Spanning Tree Protocol practice questions

A network engineer is troubleshooting an STP issue in a switched network. The network has two distribution switches connected via a trunk, and each distribution switch connects to the same access switch. The engineer notices that the root bridge is not the intended distribution switch. Upon checking, the engineer sees that the access switch has a higher priority than the distribution switches. The engineer needs to ensure that the intended distribution switch becomes the root bridge without causing a temporary loop. What should the engineer do?

Trap 1: Set the priority of the access switch to 0 using the 'spanning-tree…

Incorrect because setting the access switch priority to 0 would make it the root bridge, not the distribution switch.

Trap 2: Increase the priority of the distribution switch to 61440 using the…

Incorrect because increasing the priority makes the switch less likely to become root; the engineer wants the distribution switch to become root.

Trap 3: Disable STP on the distribution switch and manually configure it as…

Incorrect because disabling STP can cause loops and is not a recommended practice; the root bridge is elected dynamically via BPDUs.

A
Configure the 'spanning-tree vlan vlan-id root primary' command on the intended distribution switch.
Correct because this command sets the switch priority to 24576 (or lower if needed) to ensure it becomes the root bridge without manual configuration.
B
Set the priority of the access switch to 0 using the 'spanning-tree vlan vlan-id priority 0' command.
Why wrong: Incorrect because setting the access switch priority to 0 would make it the root bridge, not the distribution switch.
C
Increase the priority of the distribution switch to 61440 using the 'spanning-tree vlan vlan-id priority 61440' command.
Why wrong: Incorrect because increasing the priority makes the switch less likely to become root; the engineer wants the distribution switch to become root.
D
Disable STP on the distribution switch and manually configure it as the root bridge.
Why wrong: Incorrect because disabling STP can cause loops and is not a recommended practice; the root bridge is elected dynamically via BPDUs.

Question 2hardmultiple choice

An engineer is designing a redundant Layer 2 network with multiple VLANs. The network uses Rapid PVST+ for STP. The engineer wants to ensure that different VLANs have different root bridges to optimize traffic flow. The distribution switches are Cisco Catalyst 9300s. The engineer has configured one distribution switch as the root for VLANs 10 and 20, and the other as the root for VLANs 30 and 40. However, after implementation, the engineer notices that all VLANs have the same root bridge. What is the most likely cause?

Trap 1: The engineer enabled BPDU guard on all access ports, which prevents…

Incorrect because BPDU guard disables ports that receive BPDUs, but it does not affect the root bridge election process.

Trap 2: The engineer enabled PortFast on all trunk ports, which causes the…

Incorrect because PortFast is for access ports and does not affect root bridge election; it only speeds up transition to forwarding.

Trap 3: The engineer enabled UplinkFast, which forces the switch to become…

Incorrect because UplinkFast is a Cisco proprietary feature that improves convergence after uplink failure, but it does not force a switch to become root.

A
The engineer used the 'spanning-tree root primary' command without specifying the VLAN, which sets the priority for all VLANs.
Correct because the command without the VLAN keyword applies to all VLANs, causing the same switch to be root for all VLANs.
B
The engineer enabled BPDU guard on all access ports, which prevents the switch from receiving superior BPDUs.
Why wrong: Incorrect because BPDU guard disables ports that receive BPDUs, but it does not affect the root bridge election process.
C
The engineer enabled PortFast on all trunk ports, which causes the switch to ignore BPDUs and become root.
Why wrong: Incorrect because PortFast is for access ports and does not affect root bridge election; it only speeds up transition to forwarding.
D
The engineer enabled UplinkFast, which forces the switch to become the root bridge for all VLANs.
Why wrong: Incorrect because UplinkFast is a Cisco proprietary feature that improves convergence after uplink failure, but it does not force a switch to become root.

Question 3mediummultiple choice

A network engineer is troubleshooting a Layer 2 loop issue. The network consists of three switches: SW1, SW2, and SW3, all connected in a triangle. The engineer notices that SW1 is the root bridge. After a link failure between SW1 and SW2, the network experiences a temporary loop. The engineer wants to prevent such loops in the future by enabling a feature that provides faster convergence and prevents temporary loops during topology changes. The engineer is using Rapid PVST+. Which feature should the engineer enable?

Trap 1: Enable BPDU Guard on all switch ports.

Incorrect because BPDU Guard is used to protect access ports from receiving BPDUs, not to prevent loops during topology changes.

Trap 2: Enable Root Guard on all switch ports.

Incorrect because Root Guard prevents a port from becoming a root port, but it does not prevent loops during topology changes.

Trap 3: Enable UDLD on all fiber links.

Incorrect because UDLD detects unidirectional links, but it does not prevent loops that occur due to topology changes in a properly functioning network.

A
Enable Loop Guard on all switch ports.
Correct because Loop Guard prevents loops by keeping a port in blocking state if BPDUs are not received, ensuring that a port does not transition to forwarding incorrectly.
B
Enable BPDU Guard on all switch ports.
Why wrong: Incorrect because BPDU Guard is used to protect access ports from receiving BPDUs, not to prevent loops during topology changes.
C
Enable Root Guard on all switch ports.
Why wrong: Incorrect because Root Guard prevents a port from becoming a root port, but it does not prevent loops during topology changes.
D
Enable UDLD on all fiber links.
Why wrong: Incorrect because UDLD detects unidirectional links, but it does not prevent loops that occur due to topology changes in a properly functioning network.

Question 4hardmultiple choice

An engineer is configuring a new access switch that connects to two distribution switches via trunk links. The distribution switches are configured with Rapid PVST+ and are both running as root bridges for different VLANs. The engineer wants to ensure that the access switch does not become the root bridge for any VLAN, even if the distribution switches fail. The engineer also wants to prevent any unauthorized switch from becoming root. What configuration should the engineer apply on the access switch?

Trap 1: Configure 'spanning-tree vlan 1-4094 priority 0' and enable BPDU…

Incorrect because priority 0 makes the switch likely to become root, and BPDU Guard would disable the uplink ports if BPDUs are received, causing loss of connectivity.

Trap 2: Configure 'spanning-tree vlan 1-4094 priority 4096' and enable Loop…

Incorrect because priority 4096 is low and could allow the switch to become root if distribution switches fail; Loop Guard does not prevent root bridge election.

Trap 3: Configure 'spanning-tree vlan 1-4094 priority 61440' and enable…

Incorrect because BPDU Guard would disable the uplink ports upon receiving BPDUs, which is not desired on trunk links.

A
Configure 'spanning-tree vlan 1-4094 priority 61440' and enable Root Guard on the uplink ports.
Correct because setting the priority to 61440 ensures the switch will not become root, and Root Guard on uplinks prevents any superior BPDUs from making the switch root.
B
Configure 'spanning-tree vlan 1-4094 priority 0' and enable BPDU Guard on the uplink ports.
Why wrong: Incorrect because priority 0 makes the switch likely to become root, and BPDU Guard would disable the uplink ports if BPDUs are received, causing loss of connectivity.
C
Configure 'spanning-tree vlan 1-4094 priority 4096' and enable Loop Guard on the uplink ports.
Why wrong: Incorrect because priority 4096 is low and could allow the switch to become root if distribution switches fail; Loop Guard does not prevent root bridge election.
D
Configure 'spanning-tree vlan 1-4094 priority 61440' and enable BPDU Guard on the uplink ports.
Why wrong: Incorrect because BPDU Guard would disable the uplink ports upon receiving BPDUs, which is not desired on trunk links.

Question 5easymultiple choice

A network engineer is troubleshooting a connectivity issue in a switched network. The network uses Rapid PVST+ with multiple VLANs. The engineer notices that a host connected to an access port on SW1 cannot communicate with the default gateway, which is on a distribution switch. The access port is configured with PortFast and BPDU Guard. The engineer checks the switch logs and sees that the port went into errdisable state. What is the most likely cause of the errdisable state?

Trap 1: A broadcast storm occurred due to a loop in the network.

Incorrect because a broadcast storm would cause high CPU but not necessarily put the port in errdisable state due to BPDU Guard.

Trap 2: The host connected to the port caused a duplex mismatch.

Incorrect because a duplex mismatch can cause errors but does not trigger BPDU Guard to disable the port.

Trap 3: The cable connecting the host is faulty, causing link flaps.

Incorrect because link flaps can cause errdisable due to link flapping, but the logs specifically mention BPDU Guard, indicating a BPDU was received.

A
Another switch was connected to the access port, causing BPDU Guard to disable the port.
Correct because BPDU Guard disables a PortFast-enabled port if a BPDU is received, which happens when another switch is connected.
B
A broadcast storm occurred due to a loop in the network.
Why wrong: Incorrect because a broadcast storm would cause high CPU but not necessarily put the port in errdisable state due to BPDU Guard.
C
The host connected to the port caused a duplex mismatch.
Why wrong: Incorrect because a duplex mismatch can cause errors but does not trigger BPDU Guard to disable the port.
D
The cable connecting the host is faulty, causing link flaps.
Why wrong: Incorrect because link flaps can cause errdisable due to link flapping, but the logs specifically mention BPDU Guard, indicating a BPDU was received.

Question 6hardmultiple choice

An engineer is designing a Layer 2 network with redundancy. The network uses MST (Multiple Spanning Tree) to reduce the number of STP instances. The engineer has configured two regions: Region 1 and Region 2. The engineer notices that switches in Region 1 are not forming a single MST region, and instead, they are treating each other as if they are in different regions. The engineer checks the configuration and finds that the region name and revision number are the same on all switches in Region 1, but the VLAN-to-instance mapping is different on one switch. What is the most likely cause of the issue?

Trap 1: The root bridge for each MST instance is not configured correctly.

Incorrect because root bridge configuration does not affect region formation; it only determines the root within the region.

Trap 2: BPDU Guard is enabled on the inter-switch links, preventing BPDU…

Incorrect because BPDU Guard is typically used on access ports, not on trunk links between switches, and would not cause region mismatch.

Trap 3: PortFast is enabled on the inter-switch links, causing the switches…

Incorrect because PortFast is for access ports and should not be enabled on trunk links; it does not affect MST region formation.

A
The VLAN-to-instance mapping is not consistent across all switches in Region 1.
Correct because MST requires identical VLAN-to-instance mapping, region name, and revision number for switches to be in the same region.
B
The root bridge for each MST instance is not configured correctly.
Why wrong: Incorrect because root bridge configuration does not affect region formation; it only determines the root within the region.
C
BPDU Guard is enabled on the inter-switch links, preventing BPDU exchange.
Why wrong: Incorrect because BPDU Guard is typically used on access ports, not on trunk links between switches, and would not cause region mismatch.
D
PortFast is enabled on the inter-switch links, causing the switches to ignore BPDUs.
Why wrong: Incorrect because PortFast is for access ports and should not be enabled on trunk links; it does not affect MST region formation.

Question 7hardmultiple choice

A network engineer is troubleshooting an STP issue in a network that uses Rapid PVST+. The network has a root bridge (SW1) and a secondary root bridge (SW2). The engineer notices that after a link failure between SW1 and SW2, the network takes longer than expected to converge. The engineer checks the configuration and finds that SW2 has the 'spanning-tree uplinkfast' command enabled. The engineer also notices that SW2 has a lower priority than SW1. What is the most likely cause of the slow convergence?

Trap 1: SW2 has a lower priority than SW1, so it takes longer to become the…

Incorrect because the root bridge election is based on priority, but the convergence time is not significantly affected by priority values; Rapid PVST+ converges quickly regardless.

Trap 2: BPDU Guard is enabled on the uplink ports, which prevents BPDU…

Incorrect because BPDU Guard would disable the port if a BPDU is received, but it does not slow convergence.

Trap 3: Loop Guard is enabled on the uplink ports, which delays port…

Incorrect because Loop Guard prevents loops but does not significantly delay convergence; it may cause a port to stay blocked if BPDUs are not received.

A
UplinkFast is enabled, which is incompatible with Rapid PVST+ and causes the switch to use legacy STP convergence.
Correct because UplinkFast is not needed with Rapid PVST+ and can actually degrade performance by forcing the switch to use slower convergence mechanisms.
B
SW2 has a lower priority than SW1, so it takes longer to become the root bridge after failure.
Why wrong: Incorrect because the root bridge election is based on priority, but the convergence time is not significantly affected by priority values; Rapid PVST+ converges quickly regardless.
C
BPDU Guard is enabled on the uplink ports, which prevents BPDU exchange.
Why wrong: Incorrect because BPDU Guard would disable the port if a BPDU is received, but it does not slow convergence.
D
Loop Guard is enabled on the uplink ports, which delays port transition.
Why wrong: Incorrect because Loop Guard prevents loops but does not significantly delay convergence; it may cause a port to stay blocked if BPDUs are not received.

Question 8easymultiple choice

A network engineer is configuring a new switch that will be used as an access layer switch. The switch connects to two distribution switches via trunk links. The engineer wants to ensure that the access switch does not become the root bridge for any VLAN. The engineer also wants to provide redundancy so that if one uplink fails, the other uplink takes over quickly. The engineer is using Rapid PVST+. What configuration should the engineer apply on the access switch?

Trap 1: Configure 'spanning-tree vlan vlan-list priority 0' on the access…

Incorrect because priority 0 would make the access switch the root bridge, which is not desired.

Trap 2: Enable UplinkFast on the access switch to provide fast failover.

Incorrect because UplinkFast is not needed with Rapid PVST+ and may cause compatibility issues.

Trap 3: Enable PortFast on the trunk ports to speed up convergence.

Incorrect because PortFast is for access ports, not trunk ports, and enabling it on trunks can cause loops.

A
Configure 'spanning-tree vlan vlan-list priority 61440' on the access switch.
Correct because setting the priority to 61440 ensures the access switch will not become root, and Rapid PVST+ provides fast convergence automatically.
B
Configure 'spanning-tree vlan vlan-list priority 0' on the access switch.
Why wrong: Incorrect because priority 0 would make the access switch the root bridge, which is not desired.
C
Enable UplinkFast on the access switch to provide fast failover.
Why wrong: Incorrect because UplinkFast is not needed with Rapid PVST+ and may cause compatibility issues.
D
Enable PortFast on the trunk ports to speed up convergence.
Why wrong: Incorrect because PortFast is for access ports, not trunk ports, and enabling it on trunks can cause loops.

Question 9mediummultiple choice

A network engineer is troubleshooting a Layer 2 loop that occurred in a network using Rapid PVST+. The network has three switches: SW1 (root), SW2, and SW3. The engineer examines the topology and finds that SW2 and SW3 are connected via a link that is not supposed to be there. The engineer suspects that an unauthorized switch was connected to the network, causing the loop. The engineer wants to prevent such loops in the future by configuring a feature that will disable any port that receives a BPDU from an unauthorized switch. Which feature should the engineer configure on the access ports?

Trap 1: Enable Loop Guard on all access ports.

Incorrect because Loop Guard prevents loops when BPDUs are not received, but it does not disable the port upon receiving BPDUs.

Trap 2: Enable Root Guard on all access ports.

Incorrect because Root Guard prevents a port from becoming a root port, but it does not disable the port upon receiving BPDUs.

Trap 3: Enable UDLD on all access ports.

Incorrect because UDLD detects unidirectional links, but it does not prevent loops caused by unauthorized switches.

A
Enable BPDU Guard on all access ports.
Correct because BPDU Guard disables a port if a BPDU is received, preventing unauthorized switches from causing loops.
B
Enable Loop Guard on all access ports.
Why wrong: Incorrect because Loop Guard prevents loops when BPDUs are not received, but it does not disable the port upon receiving BPDUs.
C
Enable Root Guard on all access ports.
Why wrong: Incorrect because Root Guard prevents a port from becoming a root port, but it does not disable the port upon receiving BPDUs.
D
Enable UDLD on all access ports.
Why wrong: Incorrect because UDLD detects unidirectional links, but it does not prevent loops caused by unauthorized switches.

Question 10mediummultiple choice

A network engineer runs the following command on Switch SW1:

SW1# show spanning-tree vlan 10

VLAN0010 Spanning tree enabled protocol ieee Root ID Priority 24586 Address aabb.cc00.0100 This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 24586 (priority 24576 sys-id-ext 10) Address aabb.cc00.0100 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec

Interface           Role Sts Cost      Prio.Nbr Type

------------------- ---- --- --------- -------- ------------------------------ Gi0/1 Desg FWD 4 128.1 P2p Gi0/2 Desg FWD 4 128.2 P2p Gi0/3 Desg FWD 4 128.3 P2p

Based on this output, what can be concluded?

Trap 1: SW1 is not the root bridge; the root bridge has MAC address…

Incorrect. The output says 'This bridge is the root', so SW1 is the root bridge.

Trap 2: SW1 has a port in the Blocking state, preventing loops.

Incorrect. All ports are FWD (Forwarding), none are blocking.

Trap 3: The root bridge priority for VLAN 10 is 24576 without the system ID…

Incorrect. The priority shown is 24586, which includes the system ID extension of 10 (24576 + 10 = 24586). The base priority is 24576.

A
SW1 is the root bridge for VLAN 10, and all its interfaces are in the Designated role.
Correct. The output explicitly states 'This bridge is the root' and all interfaces are Desg FWD.
B
SW1 is not the root bridge; the root bridge has MAC address aabb.cc00.0100 but is a different switch.
Why wrong: Incorrect. The output says 'This bridge is the root', so SW1 is the root bridge.
C
SW1 has a port in the Blocking state, preventing loops.
Why wrong: Incorrect. All ports are FWD (Forwarding), none are blocking.
D
The root bridge priority for VLAN 10 is 24576 without the system ID extension.
Why wrong: Incorrect. The priority shown is 24586, which includes the system ID extension of 10 (24576 + 10 = 24586). The base priority is 24576.

Question 11mediummultiple choice

A network engineer runs the following command on Switch SW2:

SW2# show spanning-tree vlan 20

VLAN0020 Spanning tree enabled protocol ieee Root ID Priority 24596 Address aabb.cc00.0200 Cost 4 Port 1 (GigabitEthernet0/1) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32778 (priority 32768 sys-id-ext 20) Address aabb.cc00.0300 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec

Interface           Role Sts Cost      Prio.Nbr Type

------------------- ---- --- --------- -------- ------------------------------ Gi0/1 Root FWD 4 128.1 P2p Gi0/2 Desg FWD 4 128.2 P2p Gi0/3 Altn BLK 4 128.3 P2p

Based on this output, what can be concluded?

Trap 1: SW2 is the root bridge for VLAN 20.

Incorrect. The root ID shows a different bridge (aabb.cc00.0200) with lower priority.

Trap 2: The root port cost is 8.

Incorrect. The root cost is 4, as shown in the Root ID section.

Trap 3: SW2's bridge priority is 32768.

Incorrect. The bridge priority is 32778 (32768 + 20 for VLAN 20).

A
SW2 is the root bridge for VLAN 20.
Why wrong: Incorrect. The root ID shows a different bridge (aabb.cc00.0200) with lower priority.
B
GigabitEthernet0/3 is in the Blocking state to prevent a loop.
Correct. Gi0/3 is shown as Altn BLK (Alternate, Blocking), which prevents a loop.
C
The root port cost is 8.
Why wrong: Incorrect. The root cost is 4, as shown in the Root ID section.
D
SW2's bridge priority is 32768.
Why wrong: Incorrect. The bridge priority is 32778 (32768 + 20 for VLAN 20).

Question 12hardmultiple choice

A network engineer runs the following command on Switch SW3:

SW3# show spanning-tree vlan 30

VLAN0030 Spanning tree enabled protocol ieee Root ID Priority 24606 Address aabb.cc00.0400 Cost 12 Port 2 (GigabitEthernet0/2) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32798 (priority 32768 sys-id-ext 30) Address aabb.cc00.0500 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec

Interface           Role Sts Cost      Prio.Nbr Type

------------------- ---- --- --------- -------- ------------------------------ Gi0/1 Desg FWD 4 128.1 P2p Gi0/2 Root FWD 12 128.2 P2p Gi0/3 Desg FWD 4 128.3 P2p

Based on this output, what is the root path cost from SW3 to the root bridge for VLAN 30?

Trap 1: 4

Incorrect. 4 is the cost of Gi0/1 and Gi0/3, not the root path cost.

Trap 2: 16

Incorrect. There is no indication of 16.

Trap 3: 20

Incorrect. 20 is the Max Age, not a cost.

A
4
Why wrong: Incorrect. 4 is the cost of Gi0/1 and Gi0/3, not the root path cost.
B
12
Correct. The root path cost is 12, as shown in the Root ID section.
C
16
Why wrong: Incorrect. There is no indication of 16.
D
20
Why wrong: Incorrect. 20 is the Max Age, not a cost.

Question 13easymultiple choice

A network engineer runs the following command on Switch SW4:

SW4# show spanning-tree vlan 40

VLAN0040 Spanning tree enabled protocol ieee Root ID Priority 24616 Address aabb.cc00.0600 Cost 8 Port 1 (GigabitEthernet0/1) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32768 (priority 32768 sys-id-ext 40) Address aabb.cc00.0700 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec

Interface           Role Sts Cost      Prio.Nbr Type

------------------- ---- --- --------- -------- ------------------------------ Gi0/1 Root FWD 8 128.1 P2p Gi0/2 Desg FWD 4 128.2 P2p Gi0/3 Desg FWD 4 128.3 P2p

Based on this output, which port is the root port?

Trap 1: GigabitEthernet0/2

Incorrect. Gi0/2 is a designated port (Desg).

Trap 2: GigabitEthernet0/3

Incorrect. Gi0/3 is a designated port (Desg).

Trap 3: There is no root port because SW4 is the root bridge.

Incorrect. SW4 is not the root bridge; the root bridge has a different MAC address.

A
GigabitEthernet0/1
Correct. Gi0/1 is shown with role 'Root'.
B
GigabitEthernet0/2
Why wrong: Incorrect. Gi0/2 is a designated port (Desg).
C
GigabitEthernet0/3
Why wrong: Incorrect. Gi0/3 is a designated port (Desg).
D
There is no root port because SW4 is the root bridge.
Why wrong: Incorrect. SW4 is not the root bridge; the root bridge has a different MAC address.

Question 14easymultiple choice

A network engineer runs the following command on Switch SW5:

SW5# show spanning-tree vlan 50

VLAN0050 Spanning tree enabled protocol ieee Root ID Priority 24626 Address aabb.cc00.0800 Cost 4 Port 1 (GigabitEthernet0/1) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32768 (priority 32768 sys-id-ext 50) Address aabb.cc00.0900 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec

Interface           Role Sts Cost      Prio.Nbr Type

------------------- ---- --- --------- -------- ------------------------------ Gi0/1 Root FWD 4 128.1 P2p Gi0/2 Desg FWD 4 128.2 P2p Gi0/3 Desg FWD 4 128.3 P2p Gi0/4 Altn BLK 4 128.4 P2p

Based on this output, how many ports are in the Forwarding state?

Trap 1: 1

Incorrect. There are three forwarding ports.

Trap 2: 2

Incorrect. There are three forwarding ports.

Trap 3: 4

Incorrect. Gi0/4 is in BLK state.

A
1
Why wrong: Incorrect. There are three forwarding ports.
B
2
Why wrong: Incorrect. There are three forwarding ports.
C
3
Correct. Gi0/1, Gi0/2, and Gi0/3 are all in FWD state.
D
4
Why wrong: Incorrect. Gi0/4 is in BLK state.

Question 15mediummultiple choice

A network engineer runs the following command on Switch SW6:

SW6# show spanning-tree vlan 60

VLAN0060 Spanning tree enabled protocol ieee Root ID Priority 24636 Address aabb.cc00.0a00 Cost 8 Port 1 (GigabitEthernet0/1) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32768 (priority 32768 sys-id-ext 60) Address aabb.cc00.0b00 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec

Interface           Role Sts Cost      Prio.Nbr Type

------------------- ---- --- --------- -------- ------------------------------ Gi0/1 Root FWD 8 128.1 P2p Gi0/2 Desg FWD 4 128.2 P2p Gi0/3 Altn BLK 4 128.3 P2p Gi0/4 Desg FWD 4 128.4 P2p

Based on this output, what is the bridge priority of the root bridge for VLAN 60?

Trap 1: 24576

Incorrect. 24576 is the base priority, but the root ID priority shown is 24636.

Trap 2: 32768

Incorrect. 32768 is the base priority of SW6, not the root bridge.

Trap 3: 32828

Incorrect. There is no such value in the output.

A
24576
Why wrong: Incorrect. 24576 is the base priority, but the root ID priority shown is 24636.
B
24636
Correct. The Root ID priority is 24636.
C
32768
Why wrong: Incorrect. 32768 is the base priority of SW6, not the root bridge.
D
32828
Why wrong: Incorrect. There is no such value in the output.

Question 16easymultiple choice

A network engineer runs the following command on Switch SW7:

SW7# show spanning-tree vlan 70

VLAN0070 Spanning tree enabled protocol ieee Root ID Priority 24646 Address aabb.cc00.0c00 Cost 4 Port 1 (GigabitEthernet0/1) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32768 (priority 32768 sys-id-ext 70) Address aabb.cc00.0d00 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec

Interface           Role Sts Cost      Prio.Nbr Type

------------------- ---- --- --------- -------- ------------------------------ Gi0/1 Root FWD 4 128.1 P2p Gi0/2 Desg FWD 4 128.2 P2p Gi0/3 Altn BLK 4 128.3 P2p

Based on this output, which port is the alternate port?

Trap 1: GigabitEthernet0/1

Incorrect. Gi0/1 is the root port.

Trap 2: GigabitEthernet0/2

Incorrect. Gi0/2 is a designated port.

Trap 3: There is no alternate port.

Incorrect. Gi0/3 is an alternate port.

A
GigabitEthernet0/1
Why wrong: Incorrect. Gi0/1 is the root port.
B
GigabitEthernet0/2
Why wrong: Incorrect. Gi0/2 is a designated port.
C
GigabitEthernet0/3
Correct. Gi0/3 is the alternate port (Altn BLK).
D
There is no alternate port.
Why wrong: Incorrect. Gi0/3 is an alternate port.

Question 17easymultiple choice

A network engineer runs the following command on Switch SW8:

SW8# show spanning-tree vlan 80

VLAN0080 Spanning tree enabled protocol ieee Root ID Priority 24656 Address aabb.cc00.0e00 Cost 12 Port 1 (GigabitEthernet0/1) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32768 (priority 32768 sys-id-ext 80) Address aabb.cc00.0f00 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec

Interface           Role Sts Cost      Prio.Nbr Type

------------------- ---- --- --------- -------- ------------------------------ Gi0/1 Root FWD 12 128.1 P2p Gi0/2 Desg FWD 4 128.2 P2p Gi0/3 Desg FWD 4 128.3 P2p Gi0/4 Altn BLK 4 128.4 P2p

Based on this output, what is the cost of the root port?

Trap 1: 4

Incorrect. 4 is the cost of other ports, not the root port.

Trap 2: 8

Incorrect. There is no cost of 8 in the output.

Trap 3: 16

Incorrect. There is no cost of 16.

A
4
Why wrong: Incorrect. 4 is the cost of other ports, not the root port.
B
8
Why wrong: Incorrect. There is no cost of 8 in the output.
C
12
Correct. The root port Gi0/1 has a cost of 12.
D
16
Why wrong: Incorrect. There is no cost of 16.

Question 18hardmultiple choice

A network engineer runs the following command on Switch SW9:

SW9# show spanning-tree vlan 90

VLAN0090 Spanning tree enabled protocol ieee Root ID Priority 24666 Address aabb.cc00.1000 This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 24666 (priority 24576 sys-id-ext 90) Address aabb.cc00.1000 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec

Interface           Role Sts Cost      Prio.Nbr Type

------------------- ---- --- --------- -------- ------------------------------ Gi0/1 Desg FWD 4 128.1 P2p Gi0/2 Desg FWD 4 128.2 P2p Gi0/3 Desg FWD 4 128.3 P2p Gi0/4 Desg FWD 4 128.4 P2p

Based on this output, what is the base priority of the root bridge?

Trap 1: 24666

Incorrect. 24666 includes the VLAN ID; the base priority is lower.

Trap 2: 32768

Incorrect. 32768 is not shown in the output.

Trap 3: 32858

Incorrect. There is no such value.

A
24576
Correct. 24576 is the base priority (24666 - 90 = 24576).
B
24666
Why wrong: Incorrect. 24666 includes the VLAN ID; the base priority is lower.
C
32768
Why wrong: Incorrect. 32768 is not shown in the output.
D
32858
Why wrong: Incorrect. There is no such value.

Question 19mediummultiple choice

interface GigabitEthernet0/1
 spanning-tree portfast
 spanning-tree bpduguard enable

end

What is the effect of this configuration?

Trap 1: The port will go through normal STP states and will be…

PortFast skips listening/learning; BPDU Guard still triggers error-disable.

Trap 2: The port will immediately transition to forwarding and ignore any…

BPDU Guard does not ignore BPDUs; it error-disables the port.

Trap 3: The port will remain in blocking state until a BPDU is received.

PortFast forces immediate forwarding; blocking is not used.

A
The port will immediately transition to forwarding state and will be error-disabled if a BPDU is received.
PortFast causes immediate forwarding; BPDU Guard error-disables the port upon BPDU reception.
B
The port will go through normal STP states and will be error-disabled if a BPDU is received.
Why wrong: PortFast skips listening/learning; BPDU Guard still triggers error-disable.
C
The port will immediately transition to forwarding and ignore any BPDUs received.
Why wrong: BPDU Guard does not ignore BPDUs; it error-disables the port.
D
The port will remain in blocking state until a BPDU is received.
Why wrong: PortFast forces immediate forwarding; blocking is not used.

Question 20mediummultiple choice

spanning-tree vlan 10 priority 4096

What is the effect of this global configuration command?

Trap 1: The switch will have a bridge priority of 4096 for all VLANs.

The command is VLAN-specific; only VLAN 10 is affected.

Trap 2: The switch will become the root bridge for VLAN 10 immediately.

It only increases the chance; other switches with lower priority still win.

Trap 3: The switch will have a bridge priority of 4096 for VLAN 10 and all…

Other VLANs keep default priority unless separately configured.

A
The switch will have a bridge priority of 4096 for VLAN 10, increasing its chance to become root bridge.
Lower priority value is preferred; 4096 is lower than default 32768.
B
The switch will have a bridge priority of 4096 for all VLANs.
Why wrong: The command is VLAN-specific; only VLAN 10 is affected.
C
The switch will become the root bridge for VLAN 10 immediately.
Why wrong: It only increases the chance; other switches with lower priority still win.
D
The switch will have a bridge priority of 4096 for VLAN 10 and all other VLANs will use 32768.
Why wrong: Other VLANs keep default priority unless separately configured.