CCNP Composite(642-892) Hotspot 2 – Spanning Tree

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There is a hotspot question in the CCNP exam.

You study the network topology carefully, see exhibit. Then you connect to the SW-c ; issue the show spanning tree command. Please refer to the exhibit for the output. You are then required to answer the scenario questions using the information that is available.

Question 1:
Which spanning Tree Protocol has been implemented on SW-B?

A. /IEEE 802.1D
B. MSTP/IEEE 802.1s
C. PVST+
D. PVRST
E. None of the above

Explanation:
802.1D has not been implemented since this is CST (Common Spanning Tree) which only allows one instance to be run at a time per Network. In this scenario there are multiple instances. It must be PVST+ since each instance only contains one VLAN.

Question 2:
Which bridge ID belongs to SW-B?

A. 32928 000d bd33 029b
B. 24623 000f 34f5 039b
C. 32928 000d bd03 029b
D. 32768 000d bd33 029b
E. 32769 000d 65db 01dd
F. 32815 000d bd03 029b

Explanation:
Root ports are ports that point to the Root Bridge. In the exhibit, under VLAN 47 we see that fa0/2 is a root port for VLAN 47. Since we assume that all paths have equal cost we can gather that the root ports destination is the root bridge itself. In this case the Root Bridge for VLAN 47 is SW-B and according the exhibit the MAC address is 24623 000f 34f5 039b

Question 3:
Which port role has interface Fa0/2 of SW-A adopted for VLAN 47?

A. Root port
B. Nondesigned port
C. Designated port
D. Backup port
E. Alternate port

Explanation:
Refer to Explanation for previous question. So far we know that SW-B is the Root Bridge for VLAN 47. We also see that SW-C is using fa0/2 as its root port. Therefore SW-A will use fa0/1 for its Root port and fa0/2 will be designated since fa0/1 on SW-C is blocking. Note: If one segment of SPT is in blocking statusthe distantend port is not. Otherwise BPDUs could not be transmitted and would negate the redundancy.

Question 4:
Which port state is interface Fa0/2 of SW-B in for VLANs 1 and 160?

A. Listening
B. Learning
C. Disabled
D. Blocking
E. Forwarding
F. Discarding

Explanation:
For VLAN 1 and 160 we can conclude that the Root Bridge is SW-A. With this in mind SW-B will use fa0/1 for its root port and block the other since the Cost will be lower. In this case it will block fa0/2 for both VLANs (and most likely fa0/3 also since SW-D is using fa0/1 as its root port).

Question 5:
Which bridge ID belongs to SW-A?

A. 32928 000d bd33 029b
B. 24623 000f 34f5 039b
C. 32928 000d bd03 029b
D. 32768 000d bd33 029b
E. 32769 000d 65db 01dd
F. 32815 000d bd03 029b

Explanation:
We see that in VLAN 1 and VLAN 160 that fa0/1 is the root port on SW-C. As previously discussed we know that root ports point to the root bridge and assuming equal cost from switch to root and the fact that no other port is root for either VLAN that SW-A is the Root Bridge and we can gleen the information for the exhibit which list the Bridge’s VLAN.

That is all, hope to helpful for you. Best Luck for ur Composite 642-892 Exam.

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