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STP Questions 2

November 21st, 2018 in SWITCH 300-115 Go to comments

Question 1


With the use of dot1q (802.1Q) encapsulation, control frames (include STP, CDP, VTP…) are tagged with VLAN 1 if the switch native VLAN is changed -> that means STP BPDU is tagged with VLAN 1 when the native VLAN is set to VLAN 99 -> Answer A is correct.

Reference: http://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches

Control traffic continues to be accepted as untagged on the native VLAN on a trunked port, even when the “vlan dot1q tag native” command is enabled (the native VLAN is tagged with this command) -> Answer D is correct.

Reference: http://www.cisco.com/c/m/en_us/techdoc/dc/reference/cli/nxos/commands/l2/vlan-dot1q-tag-native.html

Note: Control traffic always sent on VLAN 1 when trunking.

Question 2

Question 3

Question 4


The default spanning-tree mode in Cisco switch is PVST+. This spanning-tree mode is based on the IEEE 802.1D standard and Cisco proprietary extensions. PVST+ is same as standard IEEE 802.1D but it runs on each VLAN. In the output we see the line “Spanning tree enabled protocol ieee” under “VLAN 20” so it can say the switch is running in PVST+ mode.

Question 5


If PortFast is configured on a port and it receives a BPDU the port will disable the PortFast feature (and the BPDUs are processed normally).

The “spanning-tree portfast trunk” command makes a trunk port become Forwarding immediately after coming up. Therefore this command is suitable only on trunk ports leading to Layer3 devices, e.g. routers or servers

Question 6

  1. dydx
    July 19th, 2017

    Please where are the questions?

  2. mikeSWE
    July 20th, 2017

    dydx get premium its worth it trust me

  3. CCNP boy
    July 24th, 2017

    are the Q

  4. CCNP boy
    July 24th, 2017

    Are the Qs still valid to pass this exam ? or is there a lot of new Qs ?

  5. LuciasDA
    August 14th, 2017

    STP question 2, doesn’t make sense. Most of the Exhibits are unavailable?! could you clear up the questions here please.

  6. BoZZ
    August 24th, 2017

    Q4 exibit =>

    Switch#show spanning-tree
    Spanning tree enabled protocol ieee

    STP = PVST or PVST+ = IEEE (802.1D)
    whereas RSTP = rapid pvst

  7. BoZZ
    August 24th, 2017

    Q2 Exibit:

    Switch# show spanning-tree summary

    Switch is in pvst mode
    Root bridge for:
    Extended system ID is enabled
    Portfast Default is disabled
    PortFast BPDU Guard Default is disabled
    Portfast BPDU Filter Default is disabled
    Loopguard Default is disabled
    EtherChannel misconfig guard is disabled
    UplinkFast is disabled
    BackboneFast is Enabled

    Explanation of extended system id:

  8. WrittingSoon
    November 7th, 2017

    question 6.
    why is the priority higher. for root selection doesnt it go with the switch with the lowest priority?

  9. Mike
    November 10th, 2017


    In Q1 the explanation is reversed..explanation to A) is refering to D)

  10. Marcus
    December 7th, 2017

    Another dump offer us a few more answers for Q4:
    C. The protocol is Cisco proprietary.
    D. The protocol is supported per MEC basis.
    E. The protocol does not supported by switches that utilizes EtherChannel.

    It also refers to variants A and B as correct.

    But I guess that the answer should be B and C.

    – No such command “spanning-tree mode IEEE”, so A is incorrect.
    – IEEE means PVST or PVST+, both of which are Cisco proprietary. We can find the proof in “Glossary” section of CCNP book:
    PVST+ Per-VLAN Spanning Tree Plus; a Cisco proprietary version of PVST that enables PVST, PVST+, and CST to interoperate on a switch.
    So, answer C is correct.

  11. ticnp
    March 1st, 2018


    IMO, answers should be D,E instead of A,D.

    The referred doc states that switch will accept untagged control traffic, but the question choices are about how is it *sent* and not about how or whether will it be received. So the comment about accepting untagged control traffic is correct but is not applicable to this question

    In a trunk, control traffic is sent on VLAN1, so A can’t be correct

    E states that control traffic with BPDUs for VL1, VL99 (and all others) will be sent through VLAN1. Due to the fact VLAN has been changed to 99, VLAN1 will be tagged.

  12. Anonymous
    August 23rd, 2018

    Any one who knows CCNP updated dumps ?

  13. Anonymous
    September 1st, 2018

    there is something wrong in Q1. It refers to IEEE Bpdu and not to SSTP Bpdu (Pvstp+)
    So I think the correct answer is B. D could be ok if it were SSTP Bpdu.


  14. Max
    September 4th, 2018

    Yes Q1 is not well explained
    IEEE Bpdu are always forwarded untagged (whatever is the native vlan)

  15. Elvis
    October 17th, 2018

    Q1. A and B should be correct answers.

    This list shows how PVST+ interoperates with IEEE 802.1Q or IEEE 802.1D, if the Native VLAN on an IEEE 802.1Q trunk is VLAN 1:

    VLAN 1 STP BPDUs are sent to the IEEE STP MAC address (0180.c200.0000), untagged.

    VLAN 1 STP BPDUs are also sent to the PVST+ MAC address, untagged.

    Non-VLAN 1 STP BPDUs are sent to the PVST+ MAC address (also called the Shared Spanning Tree Protocol [SSTP] MAC address, 0100.0ccc.cccd), tagged with a corresponding IEEE 802.1Q VLAN tag.

    If the Native VLAN on an IEEE 802.1Q trunk is not VLAN 1:

    VLAN 1 STP BPDUs are sent to the PVST+ MAC address, tagged with a corresponding IEEE 802.1Q VLAN tag.

    VLAN 1 STP BPDUs are also sent to the IEEE STP MAC address on the Native VLAN of the IEEE 802.1Q trunk, untagged.

    Non-VLAN 1 STP BPDUs are sent to the PVST+ MAC address, tagged with a corresponding IEEE 802.1Q VLAN tag.

    Note: Native VLAN STP BPDUs are sent untagged.

  16. NeedforCaptain
    February 24th, 2019

    Captain? Please confirm Q1.

  17. MrTadge
    April 20th, 2019

    Levi’s, your explanation confirms that’s the correct answer is as 9tut says, A and D.

    You said A and B and in these scenarios, both are untagged for Vlan 1 and 99 which wouldn’t work.

  18. c1sc0
    May 27th, 2019

    What would happen if you typed “spanning-tree portfast trunk” and the port received BPDU?
    A. port will be immediately forward
    B. trunk port can be portfast mode
    C. BDPU turn this port to err-disabled
    D. the port will disable the PortFast feature

    I believe the correct answer is A as portfast can be used on trunks for immediate forwarding. The command is used under interface. Answer D doesn’t make any sense, C is not correct. B can be also correct but A makes more sense as an answer to that question.

  19. Shtwi
    August 6th, 2019

    can anyone break down and simplify Q1 in an easy way ? the cisco doc is still not that clear

  20. alba
    October 1st, 2019

    Q1 , what is correct ? i confused with it …

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