This is an old revision of the document!
Router(config)# interface fastethernet 0/0
Router(config-if)# ip address x.x.x.x y.y.y.y
Router(config-if)# ip nat inside
Router(config-if)# no shutdown
Router(config-if)# interface serial 0/0
Router(config-if)# ip address X.X.X.X Y.Y.Y.Y
Router(config-if)# ip nat outside
Router(config-if)# no shutdown
Router(config-if)# exit
Router(config)# ip nat inside source static x.x.x.x X.X.X.X
Router# show running-config
Router# show ip nat translations
Router# show ip nat statistics
Router# clear ip nat translations *