Microsoft® Lync® Server 2013 Unleashed Second Edition

Three-Legged Firewall

A three-legged firewall approach can be used when it is not feasible to have two physically separate firewall devices separating traffic from the different network segments. Typically, a smaller organization does not have or want to manage a back-to-back firewall, so a single device is used instead to logically construct the same functionality as a back-to-back firewall provides. This single firewall device is generally at least three physical network interfaces or “legs” that are all connected to different networks: one to the public Internet, one to the perimeter network, and one to the internal network.

In this scenario, the Edge Server has two network adapters connected within the perimeter network, but these should ...