CCNA Network Infrastructure and Connectivity Practice Test 26 — 15 Questions

Question 1

Drag and drop the following steps into the correct order to troubleshoot a link-down issue on a GigabitEthernet interface using an SFP transceiver.

Accepted Answer

Identify the interface with the link-down condition using the 'show interfaces' command and note any input/output errors.. Troubleshooting begins by verifying the interface status and physical layer (steps 1-2). Next, you ensure the SFP is physically and logically recognized (step 3) before retrieving specific diagnostic data (step 4). Only after confirming the health of the transceiver do you take corrective action (step 5), because replacing hardware without diagnostics may waste resources.

Question 2

Drag and drop the following steps into the correct order to troubleshoot and resolve excessive interface errors caused by a duplex mismatch on a Cisco switch interface.

Accepted Answer

Use the show interfaces command to examine the input errors, CRC, and late collisions counters.. The correct order starts with identifying symptoms using show interfaces to see error counters like CRC and late collisions. Next, check the local interface speed and duplex with show interfaces status. Then discover the neighbor's speed and duplex, for instance via show cdp neighbors detail, to confirm a mismatch. After identifying the mismatch, configure the interface with the correct settings (e.g., speed and duplex commands). Finally, verify the resolution by running show interfaces again to ensure errors are no longer incrementing.

Question 3

Drag and drop the following steps into the correct order to configure a Cisco switch with an IPv4 management address 192.168.1.10/24, an IPv6 address 2001:db8:1::1/64, and a default gateway 192.168.1.1.

Accepted Answer

Enter global configuration mode using the configure terminal command.. Correct order: 
1. Enter global configuration mode – all subsequent configuration commands require this mode.
2. Enter interface configuration mode for VLAN 1 – the management SVI must be selected to apply IP settings.
3. Assign the IPv4 address 192.168.1.10 255.255.255.0 – sets the switch's management IPv4 address and subnet mask.
4. Enable the interface with the no shutdown command – activates the SVI so it can send and receive traffic.
5. Assign the IPv6 address 2001:db8:1::1/64 – enables IPv6 processing and statically configures a global unicast address.
6. Exit interface configuration mode to return to global configuration mode – required because the default gateway command is a global configuration command, not an interface subcommand.
7. Set the default gateway to 192.168.1.1 using the ip default-gateway command – provides the next-hop router for IPv4 traffic leaving the local subnet.

Question 4

Drag and drop the following steps into the correct order to troubleshoot a client PC that cannot connect to a remote web server.

Accepted Answer

Run ipconfig /all to verify the PC's IP address, subnet mask, and default gateway.. The correct order follows Cisco's bottom-up troubleshooting methodology: first verify local IP configuration with ipconfig, then confirm the local TCP/IP stack with a loopback ping, then verify the NIC and IP binding by pinging the assigned address. Next, test connectivity to the default gateway to ensure the local subnet and router are reachable. After that, attempt to reach the remote server's IP address with ping. If that fails, use traceroute to identify where along the path the packets are lost. This sequence efficiently isolates the fault domain from the local device to the internetwork.

Question 5

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

Accepted Answer

show interface transceiver: Outputs Digital Optical Monitoring (DOM) data such as temperature, voltage, and Tx/Rx power for installed transceivers.. show interface transceiver outputs Digital Optical Monitoring (DOM) data such as temperature, voltage, and Tx/Rx power for installed transceivers. show controllers ethernet-controller phy displays physical layer diagnostics including cable length estimates, MDI/MDI-X status, pair swaps, and link quality counters. SFP-10G-SR is a multimode fiber transceiver supporting 10 Gigabit Ethernet at 850nm over distances up to 300 meters. Cat6a is enhanced copper twisted-pair cabling rated for 10GBASE-T up to 100 meters with improved alien crosstalk performance. LC connectors are the small form-factor duplex fiber connectors commonly used with SFP and SFP+ optical modules.

Answer

show interface transceiver: Displays physical layer diagnostics including cable length estimates, MDI/MDI-X status, pair swaps, and link quality counters.

Answer

Cat6a: Multimode fiber transceiver supporting 10 Gigabit Ethernet at 850nm over distances up to 300 meters.

Question 6

Which TWO statements correctly describe interface errors and duplex mismatches on Cisco switches?

Accepted Answer

Late collisions on a half-duplex interface can indicate a duplex mismatch with the connected device.. Late collisions occur when a frame is transmitted onto the wire and collides after the first 512 bit-times of the frame. In a half-duplex Ethernet segment, a duplex mismatch causes the full-duplex side to never defer and transmit at any time, while the half-duplex side expects to detect collisions only during the collision window. When the full-duplex device sends a frame while the half-duplex device is already transmitting, the half-duplex device detects a collision after the 512-bit window, resulting in a late collision.

Answer

Runts are typically caused by CRC errors on the transmitting device.

Answer

Full-duplex interfaces use CSMA/CD to detect collisions before transmitting.

Answer

Auto-MDIX can resolve a duplex mismatch by renegotiating the speed and duplex settings.

Question 7

Which TWO statements accurately describe the encapsulation process and PDU naming across the OSI and TCP/IP models?

Accepted Answer

In the OSI model, the Network layer encapsulates data into packets, while in the TCP/IP model the Internet layer performs the same function.. The OSI Network layer and the TCP/IP Internet layer both encapsulate transport layer segments or datagrams into packets by adding a Layer 3 header (e.g., IP header). This is the fundamental encapsulation step where logical addressing is applied, and the resulting PDU is called a packet in both models. The function is identical despite the different layer names.

Answer

At the Transport layer, the TCP/IP model uses segments, while the OSI model uses packets.

Answer

Encapsulation adds headers and trailers at each layer, so the PDU size decreases as data moves down the stack.

Answer

The OSI model's Session layer is responsible for end-to-end flow control using TCP segments, while the TCP/IP model combines this into the Application layer.

Question 8

Drag and drop the following steps into the correct order to enable a third-party SFP transceiver and verify its diagnostics on a Cisco switch.

Accepted Answer

Enter global configuration mode: configure terminal. Cisco switches by default only support Cisco-branded SFP transceivers. To use a third-party transceiver, the command `service unsupported-transceiver` must be enabled in global configuration mode. After configuring the interface, the `show interfaces transceiver` command displays diagnostic information including temperature, voltage, and optical power, which helps verify proper operation.

Question 9

Drag and drop the following steps into the correct order to describe the encapsulation of data as it passes down the TCP/IP stack for transmission.

Accepted Answer

Application data is generated by the user application.. The encapsulation process starts with the application layer generating data. The transport layer packages data into segments (TCP) or datagrams (UDP). The network layer adds an IP header, creating a packet. The data link layer adds a frame header and trailer (frame). Finally, the physical layer converts the frame into bits for transmission.

Question 10

A network administrator is troubleshooting slow file transfers between two servers in different access-layer switches. The administrator runs the 'show interface' command on the uplink connecting the two switches and notices a high number of CRC errors on both ends, but a high number of late collisions on only one interface; the other interface reports no late collisions.

Accepted Answer

Duplex mismatch: the interface with late collisions is half-duplex while the other end is full-duplex. Configure both ends to auto-negotiate speed and duplex.. A is correct because a duplex mismatch causes one interface to operate in half-duplex (detecting late collisions due to CSMA/CD) while the other operates in full-duplex (no collisions). The half-duplex interface waits for the carrier sense before transmitting, but the full-duplex interface transmits immediately, causing the half-duplex side to detect collisions after the transmission window (late collisions). CRC errors occur on both ends because frames are corrupted when collisions happen. Configuring both ends to auto-negotiate ensures matching duplex and speed, resolving the issue.

Answer

Speed mismatch: one interface is set to 100 Mbps, the other to 1 Gbps. This causes frequent link flaps, resulting in CRC errors. Use the 'speed' command to match the rates.

Answer

Faulty Ethernet cable causing signal degradation, which leads to CRC errors. The late collisions are a result of the switch misdetecting collisions due to the degraded signal. Replace the cable.

Answer

A broadcast storm caused by a loop is flooding the uplink with frames, leading to CRC errors and late collisions as the switch discards excess traffic. Enable Spanning Tree Protocol to block the redundant path.

Question 11

Two routers, R1 and R2, are connected via a serial link. The interface on R1 shows 'Serial0/0 is up, line protocol is down' and no pings succeed across the link. You check the configuration and notice R1 has 'encapsulation ppp' but R2's serial interface was mistakenly left at the default encapsulation hdlc.

Accepted Answer

The mismatched encapsulation types prevent the routers from forming a Layer 2 connection, so the line protocol remains down.. The line protocol on a serial interface requires both ends to agree on the Layer 2 encapsulation type. R1 is configured with PPP (encapsulation ppp), while R2 defaults to HDLC. Since these encapsulations are incompatible, the routers cannot establish a valid Layer 2 connection, causing the line protocol to remain down despite the physical layer being up.

Answer

The IP addresses on the serial interfaces are in different subnets, so packets are dropped at Layer 3.

Answer

The serial cable is faulty, causing physical layer issues that trigger the line protocol down state.

Answer

The routers are missing a routing protocol configuration, so they cannot route traffic across the link.

Question 12

A network administrator notices that file transfers to a server are extremely slow, and on the switch interface connecting to the server, the output of 'show interfaces' indicates a high number of runts and CRC errors, but no collisions. Which of the following is the most likely cause?

Accepted Answer

The switch port is configured for full-duplex, but the server's NIC is set to half-duplex.. The combination of runts (frames smaller than 64 bytes) and CRC errors with zero collisions is a classic symptom of a duplex mismatch. When one side operates at full-duplex and the other at half-duplex, the half-duplex side will detect collisions and invoke its backoff algorithm, causing the full-duplex side to receive truncated frames (runts) and frames with invalid FCS (CRC errors). The switch interface statistics show no collisions because the switch port is full-duplex and does not detect collisions, while the server's half-duplex NIC is causing the corruption.

Answer

The cable connecting the server to the switch is faulty.

Answer

The switch port speed is set to 100 Mbps, but the server NIC is set to 10 Mbps.

Answer

The server's NIC driver is outdated, causing packet loss.

Question 13

A network technician configures a Windows 10 PC with a static IPv6 address of 2001:db8:acad:1::100/64 and a default gateway of 2001:db8:acad:2::1. The PC can communicate with other hosts in the 2001:db8:acad:1::/64 subnet, but it cannot access any resources on other subnets, even though IPv4 connectivity through the same network works normally. What is the most likely reason for this issue?

Accepted Answer

The PC's default gateway address is in a different subnet than the PC's IPv6 address.. The PC's IPv6 address is 2001:db8:acad:1::100/64, placing it in the 2001:db8:acad:1::/64 subnet. The configured default gateway is 2001:db8:acad:2::1, which belongs to the 2001:db8:acad:2::/64 subnet. For IPv6, a host will only consider a default gateway on the same link-local or on-link subnet; if the gateway address is not within the same /64 prefix as the host's address, the host cannot send packets to it directly, and all off-subnet traffic fails.

Answer

The PC's IPv6 stack has a corrupted binding that prevents routing.

Answer

The router's IPv6 routing table does not have a route back to the PC's subnet.

Answer

The DNS server for IPv6 resolution is misconfigured, causing all off-subnet traffic to fail.

Question 14

An administrator deploys a new WLAN on a Cisco 9800 WLC using WPA3-Personal (SAE) with AES encryption. A single 802.11ax laptop running Windows 10 fails to connect, displaying an authentication timeout despite entering the correct passphrase. Other clients, including legacy 802.11ac devices, connect without issue.

Accepted Answer

The laptop’s wireless adapter does not support Protected Management Frames, which are mandatory for WPA3-Personal.. WPA3-Personal (SAE) mandates the use of Protected Management Frames (PMF) as defined in IEEE 802.11w. If the laptop's wireless adapter or driver does not support PMF, it cannot complete the SAE handshake, resulting in an authentication timeout. Legacy 802.11ac clients can connect because they are using WPA2, which does not require PMF.

Answer

The WLC’s WLAN is misconfigured for WPA3-Enterprise, and the laptop lacks a supplicant for 802.1X authentication.

Answer

The WLC has disabled 802.11ax OFDMA on the 5 GHz band, preventing the 802.11ax laptop from associating.

Answer

The laptop’s driver is configured for 160 MHz channel width, which is incompatible with the WLC’s channel plan, causing authentication to fail.

Question 15

A network engineer replaces a failed 1000BASE-LX SFP on a core switch with a new transceiver of the same type. After connecting the single-mode fiber, the link remains down and a 'show interfaces gig1/0/49 transceiver' reveals an Rx power of –30 dBm, while the far-end SFP is transmitting at –3 dBm over a 2 km span. The fiber patch cord shows no visible damage.

Accepted Answer

Excessive attenuation due to a dirty or damaged fiber connector is preventing the link from coming up.. The measured Rx power of –30 dBm is far below the receive sensitivity threshold for 1000BASE-LX (typically –19 to –22 dBm), even though the transmitter is outputting a healthy –3 dBm over only 2 km. This indicates excessive loss in the optical path, most commonly caused by a dirty or damaged fiber connector. Cleaning the connector ends with an appropriate fiber cleaning tool and inspecting with a microscope would likely resolve the issue.

Answer

The new SFP is a counterfeit Cisco transceiver that cannot establish a stable link.

Answer

The SFP is not fully seated in the switch port, causing an intermittent optical connection.

Answer

The single-mode fiber distance exceeds the 10 km maximum for 1000BASE-LX, leading to severe signal dispersion.