Protocol selection is the logic a VPN client uses to decide which network protocol to try first when building a tunnel, and whether to switch to another option if the first attempt fails. Common choices can include different transport styles or tunnel methods, each with its own compatibility, performance, and security trade-offs.
It matters because the selection process controls whether remote access connects quickly, reliably, and with the intended security settings. In defense, administrators tune protocol order and fallback behavior to improve compatibility across networks and devices. In attacks, an adversary or faulty network path may interfere with one protocol while forcing repeated retries or fallbacks, which can delay or block access. Weak protocol-selection logic can also expose availability problems if a client keeps choosing a failing path instead of a working one.