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MST Questions

June 22nd, 2017 in SWITCH 300-115 Go to comments

Question 1


Instead of using Per-VLAN Spanning Tree (PVST) or Rapid PVST which runs a separate STP instance for each active VLAN (there will have 20 STP instances for 20 VLANs), Multiple Spanning Tree (MST) maps multiple VLANs into a spanning tree instance, thereby reducing the number of spanning-tree instances needed. MST also reduces switch resources and managerial burdens.

Question 2


Besides two MST instances 1 & 2, Instance 0 is a special instance for a region, known as the Internal Spanning Tree (IST). The IST always exists on all ports; you cannot delete the IST. By default, all VLANs are assigned to the IST. All other MST instances are numbered from 1 to 4094. The IST is the only STP instance that sends and receives BPDUs. All of the other MSTI information is contained in MST records (M-records), which are encapsulated within MST BPDUs.

+ The Common Spanning Tree (CST) interconnects the MST regions and any instance of 802.1D and 802.1w STP that may be running on the network
+ A Common and Internal Spanning Tree (CIST) is a collection of the ISTs in each MST region.

Question 3


Unlike Per-VLAN Spanning Tree (PVST) which maintains a spanning tree instance for each VLAN configured in the network, Multiple Spanning Tree (MST) maps multiple VLANs into a spanning tree instance, thereby reducing the number of spanning-tree instances needed. MST also reduces switch resources and managerial burdens.

Question 4

  1. dave
    April 21st, 2015

    only two questions on MST? I take it all these new 300-115 questions are supplemental to the previous exam questions….

  2. Musa
    April 24th, 2015

    I got the same questions dave..stp – 2qns now MST – 2qns.
    Does it mean they are the only qns in the exam from this category

  3. peaceful soul
    September 23rd, 2015

    Can I please have questions as well?

  4. peaceful soul
    September 23rd, 2015

    It’s only showing answers….!

  5. Anonymous
    December 28th, 2015

    Hallo all,

    Can you tell me if that dumps are nit valid ?
    Can you send me valid dumps on mail : {email not allowed}


  6. aaa
    December 29th, 2015

    how can i find the questions of the exam plz, i`m just seeing the answers !!1

  7. Sardar Cisco
    February 17th, 2016
  8. Anonymous
    March 6th, 2016

    HI ALL,

    Hi found the next question,

    DSW1 should share the same MST region with switch DSW2. Which statement is true

    and the answer is …

    Configure DSW1 with the same region name , revision number, and VLAN to instance maping as shown on DSW2..

    anyone can say me if this is the correct answer..

    thny a lot!!!

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    April 10th, 2016

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  10. Anonymous
    April 18th, 2016

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  11. Anonymous
    June 7th, 2016

    I do not think this answer is correct because you can not configure the “revision number” that is inherited from DSW2 when you connect them with a trunk port, not directly configuring it. Also, what does region name, wrong terminology, it is “VTP Domain name” and it already matches. Then VLAN to instance map, also inherited when the trunk port comes up.
    I am leaning towards C, or possibly E for the answer.

    C. DSW1 automatically inherits MST configuration from DSW2 because they have the same domain name.

    E. DSW1 is in VTP client mode with a lower configuration revision number, therefore, it automatically inherits MST configuration from DSW2.

    I think it is C, because on E, being in client mode has nothing to do with it inheriting. If it had a higher configuration revision number, even in client mode, DSW2 would inherit configuration. Kind of like the problem with B as a solution.

  12. Maxzer0
    July 23rd, 2016

    @anonymous June, 7th:

    this is wrong. Only VTP version 3 is capable of MST support and both switches are running VTP version 1.

    From Cisco:

    MST instances with the same name, revision number, and VLAN-to-instance mapping combine to form an MST region

    • Revision number—Unsigned 16-bit number that identifies the revision of the current MST
    Note You must set the revision number when required as part of the MST configuration. The
    revision number is not incremented automatically each time that the MST configuration is


    Long story short, the revision number in MST has nothing to do with the revision number in VTP, which increments automatically.

    The exact answer is:

    Configure DSW1 with the same region name, revision number, and VLAN-to-instance mapping
    as shown on DSW2

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