CCNA Switching and Network Access Practice Test 26 — 15 Questions

Question 1

A network engineer has configured an LACP EtherChannel between Switch1 and Switch2 by assigning interfaces to channel-group 1 with the mode passive on both switches. The engineer issues the show etherchannel summary command on Switch1 and sees the output below. The Port-channel interface remains down. Which action resolves the issue?

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

Accepted Answer

Change the mode on one switch to active.. When both switches are configured with LACP mode passive, neither switch initiates the negotiation process because passive mode only responds to incoming LACP packets. By changing one side to active mode, that switch will actively send LACP packets, allowing the EtherChannel to form. The Port-channel interface remains down due to this negotiation failure, not because of VLAN or physical mismatch issues.

Answer

Configure the switchport mode as trunk on both sides.

Answer

Verify that the native VLAN matches on both sides of the trunk.

Answer

Correct the speed and duplex settings on the member ports.

Question 2

An administrator connects a new access-layer switch to a distribution switch. The link comes up but remains in a blocking state and does not forward frames. The administrator issues the show command shown in the exhibit. What is the most likely reason the link is blocked?

Accepted Answer

Root Guard is configured on the port, and the new access switch is sending superior BPDUs, triggering a root-inconsistent state.. The link is blocked because Root Guard is configured on the distribution switch port. When the new access-layer switch sends superior BPDUs (with a lower bridge priority), Root Guard transitions the port to a root-inconsistent (blocking) state to protect the current root bridge from being usurped. This prevents the new switch from becoming the root bridge, which would disrupt the spanning-tree topology.

Answer

BPDU Guard is enabled on the port, and the new switch's BPDUs caused the port to enter err-disable state.

Answer

Loop Guard is enabled, and the port has stopped receiving BPDUs, leading to a loop-inconsistent state.

Answer

The port is configured with PortFast, and the new switch's BPDU triggered a loop, causing the port to err-disable.

Question 3

A user connects a Cisco IP Phone with a PC attached to the phone's PC port to switch interface GigabitEthernet0/5. The PC obtains an IP address and can reach the network, but the phone displays "Configuring IP" and never registers. Based on the exhibit outputs, what is the most likely cause?

Accepted Answer

VLAN 20 has not been created in the switch's VLAN database.. The PC obtains an IP address and can reach the network, indicating that the access VLAN (likely VLAN 1 or the native VLAN) is functioning. However, the phone displays 'Configuring IP' and never registers, which means it cannot obtain an IP address on its voice VLAN. The most likely cause is that VLAN 20, which is configured as the voice VLAN on the switchport, has not been created in the switch's VLAN database. Without the VLAN existing, the switch cannot forward traffic or DHCP requests for that VLAN, leaving the phone stuck in the IP configuration phase.

Answer

The switchport must be configured as a trunk to support voice VLANs.

Answer

The native VLAN on the trunk ports between the switch and the DHCP server is incorrectly set to VLAN 10.

Answer

The phone is manually configured to use VLAN 10 for voice traffic instead of VLAN 20.

Question 4

Which TWO statements are true regarding switch port configuration for access, voice, and trunk ports?

Accepted Answer

A switch port configured as a trunk port can simultaneously carry untagged traffic for the native VLAN and tagged traffic for multiple other VLANs.. Option A is correct because an 802.1Q trunk port transmits frames for the native VLAN untagged while tagging frames for all other allowed VLANs, allowing one link to carry both native and multiple tagged VLANs simultaneously. Option D is correct because when a voice VLAN is configured on an access port, the switch uses CDP (or LLDP-MED) to advertise the voice VLAN ID to the attached IP phone, which then tags its voice traffic with that VLAN. Option B is wrong because a port with both an access VLAN and a voice VLAN is configured as an access port with the 'switchport voice vlan' command, not as a trunk. Option C is wrong because 'switchport mode dynamic auto' only passively waits for the neighbor to initiate trunking; it is 'dynamic desirable' that actively attempts to form a trunk. Option E is wrong because the native VLAN is not automatically added to the allowed VLAN list by 'switchport trunk allowed vlan'; it must be explicitly included if it is to be permitted on the trunk.

Answer

When a port is configured with both an access VLAN and a voice VLAN, the switchport must be set to trunk mode.

Answer

The switchport mode dynamic auto command sets the port to actively attempt to form a trunk if the neighbor initiates negotiation.

Answer

Issuing the switchport trunk allowed vlan command automatically includes the native VLAN in the allowed list, so it never needs to be explicitly added.

Question 5

Which THREE statements about STP and Rapid PVST+ are correct?

Accepted Answer

Rapid PVST+ creates a separate spanning-tree instance for each VLAN, enabling per-VLAN load balancing.. Option A is correct because Rapid PVST+ (Rapid Per-VLAN Spanning Tree Plus) runs a separate 802.1w-based spanning-tree instance for every VLAN, which allows different VLANs to use different root bridges and forwarding paths, enabling per-VLAN load balancing. Option C is correct because Rapid PVST+ uses the RSTP proposal/agreement handshake (via BPDUs with the proposal and agreement flags) to rapidly synchronize ports and move them to forwarding without relying on the slow 802.1D timers. Option D is correct because BPDU Guard, typically combined with PortFast on access ports, error-disables a port if it receives a BPDU, preventing an unauthorized or misconfigured switch from affecting the topology. Option B is incorrect because PortFast is intended for access (edge) ports connected to end hosts, not trunk ports; enabling it on a trunk could cause loops or topology instability. Option E is incorrect because the root bridge is elected by the lowest bridge priority (default 32768), so to become root a switch must be given the lowest priority value, not the highest.

Answer

PortFast should be configured on trunk ports to quickly transition them to forwarding state.

Answer

To make a switch the root bridge, you should assign it the highest bridge priority value among all switches.

Question 6

Which TWO statements about 802.1Q trunking, native VLANs, and inter-VLAN routing are correct? (Choose two.)

Accepted Answer

By default, frames belonging to the native VLAN are sent untagged across an 802.1Q trunk.. By default, 802.1Q trunking treats the native VLAN (typically VLAN 1) as untagged. Frames in the native VLAN are sent without an 802.1Q tag, allowing interoperability with devices that do not understand trunking. This behavior is defined in IEEE 802.1Q and is essential for backward compatibility.

Answer

802.1Q trunking is a Cisco-proprietary protocol that uses a 4-byte tag to identify VLAN membership.

Answer

Inter-VLAN routing can be accomplished using a Layer 2 switch configured with VLAN access maps.

Answer

Switches strip the 802.1Q tag from all frames before forwarding them out of a trunk port.

Question 7

Drag and drop the items on the left to match the descriptions on the right.

Accepted Answer

switchport mode trunk: Configures a trunk port. VLANs segment a switch into multiple broadcast domains. 802.1Q trunking encapsulates frames with a VLAN tag, while the native VLAN carries untagged traffic. 'switchport mode trunk' configures a trunk port, 'show vlan brief' lists VLAN assignments, and inter-VLAN routing enables communication between VLANs typically using a router or Layer 3 switch.

Answer

VLAN: Encapsulates frames with a VLAN tag

Answer

802.1Q trunking: Carries untagged traffic on a trunk

Answer

Native VLAN: Segments a switch into multiple broadcast domains

Question 8

Drag and drop the following steps into the correct order to configure inter-VLAN routing using a router-on-a-stick topology.

Accepted Answer

On the switch, create the necessary VLANs (e.g., VLAN 10 and VLAN 20) using the 'vlan' command.. Inter-VLAN routing via router-on-a-stick requires creating VLANs on the switch, placing access ports in those VLANs, configuring a trunk to the router with the correct native VLAN to avoid mismatch, enabling the physical router interface, and then defining subinterfaces per VLAN with 802.1Q encapsulation and IP addresses. This ensures traffic from different VLANs can be routed.

Question 9

An administrator notices that hosts in VLAN 30 on SW1 cannot communicate with hosts in VLAN 30 on SW2, even though both switches are connected via an 802.1Q trunk. Traffic for VLANs 10 and 20 passes without issues across the same trunk. The trunk is configured to allow all VLANs, and the allowed VLAN list explicitly includes VLAN 30. What is the most likely cause of the problem?

Accepted Answer

The native VLAN is mismatched between SW1 and SW2, and VLAN 30 is the native VLAN on one side.. The most likely cause is a native VLAN mismatch. When the native VLAN is mismatched on an 802.1Q trunk, traffic for the native VLAN is not tagged, so frames from VLAN 30 on one switch are received as untagged frames on the other switch and placed into the switch's configured native VLAN. If the native VLAN on one side is VLAN 30 and on the other side is a different VLAN (e.g., VLAN 1), the hosts in VLAN 30 cannot communicate because the frames are interpreted as belonging to different VLANs. Traffic for VLANs 10 and 20 passes because they are not the native VLAN and are properly tagged.

Answer

The trunk encapsulation is set to ISL on one switch and 802.1Q on the other.

Answer

Spanning Tree Protocol has placed VLAN 30 in a blocking state on the trunk link.

Answer

The switched virtual interface (SVI) for VLAN 30 on SW1 is administratively down.

Question 10

A network administrator implements a set of spanning-tree enhancements to secure the switching infrastructure. Later, a help desk ticket reports that a user in a remote office cannot connect to any network resources. While investigating, the administrator notices that the switch port connecting the remote office switch to the distribution switch is in a 'root-inconsistent' state and is blocking traffic. Which protection feature, if misapplied, most likely caused this issue?

Accepted Answer

Root Guard. Root Guard is the correct answer because it forces an interface to be a designated port. If a switch receives a superior BPDU (indicating a root bridge with a lower bridge ID) on a Root Guard-enabled port, the port is placed into a 'root-inconsistent' state and blocks traffic to prevent the attached switch from becoming the root bridge. This matches the symptom described: a port in 'root-inconsistent' state blocking traffic after spanning-tree enhancements were applied.

Answer

Loop Guard

Answer

BPDU Guard

Answer

BPDU Filter

Question 11

A network engineer configures an EtherChannel between two switches. Switch A's interface is set with channel-group 1 mode active, while Switch B's identical interface is set with channel-group 1 mode auto. When verifying with show etherchannel summary, the engineer observes that the port-channel interface is down and the physical interfaces are not bundled. What is the most likely cause of the problem?

Accepted Answer

The mode 'auto' is a PAgP negotiation mode that is incompatible with the LACP active mode.. 'active' is an LACP mode that initiates negotiations, while 'auto' is a PAgP mode that passively waits for PAgP packets. Since LACP and PAgP are incompatible protocols, the interfaces will never negotiate a bundle, leaving the port-channel down. The engineer must use matching protocol modes (e.g., both LACP active/passive or both PAgP desirable/auto) for EtherChannel to form.

Answer

The LACP system priority on the active side must be lower than the auto side.

Answer

LACP requires one side to be active and the other passive; two active interfaces will not bundle.

Answer

The physical interfaces must be shut down and then re-enabled after configuring LACP for the bundle to form.

Question 12

Which TWO statements accurately describe 802.1Q trunking and inter-VLAN routing on Cisco switches?

Accepted Answer

802.1Q trunking adds a 4-byte tag that includes a 12-bit VLAN ID field, increasing the maximum frame size.. Option B is correct because 802.1Q inserts a 4-byte tag into the Ethernet frame, and that tag contains a 12-bit VLAN Identifier (VID) field supporting VLAN IDs 1-4094, which increases the frame size beyond the standard 1518 bytes (up to 1522 bytes). Option C is correct because router-on-a-stick uses one physical router interface divided into logical subinterfaces, and each subinterface is configured with encapsulation dot1q <vlan-id> plus an IP address in a distinct subnet to route between VLANs. Option A is incorrect because the native VLAN is the one VLAN whose frames are sent untagged on an 802.1Q trunk, not tagged with VLAN ID 1. Option D is incorrect because a trunk port carries traffic for multiple VLANs simultaneously, tagging frames to keep them separated. Option E is incorrect because the native VLAN is configurable per trunk port with the switchport trunk native vlan command and is not locked to VLAN 1.

Answer

The native VLAN on a trunk port sends frames with an 802.1Q tag containing VLAN ID 1.

Answer

A trunk port can only forward traffic for one VLAN at a time.

Answer

The native VLAN on a trunk cannot be changed from VLAN 1.

Question 13

Refer to the exhibit. A network administrator is troubleshooting a connectivity issue on switch SW1. Users connected to port Gi0/3 are unable to reach resources in VLAN 30. The administrator issues the show vlan brief command and receives the output shown. What is the most likely cause of the problem?

Accepted Answer

VLAN 30 is administratively shut down.. The 'show vlan brief' output shows VLAN 30 with a status of 'act/lshut' (administratively shutdown) or 'shutdown', indicating that the VLAN has been disabled via the 'shutdown' command in VLAN configuration mode. A shutdown VLAN does not forward traffic, and all access ports assigned to it become operationally inactive for that VLAN, even though the ports themselves may still be listed in the output. The SVI for VLAN 30 would also be down. Therefore, the most likely cause is that VLAN 30 has been administratively shut down.

Answer

The Gi0/3 port is in an error-disabled state due to port security violations.

Answer

The VLAN 30 SVI is administratively down.

Answer

Spanning Tree Protocol has placed Gi0/3 into a blocking state for VLAN 30.

Question 14

A network technician notices CDP native VLAN mismatch warnings between switches SW1 and SW2 on their trunk link. The technician runs 'show interfaces trunk' on SW1 and sees native VLAN 1, then on SW2 and sees native VLAN 99. Data traffic is currently passing, but the mismatch can cause broadcast loops. What should the technician do next?

Accepted Answer

Configure the native VLAN to match on both ends of the trunk.. The correct action is to configure the native VLAN to match on both ends of the trunk. CDP reports a native VLAN mismatch when the native VLANs differ on the two sides of a trunk link. Although data traffic may still pass because 802.1Q does not tag frames on the native VLAN, the mismatch can cause broadcast loops and security risks, as frames from one native VLAN may be misinterpreted on the other side. Setting both sides to the same native VLAN (e.g., VLAN 1 or VLAN 99) resolves the mismatch and ensures proper Layer 2 behavior.

Answer

Add VLAN 99 to the allowed VLAN list on the trunk interface of SW1.

Answer

Remove the trunk configuration and set both interfaces as access ports in VLAN 1.

Answer

Enable spanning‑tree PortFast on the trunk ports.

Question 15

A technician is troubleshooting a network issue where hosts in VLAN 20 on SW1 cannot communicate with hosts in VLAN 20 on SW2. Both switches are connected by an Ethernet trunk link that is up/up and configured as a trunk. The VLAN databases on both switches include VLAN 20, and the spanning tree for VLAN 20 is in a forwarding state on all ports. Hosts within VLAN 20 on each switch can communicate with each other locally. What is the most likely cause?

Accepted Answer

VLAN 20 is not in the switchport trunk allowed VLAN list on the trunk port between SW1 and SW2.. The most likely cause is that VLAN 20 is not included in the allowed VLAN list on the trunk port between SW1 and SW2. Even though the trunk is up/up and VLAN 20 exists in the VLAN database, the switchport trunk allowed vlan command restricts which VLANs can traverse the trunk. If VLAN 20 is omitted from this list, frames from VLAN 20 will be dropped at the trunk, preventing inter-switch communication for that VLAN.

Answer

The native VLAN is mismatched on the two ends of the trunk.

Answer

VLAN 20 has not been created in the VLAN database on SW2.

Answer

The trunk encapsulation is mismatched between SW1 and SW2.