IKEv2 stands for Internet Key Exchange Version 2. This VPN protocol is also referred to as IKEv2/IPsec, but as IKEv2 is never implemented without the IPsec encryption layer, it is generally shortened to just IKEv2. It is considered more lightweight and stable than OpenVPN while retaining some customizability. But it is only available over UDP, which is blocked by some firewalls.
IKEv2 is one of the newest protocols and has significant strengths, particularly its speed. It’s well-suited for mobile devices across all platforms.
ExpressVPN recommends you to use the OpenVPN and IKEv2 protocols. While L2TP/IPsec still offers encryption, there may be ways for an attacker to decrypt the VPN session.