Simple definition
IEEE 802.1X is a network access-control standard that authenticates devices or users before granting access through a wired switch port or enterprise Wi-Fi.
Technical definition
802.1X involves a supplicant (the client), an authenticator (the switch or wireless access point) and an authentication server, commonly RADIUS. EAP carries authentication information between these components; authorization can assign a VLAN or other access policy.
What is it used for?
Restrict Ethernet and Wi-Fi access to authorized users or managed devices and apply network policies after authentication.
Practical example
For example, a switch can require EAP-TLS certificate authentication before allowing a corporate laptop onto the production VLAN.
Common issues
- certificate expired
- RADIUS inaccessible
- incompatible PEF method
Key takeaway: Always adapt the diagnosis to the product version and the architecture actually deployed.