$4)$ Which one is incorrect?

a$)$ Layer $2$ switches $($bridges$)$ have a MAC address table that maps individual MAC addresses on the network to the physical ports on the switch.

b$)$ When a frame is received, the switch compares the SOURCE MAC address to the MAC address table. If the SOURCE is unknown, the switch adds it to the table along with the port number the packet was received on$.$

c$)$ The switch then compares the DESTINATION MAC address with the table. If there is an entry, the switch forwards the frame out the associated port.

d$)$ Traditionally, the switch learns IP address and port of every transmitting device.