CompTIA Network+ — All Questions

A technician connects two switches with a cable but gets no link, and finds the transmit and receive pairs are not properly crossed for that connection. Which issue is this?

• a.DHCP scope exhaustion
• b.A TX/RX reversal✓
• c.An incorrect default gateway configured on the host
• d.A duplex mismatch

A transmit/receive (TX/RX) reversal means the send and receive pairs are not correctly aligned for the devices, so no link forms. Auto-MDIX often fixes this automatically, but its absence or a miswired cable exposes it. Correcting the pinout or using the right cable type resolves it.

A copper Ethernet run of about 130 meters shows a weak, error-prone signal, while shorter runs are fine. Which cabling limitation explains this?

• a.Crosstalk between pairs
• b.A short circuit in the connector
• c.Attenuation from exceeding the distance limit✓
• d.An IP address conflict between two hosts on the segment

Attenuation is the loss of signal strength over distance, and exceeding the 100-meter copper limit degrades the signal and causes errors. Shorter runs stay within spec and work fine. Fiber or an intermediate switch is needed for longer distances.

A link works intermittently, and inspection reveals a poorly crimped RJ45 plug with loose conductors. Which fault category is this?

• a.A bad connector✓
• b.An oversubscribed uplink dropping packets during peak load
• c.A DNS misconfiguration
• d.A routing loop

A bad connector or failing termination causes intermittent connectivity as loose or misaligned conductors make unreliable contact. Re-terminating with a proper crimp restores a solid connection. Physical inspection and a cable tester confirm it.

A cable passes a basic continuity test but suffers high error rates at gigabit speeds, and testing reveals wires from different pairs were combined. Which wiring fault is this?

• a.Excessive attenuation caused by exceeding the maximum run length
• b.An open circuit
• c.Split pairs✓
• d.A short circuit

Split pairs occur when wires from two different pairs are used together, passing continuity but destroying the twist protection and causing crosstalk at speed. A wire-map test that checks pairing, not just continuity, detects it. Re-terminating to the correct standard fixes it.

A fiber transceiver will not establish a link, and a technician finds the small pluggable optic has a bent pin and a dirty connector end. Which is the most appropriate first action?

• a.Reconfigure the DHCP scope
• b.Clean and reseat or replace the transceiver✓
• c.Change the VLAN assignment on the port
• d.Increase the interface MTU to allow larger frames

Inspecting and cleaning the connector and reseating or replacing a damaged transceiver addresses physical optic faults like bent pins or contamination. Dirty or damaged optics are a common cause of no-link on fiber. Optical inspection tools confirm the condition.

On a fiber patch, no link forms until the technician swaps the two strands at one end. What was the original problem?

• a.The fiber was too short for the optic
• b.The DHCP server had run out of addresses to lease
• c.The switch port was in the wrong VLAN
• d.The fiber transmit and receive strands were reversed✓

On duplex fiber, the transmit strand of one device must reach the receive of the other; if the strands are reversed, no link forms until they are swapped. This TX/RX crossover requirement is easy to overlook. Swapping the strands at one connector resolves it.

A technician plugs a multimode patch cable into a transceiver designed for single-mode fiber and gets high loss or no link. What is the root cause?

• a.An APIPA address assigned to the host
• b.A spanning-tree loop between two switches
• c.A duplex mismatch between the switch ports
• d.A single-mode/multimode fiber mismatch✓

A fiber type mismatch, such as multimode cable with a single-mode optic (or vice versa), causes high loss or link failure. The core sizes and light sources are incompatible. Matching the cable, connector, and optic types resolves it.

An IP camera on a PoE switch loses power under load even though the switch supports PoE, and the switch reports its power budget is fully consumed. What is the likely cause?

• a.The PoE power budget is exhausted✓
• b.An incorrect subnet mask on the switch
• c.A DNS misconfiguration on the camera
• d.A spanning-tree blocking state on the camera's uplink port

Exceeding the switch's total PoE power budget starves later devices of power, causing them to drop even though PoE is supported. Adding a higher-wattage supply, a PoE injector, or fewer powered devices resolves it. Checking the per-port and total budget confirms it.

Copper cabling routed alongside fluorescent lighting and motors shows errors that worsen when the equipment runs. Which remedy directly addresses the cause?

• a.Use shielded cabling or reroute away from the interference✓
• b.Shorten the DHCP lease time
• c.Change the host's DNS server
• d.Increase the switch's MAC address table size

Interference induced on unshielded copper is best addressed with shielded cabling (or rerouting away from the source, or using fiber). Shielding drains the induced noise to ground. The correlation with nearby equipment operation points to EMI.

A user's jack is dead, but testing shows the patch panel port is cross-connected to the wrong switch port than the labeling claims. Which documentation-related fault is this?

• a.A patch panel cross-connect/mapping error✓
• b.Electromagnetic interference on the horizontal cable run
• c.A duplex mismatch
• d.An expired DHCP lease

A patch panel mapping error connects a jack to a different switch port than documented, so the intended configuration never reaches the user. Correcting the cross-connect or updating records resolves it. Accurate labeling prevents this class of mistake.

In a 2.4 GHz deployment, three nearby access points on channels 4, 7, and 9 suffer poor performance from overlapping signals. Which channel plan resolves this?

• a.Set all APs to channel 6
• b.Use channels 1, 6, and 11✓
• c.Raise every AP to maximum transmit power
• d.Bond the channels together into one wide 40 MHz channel

In 2.4 GHz, only channels 1, 6, and 11 are non-overlapping, so assigning adjacent APs to those channels eliminates the overlap. Channels like 4, 7, and 9 partially overlap and interfere. Proper channel reuse is essential in dense deployments.

Wi-Fi in a break room drops out whenever the microwave oven runs, and the interference is not from another access point. Which cause is most likely?

• a.Non-Wi-Fi RF interference✓
• b.An incorrect default gateway on the clients
• c.A DHCP scope that is exhausted
• d.Co-channel interference from another access point on the same channel

Non-Wi-Fi interference from devices like microwave ovens, cordless phones, and Bluetooth radios disrupts the 2.4 GHz band. Its correlation with the microwave running is a strong clue. A spectrum analyzer identifies such non-802.11 sources.

Users in a far corner of the warehouse get very weak Wi-Fi or none at all, while the rest of the floor is fine. Which fix best addresses this coverage gap?

• a.Replace the wired uplink with a higher-category copper cable
• b.Change the SSID name broadcast by the AP
• c.Add an access point to cover the dead zone✓
• d.Shorten the DHCP lease timer

A dead zone from insufficient coverage is resolved by adding an access point (or repositioning/adjusting antennas) to extend signal into the gap. Simply raising power on a distant AP often worsens interference elsewhere. A site survey confirms placement.

A laptop stays connected to a distant access point with a weak signal even after the user walks near a closer AP, hurting performance. What is this behavior called?

• a.A DNS resolution failure
• b.A duplex mismatch between the AP and its wired switch port
• c.A sticky client roaming problem✓
• d.An IP address conflict on the subnet

A sticky client clings to its original AP despite a stronger nearby one, degrading throughput as signal weakens. Tuning roaming thresholds or enabling 802.11k/v/r assistance encourages timely handoff. The client, not the network, decides when to roam.

Several users cannot join the secured Wi-Fi and are repeatedly prompted for the network key, though the signal is strong. Which cause is most likely?

• a.A spanning-tree loop between the AP and the switch
• b.A missing default gateway on the AP
• c.Weak signal at the client location
• d.An incorrect pre-shared key✓

Repeated authentication prompts with a strong signal typically indicate an incorrect pre-shared key (wrong passphrase). Correcting the entered key restores access. Signal strength being fine rules out coverage as the cause.

Older devices cannot connect after an AP is reconfigured, and the AP is set to require a security mode the clients do not support. Which issue is this?

• a.Attenuation from distance to the AP
• b.A security mode mismatch✓
• c.An exhausted DHCP scope
• d.A duplex mismatch on the AP's wired uplink port

A wireless security mode mismatch (for example, requiring WPA3-only while a client supports only WPA2) prevents association. A transitional/mixed mode or matching settings restores compatibility. Verifying supported modes on both ends resolves it.

During a busy all-hands meeting, a single access point serving hundreds of attendees becomes sluggish for everyone, though signal is strong. What is the likely cause?

• a.An incorrect subnet mask on the AP
• b.A dirty fiber connector on the AP's uplink
• c.Too many clients on one access point (overcapacity)✓
• d.A weak signal at every client

AP overcapacity occurs when too many clients share one radio, so airtime contention degrades performance despite good signal. Adding APs or enabling band steering spreads the load. High client counts, not weak signal, are the tell.

A client sees a strong 5 GHz signal near the access point but loses it much sooner than 2.4 GHz as they walk away. Which characteristic explains this?

• a.The client's DHCP lease expired
• b.5 GHz has shorter range than 2.4 GHz✓
• c.The switch port feeding the AP had a duplex mismatch
• d.A default gateway was missing on the client

The 5 GHz band offers higher throughput and less congestion but has shorter range and weaker obstacle penetration than 2.4 GHz. So coverage falls off faster with distance and walls. Band selection trades speed against reach.

To cover a long, narrow corridor from one end, an engineer needs to focus the AP's signal down the hallway rather than spread it in all directions. Which change helps?

• a.Disable SSID broadcast on the AP
• b.Assign the AP a static route to the corridor subnet
• c.Use a shorter DHCP lease
• d.Use a directional antenna✓

A directional antenna focuses RF energy in a specific direction, ideal for long corridors or point-to-point links, versus an omnidirectional antenna that radiates evenly. Matching antenna type and placement to the space improves coverage. Antenna choice is part of RF design.

Wi-Fi is strong in an office but drops sharply behind a room with thick concrete and metal walls. Which factor best explains the loss?

• a.An IP address conflict
• b.A DNS server outage
• c.Signal attenuation from building materials✓
• d.Co-channel interference from a distant access point on channel 11

Dense building materials like concrete and metal cause RF attenuation and reflection, sharply reducing signal behind them. Repositioning or adding an AP on the far side restores coverage. Materials are a key input to any site survey.

Guests connect to the open Wi-Fi and get an IP address, but the sign-in web page that should grant internet access never appears. Which component is likely failing?

• a.The captive portal is not loading✓
• b.The switch uplink is running at half duplex
• c.The antenna is directional instead of omnidirectional
• d.The client is too close to the access point

A captive portal is the web page that authenticates or accepts terms before granting internet access; if it fails to load, users associate but cannot browse. DNS redirection or portal server issues commonly cause this. Verifying the portal and its DNS handling resolves it.

An access point using a 5 GHz channel occasionally goes quiet and moves channels after detecting radar, briefly disrupting clients. Which mechanism causes this?

• a.A sticky client refusing to roam
• b.Crosstalk on the copper cable feeding the access point
• c.An exhausted DHCP scope on the guest VLAN
• d.Dynamic Frequency Selection (DFS) radar avoidance✓

Dynamic Frequency Selection (DFS) requires APs on certain 5 GHz channels to vacate when radar is detected, causing brief channel changes and disruption. Choosing non-DFS channels avoids it where radar is present. It is a regulatory requirement, not a fault.

A technician wants to quickly confirm whether a remote server is reachable at the IP layer and see the round-trip time. Which command is the simplest choice?

• a.ping✓
• b.netstat
• c.nslookup
• d.traceroute, which maps every router hop along the path

Ping sends ICMP echo requests and reports replies and round-trip time, confirming basic Layer 3 reachability. Success shows the path and host are responding. No reply may mean a down host, filtering, or a routing problem.

Users report a site is slow to reach, and a technician wants to see at which router hop along the path latency spikes. Which tool shows per-hop delay?

• a.arp
• b.traceroute✓
• c.ipconfig
• d.netstat, which lists active connections and listening ports

Traceroute (tracert on Windows) lists each router hop and the delay to it, revealing where latency spikes or the path breaks. It increments the TTL to elicit responses from intermediate routers. It complements ping for locating path problems.

A technician suspects a specific DNS record is wrong and wants to query the DNS server directly for that record type. Which tool is appropriate?

• a.ipconfig, which displays the local interface addressing
• b.nslookup✓
• c.ping
• d.netstat

nslookup (or dig) queries DNS servers directly and can request specific record types such as MX, A, or CNAME. It isolates name-resolution problems from other issues. Comparing results across resolvers reveals inconsistencies.

A Windows client is stuck with a bad DHCP lease, and a technician wants to force it to drop the current address and request a fresh one. Which commands accomplish this?

• a.nslookup and arp
• b.ping and traceroute
• c.ipconfig /release and /renew✓
• d.netstat combined with the route print command

Running ipconfig /release then ipconfig /renew forces the client to give up its lease and request a new one from the DHCP server. This resolves stale or incorrect leases. It is a quick fix for many client addressing problems.

A technician wants to see which TCP ports a server is currently listening on and what connections are established. Which command shows this?

• a.ping
• b.netstat✓
• c.tracert
• d.nslookup, which resolves hostnames to addresses

netstat lists active connections, listening ports, and their states on the local host. It confirms whether a service is listening and which endpoints are connected. It is a first check when an application will not accept connections.

A host cannot reach a device on its own subnet, and a technician wants to view the cached IP-to-MAC mappings the host has learned. Which command displays this table?

• a.ping -t
• b.arp -a✓
• c.ipconfig /all
• d.netstat -r, which prints the local routing table

The arp -a command displays the ARP cache, mapping recently contacted IP addresses to their MAC addresses. A wrong or missing entry can explain local delivery failures. Clearing a stale entry can restore connectivity.

A technician wants a single tool that both traces the path to a destination and, over time, measures packet loss at each hop. Which utility combines these?

• a.arp
• b.pathping/mtr✓
• c.ipconfig
• d.nslookup, used to query DNS record types

Pathping (Windows) and mtr (Unix) combine traceroute with continuous statistics, reporting per-hop latency and packet loss over time. This pinpoints the hop where loss originates. It is more diagnostic than a single traceroute pass.

A technician suspects a host is missing a route and wants to view the local routing table to confirm the default gateway and any static routes. Which command shows this?

• a.nslookup for the destination hostname
• b.route print✓
• c.ping -t
• d.arp -a

The route print command (or ip route on Linux) displays the host's local routing table, including the default gateway and any static routes. A missing or wrong default route explains failures reaching remote networks. It is key when local traffic works but remote does not.

To analyze the exact contents of packets during a subtle protocol failure, a technician needs to capture and decode frames on the wire. Which tool fits?

• a.ipconfig
• b.arp, which only shows the local address cache
• c.ping
• d.Wireshark/tcpdump✓

A protocol analyzer like Wireshark or tcpdump captures and decodes packets, exposing headers and payloads for deep analysis. It reveals malformed exchanges that summaries hide. A SPAN/mirror port often feeds it the traffic.

An engineer wants to measure the actual throughput achievable between two hosts by generating test traffic in a controlled way. Which tool is designed for this?

• a.arp -a
• b.tracert to the far-end host's address
• c.nslookup
• d.iperf✓

iperf generates controlled TCP or UDP traffic between a client and server to measure achievable throughput, jitter, and loss. It isolates network capacity from application behavior. Results guide capacity and QoS decisions.

A security technician wants to discover which hosts are alive on a subnet and which TCP ports they have open. Which tool provides this scan?

• a.ipconfig
• b.ping -t
• c.nmap✓
• d.netstat run on each individual host

nmap scans a range of hosts to discover live systems and their open ports and services. It is a standard reconnaissance and audit tool. Results reveal exposure and help verify firewall rules.

After a DNS record was corrected, a Windows client still resolves the old address because of local caching. Which command clears the client's DNS cache?

• a.netstat -a to list all connections and ports
• b.arp -d
• c.ipconfig /flushdns✓
• d.route add

ipconfig /flushdns clears the Windows DNS resolver cache so the client queries fresh records instead of stale cached ones. It resolves cases where a record changed but the client still returns the old value. Restarting the resolver service does the same.

Traffic to a cloud service routes over a very long path across several continents, adding significant delay even though no link is congested. Which factor is responsible?

• a.Path length / propagation delay✓
• b.Insufficient link bandwidth
• c.Packet loss from bad cabling
• d.A duplex mismatch between two switches in the path

Propagation and path length add latency independent of congestion; a longer route simply takes more time end to end. Choosing a closer endpoint or better-peered path reduces it. High RTT with low utilization points here rather than to congestion.

During peak hours a WAN link is saturated and applications slow down, and monitoring shows the interface at 100 percent with rising output drops. What is the cause?

• a.A DNS misconfiguration
• b.A missing default gateway on the affected hosts
• c.Bandwidth saturation (congestion)✓
• d.An IP address conflict

Bandwidth saturation occurs when demand exceeds link capacity, filling queues and dropping packets during peaks. Adding capacity, shaping, or QoS relieves it. The correlation with peak load and full utilization confirms congestion.

A link shows intermittent packet loss and rising interface error counters, and replacing a marginal cable clears both. Which was the underlying cause?

• a.A DNS server outage
• b.Physical-layer errors from a faulty cable✓
• c.An access control list blocking the traffic at the router
• d.An exhausted DHCP scope

Physical errors from a marginal cable or connector corrupt frames, showing up as CRC/input errors and causing intermittent loss. Replacing the faulty cable removes the errors. Error counters are the diagnostic that points to Layer 1.

A saturated link makes interactive traffic laggy because oversized buffers hold packets far too long before forwarding them. What is this phenomenon called?

• a.Co-channel interference on the wireless segment
• b.Attenuation
• c.Bufferbloat✓
• d.A routing loop

Bufferbloat is excessive latency caused by overly large buffers that queue packets instead of dropping them promptly, hurting interactive traffic. Active queue management (such as CoDel) mitigates it. It appears as high latency under load without heavy loss.

Traffic reaches a server fine but return traffic takes a different path, and a stateful firewall drops the flow because it never saw the outbound side. Which condition is this?

• a.An exhausted DHCP address pool on the subnet
• b.Asymmetric routing✓
• c.A duplex mismatch
• d.A DNS misconfiguration

Asymmetric routing sends forward and return traffic over different paths, which can break stateful devices that must see both directions of a flow. Aligning the paths or making the device state-aware of both resolves it. It often appears after redundancy or route changes.

A VPN tunnel drops large packets while small ones pass, and the problem clears when the interface's maximum frame size is lowered. Which issue caused it?

• a.A spanning-tree loop between the tunnel endpoints
• b.A DNS resolution failure
• c.An MTU mismatch✓
• d.A duplicate IP address on the tunnel

An MTU mismatch or fragmentation problem drops or mishandles packets larger than a link allows, especially where encapsulation shrinks the usable size. Lowering the MTU or enabling proper path MTU discovery resolves it. Small packets passing while large ones fail is the classic symptom.

Two switch ports show late collisions and poor throughput because one end is set to full duplex and the other to half. What is the recommended fix?

• a.Set both ends to autonegotiate or matching duplex✓
• b.Assign the ports to different VLANs
• c.Replace the switch with a router
• d.Increase the interface MTU to reduce collisions on the link

Setting both ends to autonegotiate (or both to the same fixed duplex) resolves a duplex mismatch that causes late collisions and slow throughput. Mismatched fixed settings are a common misconfiguration. Matching the configuration on both ends is essential.

After a redundant switch link was added without loop prevention, switch CPUs spike to 100 percent and the whole segment slows to a crawl. Which problem does this indicate?

• a.An expired DHCP lease on the clients
• b.A DNS misconfiguration
• c.An access control list dropping legitimate traffic at the edge
• d.A broadcast storm from a switching loop✓

A broadcast storm from a Layer 2 loop floods frames endlessly, spiking switch CPU and saturating the segment. Enabling or verifying spanning tree stops it. The sudden onset after adding a redundant link is the giveaway.

Web pages take several seconds to begin loading, but once resolved they download quickly, and the assigned DNS server is geographically distant. Which fix most directly helps?

• a.Enable jumbo frames on the client's network adapter
• b.Increase the link bandwidth
• c.Configure a faster, closer DNS resolver✓
• d.Replace the copper cabling with fiber

Slow initial page loads with fast downloads point to slow DNS resolution; using a closer or faster resolver cuts the lookup delay. The quick transfer once resolved rules out bandwidth. Testing with nslookup timing confirms the cause.

A traceroute shows the same set of routers repeating and packets eventually dying with TTL-exceeded messages, and users cannot reach the destination. Which problem is this?

• a.A duplex mismatch
• b.A routing loop✓
• c.Electromagnetic interference on the copper uplink
• d.A DHCP scope exhaustion

A routing loop sends packets circling between routers until the TTL expires, producing TTL-exceeded messages and unreachable destinations. Correcting the conflicting routes breaks the loop. The repeating hops in traceroute are the telltale sign.

After a QoS change, backup traffic monopolizes the link and voice suffers because the policy failed to reserve capacity for voice. Which is the underlying issue?

• a.A QoS misconfiguration✓
• b.A dirty fiber connector on the WAN uplink
• c.A DNS outage
• d.A duplicate IP address

A QoS misconfiguration that fails to classify or reserve priority for voice lets bulk traffic starve it during congestion. Correcting the classification and queuing restores voice quality. The change coinciding with the problem points to the policy.

An old segment built around a hub shows many collisions and poor performance as more devices are added. Which characteristic of the hub explains this?

• a.The hub blocks redundant links using spanning tree
• b.The hub is one shared, half-duplex collision domain✓
• c.The hub exhausts the DHCP scope
• d.The hub routes between VLANs at Layer 3

A hub creates a single shared collision domain running half duplex, so collisions rise as devices and traffic increase. Replacing it with a switch gives each port its own collision domain and full duplex. This is why hubs are obsolete for modern LANs.

A high-latency, high-bandwidth WAN link achieves far less throughput than its capacity for a single TCP transfer, and the small TCP window cannot keep the long pipe full. Which fix helps?

• a.Disable QoS on the link
• b.Lower the interface MTU
• c.Enable TCP window scaling✓
• d.Shorten the DHCP lease duration for the clients

On a long fat network, a small TCP window limits throughput because the sender cannot keep enough data in flight for the high latency. Enabling window scaling (larger windows) lets a single flow fill the pipe. This explains low single-stream throughput despite ample bandwidth.

VoIP calls sound choppy with syllables clipped, and monitoring shows packets arriving at uneven intervals though few are lost. Which mitigation best addresses the cause?

• a.Replace the DNS server with a local one
• b.Assign the phones static IP addresses
• c.Add a jitter buffer and prioritize voice with QoS✓
• d.Increase the DHCP scope size on the voice VLAN

Choppy audio from uneven packet arrival is caused by jitter, and a properly sized jitter buffer plus QoS prioritization smooths it. The low loss rules out congestion drops as the main issue. Marking and queuing voice traffic reduces the jitter itself.

After terminating a cable, a technician needs to confirm each pin connects to the correct pin at the far end with no miswires. Which tool verifies the wire map?

• a.A cable tester✓
• b.A loopback plug
• c.A tone generator paired with an inductive probe
• d.A spectrum analyzer

A cable tester with a wire-map function confirms pin-to-pin correctness and flags opens, shorts, reversed, or split pairs. It validates that the termination follows the intended standard. It is the standard check after terminating a run.

A technician needs to find which wall jack corresponds to an unlabeled cable end in a crowded telecom closet. Which tool pair helps locate it?

• a.A protocol analyzer capturing frames on the link
• b.A multimeter
• c.An OTDR
• d.A tone generator and inductive probe✓

A tone generator places an audible signal on a wire, and an inductive probe detects that tone to trace and identify the specific cable or jack. It is standard for locating cables in bundles or panels. It complements, rather than replaces, continuity testing.