Question: Interpreting show stp (1)

 In 200-301 V1 Ch10: RSTP and EtherChannel, 200-301 V1 Part 3: VLANs, STP

To analyze Spanning Tree for #CCNA, you need to think about the root switch, then the root ports on the non-root switches, and then designated ports. That analysis usually begins with the show spanning-tree command – a command that packs an incredible amount of meaning into its relatively short output. Mastering every tidbit of meaning from show spanning-tree is a great place to avoid mistakes and pick up points on the exam. Here’s a new practice question that gives you some exercise.


Which answers show facts confirmed by the output from local switch SW4 about the root switch and the listed port G0/1?

SW4> show spanning-tree vlan 1
  Spanning tree enabled protocol rstp
  Root ID    Priority    24577
             Address     fa16.3e9a.25be
             Cost        4
             Port        2 (GigabitEthernet0/1)
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
  1. The local switch (SW4) is the root switch
  2. Some other switch is the root switch
  3. The output does not confirm whether the local switch (SW4) is the root switch or not
  4. Port G0/1 is a port on the root switch
  5. Port G0/1 is a port on the local switch (SW4)
  6. Port G0/1 is a port on some other switch that may or may not be the root switch

As usual, I’ll post the answer in just a few days. At that time, a link to the answer will appear towards the bottom of this page, just above where the comments begin.

Answer: Forwarding and Encapsulation
Interpreting show stp (1) - Answers
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Aaron Timmons

It is B, since the cost is 4 we can say that the interface in a GIG interface !!

and the other in E, Because it is a local interface on the switch that is connected to the root with the cost of 4 !!

Punya Athma

Choices:- A, and, E.

Reasons:- for, (A). Low bridge priority value.

(E). Path cost 4 is a GEthernet port cost. G0/1 is in fact a port from local switch to the root switch. This port listed in the output of show spanning tree, command, is in accordance with the network topology, of this question.

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