Network Troubleshooting

A workstation loses connectivity to a server after the server's network card was replaced with a new one bearing a different MAC address. The workstation can ping other hosts on the same subnet fine, and the server responds to pings from every host except this one workstation. Using CLI tools, you notice the workstation still lists the server's IP mapped to the OLD MAC address. Which command should you run on the workstation to immediately resolve the issue?

A technician suspects that two hosts on the same subnet are experiencing intermittent connectivity because a workstation may be caching an outdated hardware address for the default gateway. The technician wants to inspect and, if necessary, clear the local table that maps IP addresses to MAC addresses on the affected workstation. Which command-line tool should the technician use?

A technician installs a new workstation in a warehouse. The Ethernet cable runs from a switch in the IDF, through a cable tray, and terminates at a wall jack roughly 130 meters away. The workstation intermittently drops its link and negotiates at only 100 Mbps despite being connected to a Gigabit switch. A cable tester shows correct wiremap and no shorts or opens. What is the MOST likely cause?

A user reports that their workstation loses network connectivity several times a day. A technician replaces the patch cable and the port stays up longer but still drops. The interface counters on the switch show a steadily increasing number of alignment and CRC errors, and wiggling the cable at the wall jack momentarily restores the link. What is the MOST likely cause?

A technician just terminated a new Cat6 patch cable using RJ45 connectors at both ends. When the cable is plugged in, the workstation gets no link light. The technician suspects the termination is wrong. Which tool should be used to confirm that each wire is connected to the correct pin on both ends?

A technician is investigating slow file transfers between a workstation and a server that traverses a single access switch. The switch port connected to the workstation shows a steadily increasing count of CRC errors, late collisions, and runts, while throughput drops sharply under load. The switch port is hardcoded to 100 Mbps full duplex, and the workstation NIC is set to auto-negotiate. What is the MOST likely cause of these symptoms?

A technician terminates several new Cat6 drops. Users on those drops report intermittent slow transfers, and interface counters show elevated errors. Inspecting the terminations, the technician notices that the twisted pairs were untwisted about an inch back before being punched into the jacks. Which physical-layer issue is MOST likely causing the degraded performance?

A Linux administrator is troubleshooting an issue where a company's mail is being delivered to the wrong server. The web page and general name resolution for the domain both work correctly. The administrator needs to query the domain's authoritative DNS server directly to view only its mail-routing records and confirm which host they point to. Which command should the administrator run?

Users report that when they browse to intranet.company.local they are directed to a decommissioned server's old IP address instead of the new server. A technician confirms the new server is online and reachable by its correct IP. Running nslookup on a client returns the old IP for the hostname. Which action will most directly resolve the issue?

A network technician has resolved an intermittent connectivity issue on a distribution switch by replacing a failing SFP module, and has confirmed that all affected users now have stable connectivity. According to the CompTIA troubleshooting methodology, what should the technician do next?

Users on a subnet report intermittent connectivity to a file server. A technician runs a packet capture and notices that the file server's IP address is sometimes mapped to one MAC address and other times to a different MAC address. Pings to the server succeed and fail in an alternating pattern. What is the MOST likely cause of this behavior?

A user reports intermittent slow file transfers and occasional dropped connections at a workstation located in a manufacturing area. The copper drop runs along a conduit that passes beside several large fluorescent light fixtures and a motor-driven conveyor. A cable tester shows correct wiremap and continuity, and the switch port shows a rising CRC error counter that spikes when the machinery runs. What is the MOST likely cause?

A technician is investigating a fiber uplink between two buildings that recently began showing intermittent errors and reduced throughput. Optical light-level readings at the receiving switch are several dB below the manufacturer's minimum acceptable receive power, though the fiber still passes traffic sporadically. Which condition BEST explains these symptoms?

A help desk technician receives three separate tickets within ten minutes: one user cannot reach a file share, another reports slow email, and a third cannot print. Before forming any theories, the technician wants to follow the CompTIA troubleshooting methodology correctly. What should the technician do FIRST?

A network technician is following the CompTIA troubleshooting methodology after users report they can no longer reach an internal file server. The technician has already gathered information, questioned affected users, and determined the scope of the problem. As part of identifying the problem, what should the technician do next before moving on to establishing a theory?

A Linux server suddenly stops responding to connections from other subnets, though it can still reach devices on its own local network. A technician logs in at the console and needs to quickly confirm the interface's assigned IP address, subnet mask, and whether a default gateway problem exists. Which CLI tool should the technician run FIRST to view the interface's current IP configuration?

A user reports intermittent loss of network connectivity on their workstation. When you check the device, Windows displays a warning that 'another device on the network is using this IP address.' The workstation was recently configured with a static IP address by a junior technician. What is the MOST likely cause of this issue?

A user reports that a company web application at portal.corp.example loads a certificate error page for an old server. Other users on different subnets reach the correct new server without issue. The DNS A record was updated yesterday to point to a new IP. From the affected Windows workstation, nslookup portal.corp.example returns the correct new IP address, but the browser still connects to the old server. Which action is MOST likely to resolve the issue?

A technician suspects that a server's newly installed network interface card (NIC) is faulty. The switch port, cable, and patch panel have all been verified as good using a cable tester, yet the interface will not establish a link. The technician wants to confirm whether the NIC itself can transmit and receive signals independently of any external network path. Which tool should the technician use to isolate the NIC?

A technician suspects that a compromised Windows workstation is establishing unauthorized outbound connections to an external host. The technician needs a built-in CLI command to display all active TCP connections along with the local and remote IP addresses, ports, and connection states. Which command should the technician use?