ICND2 – STP Questions 2

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Question 1

[am4show have=’p2;’]Which process is associated with spanning-tree convergence?

A. determining the path cost
B. electing designated ports
C. learning the sender bridge ID
D. assigning the port ID

 

Answer: B[/am4show]

Explanation

SPT must performs three steps to provide a loop-free network topology:

1. Elects one root bridge
2. Select one root port per nonroot bridge
3. Select one designated port on each network segment -> Answer B is correct.

Question 2

[am4show have=’p2;’]Which term describes a spanning-tree network that has all switch ports in either the blocking or forwarding state?

A. redundant
B. spanned
C. provisioned
D. converged

 

Answer: D[/am4show]

Explanation

Spanning Tree Protocol convergence (Layer 2 convergence) happens when bridges and switches have transitioned to either the forwarding or blocking state. When layer 2 is converged, root bridge is elected and all port roles (Root, Designated and Non-Designated) in all switches are selected.

Question 3

[am4show have=’p2;’]Refer to the exhibit. Which switch provides the spanning-tree designated port role for the network segment that services the printers?

A. Switch1
B. Switch2
C. Switch3
D. Switch4

 

Answer: C[/am4show]

Explanation

First, the question asks what switch services the printers, so it can be Switch 3 or Switch 4 which is connected directly to the Printers.

Next, by comparing the MAC address of Switch 3 and Switch 4 we found that the MAC of Switch 3 is smaller. Therefore the interface connected to the Printers of Switch 3 will become designated interface and the interface of Switch 4 will be blocked. The picture below shows the roles of all ports:

 

DP: Designated Port
RP: Root Port
BP: Blocked Port

(Please notice that Switch 1 will become the root bridge because of its lowest priority, not Switch 3)

Question 4

[am4show have=’p2;’]If primary and secondary root switches with priority 16384 both experience catastrophic losses, which tertiary switch can take over?

A. a switch with priority 20480
B. a switch with priority 8192
C. a switch with priority 4096
D. a switch with priority 12288

 

Answer: A[/am4show]

Explanation

This is a tricky question. We know the switch with lowest value of priority is elected the root switch. Therefore in this question the switches with priority of 4096, 8192, 12288 (which are lower than the current value of the root bridge 16384) are not joining the root bridge election by somehow. The only suitable answer is the switch with priority 20480 will become the root bridge.

Question 5

[am4show have=’p2;’]What kind of data message is send to elect the root bridge?

A. BPDU
B. Segment
C. Packets
D. Hello

 

Answer: A[/am4show]

Question 6

[am4show have=’p2;’]Which type does a port become when it receives the best BPDU on a bridge?

A. the backup port
B. the root port
C. the designated port
D. the alternate port

 

Answer: B[/am4show]

Question 7

[am4show have=’p2;’]Which value can you modify to configure a specific interface as the preferred forwarding interface?

A. the VLAN priority
B. the hello time
C. the port priority
D. the interface number

 

Answer: C[/am4show]

Question 8

[am4show have=’p2;’]Which VLAN bridge priority value is assigned by the set spantree root command?

A. 8192
B. 16384
C. 28672
D. 32768

 

Answer: A[/am4show]

Question 9

[am4show have=’p2;’]Which two statements about the spanning-tree bridge ID are true? (Choose two)

A. It is composed of a 4-bit bridge priority and a 12-bit system ID extension.
B. The bridge ID is transmitted in the IP header to elect the root bridge.
C. The system ID extension is a value between 1 and 4095.
D. It is composed of an 8-bit bridge priority and a 16-bit system ID extension.
E. The bridge priority must be incremented in blocks of 4096.

 

Answer: A E[/am4show]