Differences between MAC lockdown and port security
Because port-security relies upon MAC addresses, it is often confused with the MAC Lockdown feature. However, MAC Lockdown is a completely different feature and is implemented on a different architecture level.
Port security maintains a list of allowed MAC addresses on a per-port basis. An address can exist on multiple ports of a switch. Port security deals with MAC addresses only while MAC Lockdown specifies both a MAC address and a VLAN for lockdown.
MAC Lockdown, on the other hand, is not a "list." It is a global parameter on the switch that takes precedence over any other security mechanism. The MAC Address is only allowed to communicate using one specific port on the switch.
MAC Lockdown is a good replacement for port security to create tighter control over MAC addresses and which ports they are allowed to use (only one port per MAC Address on the same switch in the case of MAC Lockdown). (You can still use the port for other MAC addresses, but you cannot use the locked MAC address on other ports.)
Using only port security the MAC Address could still be used on another port on the same switch. MAC Lockdown, on the other hand, is a clear one-to-one relationship between the MAC Address and the port. Once a MAC address has been locked to a port it cannot be used on another port on the same switch.
The switch does not allow MAC Lockdown and port security on the same port.