The MAIN use of Layer 2 Tunneling Protocol (L2TP) is to tunnel data

 The main use of Layer 2 Tunneling Protocol (L2TP) is to tunnel data in the Point-to-Point Protocol (PPP). L2TP is a tunneling protocol that operates at the data link layer (Layer 2) of the OSI model, and is used to support virtual private networks (VPNs) or as part of the delivery of services by ISPs. L2TP does not provide encryption or authentication by itself, but it can be combined with IPsec to provide security and confidentiality for the tunneled data. L2TP is commonly used to tunnel PPP sessions over an IP network, such as the Internet. PPP is a protocol that establishes a direct connection between two nodes, and provides authentication, encryption, and compression for the data transmitted over the connection. PPP is often used to connect a remote client to a corporate network, or a user to an ISP. By using L2TP to encapsulate PPP packets, the connection can be extended over a public or shared network, creating a VPN. This way, the user can access the network resources and services securely and transparently, as if they were directly connected to the network. The other options are not the main use of L2TP, as they involve different protocols or layers. L2TP does not tunnel data through a firewall, but rather over an IP network. L2TP does not operate at the session layer or the transport layer, but at the data link layer. L2TP does not use the Payload Compression Protocol (PCP), but rather the Point-to-Point Protocol (PPP). References: Layer 2 Tunneling Protocol - Wikipedia; What is the Layer 2 Tunneling Protocol (L2TP)? - NordVPN; Understanding VPN protocols: OpenVPN, L2TP, WireGuard & more.