Network Troubleshooting

A network administrator is troubleshooting an issue with a newly deployed Power over Ethernet (PoE+) pan-tilt-zoom (PTZ) IP camera installed at the end of a 85-meter Category 6 UTP cable run. The camera initializes and streams video normally during daylight, but repeatedly reboots whenever its infrared (IR) illuminators turn on at night. A basic wiremapper confirms all eight conductors have pin-to-pin continuity and proper T568B pinout. Which TWO of the following physical layer causes or diagnostic approaches are most appropriate to identify and resolve this failure?

A network administrator is configuring three adjacent 2.4 GHz wireless access points in an office floor plan. Which combination of channels should be assigned to these access points to prevent co-channel and adjacent-channel interference?

A network engineer is investigating intermittent packet loss and database session drops across a newly provisioned IPsec VPN tunnel between two enterprise data centers. After analyzing interface counters and running test ping sweeps with custom payload sizes, the engineer successfully proves that an MTU mismatch is causing packet fragmentation errors and confirms that lowering the tunnel interface MTU in a staging sandbox completely eliminates the drop count. According to the CompTIA troubleshooting methodology, which action should the engineer perform NEXT?

A network engineer is troubleshooting IP configuration failures on a newly provisioned subinterface for host workstations on VLAN 40 ($10.40.16.0/22$). Client devices on this VLAN are unable to communicate with remote subnets and consistently auto-assign Automatic Private IP Addressing (APIPA) addresses in the range of $169.254.x.x$. Packet captures performed on the router interface `Gi0/0.40` reveal that incoming `DHCPDISCOVER` broadcast frames from clients are arriving at the router interface, but no corresponding unicast packets are forwarded to the centralized DHCP server located at $10.10.2.100/24$.

The subinterface configuration on the router is displayed below:

text
interface GigabitEthernet0/0.40
encapsulation dot1Q 40
ip address 10.40.16.1 255.255.252.0

Which of the following identifies the root cause of this issue and the correct command required on interface `Gi0/0.40` to resolve host connectivity?

A network administrator needs to display a list of all active network connections and listening ports on a local Windows host to inspect running network services. Which command-line utility should the administrator execute?

A network engineer is troubleshooting a name resolution issue on a corporate client workstation. When the engineer runs `nslookup internal.example.com 10.20.4.15`, the hostname successfully resolves to `10.20.4.100`. However, standard web browsers and ping utilities on the workstation report an error stating that the host cannot be found. Which of the following potential root causes best explain why direct `nslookup` queries succeed while system applications fail to resolve the hostname? (Select TWO.)

A network administrator suspects that an unauthorized device acting as a rogue DHCP server is responding to client requests on a local subnet and handing out invalid default gateway addresses. The administrator connects a laptop running a packet analyzer to a mirrored port on the switch. Which display filter should the administrator apply in the packet analyzer to isolate traffic originating specifically from DHCP servers?

A network technician is systematically troubleshooting a connectivity failure from a client workstation to a remote application server. Place the following command-line utilities in the logical order they should be executed to isolate the issue from local interface settings out to remote route reachability.

A network engineer is diagnosing intermittent performance issues and log warnings on an inter-switch trunk link connecting Switch-Alpha (GigabitEthernet0/1) to Switch-Beta (GigabitEthernet0/1). The console on Switch-Alpha displays `%CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet0/1 (10), with Switch-Beta GigabitEthernet0/1 (20)`. Concurrently, interface statistics for GigabitEthernet0/1 on Switch-Alpha show a steadily increasing count of late collisions and Frame Check Sequence (FCS) errors. Which TWO of the following root causes are directly responsible for the observed log messages and interface error counters?

A network administrator is troubleshooting an issue where a user's workstation periodically attempts to connect to an old IP address (10.1.5.50) when reaching `db.internal.corp`, despite the DNS server returning the updated IP address (10.1.5.200) for other hosts. The administrator inspects the client using a local command-line diagnostic tool and views the following output snippet:

text
Record Name . . . . . : db.internal.corp
Record Type . . . . . : 1
Time To Live . . . . : 86400
Data Length . . . . . : 4
Section . . . . . . . : Answer
A (Host) Record . . . : 10.1.5.50

Which of the following actions should the administrator take on the client workstation to resolve this issue and ensure it uses the correct IP address? (Select TWO.)

Match each network diagnostic requirement or operational anomaly to the most appropriate diagnostic hardware tool or packet analyzer syntax.

A Linux server configured with the IPv4 address $192.168.120.45/24$ is unable to establish connections with servers on external subnets. Local subnet communication functions normally. The network administrator runs `ip route show` on the server and reviews the following routing table output:

text
default via 192.168.121.1 dev eth0
192.168.120.0/24 dev eth0 proto kernel scope link src 192.168.120.45

Which of the following identifies the root cause of the connectivity failure?

Users on a remote office subnet ($10.240.12.0/24$) report that they cannot access a cloud database hosted at $172.16.50.100$. Follow the standard CompTIA network troubleshooting methodology to arrange the administrative actions into the correct logical sequence from first step to last step.

During network maintenance, an administrator inspects a newly crimped Category 6 UTP cable that passes basic DC continuity testing but fails Gigabit performance certification due to severe Near-End Crosstalk (NEXT). Visual inspection reveals that the wire pairs were untwisted by approximately 5 centimeters (2 inches) prior to inserting them into the RJ-45 modular plug. Which of the following physical layer corrective actions should the administrator perform to resolve this issue?

A network technician is troubleshooting severe packet loss and link flapping on a 60-meter Category 6 UTP cable drop connecting a workstation to a access switch. A basic wiremap tester indicates that all eight conductors maintain correct end-to-end pin continuity with no open or short circuits. However, when testing the link with a Time-Domain Reflectometer (TDR), the device indicates a significant signal reflection and impedance anomaly at exactly 32 meters from the local patch panel. Which of the following physical cable conditions is the TDR identifying that the basic wiremap tester failed to detect?

A network technician receives a ticket stating that remote users at a new satellite office cannot reach the company's internal intranet application. The technician interviews affected users, duplicates the failure on a test host, and receives a 'Destination Host Unreachable' message. The technician then formulates a hypothesis that an incorrect VLAN tagging policy on the WAN router interface is stripping traffic. To verify this, the technician runs a packet capture on the router interface and confirms that frames are arriving with an unexpected VLAN ID tag, validating the root cause. According to the CompTIA troubleshooting methodology, which of the following steps should the technician execute NEXT?

A network technician is performing diagnostic testing on several physical cabling installations across a enterprise facility. Match each physical layer cabling issue on the left with its underlying root cause or correct remediation on the right.

A network administrator receives reports that a workstation at IP address 192.168.10.45 periodically loses connectivity to the default gateway. The administrator runs the `arp -a` command on the workstation and views the following output:

Interface: 192.168.10.45 --- 0x2
Internet Address Physical Address Type
192.168.10.1 00-11-22-33-44-55 dynamic
192.168.10.12 00-11-22-33-44-55 dynamic

Which of the following conditions is most directly indicated by this terminal output?

A network administrator is investigating high latency and severe throughput degradation on a critical database server connected to switch port FastEthernet0/12. An inspection of the switch port statistics shows a high count of late collisions, alignment errors, and frame check sequence (FCS) errors on FastEthernet0/12 during heavy traffic periods. The switch interface is set to default auto-negotiation settings, whereas the server's network interface card (NIC) was recently manually forced to 100 Mbps Full Duplex. Which of the following is the most likely root cause of the late collisions recorded on the switch port?

A network technician is troubleshooting a newly installed server connected to VLAN 50 ($192.168.50.0/24$). The server is configured to obtain IP settings dynamically but continually configures an IP address of $169.254.112.45$. The organization's centralized DHCP server is located on VLAN 10 ($192.168.10.5$) and correctly services hosts on VLAN 10. Which of the following root causes and remediation steps accurately address this connectivity issue? (Select TWO.)