If authentication methods or mechanisms are missing or inadequate, this may result in vulnerabilities. For example, the IEEE 802.1X (Port-Based Network Access Control) standard defines the EAP (Extensible Authentication Protocol). However, some of the EAP methods described contain vulnerabilities. For example, EAP-MD5 is vulnerable to man-in-the-middle and dictionary attacks. Passwords can be guessed if EAP-MD5 is used and communication can also be intercepted.