37. Assuming that all switches in a network have the default bridge priority for each MST instance, what effect does the command spanning-tree mst 10 root primary have when entered on a single switch?
- sets the bridge priority on the switch to 24586 for MST instance 10
- sets the bridge priority on the switch to 24576 for MST instance 10
- sets the bridge priority on the switch to 28672 for MST instance 10
- sets the bridge priority on the switch to 24582 for MST instance 10
Explanation: In MST configuration, an MST instance priority can be defined in one of two methods:
- spanning-tree mst instance-number priority priority, where the priority is a value between 0 and 61,440, in increments of 4096
- spanning-tree mst instance-number root {primary | secondary}[diameter diameter], where the primary keyword sets the priority to 24,576, and the secondary keyword sets the priority to 28,672
38. Which number is assigned to the internal spanning tree MST instance?
- 0
- 1
- 15
- 16
Explanation: MST uses a special STP instance called the internal spanning tree (IST), which is always the first instance, instance 0.
39. A network administrator is configuring MST on switch SW1 to change VLANs mapping to instances. Under which configuration mode should the administrator enter the instance instance-number vlan vlan-id command?
- SW1#
- SW1(config)#
- SW1(config-if)#
- SW1(config-mst)#
Explanation: To map VLANs to an MST instance, the MST configuration submode must be entered with the command spanning-tree mst configuration. The prompt is changed to SW1(config-mst)#. VLANs are assigned to a different MST instance with the command instance instance-number vlan vlan-id.
40. How many MST instances are supported by Cisco switches by default?
- 8
- 16
- 32
- 64
Explanation: Cisco supports up to 16 MST instances by default. These MST instances are numbered 0 to 15.
41. Which term is used to describe a grouping of MST switches with the same high-level configuration?
- region
- domain
- instance
- container
Explanation: A grouping of MST switches with the same high-level configuration is known as an MST region.
42. What is a parameter that must match for all switches in the same MST region?
- IOS version
- region name
- switch model
- bridge priority
Explanation: The MST region name must match for all switches in the same MST region. This parameter can be adjusted through the MST configuration.
43. What are two misconfigurations within an MST region that might introduce port blocking unintentionally? (Choose two.)
- trunk link pruning
- VLAN assignment to the IST
- too many VLANs assigned to an instance
- misconfigured region name across the MST region
- misconfigured revision number across the MST region
Explanation: VLAN assignment to the IST and trunk link pruning are two common misconfigurations within the MST region. A misconfigured region name or misconfigured revision number will cause the failure in forming the MST region.
44. Refer to the exhibit. A network administrator issues the show spanning-tree mst configuration command to verify the MST configuration. How many VLANs are assigned to IST?
- 4071
- 4072
- 4073
- 4094
Explanation: By default, all VLANs are assigned to IST before VLANs are assigned to other instances. In the configuration shown, IST contains all VLANs except for the 23 VLANs assigned to instances 1 and 2, which is 4071 VLANs.
45. What is a solution to mitigate the MST misconfiguration caused by improper trunk link pruning?
- Allow the VLANs associated with the IST on all trunk links.
- Move the affected VLAN to an MSTI instance other than the IST.
- Ensure that the MST region name is consistent across MST regions.
- Ensure that only VLANs in the same MSTI for a trunk link are pruned.
Explanation: An effective approach to mitigate the MST misconfiguration caused by improper trunk link pruning is to only prune all the VLANs in the same MSTI for a trunk link.
46. Which two scenarios are examples of MST region boundaries? (Choose two.)
- a port connected to a server
- a port connected to a trunk link
- a port connected to a workstation
- a port connected to another switch that runs RSTP
- a port connected to another switch in a different MST region
Explanation: An MST region boundary is any port that connects to a switch that is in a different MST region or that connects to 802.1D (original STP) or 802.1W (RSTP) BPDUs.
47. What is a solution to mitigate the MST misconfiguration that contains improper VLAN assignment to the IST?
- Move all active VLANs to the IST.
- Allow the VLANs associated with the IST on all trunk links.
- Ensure that the MST region name is consistent across MST regions.
- Ensure that only VLANs in the same MSTI for a trunk link are pruned.
Explanation: Two solutions to mitigate the MST misconfiguration caused by improper VLAN assignment to the IST are as follows:
- Move affected VLANs to an MSTI other than the IST.
- Allow the VLANs associated with the IST on all trunk links.
48. What is the default MST region name on Cisco switches?
- cisco
- region
- mst_region
- an empty string
Explanation: MST regions are recognized by switches that share a common name. By default, a region name is an empty string.
“Do I Know This Already?” Quiz Answers:
1. Which of the following issues does MST solve? (Choose two.)
- Enables traffic load balancing for specific VLANs
- Reduces the CPU and memory resources needed for environments with large numbers of VLANs
- Overcomes MAC address table scaling limitations for environments with large numbers of devices
- Detects issues with cabling that transmits data in one direction
- Prevents unauthorized switches from attaching to the Layer 2 domain
Explanation: MST enables traffic load balancing for specific VLANs through assignment of VLANs to specific instances that might have different topologies. MST also reduces the amount of CPU and memory processing as multiple VLANs are associated with an MST instance.
2. With MST, VLANs are directly associated with ______.
- areas
- regions
- instances
- switches
Explanation: VLANs are associated with MST instances, and an instance defines the Layer 2 forwarding topology for the VLANs that are associated to it.
3. What do CST and 802.1D have in common?
- They support only one topology.
- They support multiple topologies.
- They allow for load balancing of traffic across different VLANs.
- They provide switch authentication so that inter-switch connectivity can occur.
Explanation: The original 802.1D specification accounted for one topology for all the VLANs, and Common Spanning Tree (CST) uses one topology for building a loop-free topology.
4. True or false: The MST root bridge advertises the VLAN-to-instance mappings to all other MST switches.
- True
- False
Explanation: MST uses an internal spanning tree (IST) to advertise itself and other MST instances for building the topology. The local switch configuration associates VLANs to the MST instances.
5. True or false: The MST configuration version is locally significant.
- True
- False
Explanation: The MST configuration is relevant to the entire MST region and should be the same for all switches in the region.
6. True or false: The MST topology can be tuned for root bridge placement, just like PVST+ and RSTP.
- True
- False
Explanation: The MST topology can be tuned by setting priority, port cost, and port priority for each MST instance.
7. MST regions can interact with PVST+/RSTP in which of the following ways? (Choose two.)
- The MST region is the root bridge for all VLANs.
- The MST region is the root bridge for some VLANs.
- The PVST+/RSTP topology is the root bridge for all VLANs.
- The PVST+/RSTP topology is the root bridge for some VLANs.
Explanation: MST can interact with PVST+/RSTP environments by acting as a root bridge for all VLANs or ensuring that the PVST+/RSTP environment is the root bridge for all VLANs. MST cannot be a root bridge for some VLANs and then let the PVST+/RSTP environment be the root bridge for other VLANs.
