Simple definition
Port Security is a switching feature that limits which MAC addresses are allowed to use an access port.
Technical definition
Depending on the platform, MAC addresses can be configured manually, learned dynamically, or retained as sticky addresses. A MAC limit and a violation action define what happens when an unauthorized address appears.
How it works / role
The switch learns or compares the source MAC address of frames received on the port. If the configured limit or policy is violated, it can drop traffic, log the event, or place the port into an err-disabled or shutdown state depending on the selected mode.
What is it used for?
Reduce unauthorized wired connections and limit accidental or malicious use, such as connecting an unmanaged personal switch to an access port.
Practical example
A user port allows one sticky MAC address. After the PC is replaced, the old address must be removed or relearned before the new device can communicate.
Common issues
- A sticky MAC remains after a device replacement
- The port is disabled after a violation
- An IP phone plus PC requires more than one MAC address
- The control can be bypassed if an allowed MAC address is spoofed
Key takeaway: Port Security controls MAC addresses seen on a port; it is not a substitute for 802.1X or strong network authentication.