CCNA Network Infrastructure and Connectivity Practice Test 28 — 15 Questions

Question 1

A network technician replaced a faulty SFP transceiver on a switch port. After replacement, the port remains in a down/down state. The technician verifies the fiber cable is securely connected at both ends and observes that the remote switch port is also in a down/down state. What should the technician do next?

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

Accepted Answer

Check the running configuration for the no shutdown command on the interface.. The most common cause of a port remaining in a down/down state after replacing a faulty SFP is that the interface is administratively down. The 'no shutdown' command must be applied to bring the interface up. Since the technician already verified physical connectivity and both ends show down/down, the issue is likely at the configuration layer, not the physical layer.

Answer

Verify that the speed and duplex settings are set to auto-negotiation.

Answer

Check whether the SFP module type is incompatible with the switch.

Answer

Verify the VLAN assignment on the port.

Question 2

A wireless client associates to an AP and successfully authenticates to the correct SSID, but it does not obtain an IP address. The WLC is running in local mode. What should the technician do next?

Accepted Answer

Verify the VLAN mapping on the WLC for the client’s WLAN.. When a wireless client authenticates to the SSID but fails to obtain an IP address, the most likely cause is a VLAN mapping mismatch on the WLC. In local mode, the WLC maps the WLAN to a specific VLAN (via the interface or VLAN tag), and if that VLAN does not have a DHCP relay or is not trunked to the correct switch, the client's DHCP requests will never reach the DHCP server. This is a common Layer 2 connectivity issue that prevents IP address assignment even though authentication succeeds.

Answer

Check the DHCP server to ensure it has available leases.

Answer

Verify the AP’s operating channel for interference.

Answer

Verify the WPA3 PSK on the client.

Question 3

Refer to the exhibit. A network engineer is troubleshooting a serial link between two routers that is not coming up. The engineer issues the show controllers command on one router and sees the output shown. What is the most likely cause of the issue?

Accepted Answer

The clock rate command is missing on the DCE serial interface.. The 'show controllers' output indicates the router is the DCE (Data Communications Equipment) on the serial link, but no clock rate has been configured. For a serial interface to come up, the DCE end must provide clocking via the 'clock rate' command. Without it, the interface will remain down (line protocol down) because no clock signal is present to synchronize data transmission.

Answer

The serial cable type is incorrectly identified.

Answer

The encapsulation mismatch is causing the line protocol to stay down.

Answer

The serial interface is administratively shut down.

Question 4

A technician is troubleshooting a dual-stack network where an IPv6-only host cannot reach an IPv4 resource. The technician issues the show ipv6 interface brief command on the local router and notices the interface facing the host has a link-local address but no global unicast address. The technician then checks the running configuration and finds that the command ipv6 unicast-routing is missing. What is the most likely cause?

Accepted Answer

IPv6 unicast routing has not been enabled on the router.. The missing `ipv6 unicast-routing` command means the router is not acting as an IPv6 router, so it does not send Router Advertisement (RA) messages. Without RAs, the host cannot autoconfigure a global unicast address or learn a default gateway, breaking IPv6 connectivity to any IPv4 resource even if NAT64 is present.

Answer

An IPv6 access list on the router is blocking Router Advertisement messages.

Answer

The IPv4 resource is not configured for NAT64 translation.

Answer

The host has an incorrect default gateway for IPv6.

Question 5

Refer to the exhibit. An administrator notices that all interfaces on R1 are in an administratively down state. The administrator issues the show version command and sees the following output. What is the most likely cause of the issue?

Accepted Answer

The configuration register is set to 0x2142, causing the router to ignore the startup configuration.. The configuration register value 0x2142 tells the router to ignore the startup configuration during boot, loading only the default factory configuration. This causes all interfaces to be in an administratively down state because no interface configurations from the startup-config are applied. The administrator sees the interfaces as administratively down because the default configuration does not include any 'no shutdown' commands.

Answer

The router IOS image is corrupted and needs to be reinstalled.

Answer

The interfaces have been manually shut down in the running configuration, and the startup-config file is empty.

Answer

The router experienced a memory error during boot and failed to load the startup configuration.

Question 6

A technician is troubleshooting a connection between two routers, R1 and R2, connected back-to-back using Ethernet cables. Both routers have their interfaces configured and are in an 'up/up' state. R1's interface uses 192.168.1.1/24, and R2's interface uses 192.168.2.1/24. When the technician attempts to ping R2 from R1, the ping fails. What is the most likely cause?

Accepted Answer

The IP addresses assigned to the interfaces belong to different subnets, preventing direct Layer 3 communication.. The ping fails because R1's interface is configured with IP address 192.168.1.1/24, which places it in the 192.168.1.0/24 subnet, while R2's interface uses 192.168.2.1/24, placing it in the 192.168.2.0/24 subnet. For two devices to communicate directly at Layer 3 over a single Ethernet link, their IP addresses must belong to the same subnet. Since these addresses are in different subnets, R1 will see the destination as unreachable and will not even attempt to send an ARP request for R2's MAC address, resulting in a failed ping.

Answer

The Ethernet cable is faulty, causing intermittent physical layer failures.

Answer

A duplex mismatch exists between R1 and R2, causing one-way communication.

Answer

A routing protocol is not configured to allow the routers to learn about each other's directly connected networks.

Question 7

A network engineer notices that after issuing the no shutdown command on interface GigabitEthernet0/0 of a router, the interface remains down. The output of show interfaces GigabitEthernet0/0 displays 'GigabitEthernet0/0 is down, line protocol is down'. The physically connected switch port is also administratively down. What is the most likely cause?

Accepted Answer

The connected switch port is administratively down.. The output 'GigabitEthernet0/0 is down, line protocol is down' indicates that both Layer 1 and Layer 2 are down. Since the directly connected switch port is administratively down, the router interface detects no carrier and remains down/down even after the local no shutdown command. Therefore, option A is the most likely cause.

Answer

Mismatched encapsulation types on the router and switch.

Answer

Speed and duplex mismatch between the router and switch.

Answer

Incorrect native VLAN configuration on the trunk link.

Question 8

Refer to the exhibit. A network engineer is troubleshooting a connectivity issue on R1. The serial link to R2 on interface Serial0/1 is using HDLC encapsulation, and the physical cable has been verified as good. The engineer has confirmed that the encapsulation type matches on both routers and that the clock rate is correctly configured on the DCE end. Based on the output, what is the most likely cause of the line protocol down state on Serial0/1?

Accepted Answer

The keepalive packets are not being received, causing the protocol to stay down.. The output shows that the line protocol is down while the physical layer (Serial0/1 is up). With HDLC encapsulation and clock rate confirmed correct, the most likely cause is that keepalive packets are not being exchanged between R1 and R2. HDLC uses keepalives to maintain the data link layer; if they are not received (e.g., due to a misconfiguration like 'no keepalive' on one side or a faulty cable), the protocol state will remain down even though the physical layer is operational.

Answer

The encapsulation type is mismatched between R1 and R2.

Answer

The clock rate has not been configured on the DCE end of the serial link.

Answer

The IP address configured on Serial0/1 conflicts with another interface.

Question 9

Refer to the exhibit. A network engineer is troubleshooting intermittent connectivity between a branch router and the upstream switch. The switch port is manually configured for full-duplex, and the Ethernet cable has been tested and is working properly. The engineer runs the show interfaces GigabitEthernet0/0 command on the router and receives the output shown. Based on the output, what is the most likely cause of the problem?

Accepted Answer

The router interface is operating in half-duplex while the switch port is full-duplex, causing a duplex mismatch.. The output shows the router interface is operating in half-duplex (as indicated by 'Half-duplex' in the show interfaces output), while the switch port is manually configured for full-duplex. This duplex mismatch causes the router to use CSMA/CD and detect collisions, while the switch transmits without collision detection, leading to late collisions, CRC errors, and intermittent connectivity. The correct fix is to set both sides to the same duplex setting, ideally full-duplex.

Answer

The switch port is configured for half-duplex instead of the expected full-duplex.

Answer

The cable is faulty, causing excessive late collisions and CRC errors.

Answer

The excessive input errors are a result of a broadcast storm on the network.

Question 10

A branch router has two equal-cost static routes to the same destination network. Both routes are displayed in the output of the show ip route command, and pings from the router to both next-hop IP addresses succeed. Despite this, all traffic heading toward that destination is egressing only a single interface. The technician suspects Cisco Express Forwarding (CEF) is not performing load balancing as expected. What should the technician do next?

Accepted Answer

Issue the show ip cef detail command to inspect the CEF FIB entry and verify both adjacencies are present.. CEF performs load balancing over equal-cost paths using a hash of the packet's destination (or source/destination) address to select a path. The interface bandwidth is not a factor for equal-cost load balancing; it is used for metric calculation in routing protocols, not for CEF path selection. When traffic uses only one interface despite two equal-cost routes in the routing table, you should verify that CEF has installed both paths in its FIB and resolved both next-hop addresses to adjacencies. The command 'show ip cef detail' displays the FIB entry and associated adjacencies, confirming both paths are available for load balancing.

Answer

Check the interface output rates with show interface to see if both interfaces are transmitting traffic.

Answer

Display the routing table again with show ip route to ensure both static routes are still installed.

Answer

Verify the bandwidth configured on the outgoing interfaces using show interfaces or show running-config.

Question 11

A network administrator is configuring VLANs on a Cisco Catalyst switch. The design requires that VLAN 10 traffic and VLAN 20 traffic share the same physical uplink to a router, but each VLAN must remain logically separate at Layer 2. The router interface is configured with 802.1Q encapsulation. Which statement correctly describes how the router will process frames arriving from both VLANs on that single physical interface?

Accepted Answer

The router will use subinterfaces, each associated with a VLAN ID, to terminate the 802.1Q tags and route between the VLANs.. Router-on-a-stick uses a single physical router interface configured with 802.1Q encapsulation and multiple subinterfaces, each mapped to a VLAN ID. The router terminates the VLAN tags, assigns each subinterface an IP address as the default gateway for that VLAN, and routes traffic between VLANs at Layer 3. This meets the requirement of sharing one uplink while maintaining logical separation of VLAN 10 and VLAN 20.

Answer

The router will forward tagged frames between VLAN 10 and VLAN 20 at Layer 2, acting as a transparent bridge for those VLANs.

Answer

The router will strip the 802.1Q tag and route traffic between VLAN 10 and VLAN 20 without requiring any subinterfaces.

Answer

The router will require a separate physical interface for each VLAN because 802.1Q does not support multiple VLANs on one link.

Question 12

A network engineer is configuring a new Cisco Catalyst 9300 switch. The switch currently has all interfaces in VLAN 1, and the engineer needs to segment traffic for the Finance department. The engineer creates VLAN 20 and assigns it the name 'Finance'. Which command sequence is required to place access ports FastEthernet 1/0/1 through 1/0/10 into VLAN 20?

Accepted Answer

Switch(config)# interface range FastEthernet 1/0/1 - 10
Switch(config-if-range)# switchport mode access
Switch(config-if-range)# switchport access vlan 20. To assign multiple access ports to a VLAN, you must enter interface range configuration, set the ports to access mode, and then assign the VLAN. The switchport mode access command ensures the ports operate as access ports, and switchport access vlan 20 assigns the VLAN. This is the standard and efficient way to configure multiple ports simultaneously on Cisco switches.

Answer

Switch(config)# vlan 20
Switch(config-vlan)# name Finance
Switch(config-vlan)# exit
Switch(config)# interface range FastEthernet 1/0/1 - 10
Switch(config-if-range)# switchport trunk allowed vlan 20

Answer

Switch(config)# interface range FastEthernet 1/0/1 - 10
Switch(config-if-range)# switchport mode trunk
Switch(config-if-range)# switchport trunk native vlan 20

Answer

Switch(config)# vlan 20
Switch(config-vlan)# name Finance
Switch(config-vlan)# interface FastEthernet 1/0/1 - 10
Switch(config-if-range)# switchport access vlan 20

Question 13

A network administrator is configuring a Cisco switch. The switch has a management VLAN 99 with IP address 10.10.99.5/24 and default gateway 10.10.99.1. The administrator wants to verify that the switch can reach a server at 10.10.99.100. Which command should be used on the switch to test reachability?

Accepted Answer

ping 10.10.99.100. To verify reachability to a specific IP address from a Cisco switch, the ping command is the correct tool. It sends ICMP echo requests and waits for replies, providing immediate feedback on whether the destination is reachable. Other commands like show ip interface brief or show ip route only display configuration or routing information and do not test actual connectivity.

Answer

show ip route

Answer

show ip interface brief

Answer

traceroute 10.10.99.100

Question 14

A network engineer is configuring a new Cisco switch that will carry traffic for multiple VLANs between two buildings. The link between the two switches must transport frames for VLAN 10, 20, and 30, and both switches must be able to identify which VLAN each frame belongs to. Which configuration should be applied to the inter-switch link on both switches?

Accepted Answer

Configure the ports as trunk ports using 802.1Q encapsulation.. The inter-switch link must carry frames for multiple VLANs while preserving VLAN identity, which is exactly what an 802.1Q trunk does. Access ports serve only one VLAN, ISL is a legacy nonstandard encapsulation, and routed ports operate at Layer 3 and cannot transport VLAN-tagged frames. Configuring 802.1Q trunking on both ends ensures frames for VLAN 10, 20, and 30 are tagged and correctly identified by the receiving switch.

Answer

Configure the ports as trunk ports using ISL encapsulation.

Answer

Configure the ports as routed ports with IP addresses in each VLAN subnet.

Answer

Configure the ports as access ports and assign them to VLAN 10.

Question 15

A technician is connecting a new Cisco switch to an existing switch using a copper cable. The link between the two switches must carry traffic for multiple VLANs. Which command must be configured on the interface connecting to the other switch to allow multiple VLANs to traverse the link?

Accepted Answer

switchport mode trunk. To carry traffic for multiple VLANs over a single inter-switch link, the interface must be configured as a trunk. The command switchport mode trunk sets the interface to permanent trunking mode, allowing 802.1Q-tagged frames for multiple VLANs to traverse the link. Other commands like nonegotiate or allowed vlan list are supplementary and only apply after trunk mode is enabled.

Answer

switchport mode access

Answer

switchport nonegotiate

Answer

switchport trunk allowed vlan all