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MST Questions

September 7th, 2017 in SWITCH 300-115 Go to comments

Question 1

Explanation

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

Explanation

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.

Note:
+ 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

Explanation

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

Question 5

Comments
  1. Matrix
    October 3rd, 2017

    @Jer: congratulations. Is it 100% valid?

  2. Anonymous
    October 15th, 2017

    Hello Guys,

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  3. oz
    November 22nd, 2017

    Guys,

    i got like 2 or 3 new questions today, some of the questions seems similar but with new options. the only i can remember is:

    1. how to enable the root for vlans 10 and 20 on MST 1 .

    they give you the commands but they are tricky.

    by studing only this material you won’t pass, go a little beyond.

    Good Luck.

  4. I like butter on my butter
    December 4th, 2017

    For those wondering, here is a sample MST configuration:
    spanning-tree mode mst
    spanning-tree mst configuration
    name MYMSTCONFIGLOL (this is optional)
    revision 1
    !! Here is where you define the VLAN configurations !!
    instance 1 vlan XX, YY, ZZ
    instance 2 vlan AA, BB, CC

    This will run MST into 2 instances (3 if you count the IST). Instance 1 would be VLANS XX, YY, and ZZ. I’m sure you can figure out the rest.

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