Tyler is a junior network engineer and has been reading about the ability to connect two ports on one switch to two ports on another switch using ethernet cables to double the amount of bandwidth available between the switches. He has not yet set up a port aggregation protocol and notices an increasing amount of broadcast traffic being sent back and forth between the two switches. Which of the following is likely not set up on these switches that would have prevented this until he configures some sort of port or link aggregation method? 

a. EIGRP 

b. RIP 

c. BPDU guard 

d. STP