L2TP stands for Layer 2 Tunneling Protocol, and it doesn’t provide any encryption by itself. L2TP VPN usually uses an authentication protocol, IPSec (Internet Protocol Security), for strong encryption and authentication, which gives it an ultimate edge on some other most used protocols like PPTP. The L2TP protocol uses UDP ports 1701.
RFC 2867: RADIUS Accounting Modifications for Tunnel RFC 2867 RADIUS Tunnel Accounting Support June 2000 In order to collect usage data regarding tunneling, new RADIUS attributes are needed; this document defines these attributes. In addition, several new values for the Acct-Status-Type attribute are proposed. Specific recommendations for, and examples of, the application of this attribute for the L2TP protocol can be found in RFC 2809. 第二层隧道协议 - 维基百科，自由的百科全书 RFC 3817： Layer 2 Tunneling Protocol (L2TP) Active Discovery Relay for PPP over Ethernet (PPPoE) RFC 3931： Layer Two Tunneling Protocol - Version 3 (L2TPv3) RFC 4045： Extensions to Support Efficient Carrying of Multicast Traffic in Layer-2 Tunneling Protocol (L2TP)
VPN — IPsec — L2TP/IPsec | pfSense Documentation
Jan 12, 2014 L2TP (remote access) - Sophos L2TP (remote access) The Layer Two Tunneling Protocol (L2TP) enables you to provide connections to your network through private tunnels over the internet. The firewall supports L2TP as defined in RFC 3931. Add L2TP Connection. PPTP (Remote Access) Clientless Access
RFC 3145 - L2TP Disconnect Cause Information (RFC3145)
What is L2TP VPN Service? | SaturnVPN Published in 1999 as proposed standard RFC 2661, L2TP has its origins primarily in two older tunneling protocols for Point-to-Point communication: Cisco’s Layer 2 Forwarding Protocol (L2F) and USRobotics Point-to-Point Tunneling Protocol (PPTP). A new version of this protocol, L2TPv3, was published as proposed standard RFC 3931 in 2005.