Sometimes customers face very specific networking requirements or they might be restricted in the amount of available IP addresses that can be allocated to Virtual Services which are used to publish or load balance applications. With the pool of available IPv4 addresses nearly being depleted, the latter scenario is not uncommon. These sort of problems highlight the need for a flexible solution which allows the use of a single IP address for multiple applications while maintaining the full flexibility of load balancing options that you would otherwise also have in a ‘typical’ setup.

Before we move on, it is important to understand how routing/load balancing decisions are being made.

Consider the scenario outlined in the diagram above: a Microsoft Exchange 2013 environment is load balanced on a single virtual IP address: 192.168.10.80.

Whenever traffic hits the virtual IP address – which is configured as a Virtual Service in the LoadMaster – the combination of the IP address and the specific – configured - TCP port will trigger the LoadMaster to use the settings defined in the Virtual Service and forward traffic to the Real Servers that are associated with that Virtual Service.

Without additional configuration, that Virtual Service would operate at Layer 4 and pass along any traffic that comes in through the aforementioned IP address and TCP port combination. The combination of an IP address with a specific TCP port is always unique. As such, once you have configured a Virtual Service, you cannot create another Virtual Service using the same IP address and TCP port.