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

QUESTION NO: 56
Company uses MSTP within their switched LAN. What is the main purpose of Multiple Instance Spanning Tree Protocol (MSTP)?
A. To enhance Spanning Tree troubleshooting on multilayer switches
B. To reduce the total number of spanning tree instances necessary for a particular topology
C. To provide faster convergence when topology changes occur in a switched network
D. To provide protection for STP when a link is unidirectional and BPDUs are being sent but not received
E. None of the other alternatives apply
Answer: B
Explanation:
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.
Each could be tuned to result in a different topology, so that Instance 1 would forward on the left uplink, while Instance 2 would forward on the right uplink. Therefore, VLAN A would be mapped to Instance 1,and VLAN B to Instance 2. To implement MST in a network, you need to determine the following:

QUESTION NO: 57
Which of the following specifications is a companion to the IEEE 802.1w Rapid Spanning Tree Protocol (RSTP) algorithm, and warrants the use multiple spanning-trees?
A. IEEE 802.1s (MST)
B. IEEE 802.1Q (CST)
C. Cisco PVST+
D. IEEE 802.1d (STP)
E. None of the other alternatives apply
Answer: A
Explanation:
MST uses the modified RSTP version called the Multiple Spanning Tree Protocol (MSTP). 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 PVST+. MST 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 new 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 (forwarding paths). In large networks, you can more easily administer the network and use redundant paths by locating different VLAN and spanning tree instance assignments in different parts of the network. A spanning tree instance can exist only on bridges that have compatible VLAN instance assignments. You must configure a set of bridges with the same MST configuration information, which allows them to participate in a specific set of spanning tree instances. Interconnected bridges that have the same MST configuration are referred to as an MST region.

QUESTION NO: 58
Which of the following specification will allow you to: associate VLAN groups to STP instances so you can provide multiple forwarding paths for data traffic and enable load balancing?
A. IEEE 802.1d (STP)
B. IEEE 802.1s (MST)
C. IEEE 802.1Q (CST)
D. IEEE 802.1w (RSTP)
Answer: B
Explanation: IEEE 802.1s MST Overview
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 PVST+. MST is backward compatible with 802.1D STP, 802.1w (rapid spanning tree protocol [RSTP]), and the Cisco PVST+ architecture.

QUESTION NO: 59
Which three items are configured in MST configuration submode? (Select three)
A. Region name
B. Configuration revision number
C. VLAN instance map
D. IST STP BPDU hello timer
E. CST instance map
F. PVST+ instance map
Answer: A,B,C

QUESTION NO: 60
By default, all VLANs will belong to which MST instance when using Multiple STP?
A. MST00
B. MST01
C. the last MST instance configured
D. none
Answer: A
Explanation:
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. By default all VLANs are belonged to MST00 instance.