CCNA Switching and Network Access Practice Test 28 — 15 Questions

Question 1

Users report that their PCs take over 30 seconds to obtain IP addresses and reach the network after being powered on. A network technician checks a switch port connected to a PC and observes that the port transitions through blocking, listening, learning, and then forwarding states, taking about 30 seconds to complete. The switch is running standard 802.1D STP. The technician confirms the port is an access port and only connects to a PC. What should the technician do next?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Enable PortFast on the access port.. The 30-second delay is caused by the standard 802.1D STP port states (blocking → listening → learning → forwarding). Since the port is an access port connecting only to a PC (an end host), there is no risk of a bridging loop. Enabling PortFast immediately transitions the port to the forwarding state, bypassing the listening and learning states and eliminating the delay.

Answer

Reduce the STP forward delay timer globally on the switch.

Answer

Disable STP on the access VLAN assigned to the port.

Answer

Enable Rapid PVST+ on the switch.

Question 2

A network engineer notices that a root port on a switch has transitioned to a loop-inconsistent state. The port was previously receiving BPDUs normally, but after a suspected unidirectional fiber cut, it no longer receives BPDUs. What is the most likely cause?

Accepted Answer

Loop Guard is active on the root port and transitioned it to loop-inconsistent state upon BPDU loss.. Loop Guard is a Spanning Tree Protocol (STP) enhancement that prevents alternate or root ports from becoming designated forwarding ports when BPDUs are no longer received. When a unidirectional fiber cut causes BPDU loss on a root port, Loop Guard transitions the port to the loop-inconsistent state, blocking traffic until BPDUs are received again. This matches the scenario exactly, making option B correct.

Answer

BPDU Guard is enabled on the port, causing it to be placed in error-disabled state.

Answer

UDLD has detected a unidirectional link and has shut down the port.

Answer

Root Guard is preventing the port from transitioning to designated forwarding after losing BPDUs.

Question 3

Refer to the exhibit. A network administrator is troubleshooting a trunk link between SW1 and SW2. The trunk on interface GigabitEthernet0/0 on SW1 is not passing traffic, and all VLANs are isolated. The administrator issues the command 'show interfaces GigabitEthernet0/0 trunk' on SW1. What is the most likely cause of the issue?

Accepted Answer

The trunk encapsulation is set to ISL on SW1, but the peer switch only supports 802.1Q.. The 'show interfaces trunk' output on SW1 would show the trunk as up but not passing traffic if the encapsulation is set to ISL while SW2 only supports 802.1Q. Cisco switches default to Dynamic Trunking Protocol (DTP) and may negotiate ISL on older hardware, but if the peer does not support ISL, the trunk fails to form correctly, isolating all VLANs. The mismatch in encapsulation prevents proper frame tagging, causing all VLAN traffic to be dropped.

Answer

The native VLAN is mismatched between SW1 and SW2.

Answer

The interface is configured as an access port instead of a trunk.

Answer

The interface is administratively shut down.

Question 4

A network technician is troubleshooting an inter-VLAN routing issue on a multilayer switch. Hosts on VLAN 10 can reach the SVI for VLAN 10 (10.0.10.1) but cannot reach hosts on VLAN 20. The technician has verified that 'ip routing' is enabled and that the 'show ip route' command displays directly connected routes for both VLANs. No static routes are configured. What should the technician do next?

Accepted Answer

Check the ARP table for entries on VLAN 20.. The hosts on VLAN 10 can reach the SVI (10.0.10.1) but not hosts on VLAN 20, which indicates that Layer 3 routing is working (ip routing enabled, directly connected routes present). The issue is likely that the switch does not have the MAC address of the destination host in VLAN 20 in its ARP table, so it cannot forward frames to that host. Checking the ARP table for VLAN 20 entries will reveal whether the switch has resolved the Layer 3-to-Layer 2 address mapping for the destination.

Answer

Issue the 'show ip routing' command again to confirm routing is enabled.

Answer

Configure a default route pointing to the next-hop gateway.

Answer

Verify the VLAN membership of the destination host on VLAN 20.

Question 5

Refer to the exhibit. A network engineer notices that a user connected to GigabitEthernet0/5 cannot access the network. The engineer issues the show port-security interface GigabitEthernet0/5 command. Based on the output, what is the most likely cause of the issue?

Accepted Answer

An unauthorized device with a different MAC address was connected, triggering a port-security violation and placing the port in an error-disabled state.. The output of 'show port-security interface GigabitEthernet0/5' would show a port status of 'err-disabled' and a security violation count greater than zero. This occurs because an unauthorized device with a different MAC address connected to the port, triggering a port-security violation (typically a security violation action of 'shutdown'), which places the interface in an error-disabled state. This matches the scenario where the user cannot access the network.

Answer

The interface is administratively shut down.

Answer

The sticky MAC address feature is disabled, allowing any MAC address to cause a violation.

Answer

The maximum number of secure MAC addresses has been exceeded, causing the port to err-disable.

Question 6

A network engineer notices that after adding a new switch to the network, a different switch unexpectedly becomes the STP root bridge, disrupting all VLANs. The new switch has the default priority (32768) but has a lower MAC address than all existing switches. What is the most likely cause?

Accepted Answer

The existing root bridge has a bridge priority lower than the default value of 32768. The existing root bridge has a bridge priority lower than the default value of 32768, so even though the new switch has the default priority, its lower MAC address does not make it the root. STP elects the root bridge based on the lowest bridge ID (priority + MAC address). Since the existing root already has a lower priority, it remains the root. The new switch's lower MAC address only becomes a tiebreaker when priorities are equal, which is not the case here.

Answer

The new switch is running PVST+ while the existing switches use Rapid PVST+

Answer

Root Guard is enabled on the new switch’s uplink ports facing the existing root

Answer

The new switch was added with a bridge priority of 4096

Question 7

Refer to the exhibit. A network engineer is troubleshooting an EtherChannel on R1 that is not passing traffic. The output of the show etherchannel summary command is displayed. What is the most likely cause?

Accepted Answer

One side is configured with LACP active and the other side is configured with mode 'on' (static).. The 'show etherchannel summary' output shows the port-channel is down (flags indicate 'D' for down), and the most common cause when one side is configured with LACP active and the other with mode 'on' (static) is a protocol mismatch. LACP active expects to negotiate with another LACP-enabled port, but static mode 'on' forces the link up without negotiation, causing the EtherChannel to fail to form. This mismatch prevents the exchange of LACP frames, leaving the bundle in an error-disabled or non-functional state.

Answer

The local switch is configured with LACP passive while the remote switch is set to LACP active.

Answer

The remote switch is configured with PAgP desirable while the local switch uses LACP.

Answer

The port-channel member interfaces are configured as access ports, preventing LACP from negotiating.

Question 8

Refer to the exhibit. A network engineer configured an EtherChannel between SW1 and SW2 using LACP. After the configuration is applied, the Port-channel 1 interface remains in a down state and does not pass traffic. The engineer runs the show etherchannel detail command on SW1. Based on the output, what is the most likely cause of the problem?

Accepted Answer

The interface Gi0/1 is administratively down.. An EtherChannel requires all member ports to have consistent VLAN configurations. However, if one port (Gi0/2) has a native VLAN mismatch, only that port is suspended/excluded from the channel. The port-channel can still become active using other valid members. In this scenario, the port-channel remains down because Gi0/1 is administratively down, leaving no valid member ports to form the channel. The show etherchannel detail output would indicate Gi0/1 in an administratively down state and Gi0/2 in a suspended state due to the native VLAN mismatch.

Answer

The native VLAN is mismatched on member interface Gi0/2.

Answer

The load-balancing method on the port-channel is set incorrectly to src-dst-ip.

Answer

Spanning Tree Protocol has placed the port-channel in a blocking state due to a loop.

Question 9

Refer to the exhibit. A network engineer expects SW1 to be the root bridge for VLAN 1, but the show spanning-tree vlan 1 output on SW2 shows that SW2 is the root. What is the most likely cause of this issue?

Accepted Answer

The trunk link between SW1 and SW2 is down.. If the trunk link between SW1 and SW2 is down, SW2 will not receive BPDUs from SW1. Without BPDUs, SW2 assumes it is the root bridge for VLAN 1 (since every switch defaults to root for its own VLANs). This explains why SW2's show spanning-tree output shows itself as root, even if SW1 has a lower bridge priority.

Answer

SW1 is configured with a priority of 32769 but has a higher MAC address than SW2.

Answer

Spanning tree is disabled on SW1 for VLAN 1.

Answer

SW1 has a bridge priority of 4096, but BPDU guard is configured on SW2's port to SW1, causing the port to be err-disabled.

Question 10

Refer to the exhibit. A network engineer notices packet loss and sluggish application performance on a branch-office uplink. While troubleshooting, the engineer executes the show interfaces GigabitEthernet0/1 command on the router. Based on the output, what is the most likely cause of the performance issue?

Accepted Answer

An upstream device is sending traffic at a rate higher than this interface can transmit, causing the output queue to overflow.. The interface shows a high number of output drops, indicating that the output queue is experiencing congestion and packets are being dropped because the router cannot transmit traffic as fast as it is being received from the upstream device. This causes packet loss and sluggish performance.

Answer

The interface is experiencing excessive collisions due to a duplex mismatch.

Answer

The interface is receiving corrupted frames, indicated by the zero input errors on the interface.

Answer

The output queue is full because its size is too small, and increasing the queue depth will resolve the packet loss.

Question 11

Refer to the exhibit. An engineer configured PortFast on interface GigabitEthernet0/1, which connects to a server that does not participate in spanning tree. However, the port remains in the listening state for the full forward delay period before transitioning to forwarding. The engineer issues the show spanning-tree vlan 10 detail command. Based on the output, what is the most likely cause?

Accepted Answer

The port is configured as a trunk, so PortFast is not active.. PortFast is designed to immediately transition a port to the forwarding state, bypassing the listening and learning states. However, PortFast is only effective on access ports; if the interface is configured as a trunk port, PortFast is automatically disabled by the switch. The output of 'show spanning-tree vlan 10 detail' would confirm the port is a trunk, explaining why it still goes through the full forward delay.

Answer

BPDU Guard is enabled on the port, causing it to block.

Answer

The forward delay timer is set too high, and PortFast cannot override it.

Answer

The server is sending BPDUs, causing the port to lose its PortFast state.

Question 12

A network engineer is configuring a new switch port for a VoIP phone that will have a PC daisy-chained behind it. The engineer wants to ensure that voice traffic is tagged with VLAN 100 and data traffic is untagged in VLAN 200. Which configuration should be applied to the switch port?

Accepted Answer

Configure the port as an access port in VLAN 200 and enable voice VLAN 100 with the switchport voice vlan 100 command.. The correct configuration uses the voice VLAN feature on an access port. The port is set to access VLAN 200 for data traffic, and the voice VLAN 100 is enabled. The VoIP phone will tag voice frames with VLAN 100, while the PC's data frames remain untagged and are placed in VLAN 200. This is the standard Cisco approach for connecting a phone and PC on a single switch port.

Answer

Configure the port as a trunk port with native VLAN 200 and allowed VLAN 100.

Answer

Configure the port as an access port in VLAN 100 and enable voice VLAN 200 with the switchport voice vlan 200 command.

Answer

Configure the port as a trunk port with native VLAN 100 and allowed VLAN 200.

Question 13

A network administrator is configuring a new Cisco Catalyst switch and needs to ensure that the native VLAN for 802.1Q trunk port GigabitEthernet1/0/1 is VLAN 99, which is not the default. The administrator enters the command 'switchport trunk native vlan 99' on the interface. However, after applying the configuration, the administrator notices that untagged traffic from the native VLAN is not being forwarded correctly. What is the most likely cause of this issue?

Accepted Answer

The native VLAN must be configured on both ends of the trunk link, and the other end is still using the default native VLAN.. The native VLAN on an 802.1Q trunk must be consistent on both ends. If one side uses VLAN 99 and the other uses VLAN 1, untagged frames are classified differently, leading to connectivity problems for devices in the native VLAN. Ensuring both switches use the same native VLAN resolves the issue.

Answer

VLAN 99 must be created in the VLAN database before it can be used as the native VLAN.

Answer

The native VLAN configuration requires the 'switchport mode trunk' command to be applied first.

Answer

The command 'switchport trunk native vlan 99' is only valid on access ports, not on trunk ports.

Question 14

A network engineer is implementing Rapid PVST+ on a Cisco switch. The engineer wants to ensure that a specific interface is immediately placed into the forwarding state when it is connected to an end device, but also wants to prevent the interface from causing a loop if a switch is inadvertently connected. Which feature should be configured on the interface?

Accepted Answer

PortFast and BPDU Guard. PortFast allows an interface to go to forwarding immediately for end devices, while BPDU Guard disables the port if BPDUs are detected, preventing loops from unexpected switches. This combination is ideal for access ports connecting to hosts, ensuring rapid connectivity and network stability.

Answer

UplinkFast and BackboneFast

Answer

PortFast and Root Guard

Answer

BPDU Filtering and Loop Guard

Question 15

A network administrator is configuring a new switch and needs to set up VLANs. The administrator wants to ensure that VLAN 10 is used for voice traffic and VLAN 20 for data traffic on a port connected to an IP phone and a PC. Which two commands are required on the interface to achieve this configuration? (Choose two.)

Accepted Answer

switchport voice vlan 10. To support both voice and data on a single port, the interface must be in access mode with a voice VLAN. The 'switchport access vlan 20' command assigns the data VLAN, and 'switchport voice vlan 10' assigns the voice VLAN. The phone tags voice traffic, while data traffic remains untagged.

Answer

switchport mode access

Answer

switchport mode trunk

Answer

switchport trunk encapsulation dot1q