Definition
IKEv2 (Internet Key Exchange version 2), defined in RFC 7296, is a protocol for negotiating IPSec security associations. Strictly speaking, IKEv2 is only the key-exchange and configuration protocol — the actual data is encrypted by IPSec — but the combination 'IKEv2/IPSec' is so common that the name 'IKEv2' is often used for the whole stack. Microsoft and Cisco co-developed it as a replacement for the older, more complex IKEv1.
Why It Is Common on Mobile
IKEv2 was designed with MOBIKE (Mobility and Multihoming Extension), which lets a connection survive network changes — switching from Wi-Fi to cellular, moving between Wi-Fi hotspots, brief signal loss — without re-handshaking. Combined with native support in iOS, macOS, and Windows, this makes IKEv2 a strong default for mobile VPNs. Reconnection is typically near-instant, which is critical for users who move between networks frequently.
Trade-Offs
Strengths: fast, stable on mobile, built into most modern operating systems, well-audited. Weaknesses: uses fixed UDP ports (500 and 4500) that are easily blocked by restrictive networks; less common open-source third-party implementations than OpenVPN; slightly less flexible than OpenVPN for unusual network conditions. IKEv2 is the right choice when you want speed, stability, and native OS support; OpenVPN or WireGuard are better when you need to bypass restrictive networks or run on unusual platforms.