Free Network Troubleshooting practice questions

Slow “start” with fast transfer afterward is a classic DNS symptom: the delay happens during lookup, not throughput. The safest confirmation is comparing access by IP (bypasses DNS) versus hostname (requires DNS). If IP works immediately but hostname is slow/fails, DNS settings or the DNS server path is the fault domain.

169.254.x.x is APIPA, commonly assigned when DHCP fails. With multiple users affected, the fault domain is likely DHCP service down, VLAN misconfiguration, or scope exhaustion—not a single client. The exam-friendly next step is to renew the lease and check the DHCP server/scope on the network side.

When a known-good device is stable in the same location, the fault domain is the client. The most exam-appropriate next step is client-side: drivers and power management are common causes of intermittent disconnects, especially after updates or when running on battery.

Drops that happen while walking and always in the same physical spot point to a roaming boundary: the laptop is leaving one access point's cell before the next one is strong enough to hand off cleanly, which is a coverage-overlap or channel-plan problem in the wireless design. DHCP scope exhaustion would leave the device with an APIPA address wherever it is, not drop it in one hallway. Client isolation blocks traffic between wireless clients but does not disconnect a device from the network. A duplex mismatch on an AP uplink slows throughput for everyone on that AP; it does not cause disconnects tied to movement.

A ceiling around 90–95 Mbps strongly suggests a 100 Mbps Fast Ethernet link negotiation, often caused by a bad cable pair, damaged connector, or a port negotiating down. Checking link speed and swapping the cable are low-risk, high-signal tests aligned with A+ troubleshooting order.

VoIP quality depends on low jitter and low packet loss, not on download Mbps. When call quality collapses exactly while someone uploads large files, the outbound queue on the WAN link is filling and voice packets wait behind bulk data, which produces jitter and robotic audio; this is upload saturation, often called bufferbloat, and QoS or limiting uploads is the usual fix. A codec mismatch would make calls fail or sound bad all the time, not only during uploads. DNS is not involved once a call is set up. A duplex mismatch on the phone's own port would degrade that phone constantly and would not track other users' uploads.

Because the same workstation and the already-replaced cable become stable the moment they move to a different port, the fault is isolated to the original switch port or its hardware path; document it and take that port out of service. A duplex mismatch on the workstation would follow the workstation to the new port and would show as late collisions and CRC errors, not link flapping. DHCP scope exhaustion leaves the client with an APIPA address and no connectivity, but the physical link stays up. A wrong VLAN gives a link that is up but cannot reach its resources; it does not make the link itself go up and down.

Port flapping with the link light dropping and the switch logging link up/down events is a physical-layer problem, so the fastest, lowest-risk isolation step is to reseat and swap the patch cable with a known-good one, then work outward to the wall jack, the switch port, and the NIC. Moving the port to another VLAN changes Layer 2 membership but does nothing for a physical link that is dropping. Disabling and re-enabling the NIC resets the adapter once and would not stop a recurring physical drop. A driver update is worth trying later if the cable, jack, and port all test good, but it is not the first step when the switch itself is logging link loss.

If the gateway is reachable, the local link and IP addressing are likely fine. Failure to reach a public IP indicates the break is beyond the gateway (WAN/router/modem/ISP). DNS also fails because there’s no upstream path, not because Wi-Fi disconnected.

The gateway pings are stable over Ethernet from the same laptop but spike wildly over Wi-Fi, which isolates the variable latency to the wireless link: RF interference, channel contention, weak signal, or retries. A duplex mismatch is a wired-Ethernet fault and would have appeared on the wired test, which was clean. A damaged Ethernet cable is ruled out for the same reason. An overloaded switch port would affect the wired path and would not vanish when the laptop moves to a cable on the same switch.