Which encryption protocol is most commonly used in site-to-site or device-to-device VPN connections?

TLS (Transport Layer Security) is primarily used to secure application-layer communication, such as HTTPS, rather than directly securing network layer VPN tunnels for site-to-site or device-to-device connections.

SSL (Secure Sockets Layer) is an older, deprecated predecessor to TLS and is not commonly used for new VPN implementations due to known vulnerabilities.

L2TP (Layer 2 Tunneling Protocol) is a tunneling protocol that often relies on IPsec for encryption and security, meaning L2TP itself does not provide encryption but rather tunnels traffic.

IPsec (Internet Protocol Security) is a suite of protocols that provides cryptographic security for IP communications, making it the most commonly used protocol to secure site-to-site VPNs and remote-access VPNs for device-to-device connectivity. It operates at the network layer and provides authentication, integrity, and confidentiality for entire packets.