SNAT and Tranpanrency on Load Balancer (general) - also valid for Skype for Business

The KEMP LoadMaster combines versatility with ease-of-use to speed deployment of the complete portfolio of advanced messaging applications and protocols used by Microsoft Lync Server 2010/ 2013. Layer 7 health checking at the LoadMaster ensures that should one of the servers become inaccessible, the load balancer will take that server off-line, while automatically re-routing and reconnecting users to other functioning servers.

The entire KEMP LoadMaster product family, including the Virtual LoadMaster (VLM) supports Microsoft Lync 2010/ 2013, and includes a comprehensive first year warranty and technical support agreement.

Microsoft Lync Server 2010/ 2013 supports two load balancing solutions: DNS load balancing and hardware load balancing. You can choose different load balancing solutions for each pool in your deployment. Hardware load balancers are also required to provide load balancing for the internal and external web services when DNS load balancing is used.

Overview of High Availability options per Lync Server Role

Load balancers can be configured to support Network Address Translation (NAT) using one of the following modes:

Full-NAT (SNAT) mode (also known as proxy, secure NAT, source NAT, or SNAT mode). In full-NAT mode, both the source and IP destinations are changed as packets pass through the load balancer.

Half-NAT (DNAT) mode (also known as transparency, destination NAT, DNAT mode or Load Balancers Default Gateway LBDG). In half-NAT mode, the destination IP address is changed as packets pass through the load balancer, but the source IP address remains intact.

Load balancing using Direct Server Return configuration is not supported.

The following table describes the supported configurations for full-NAT and half-NAT modes in Microsoft Terms:

Kemp Terminology:
Full-NAT (SNAT) mode is the equivalent of KEMP Non-transparency mode.

Half-NAT (DNAT or LBDG) mode is the equivalent of KEMP Transparency mode.

How to configuring NAT options:

In an later blog post, I will explain more in detail how to setup KEMP Load Balancer.
I will show you the Hyper-V general setup, as well as the main configuration.


  1. Mr Thomas, Just want to ask one question here.. for scale consolidated edge with HLB.. does it support SNAT or need to do the IP forwarding from the HLB?

  2. Hi,
    there is a bit more you have to know about Edge Server.
    Generally, you have a good explanation here:

    This also depends on how you setup a HLB, one/ two armed.


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