Port security
interface fastethernet0/0
switchport port-security
switchport port-security maximum 1 (the default)
switchport port-security aging absolute (the default)
switchport port-securty aging 1
Principles, theories, labs ...
interface fastethernet0/0
switchport port-security
switchport port-security maximum 1 (the default)
switchport port-security aging absolute (the default)
switchport port-securty aging 1