Reviewing Tunneling Protocols

The tunneling protocol is the specific technology that defines how data is encapsulated, transmitted, and unencapsulated across a VPN connection. Varying implementations of tunneling protocols exist and correspond with different layers of the Open System Interconnection (OSI) standards-based reference model. The OSI model is composed of seven layers, and VPN tunneling protocols use either Layer 2 or Layer 3 as their unit of exchange. Layer 2, a more fundamental network layer, uses a frame as the unit of exchange, and Layer 3 protocols use a packet as a unit of exchange.

The most common Layer 2 VPN protocols are the Point-to-Point Tunneling Protocol (PPTP) and the Layer 2 Tunneling Protocol (L2TP), both of which are fully supported protocols in Windows Server and are also natively available in Microsoft’s Forefront Threat Management Gateway (TMG) and Unified Access Gateway (UAG) products.