The Ultimate CCNA RSTP Quiz

2.

Refer to the exhibit:Why has this switch not been elected the root bridge for VLAN1?

It has more than one internee that is connected to the root network segment.
It is running RSTP while the elected root bridge is running 802.1d spanning tree.
It has a higher MAC address than the elected root bridge.
It has a higher bridge ID than the elected root bridge.

Correct Answer

A. It has a higher bridge ID than the elected root bridge.

Explanation

As we can see from the output above, the priority of the root bridge is 20481 while that of the local bridge is 32769.

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3.

Refer to the exhibit. Which statement is true?

The Fa0/11 role confirms that SwitchA is the root bridge for VLAN 20.
VLAN 20 is running the Per VLAN Spanning Tree Protocol.
The MAC address of the root bridge is 0017.596d.1580.
SwitchA is not the root bridge, because not all of the interface roles are designated.

Correct Answer

A. SwitchA is not the root bridge, because not all of the interface roles are designated.

Explanation

Only non-root bridge can have root port. Fa0/11 is the root port so we can confirm this switch is not the root bridge -> A is not correct.

From the output we learn this switch is running Rapid STP, not PVST -> B is not correct.

0017.596d.1580 is the MAC address of this switch, not of the root bridge. The MAC address of the root bridge is 0017.596d.2a00 -> C is not correct.

All of the interface roles of the root bridge are designated. SwitchA has one Root port and 1 Alternative port so it is not the root bridge -> D is correct.

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4.

Refer to the exhibit. The output that is shown is generated at a switch. Which three of these statements are true? (Choose three)

All ports will be in a state of discarding, learning or forwarding.
Thirty VLANs have been configured on this switch.
The bridge priority is lower than the default value for spanning tree.
All interfaces that are shown are on shared media.
All designated ports are in a forwarding state.
The switch must be the root bridge for all VLANs on this switch.

Correct Answer(s)

A. All ports will be in a state of discarding, learning or forwarding.
A. The bridge priority is lower than the default value for spanning tree.
A. All designated ports are in a forwarding state.

Explanation

From the output, we see that all ports are in Designated role (forwarding state) -> A and E are correct.

The command “show spanning-tree vlan 30″ only shows us information about VLAN 30. We don’t know how many VLAN exists in this switch -> B is not correct.

The bridge priority of this switch is 24606 which is lower than the default value bridge priority 32768 -> C is correct.

All three interfaces on this switch have the connection type “p2p”, which means Point-to-point environment – not a shared media -> D is not correct.

The only thing we can specify is this switch is the root bridge for VLAN 3o but we can not guarantee it is also the root bridge for other VLANs -> F is not correct.

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5.

Which two states are the port states when RSTP has converged? (choose two)

Blocking
Learning
Disabled
Forwarding
Listening

Correct Answer(s)

A. Blocking
A. Forwarding

Explanation

RSTP only has 3 port states that are discarding, learning and forwarding. When RSTP has converged there are only 2 port states left: discarding and forwarding but the answers don’t mention about discarding state so blocking state (answer A) may be considered the best alternative answer.

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6.

Which two of these statements regarding RSTP are correct? (Choose two)

RSTP cannot operate with PVST+.
RSTP defines new port roles.
RSTP defines no new port states.
RSTP is a proprietary implementation of IEEE 802.1D STP.
RSTP is compatible with the original IEEE 802.1D STP.

Correct Answer(s)

A. RSTP defines new port roles.
A. RSTP is compatible with the original IEEE 802.1D STP.

Explanation

RSTP defines new port roles to enhance the functionality and efficiency of spanning tree protocol. These new port roles include alternate port, backup port, and edge port. RSTP also maintains compatibility with the original IEEE 802.1D STP, ensuring that existing STP implementations can seamlessly transition to RSTP without any compatibility issues.

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7.

Refer to the exhibit. Each of these four switches has been configured with a hostname, as well as being configured to run RSTP. No other configuration changes have been made. Which three of these show the correct RSTP port roles for the indicated switches and interfaces? (Choose three)

SwitchA, Fa0/2, designated
SwitchA, Fa0/1, root
SwitchB, Gi0/2, root
SwitchB, Gi0/1, designated
SwitchC, Fa0/2, root
SwitchD, Gi0/2, root

Correct Answer(s)

A. SwitchA, Fa0/2, designated
A. SwitchA, Fa0/1, root
A. SwitchD, Gi0/2, root

Explanation

The question says “no other configuration changes have been made” so we can understand these switches have the same bridge priority. Switch C has lowest MAC address so it will become root bridge and 2 of its ports (Fa0/1 & Fa0/2) will be designated ports -> E is incorrect. Because SwitchC is the root bridge so the 2 ports nearest SwitchC on SwitchA (Fa0/1) and SwitchD (Gi0/2) will be root ports -> B and F are correct. Now we come to the most difficult part of this question: SwitchB must have a root port so which port will it choose? To answer this question we need to know about STP cost and port cost. In general, “cost” is calculated based on bandwidth of the link. The higher the bandwidth on a link, the lower the value of its cost. Below are the cost values you should memorize:SwitchB will choose the interface with lower cost to the root bridge as the root port so we must calculate the cost on interface Gi0/1 & Gi0/2 of SwitchB to the root bridge. This can be calculated from the “cost to the root bridge” of each switch because a switch always advertises its cost to the root bridge in its BPDU. The receiving switch will add its local port cost value to the cost in the BPDU.One more thing to notice is that a root bridge always advertises the cost to the root bridge (itself) with an initial value of 0.Now let’s have a look at the topology again

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8.

Which command enables RSTP on a switch?

Spanning-tree mode rapid-pvst
Spanning-tree uplinkfast
Spanning-tree backbonefast
Spanning-tree mode mst

Correct Answer

A. Spanning-tree mode rapid-pvst

Explanation

The correct answer is "spanning-tree mode rapid-pvst". This command enables Rapid Spanning Tree Protocol (RSTP) on a switch. RSTP is an evolution of the Spanning Tree Protocol (STP) that provides faster convergence and better network stability. By enabling RSTP, the switch will use the rapid-pvst mode, which is a Cisco proprietary implementation of RSTP. This mode allows for faster convergence times and supports Per-VLAN Spanning Tree (PVST) where each VLAN has its own spanning tree instance.

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9.

Refer to the exhibit. At the end of an RSTP election process, which access layer switch port will assume the discarding role?

Switch3, port fa0/1
Switch3, port fa0/12
Switch4, port fa0/11
Switch4, port fa0/2
Switch3, port Gi0/1

Correct Answer

A. Switch4, port fa0/11

Explanation

In this question, we only care about the Access Layer switches (Switch3 & 4). Switch 3 has a lower bridge ID than Switch 4 (because the MAC of Switch3 is smaller than that of Switch4) so both ports of Switch3 will be in forwarding state. The alternative port will surely belong to Switch4.

Switch4 will need to block one of its ports to avoid a bridging loop between the two switches. But how does Switch4 select its blocked port? Well, the answer is based on the BPDUs it receives from Switch3. A BPDU is superior than another if it has:

1. A lower Root Bridge ID
2. A lower path cost to the Root
3. A lower Sending Bridge ID
4. A lower Sending Port ID

These four parameters are examined in order. In this specific case, all the BPDUs sent by Sswitch3 have the same Root Bridge ID, the same path cost to the Root and the same Sending Bridge ID. The only parameter left to select the best one is the Sending Port ID (Port ID = port priority + port index). In this case the port priorities are equal because they use the default value, so Switch4 will compare port index values, which are unique to each port on the switch, and because Fa0/12 is inferior to Fa0/1, Switch4 will select the port connected with Fa0/1 (of Switch3) as its root port and block the other port -> Port fa0/11 of Switch4 will be blocked (discarding role).

If you are still not sure about this question, please read my RSTP tutorial.

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The Ultimate CCNA Rstp Quiz

Which three statements about RSTP are true? (Choose three)

Quiz Preview

Refer to the exhibit:Why has this switch not been elected the root bridge for VLAN1?

Refer to the exhibit. Which statement is true?

Refer to the exhibit. The output that is shown is generated at a switch. Which three of these statements are true? (Choose three)

Which two states are the port states when RSTP has converged? (choose two)

Which two of these statements regarding RSTP are correct? (Choose two)

Refer to the exhibit. Each of these four switches has been configured with a hostname, as well as being configured to run RSTP. No other configuration changes have been made. Which three of these show the correct RSTP port roles for the indicated switches and interfaces? (Choose three)

Which command enables RSTP on a switch?

Refer to the exhibit. At the end of an RSTP election process, which access layer switch port will assume the discarding role?