ICND2 DIKTA Chp2 Q5 help

cmztech

I'm in the Wendell Odom book 200-101. DIKTA Chapter 2, Question 5

5. Switch SW3 is receiving only two hello BPDU's, both of which identify the same root switch, received on the two interfaces listed as follows:

SW3# show interfaces status

Port, Status, Vlan, Duplex, Speed, Type
Fa0/13, connected, 1, a-half, a-100, 10/100BaseTX
Gi0/1, connected, 1, a-full, a-1000, 1000BaseTX

SW3 has no STP-related configuration commands. The hello received on Fa0/13 lists root cost 10, and the hello received on Gi0/1 list root cost 20. Which of the following is true about STP on SW3?

a. SW3 will choose Fa0/13 as its root port
b. SW3 will choose Gi0/1 as its root port
c. SW3's Fa0/13 will become a designated port
d. SW3's Gi0/1 will become a designated port


Okay, that is the question. I say the answer is A.
The book says the answer is B.

Can someone explain or is this a typo? Thanks

clarson

the switch computes the cost to the root bridge as the root cost + the port cost. So the switch's computed cost is
a) 10 + 19 = 29
b) 20 + 4 = 24

the switch chooses b or gi0/1.

cmztech

ohh, I see. When you put it that way, now it makes complete sense. I forgot to add+ the port cost to the cost that was being advertised by the neighbors BPDU.

Thanks!