external access (client resolves a namespace to a virtual IP) - they are then routed to one of a pool of client access servers within a load balance cluster. From thier the Client Access Server will query AD (by performing a service discovery) for the Exchange Version and where abouts the mailbox exists in the DAG's mailbox servers - it then proxies the request to the appropriate mailbox server (including re-routing the request through another client access server if the mailbox server is not directly reachable from the current Client Access Server.

In order to setup load balancing in Exchange 2013 we will have two servers with Client Access and Mailbox roles installed.

At the perimeter we will have a layer 4 load balancer which uses a virtual IP and a DNS entry we configured on the external DNS server - or if we don't have access to that technology we can utilize the "round-robin" feature on the AD DNS server e.g. OR alterntivaley we could setup a namespace for our servers - which in turn will require us to install the clustering feature on both of the servers.

We will then require to make some changes to the hostname used for "Outlook Anywhere" feature on the client access server - they must both conform to the same name (

Get-ClientAccessServer | Get-OutlookAnywhere | select identity,*hostname // To check the current hostnames

Get-OutlookAnywhere | Set-OutlookAnywhere -InternalHostname -InternalClientsRequireSsl $false // Sets the hostname for Outlook Anywhere

And finally we can check that they resolve correctly:


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