L2TPIPsec

L2TPIPsec, or L2TP over IPsec, is a VPN protocol stack that combines Layer 2 Tunneling Protocol with IPsec to provide secure remote access over an IP network. L2TP creates a tunnel for PPP frames, while IPsec provides encryption, integrity, and authentication for the traffic carried inside that tunnel.

How it works: The client and VPN server negotiate IPsec security associations using IKE (v1 or v2). The IPsec tunnel is established in tunnel mode, and L2TP messages are transmitted within the protected IPsec payload. NAT traversal (NAT-T) allows operation through devices performing network address translation by encapsulating ESP in UDP. Typically, L2TP uses UDP port 1701, while IPsec uses UDP ports 500 (IKE) and 4500 (NAT-T) and the ESP protocol for data encryption.

Deployment and credentials: Security relies on IPsec algorithms and authentication methods, commonly using pre-shared keys or X.509 certificates. L2TP/IPsec is widely supported across major operating systems and devices, including Windows, macOS, iOS, Android, and Linux, making it a common choice for both enterprise and consumer VPN deployments.

Security and considerations: L2TP/IPsec is generally viewed as more secure than PPTP when configured correctly, thanks to IPsec’s encryption and authentication. Its effectiveness depends on strong IPsec configurations (encryption and integrity algorithms, key exchange parameters) and robust credential management. Potential drawbacks include performance overhead due to double encapsulation and possible compatibility issues with firewalls or NAT devices if NAT-T or ESP is blocked.