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Cisco CCNP SWITCH 642-813 Exam Questions with Explanation – Chapter 1 (61-65)

Chapter 1 – Implement VLAN based solution, given a network design and a set of requirements

Which MST configuration statement is correct?
A. MST configurations can be propagated to other switches using VTP.
B. After MST is configured on a Switch, PVST+ operations will also be enabled by default.
C. MST configurations must be manually configured on each switch within the MST region.
D. MST configurations only need to be manually configured on the Root Bridge.
E. MST configurations are entered using the VLAN Database mode on Cisco Catalyst switches.
Answer: C
MST configuration must be manually be configured on each switch within the MST region.

While logged into a Company switch you issue the following command:
CompanySwitch(config-mst)# instance 10 vlan 11-12
What does this command accomplish?
A. It enables a PVST+ instance of 10 for vlan 11 and vlan 12
B. It enables vlan 11 and vlan 12 to be part of the MST region 10
C. It maps vlan 11 and vlan 12 to the MST instance of 10.
D. It creates an Internal Spanning Tree (IST) instance of 10 for vlan 11 and vlan 12
E. It create a Common Spanning Tree (CST) instance of 10 for vlan 11 and vlan 12
F. It starts two instances of MST, one instance for vlan 11 and another instance for vlan 12.
Answer: C
MST extends the IEEE 802.1w rapid spanning tree (RST) algorithm to multiple spanning trees. This extension provides both rapid convergence and load balancing in a VLAN environment. MST converges faster than Per VLAN Spanning Tree Plus (PVST+) and is backward compatible with 802.1D STP, 802.1w (Rapid Spanning Tree Protocol [RSTP]), and the Cisco PVST+ architecture. MST allows you to build multiple spanning trees over trunks. You can group and associate VLANs to spanning tree instances. Each instance can have a topology independent of other spanning tree instances. This architecture provides multiple forwarding paths for data traffic and enables load balancing. Network fault tolerance is improved because a failure in one instance (forwarding path) does not affect other instances.
Map the VLANs to an MST instance. If you do not specify the vlan keyword, you can use the no keyword to unmap all the VLANs that were mapped to an MST instance. If you specify the vlan keyword, you can use the no keyword to unmap a specified VLAN from an MST instance. Switch(config-mst)# instance instance_number vlan vlan_range

Refer to the show spanning-tree mst configuration output shown in the exhibit. What should be changed in the configuration of the switch SW_2 in order for it to participate in the same MST region?
A. Switch SW_2 must be configured with an instance number of 2.
B. Switch SW_2 must be configured with a different VLAN range.
C. Switch SW_2 must be configured with the revision number of 1.
D. Switch SW_2 must be configured with a different MST name.
Answer: C
MST is built on the concept of mapping one or more VLANs to a single STP instance. Multiple instances of STP can be used (hence the name MST), with each instance supporting a different group of VLANs.
In most networks, a single MST region is sufficient, although you can configure more than one region. Within the region, all switches must run the instance of MST that is defined by the following attributes: MST configuration name (32 characters) MST configuration revision number (0 to 65535) MST instance-to-VLAN mapping table (4096 entries) Example of configuration of MST
Switch(config)# spanning-tree mode mst Switch(config)# spanning-tree mst configuration Switch(config-mst)# name name Switch(config-mst)# revision version The configuration revision number gives you a means to track changes to the MST region configuration. Each time you make changes to the configuration, you should increase the number by one. Remember that the region configuration (including the revision number) must match on all switches in the region. Therefore, you also need to update the revision numbers on the other switches to match. Switch(config-mst)# instance instance-id vlan vlan-list The instance-id (0 to 15) carries topology information for the VLANs listed in vlan-list. The list can contain one or more VLANs separated by commas. You can also add a range of VLANs to the list by separating numbers with a hyphen. VLAN numbers can range from 1 to 4094. (Remember that by default, all VLANs are mapped to instance 0, the IST.) Switch(config-mst)# show pending region configuration: Switch(config-mst)# exit
So belong the routers in same MST region, MST attributes should be same, in Company2 router revision number is not same so to make belong the Company2 router on same MST region, revision number should be 1.

The network administrator maps VLAN 10 through 20 to MST instance 2. How will this information be propagated to all appropriate switches?
A. Information will be carried in the RSTP BPDUs.
B. It will be propagated in VTP updates.
C. Information stored in the Forwarding Information Base and the switch will reply on query.
D. Multiple Spanning Tree must be manually configured on the appropriate switches.
Answer: D
Recall that the whole idea behind MST is the capability to map multiple VLANs to a smaller number of STP instances. Inside a region, the actual MST instances (MSTIs) exist alongside the IST. Cisco supports a maximum of 16 MSTIs in each region. IST always exists as MSTI number 0, leaving MSTI 1 through 15 available for use. MST must be manually configured on the all switch belongs to same MST region.

Refer to the exhibit. Switch S2 contains the default configuration. Switches S1 and S3 both have had the command spanning-tree mode rapid-pvst issued on them. What will be the result?
A. IEEE 802.1D and IEEE 802.1w are incompatible. All three switches must use the same standard or no traffic will pass between any of the switches.
B. Switches S1, S2, and S3 will be able to pass traffic between themselves.
C. Switches S1, S2, and S3 will be able to pass traffic between themselves. However, if there is a topology change, Switch S2 will not receive notification of the change.
D. Switches S1 and S3 will be able to exchange traffic but neither will be able to exchange traffic with Switch S2
Answer: B
Cisco Catalyst switches support three types of STPs, which are PVST+, rapid-PVST+ and MST. PVST+ is based on IEEE802.1D standard and includes Cisco proprietary extensions such as BackboneFast, UplinkFast, and PortFast. Rapid-PVST+ is based on IEEE 802.1w standard and has a faster convergence than 802.1D. RSTP (IEEE 802.1w) natively includes most of the Cisco proprietary enhancements to the 802.1D Spanning Tree, such as BackboneFast and UplinkFast. Rapid-PVST+ uses the same BPDU format as the 802.1D and it is backward compatible. It is difficult to convert all the switches in the enterprise network at the same time to rapid-PVST+. Because of the backward compatibility, you can convert phase by phase.

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