Network Troubleshooting

486 questions

All types486 Multiple choice248 Multiple select111 Matching61 Ordering66

A network technician is installing a new VoIP phone at a user's desk. The technician must trace an unlabeled UTP cable run from the office wall jack back to its corresponding port on the patch panel in the equipment closet. Once identified, the technician must also confirm that the switch port is actively supplying electrical power over the ethernet wiring to power the phone. Which TWO of the following tools should the technician use to accomplish these tasks? (Select TWO.)

Select all that apply

Tone generator and probe

PoE tester

Optical Time-Domain Reflectometer (OTDR)

Packet analyzer

Show answer & explanation

Answer: Tone generator and probe; PoE tester

Answer

The correct tools to select are the tone generator and probe (to trace the physical cable path from the desk wall jack to the patch panel) and the PoE tester (to detect and verify electric power delivery on the twisted-pair switch port).

Tracing an unlabelled copper run requires emitting an electrical tone via a tone generator at the wall jack and listening for that signal with an inductive probe at the patch panel. Confirming that power is being delivered to the VoIP phone requires a PoE tester to measure active DC power on the Ethernet port.

Step-by-Step Solution

Identify the physical cable tracing tool.

Select the tone generator and probe, which places a tone signal on unshielded twisted-pair (UTP) copper wire and detects it audibly at the patch panel.

Tracing physical copper cable runs across walls and ceilings requires an inductive tone probe.

Identify the power verification tool.

Select the PoE tester, which verifies voltage standards (such as 802.3af/at/bt) supplied by the switch port.

VoIP phones rely on Power over Ethernet (PoE) supplied across the copper Ethernet conductors.

Key Concept

Utilizing basic hardware testers for copper cable identification and Power over Ethernet (PoE) verification.

Question 302Question →

A network engineer is conducting diagnostic procedures across an enterprise network suffering from physical and application-layer anomalies. Match each specific physical or protocol troubleshooting scenario to the most appropriate hardware testing tool or packet analyzer capability.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Matching pairings: Pinpointing copper impedance mismatches maps to Copper Time-Domain Reflectometer (TDR); Locating fiber fusion splice attenuation maps to Optical Time-Domain Reflectometer (OTDR); Inspecting DHCP Option 53 fields maps to Protocol Packet Analyzer; Validating SFP+ transceiver internal hardware maps to Hardware Loopback Plug.

Each diagnostic scenario maps to a specialized tool based on the underlying medium and OSI layer. Copper TDR evaluates electrical impedance reflection on metallic cables. Fiber OTDR analyzes light backscatter along optical strands. Packet analyzers decode packet payload structures such as DHCP options. Loopback plugs reflect local transmission back to reception for hardware verification.

Step-by-Step Solution

Analyze copper cabling distance-to-fault requirements.

Identify that TDR uses electrical signal reflection timing to locate physical cable anomalies on metallic conductors.

Impedance shifts cause partial pulse reflections measured by a TDR.

Analyze optical fiber reflective events and attenuation measurement requirements.

Identify that OTDR measures Rayleigh backscattering and Fresnel reflections to map fiber splices and optical breaks.

Optical fiber requires light pulse reflections rather than electrical signals.

Determine Layer 7 protocol analysis requirements for rogue server detection.

Select a protocol packet analyzer to filter and decode DHCP packet headers and Option payload attributes.

Hardware line testers cannot inspect protocol payload structures or frame headers.

Evaluate port-level hardware isolation diagnostics.

Select a hardware loopback plug to mirror Tx to Rx on the local transceiver.

Testing a NIC or transceiver without a remote partner requires routing local output back into local input.

Key Concept

Selecting proper physical layer hardware diagnostic tools and packet analyzers based on medium type and protocol troubleshooting requirements.

Estimated Time:2m 0s

Question 303Question →

A network technician is troubleshooting an enterprise building interconnect where a newly provisioned multi-mode fiber link experiences high frame loss, while workstation clients on the attached Ethernet segment fail to receive automatic IP configurations. Which of the following diagnostic tools or analyzer filters should the technician utilize to isolate these physical and application layer issues? (Select TWO.)

Select all that apply

An Optical Time-Domain Reflectometer (OTDR) to identify attenuation, macrobends, and distance to optical breaks along the fiber cable run.

A packet analyzer filter configured for UDP ports 67 and 68 to inspect DHCP request and acknowledgment frames.

A copper Time-Domain Reflectometer (TDR) to evaluate optical insertion loss and light signal polarization across the strand.

A packet analyzer filter configured for TCP port 67 to capture connection-oriented DHCP handshake traffic.

Show answer & explanation

Answer: An Optical Time-Domain Reflectometer (OTDR) to identify attenuation, macrobends, and distance to optical breaks along the fiber cable run.; A packet analyzer filter configured for UDP ports 67 and 68 to inspect DHCP request and acknowledgment frames.

Answer

The technician should use an Optical Time-Domain Reflectometer (OTDR) to diagnose the fiber link and apply a packet analyzer filter for UDP ports 67 and 68 to capture DHCP traffic.

An OTDR is specifically designed to locate physical anomalies and measure signal attenuation in optical fiber links. Furthermore, DHCP relies on UDP (ports 67 and 68), so filtering for these UDP ports allows the technician to capture and analyze automatic IP address assignment traffic.

Step-by-Step Solution

Analyze the physical layer diagnostic requirement for the multi-mode fiber connection.

Identify that testing optical fiber cabling for breaks, loss, or bends requires an Optical Time-Domain Reflectometer (OTDR), as copper TDR tools cannot test optical media.

OTDRs measure light backscatter to pinpoint distance-to-fault on fiber strands.

Analyze the protocol analyzer requirement for client IP address configuration failures.

Identify DHCP as the underlying protocol for automatic IP configuration and recall that DHCP uses UDP ports 67 and 68.

Setting the packet capture filter to UDP ports 67 and 68 isolates DHCP Discover/Offer/Request/ACK traffic.

Key Concept

Selecting appropriate hardware testers (OTDR vs. TDR) for fiber cabling and filtering protocol traffic (DHCP over UDP 67/68) using packet analyzers.

Question 304Question →

A network administrator is investigating high frame error rates and severe throughput degradation on a newly commissioned Category 6 UTP cable run connecting a desktop computer to an enterprise switch. A basic continuity cable tester confirms that all eight conductors are connected pin-for-pin ( $1 \rightarrow 1$ , $2 \rightarrow 2$ , etc.) on both ends without any opens or shorts. However, when high-bandwidth data transmission occurs, extreme Near-End Crosstalk (NEXT) occurs. Which wiring fault is present, and which diagnostic capability is required to detect it?

A split pair condition, which requires a cable certifier/analyzer capable of checking pair geometry and frequency-dependent crosstalk rather than basic DC continuity.

An open conductor on the transmit pair, which requires a Time-Domain Reflectometer (TDR) to measure signal reflection times and locate the distance to the fault.

A short circuit between adjacent wire pairs, which requires a digital multimeter set to resistance mode to verify zero-ohm impedance across conductors.

An improper pinout configuration exceeding length standards, which requires a tone generator and inductive probe to track signal attenuation along the cable run.

Show answer & explanation

Answer: A split pair condition, which requires a cable certifier/analyzer capable of checking pair geometry and frequency-dependent crosstalk rather than basic DC continuity.

Answer

A split pair condition, which requires a cable certifier/analyzer capable of checking pair geometry and frequency-dependent crosstalk rather than basic DC continuity.

The correct option correctly identifies a split pair wiring fault. In a split pair, pin-to-pin electrical continuity is maintained, so simple DC wiremap testers report the cable as correctly wired. However, because the physical twists intended for noise cancellation are split across different signal paths, high-frequency electromagnetic interference (crosstalk) ruins high-speed data transmission. Only a cable certifier evaluating Near-End Crosstalk (NEXT) at high frequencies can pinpoint this condition.

Step-by-Step Solution

Analyze the physical layer symptoms and initial test results.

The basic wiremap/continuity tester confirms 1-to-1 electrical continuity on all 8 pins, ruling out open circuits, short circuits, or standard pin transposition.

Basic continuity testers use direct current (DC) signals to verify electrical paths from end to end.

Evaluate why Near-End Crosstalk (NEXT) occurs under load despite DC continuity passing.

Identified that twisted pair noise cancellation relies on differential signaling across tightly twisted wire pairs.

If a conductor from one pair is accidentally swapped with a conductor from another pair (split pair), DC continuity remains intact, but the magnetic field cancellation fails, introducing severe electromagnetic interference (crosstalk) when AC data signals are applied.

Select the appropriate diagnostic hardware tester.

A high-frequency cable certifier/analyzer must be used to perform RF crosstalk testing and detect split pair anomalies.

Simple continuity testers or tone probes cannot detect split pairs because they do not evaluate high-frequency magnetic coupling between pairs.

Key Concept

Distinguishing between simple DC continuity testing and high-frequency RF cable certifier analysis to detect split pair faults.

Question 305Question →

A network technician is investigating an issue where wireless VoIP handsets drop calls when roaming between access points in a newly constructed distribution center. The technician established a theory that 802.11r fast transition roaming was omitted from the new access point WLAN profile, tested this theory in a staging environment, and confirmed the cause. According to the CompTIA troubleshooting methodology, which of the following tasks should the technician perform NEXT? (Select TWO).

Select all that apply

Develop a detailed plan of action to modify the wireless controller profile to enable fast transition roaming.

Identify potential side effects and operational impacts on legacy wireless clients prior to executing the change.

Conduct roaming tests with handsets across all distribution center zones to confirm call continuity.

Update the central ticketing system with the root cause, configuration steps, and final resolution details.

Show answer & explanation

Answer: Develop a detailed plan of action to modify the wireless controller profile to enable fast transition roaming.; Identify potential side effects and operational impacts on legacy wireless clients prior to executing the change.

Answer

The technician should develop a detailed plan of action to modify the wireless controller profile and identify potential side effects on legacy wireless clients.

Once a theory of probable cause has been tested and confirmed (Step 3), the technician must proceed to Step 4 of the CompTIA troubleshooting methodology: Establish a plan of action to resolve the problem and identify potential effects. Developing a detailed configuration plan for the wireless controller and analyzing potential impacts on legacy devices represent the two core responsibilities of this step.

Step-by-Step Solution

Identify current phase in CompTIA 7-step methodology

The technician has completed Step 3 (Test the theory to determine cause) by confirming the theory in a test environment.

Determining the current phase dictates what phase must logically follow.

Determine the next sequential phase

Step 4 is 'Establish a plan of action to resolve the problem and identify potential effects'.

CompTIA methodology strictly follows: 1. Identify problem → 2. Establish theory → 3. Test theory → 4. Plan of action & identify potential effects → 5. Implement solution → 6. Verify system functionality → 7. Document findings.

Select matching actions for Step 4

Formulating the deployment plan for enabling 802.11r and analyzing how legacy devices might react are both components of Step 4.

Planning changes and assessing risk/effects must occur before deploying changes to live infrastructure.

Key Concept

CompTIA Troubleshooting Methodology - Plan of Action and Identifying Potential Effects

Estimated Time:1m 30s

Question 306Question →

A network technician is troubleshooting an intermittent network connection on a 75-meter Category 6 horizontal copper cable run servicing an enterprise workstation. A basic wiremapper confirms that all eight conductors show proper pin-to-pin continuity and standard T568B alignment with no open or short circuits. However, when high-bandwidth file transfers occur, the switch port interface logs a rapidly increasing counter of Cyclic Redundancy Check (CRC) errors and late collisions. Which of the following diagnostic tools should the technician use to pinpoint the precise location and cause of signal degradation along the hidden cable run?

Use a Time-Domain Reflectometer (TDR) or advanced cable certifier to analyze signal attenuation, return loss, and distance to impedance mismatches.

Use a basic continuity wiremapper to re-test the pinout map at both the patch panel and wall outlet ends.

Use a tone generator and inductive probe to trace the physical path of the cable through the building ceiling and walls.

Use a digital multimeter to measure the total DC loop resistance across the individual conductor pairs.

Show answer & explanation

Answer: Use a Time-Domain Reflectometer (TDR) or advanced cable certifier to analyze signal attenuation, return loss, and distance to impedance mismatches.

Answer

The technician should use a Time-Domain Reflectometer (TDR) or cable certifier to measure high-frequency performance metrics such as return loss, attenuation, and distance to impedance anomalies.

A Time-Domain Reflectometer (TDR) or full cable certifier transmits electrical pulses down a cable run and measures the time and amplitude of reflections caused by impedance changes. This enables pinpointing the exact location of physical damage, tight bends, split pairs, or excessive Near-End Crosstalk (NEXT) that cause CRC errors under load, even when basic continuity tests pass.

Step-by-Step Solution

Analyze the symptoms and preliminary test results.

The cable passes simple DC continuity tests (8/8 pins, standard T568B wiremap), but produces CRC errors under high network traffic load.

Basic continuity tools verify physical conductor connections but cannot evaluate high-frequency transmission characteristics such as crosstalk, attenuation, or return loss.

Evaluate required diagnostic capabilities to locate the fault.

The tool must send high-frequency signal pulses and analyze reflections returned from physical anomalies along the 75-meter cable run.

CRC errors under load indicate dynamic physical layer defects (e.g., sharp bend radius, pinched jacket, crushed internal pair twist) causing impedance shifts.

Select the appropriate diagnostic testing device.

A Time-Domain Reflectometer (TDR) or comprehensive cable certifier measures reflection timing and magnitude to identify the exact distance to impedance anomalies and high-frequency noise.

TDR technology calculates distance to cable defects by analyzing signal reflections caused by impedance changes.

Key Concept

TDR and Cable Certification Testing for High-Frequency Physical Layer Faults

Estimated Time:2m 0s

Question 307Question →

Match each command-line troubleshooting utility syntax with its precise diagnostic objective during complex network failure isolation.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Matching summary: `netstat -ano` correlates active network sockets to process IDs; `pathping -n 192.168.1.254` measures path statistics over time while suppressing intermediate host name lookups; `dig +trace example.com` tracks iterative DNS delegation from root to authoritative servers; and `arp -a` views local Layer 2 MAC-to-IP address resolution bindings.

Each command-line utility is correctly paired to its specific diagnostic layer and functional flag set: `netstat -ano` correlates network ports and sockets to process IDs; `pathping -n` computes packet loss across network hops over time without waiting for reverse DNS lookups; `dig +trace` follows the hierarchical DNS query path from root name servers; and `arp -a` displays the local host's hardware address resolution table.

Step-by-Step Solution

Analyze transport layer and process socket binding utilities.

Identify that `netstat -ano` displays numerical listening/active ports alongside process IDs (PIDs).

The `-o` flag is uniquely responsible for outputting owning process IDs, while `-n` disables name resolution.

Analyze path statistics utilities combining reachability and hop latency.

Identify that `pathping` calculates packet loss per hop over time, and `-n` speeds execution by omitting hostname lookups.

Pathping sends multiple pings to each hop over a measurement interval to isolate congested or failing routers.

Analyze hierarchical DNS troubleshooting tools.

Identify that `dig +trace` performs iterative DNS resolution starting from root servers (`.`).

The `+trace` flag disables recursive reliance on local resolvers and steps through the DNS hierarchy directly.

Analyze Layer 2 mapping commands.

Identify that `arp -a` inspects the ARP table containing IP-to-MAC physical mappings.

ARP operates between Layer 2 and Layer 3 to resolve IPv4 addresses to local network interface hardware addresses.

Key Concept

Command-Line Diagnostic Utilities, Syntax Switches, and OSI Layer Operational Scopes

Question 308Question →

A network administrator is investigating a report that newly provisioned database servers residing on VLAN 30 attached to Switch-A cannot communicate with application servers on VLAN 30 connected to Switch-B. Both switches are connected via an 802.1Q trunk on interface GigabitEthernet0/1. The administrator executes a troubleshooting command on Switch-A and observes the following output:

Port	Mode	Encapsulation	Status	Native vlan
Gi0/1	on	802.1q	trunking	1

Port	Vlans allowed on trunk
Gi0/1	1-20, 40-100

Local pings from the database servers to Switch-A's Layer 3 VLAN 30 interface succeed, but traffic crossing to Switch-B is completely dropped. Which of the following identifies the root cause of this connectivity failure?

VLAN 30 is missing from the list of allowed VLANs configured on the trunk interface.

A native VLAN mismatch exists because Switch-A uses VLAN 1 while Switch-B is configured to send tagged frames for VLAN 30.

A duplex mismatch on interface Gi0/1 is causing late collisions that drop all frames tagged with VLAN 30.

Switch-A has been configured with an improper Spanning Tree Protocol (STP) priority, placing interface Gi0/1 into a blocking state.

Show answer & explanation

Answer: VLAN 30 is missing from the list of allowed VLANs configured on the trunk interface.

Answer

VLAN 30 is missing from the list of allowed VLANs configured on the trunk interface.

The trunk output clearly shows that interface Gi0/1 only permits VLANs in the ranges 1-20 and 40-100. Because VLAN 30 is omitted from this allowed list, Switch-A drops all ingress and egress frames tagged for VLAN 30 on this trunk interface.

Step-by-Step Solution

Analyze the CLI trunk output on Switch-A

Interface Gi0/1 is configured as an 802.1Q trunk with native VLAN 1.

Understanding the trunk parameters helps determine how traffic is pruned or allowed across the switch link.

Inspect the 'Vlans allowed on trunk' field

The allowed VLAN range is 1-20 and 40-100.

VLAN 30 falls into the gap between 20 and 40, meaning traffic belonging to VLAN 30 is automatically pruned and dropped at the trunk boundary.

Formulate the corrective action

Add VLAN 30 to the allowed VLAN list on interface Gi0/1 using switchport trunk allowed vlan add 30.

Including VLAN 30 in the allowed list permits tagged frames for VLAN 30 to traverse the trunk link between Switch-A and Switch-B.

Key Concept

802.1Q Trunk Allowed VLAN List Pruning

Question 309Question →

An administrator is troubleshooting remote network connectivity for a client workstation configured with the following static IPv4 parameters:

- IP Address: $10.88.32.180$
- Subnet Mask: $255.255.240.0$
- Default Gateway: $10.88.48.1$

The workstation can successfully reach local hosts within the $10.88.32.0/20$ range, but all attempts to communicate with external networks fail. Physical layer diagnostics and switchport configurations are verified to be fully operational. Which of the following represents the root cause of the connectivity failure?

The configured default gateway IP address resides outside the host's IPv4 subnet boundary.

The host IP address is an unassignable subnet broadcast address for the /20 prefix.

The switch ports are assigned to separate untagged VLANs, preventing Layer 2 broadcast discovery.

The router gateway interface has dropped outbound frames due to a transport port and protocol mismatch.

Show answer & explanation

Answer: The configured default gateway IP address resides outside the host's IPv4 subnet boundary.

Answer

The configured default gateway IP address resides outside the host's IPv4 subnet boundary.

The correct option correctly identifies that the gateway IP address (

10.88.48.1

) is located on a different logical IPv4 subnet than the host (

10.88.32.180/20

). A subnet mask of

255.255.240.0

creates subnets in increments of

16

in the third octet. The host's local subnet spans from

10.88.32.0

10.88.47.255

. Because

10.88.48.1

is outside this range, the host cannot communicate with its gateway to route traffic off the local network.

Step-by-Step Solution

Determine the subnet increment and network boundaries for a /20 mask.

A mask of 255.255.240.0 has a 3rd octet block size of 256 - 240 = 16.

Calculating the subnet range identifies which IP addresses belong to the same local broadcast domain.

Identify the specific subnet range for host IP 10.88.32.180.

The network ID is 10.88.32.0 and the valid host range spans 10.88.32.1 through 10.88.47.254, with 10.88.47.255 as the broadcast address.

Evaluating the lower and upper bounds confirms the extent of local IP reachability.

Compare the configured default gateway address against the local subnet bounds.

The default gateway 10.88.48.1 falls into the next subnet block (10.88.48.0/20).

A host cannot ARP for or send traffic directly to a default gateway that does not reside within its local subnet.

Key Concept

Default Gateway Subnet Boundary Troubleshooting

Question 310Question →

A network technician needs to verify basic Layer 3 IP reachability to a default gateway host at 192.168.1.1 by transmitting ICMP Echo Request messages. Which command-line utility should the technician use?

ping

nslookup

netstat

dig

Show answer & explanation

Answer: ping

Answer

The ping command is used to test ICMP reachability to an IP address.

The ping utility sends ICMP Echo Request messages to an IP address to evaluate reachability and measure network response latency.

Step-by-Step Solution

Identify the primary network troubleshooting task

The requirement is to test basic Layer 3 connectivity using ICMP Echo Request packets to host 192.168.1.1.

Determining if a target responds to ICMP packets establishes whether basic IP routing and interface availability exist between hosts.

Select the utility designed for ICMP reachability checks

The ping tool is specifically built to transmit ICMP Echo Requests and process Echo Replies.

Alternative command-line utilities such as nslookup or dig query DNS records, while netstat reports local protocol sockets and active sessions.

Key Concept

Utilizing Command-Line Network Troubleshooting Utilities

Question 311Question →

A network administrator is troubleshooting an issue where workstations on a newly provisioned subnet, VLAN 55 ( $172.18.16.0/21$ ), fail to acquire dynamic IP configurations and instead assign themselves addresses in the range $169.254.1.1$ to $169.254.254.254$ .

The central DHCP server ( $10.100.5.10$ ) resides on VLAN 10. The Layer 3 switch routing interface for VLAN 55 is configured as follows:

text
interface Vlan55
ip address 172.18.16.1 255.255.248.0
ip helper-address 10.100.5.10

A packet capture performed at the DHCP server shows that unicast `DHCPDISCOVER` packets forwarded by the Layer 3 switch arrive at the server with a Gateway IP Address (GIADDR) of $172.18.16.1$ , but the DHCP server returns no `DHCPOFFER`. All other subnets using this DHCP server are receiving leases normally.

Which of the following is the MOST likely root cause of this failure?

The `ip helper-address` command must be configured on the DHCP server interface on VLAN 10 rather than on the client VLAN interface.

The client workstations have a misconfigured default gateway that prevents APIPA addresses from routing across VLAN boundaries.

The DHCP server does not have an active scope defined that matches the network segment of the GIADDR (172.18.16.0/21).

The /21 subnet mask defines 2,046 usable host addresses, which exceeds the maximum address pool capacity allowed per DHCP scope.

Show answer & explanation

Answer: The DHCP server does not have an active scope defined that matches the network segment of the GIADDR (172.18.16.0/21).

Answer

The DHCP server lacks an active scope matching the GIADDR network segment (172.18.16.0/21).

When a DHCP relay agent forwards client broadcasts to a central DHCP server, it inserts its local interface IP address into the GIADDR field of the DHCP packet header. The central DHCP server relies on GIADDR to match incoming requests to an active DHCP scope. If the server does not have an active scope corresponding to the relay agent's subnet (172.18.16.0/21), it cannot allocate an address and drops the request without responding.

Step-by-Step Solution

Analyze client symptoms and network packet capture evidence.

Workstations self-assign APIPA addresses (169.254.x.x), indicating DHCP requests are unfulfilled. The packet capture confirms DHCPDISCOVER packets arrive at the central server with GIADDR = 172.18.16.1.

Because the relay agent correctly forwards unicast DHCPDISCOVER packets to 10.100.5.10, physical and Layer 3 reachability between the relay agent and DHCP server is functional.

Evaluate how a DHCP server processes relayed requests based on the GIADDR field.

The server inspects GIADDR (172.18.16.1) to identify which subnet pool to allocate an IP address from.

DHCP servers use the GIADDR IP address to perform a lookup in their scope database for a matching subnet.

Identify why no DHCPOFFER is returned while other subnets function normally.

If no scope exists or if the scope for 172.18.16.0/21 is deactivated/deconfigured, the DHCP server cannot select an available address and silently drops the request.

A missing or inactive scope corresponding to the GIADDR prevents address allocation.

Key Concept

DHCP Relay GIADDR Scope Selection

Estimated Time:2m 0s

Question 312Question →

A network administrator is investigating an issue where database servers in a secondary rack lose connectivity to primary application servers during nightly backup windows. The administrator gathered user reports, confirmed the link failures, established a theory that an automated backup job was saturating the inter-switch trunk, and performed packet captures during a test run to confirm this theory as the verified root cause. According to the CompTIA troubleshooting methodology, which of the following should the network administrator do NEXT?

Establish a plan of action to rate-limit backup traffic and identify potential side effects.

Apply a Quality of Service (QoS) policy on the trunk switchports to prioritize application traffic.

Execute end-to-end ping and database query benchmarks to confirm uninterrupted connectivity.

Update the infrastructure ticketing system with the packet capture findings and resolution history.

Show answer & explanation

Answer: Establish a plan of action to rate-limit backup traffic and identify potential side effects.

Answer

Establish a plan of action to rate-limit backup traffic and identify potential side effects.

The scenario describes a technician who has successfully tested their theory and verified the root cause using packet captures (Step 3). According to the CompTIA troubleshooting methodology, the direct next phase is Step 4: Establish a plan of action to resolve the problem and identify potential side effects.

Step-by-Step Solution

Identify current position in CompTIA 7-step troubleshooting methodology.

The technician completed Step 1 (Identify problem), Step 2 (Establish theory of probable cause), and Step 3 (Test theory to determine cause by analyzing packet captures).

Determining the completed step dictates the required next action in the rigid methodology sequence.

Determine the sequential next step following Step 3.

Step 4 is 'Establish a plan of action to resolve the problem and identify potential side effects'.

Before making changes in a production network, a technician must design the remediation steps and evaluate potential operational risks or unwanted impacts.

Match the correct step to the corresponding option.

Developing a plan to rate-limit backup traffic while considering potential side effects directly aligns with Step 4.

This maintains administrative safety and adherence to proper change management controls before implementation.

Key Concept

CompTIA 7-Step Troubleshooting Methodology Sequence

Estimated Time:1m 15s

Question 313Question →

A systems engineer executes the following command to diagnose a connection failure to an internal application server:

text
$ dig @10.0.4.15 app.internal.net A

;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 48219
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; QUESTION SECTION:
;app.internal.net. IN A

;; AUTHORITY SECTION:
internal.net. 3600 IN SOA ns1.internal.net. admin.internal.net. ( 2026072601 7200 3600 1209600 3600 )

Based on the output snippet, which of the following best explains why no IP address was returned for the query?

The DNS server is reachable and authoritative for the domain, but no resource record matching the requested host name and type exists.

The query failed because the client requested an IPv4 A record when the server only supports IPv6 AAAA record resolution.

The command line output indicates that the local client resolver cache has overwritten the authoritative DNS server response.

The DNS query timed out because UDP port 53 traffic was blocked by an intermediate network firewall.

Show answer & explanation

Answer: The DNS server is reachable and authoritative for the domain, but no resource record matching the requested host name and type exists.

Answer

The DNS server is reachable and authoritative for the domain, but no resource record matching the requested host name and type exists.

The correct response identifies that the server successfully answered the query with status NOERROR and zero answer records, supplying the zone SOA record in the authority section. This specific combination signifies a NODATA response, proving the server is authoritative for internal.net but no A record exists for app.internal.net.

Step-by-Step Solution

Examine the dig response header status and section counts

The header shows status: NOERROR, QUERY: 1, ANSWER: 0, AUTHORITY: 1.

Understanding the header flag summary reveals whether the query succeeded at the protocol layer and if any answer records were returned.

Analyze the AUTHORITY section contents

The AUTHORITY section contains the Start of Authority (SOA) record for internal.net.

When a DNS server returns NOERROR with 0 answer records alongside an SOA record, it indicates a NODATA condition (the domain exists on the authoritative server, but the requested host 'app' does not have an A record).

Differentiate NODATA from network transport failures or local resolver issues

Network communication succeeded on port 53 and direct query was made to 10.0.4.15.

Eliminates firewall blocking (which causes timeouts) and local cache interference (since dig directly queries the specified IP).

Key Concept

Interpreting dig output sections and DNS NODATA / SOA responses during resolution troubleshooting.

Estimated Time:1m 15s

Question 314Question →

A system administrator notices that industrial telemetry sensors on a smart factory floor periodically lose connectivity with an edge gateway after a recent firmware rollout. The administrator duplicated the issue in a lab environment and hypothesized that an aggressive handshake timeout in the new firmware was causing session drops. After adjusting the timeout parameter in the lab, the connectivity issues ceased and the theory was confirmed. According to the CompTIA troubleshooting methodology, which of the following actions should the administrator perform next?

Establish a plan of action to resolve the issue on the production edge gateways and identify potential side effects.

Verify full system functionality by conducting end-to-end monitoring across all production factory floor sensors.

Document the root cause, testing steps, and final resolution in the organization's ticketing system.

Interview the factory floor operators to gather additional symptoms and determine if any physical changes were made.

Show answer & explanation

Answer: Establish a plan of action to resolve the issue on the production edge gateways and identify potential side effects.

Answer

Establish a plan of action to resolve the issue on the production edge gateways and identify potential side effects.

The scenario describes a technician who has already established and successfully tested a theory in a lab environment (Step 3). According to the CompTIA troubleshooting methodology, the next phase is Step 4: Establish a plan of action to resolve the problem and identify potential side effects.

Step-by-Step Solution

Identify the current phase of the CompTIA Troubleshooting Methodology.

The scenario states that the administrator duplicated the issue and verified that altering the timeout parameter fixed the problem in the lab, confirming the cause.

Confirming the cause in a lab environment completes Step 3 (Test the theory to determine cause).

Determine the immediate next step in the standard 6-step CompTIA sequence.

Step 4 is 'Establish a plan of action to resolve the problem and identify potential side effects.'

Before applying fixes to production infrastructure, a plan must be formulated to minimize downtime and prevent unintended side effects.

Key Concept

CompTIA Troubleshooting Methodology Steps (Identify problem -> Establish theory -> Test theory -> Plan of action & implement -> Verify functionality -> Document findings)

Estimated Time:1m 15s

Question 315Question →

A network technician is investigating performance degradation in a newly renovated office wing. Users report high packet loss and frequent disconnections when connected to the 2.4 GHz wireless network. An RF spectrum audit reveals that neighboring access points in the wing are currently operating on channels 1, 4, and 6. Which of the following configuration changes should the technician implement to resolve the transmission issues?

Reconfigure the access point operating on channel 4 to use channel 11.

Change the access point operating on channel 4 to operate on channel 3 to align closer with channel 1.

Increase the DHCP scope lease pool on the local router servicing the wireless subnet.

Modify the access switch port duplex setting from full-duplex to half-duplex for the access point.

Show answer & explanation

Answer: Reconfigure the access point operating on channel 4 to use channel 11.

Answer

Reconfigure the access point operating on channel 4 to use channel 11.

In 2.4 GHz Wi-Fi deployments, 20 MHz channels require a 5-channel separation to prevent overlapping frequencies. Channels 1, 6, and 11 are the standard non-overlapping channels. Operating on channel 4 causes adjacent-channel interference with neighboring access points on channels 1 and 6. Reconfiguring the channel 4 access point to channel 11 establishes a clean, non-overlapping channel design.

Step-by-Step Solution

Analyze the 2.4 GHz channel deployment plan.

Identified channels in use: 1, 4, and 6.

The 2.4 GHz band has 14 total channels, but only channels 1, 6, and 11 do not overlap with one another.

Identify the cause of wireless performance degradation.

Channel 4 partially overlaps with channel 1 and channel 6, creating adjacent-channel interference (ACI).

Adjacent-channel interference causes signal degradation and frame corruption because radios cannot cleanly decode transmissions from partially overlapping frequencies.

Determine the proper non-overlapping channel configuration.

Reassign channel 4 to channel 11.

Using channel 11 completes a proper 1/6/11 non-overlapping channel cell pattern across the office wing.

Key Concept

2.4 GHz Non-Overlapping Channel Selection and Adjacent-Channel Interference Mitigation

Estimated Time:1m 30s

Question 316Question →

A network technician is troubleshooting an IP security camera that fails to power on when connected to an RJ-45 wall jack configured for Power over Ethernet (PoE). The technician needs to measure the precise electrical DC voltage output across the specific copper pins at the wall jack to confirm whether the switch port is supplying power. Which hardware tool should the technician use to perform this measurement?

Digital multimeter

Time-Domain Reflectometer (TDR)

Tone generator and probe

Wiremap tester

Show answer & explanation

Answer: Digital multimeter

Answer

A digital multimeter is the correct tool to measure electrical DC voltage across copper cable pins.

A digital multimeter measures electrical potential (DC voltage), current, and resistance. Placing the multimeter test leads across the active PoE conductor pins allows the technician to confirm whether adequate DC power is reaching the wall jack.

Step-by-Step Solution

Identify the primary diagnostic requirement specified in the scenario.

The requirement is to measure electrical DC voltage across specific cable pins providing Power over Ethernet (PoE).

Verifying voltage levels isolates power delivery failures from end-device hardware defects.

Evaluate the capabilities of standard hardware diagnostic tools.

A digital multimeter directly measures electrical voltage (volts), current (amperes), and resistance (ohms).

Cable testing tools such as TDRs, wiremappers, and tone probes test physical continuity, pin alignment, or cable tracing, but lack electrical voltage measurement functions.

Key Concept

Selecting appropriate hardware testing tools for physical layer electrical measurements

Estimated Time:1m 0s

Question 317Question →

A network administrator is investigating intermittent performance issues on a database server connected to a distribution switch via a multi-mode fiber optic trunk. System logs reveal high physical-layer frame error counts as well as unexpected database session terminations. Which TWO diagnostic actions should the administrator take to accurately pinpoint the physical cable fault and analyze the session disruptions?

Select all that apply

Connect an Optical Time-Domain Reflectometer (OTDR) to the fiber run to measure signal attenuation and identify the exact distance to any physical breaks or excessive splices.

Attach a copper Time-Domain Reflectometer (TDR) to the fiber patch panel to locate impedance mismatches along the optical strand.

Use a packet analyzer with a display filter isolating TCP RST flags and TCP retransmissions to analyze connection teardowns.

Configure a packet analyzer capture filter for UDP port 80 to detect Layer 2 Ethernet framing errors occurring on the physical interface.

Show answer & explanation

Answer: Connect an Optical Time-Domain Reflectometer (OTDR) to the fiber run to measure signal attenuation and identify the exact distance to any physical breaks or excessive splices.; Use a packet analyzer with a display filter isolating TCP RST flags and TCP retransmissions to analyze connection teardowns.

Answer

The correct diagnostic actions are using an Optical Time-Domain Reflectometer (OTDR) to locate physical fiber defects and configuring a packet analyzer display filter for TCP RST flags and retransmissions to evaluate session terminations.

The correct diagnostic steps involve applying an Optical Time-Domain Reflectometer (OTDR) to analyze light reflections and locate physical defects along the multi-mode fiber run, alongside employing a packet analyzer configured with TCP control flag filters (such as TCP RST and retransmission markers) to trace transport-layer session terminations.

Step-by-Step Solution

Identify the physical medium and select the appropriate hardware testing device.

Since the uplink utilizes multi-mode fiber optic cabling, an Optical Time-Domain Reflectometer (OTDR) must be selected rather than a metallic/copper TDR.

OTDRs specifically analyze optical attenuation, backscatter, and distance to faults in fiber optic cables.

Select the appropriate software analysis tool and protocol filter for troubleshooting transport layer session terminations.

Configure a packet analyzer (such as Wireshark or tcpdump) with a filter focused on TCP control flags (specifically TCP RST) and retransmissions.

Database connection terminations operating over connection-oriented TCP emit RST or FIN packets when abnormally severed, which are captured at Layer 4.

Key Concept

Selecting media-appropriate hardware testers (OTDR for fiber optic reflection analysis) and configuring transport-layer packet capture filters for session troubleshooting.

Estimated Time:2m 0s

Question 318Question →

A workstation on an enterprise network cannot connect to an internal intranet portal by its hostname `portal.local`. A network technician must execute a systematic diagnostic process to isolate whether the issue originates from local client caching, the default DNS resolver, or the authoritative DNS server configuration. In what order should the technician execute the following troubleshooting steps?

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence begins with inspecting the local cache (`ipconfig /displaydns`), flushing stale entries (`ipconfig /flushdns`), testing standard resolution against the default server (`nslookup portal.local`), and finally querying the authoritative DNS server directly (`nslookup portal.local 10.10.10.10`).

The correct order follows standardCompTIA troubleshooting methodology: non-destructive inspection of local client cache (`ipconfig /displaydns`), clearing stale local data (`ipconfig /flushdns`), testing normal client DNS query behavior (`nslookup portal.local`), and isolating infrastructure components by directly querying the authoritative server (`nslookup portal.local 10.10.10.10`).

Step-by-Step Solution

Examine the local system resolver cache.

Identifies if an incorrect IP mapping is stored locally in client memory.

Troubleshooting methodology specifies gathering data non-destructively before modifying local client cache.

Clear the local system resolver cache.

Removes cached records, forcing future queries to hit network DNS infrastructure.

Eliminates stale entries as the root cause of the resolution failure.

Test resolution through the standard configured DNS server.

Determines whether the client's assigned primary DNS server can resolve the hostname.

Evaluates standard network path name resolution performance.

Bypass the default resolver by querying the authoritative DNS server explicitly.

Determines if the authoritative zone contains the valid record or if forwarders/recursive resolvers are failing.

Isolates upstream server configuration errors from local client or recursive DNS server issues.

Key Concept

Systematic DNS Troubleshooting Methodology

Question 319Question →

A network engineer is responding to reports of severe latency and packet loss affecting handheld inventory scanners in a fulfillment warehouse. A spectrum analysis of the 2.4 GHz band shows that three adjacent Access Points (APs) covering the same zone are configured to use Channel 1, Channel 3, and Channel 4, respectively. Which of the following identifies the primary cause of the wireless connectivity issues?

Adjacent-channel interference caused by overlapping 2.4 GHz channels

Exhaustion of the DHCP scope assigned to the wireless management VLAN

Native VLAN mismatch across the 802.1Q trunk connection to the APs

Physical duplex mismatch between the AP ethernet interfaces and switchports

Show answer & explanation

Answer: Adjacent-channel interference caused by overlapping 2.4 GHz channels

Answer

Adjacent-channel interference caused by overlapping 2.4 GHz channels

The 2.4 GHz Wi-Fi spectrum only contains three non-overlapping channels: Channel 1, Channel 6, and Channel 11. Assigning channels 1, 3, and 4 causes adjacent-channel interference (ACI), where transmissions on neighboring channels corrupt each other's RF signals, leading to high packet loss and latency.

Step-by-Step Solution

Analyze the 2.4 GHz spectrum channel configuration

Channels 1, 3, and 4 overlap significantly in frequency ranges

The 2.4 GHz Wi-Fi spectrum has 22 MHz channel widths spaced 5 MHz apart, requiring at least 5 channels of separation to prevent overlap.

Identify standard non-overlapping channel deployment guidelines

Standard non-overlapping channels in North America/International 2.4 GHz Wi-Fi are 1, 6, and 11

Configuring APs on adjacent overlapping channels (such as 1, 3, and 4) creates adjacent-channel interference (ACI), causing signal corruption and frame retransmissions.

Key Concept

2.4 GHz Non-Overlapping Channel Planning

Question 320Question →

A network technician is troubleshooting an IP surveillance camera that repeatedly reboots whenever its high-power infrared illuminators activate at night. The camera is powered via Power over Ethernet (PoE) over an 85-meter Category 6 UTP cabling drop. A basic wiremapper confirms correct T568B pinout continuity with no opens or shorts. Which TWO of the following diagnostic findings or procedures are most accurate for identifying and resolving this physical cabling issue?

Select all that apply

High DC resistance resulting from a poor RJ-45 crimp or oxidized IDC punch-down point causes excessive voltage drop when current draw increases.

Using a cable certifier to measure DC loop resistance and resistance unbalance across the individual conductor pairs.

Using a basic continuity wiremapper to measure signal attenuation and high-frequency crosstalk under peak power load.

Deploying an Optical Power Meter (OPM) to measure signal loss along the copper conductor run.

Show answer & explanation

Answer: High DC resistance resulting from a poor RJ-45 crimp or oxidized IDC punch-down point causes excessive voltage drop when current draw increases.; Using a cable certifier to measure DC loop resistance and resistance unbalance across the individual conductor pairs.

Answer

The issue is caused by high DC resistance on the copper conductors (such as a poor crimp or oxidized punch-down), which leads to excessive voltage drop when the camera's current consumption spikes. To properly diagnose this physical layer issue, a cable certifier must be used to measure DC loop resistance and resistance unbalance.

Power over Ethernet (PoE) delivery over long copper runs relies on low DC resistance across wire pairs. High resistance caused by loose IDC terminations or poor crimps creates an excessive voltage drop under heavy current load (such as when IR LEDs engage). Because basic wiremappers only verify 1-to-1 pin connectivity, a cable certifier capable of testing DC loop resistance and unbalance is required to detect high-resistance faults.

Step-by-Step Solution

Analyze the failure symptom under load.

The camera operates normally until IR illuminators turn on, increasing current draw (

I

). According to Ohm's Law (

V_{drop} = I \times R

), higher current through elevated resistance (

R

) produces a large voltage drop (

V_{drop}

), causing the device to brown out.

Basic wiremappers apply minimal current to verify pin continuity, concealing high-resistance terminations.

Select the appropriate diagnostic tool.

Deploy a cable certifier configured to measure DC loop resistance and resistance unbalance.

Advanced cable certifiers detect resistance anomalies across wire pairs that standard continuity testers cannot identify.

Key Concept

DC Loop Resistance and Voltage Drop in PoE Cabling

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