CompTIA Network+ · Domain 5 · 24% of the examNetwork Troubleshooting

Answer: C. Test the theory to determine the cause

After establishing a theory of probable cause, you test it to confirm the cause; if it isn't confirmed, you form a new theory or escalate. Making a plan of action comes only after the theory is confirmed.

Answer: D. Verify full system functionality and implement preventive measures if applicable

After implementing the solution, the next step is to verify that everything works end to end and add preventive measures, such as better cable management. Documentation happens throughout the process, but closing the ticket before verifying risks missing a remaining problem.

Answer: A. Electromagnetic interference corrupting frames on the cable

CRC errors mean frames are arriving corrupted, and running UTP next to a motor is a classic source of interference; rerouting the cable or using STP fixes it. A duplex mismatch can also cause errors, but both ends have confirmed full duplex, so it's ruled out.

Answer: B. The switch's PoE power budget has been exceeded

When the switch's total PoE budget is used up, it refuses power to more ports, so the last APs to connect stay dark. A wrong VLAN would stop the APs from passing traffic, but they would still power on.

Answer: D. SW2

The root bridge has the lowest bridge ID, and priority is compared before the MAC address, so SW2 (4096) wins. SW3 has the lowest MAC, but MAC addresses only break ties between switches with equal priority.

Answer: C. The default gateway is outside the workstation's subnet; it should be 10.10.10.65

A /26 makes blocks of 64, so 10.10.10.70 is in 10.10.10.64/26 (hosts .65-.126), while .1 is in the 10.10.10.0/26 subnet and can't be reached directly. A DNS problem would break name lookups, not reaching remote hosts by IP.

Answer: A. DHCP address pool exhaustion

The range .10-.240 holds 231 addresses; 215 + 40 = 255 requests, so the pool runs out and the leftover clients fall back to APIPA. A rogue DHCP server would hand out addresses from its own range, not leave clients with 169.254.x.x.

Answer: C. Jitter

Jitter is variation in packet delay, and real-time voice suffers when packets arrive at uneven intervals. Average latency of 40 ms is well within acceptable limits for voice, so latency itself isn't the problem.

Answer: B. Move the access points to the non-overlapping channels 1, 6 and 11, and steer capable clients to 5 GHz or 6 GHz

Channels 4 and 8 overlap with their neighbors, causing interference; using only 1, 6 and 11 (and moving clients to the wider 5/6 GHz bands) cuts the overlap. Raising transmit power makes overlapping cells interfere with each other even more.

Answer: D. A bottleneck at the 100 Mbps uplink

Every transfer has to cross the uplink, so the 100 Mbps link caps throughput no matter how fast the desktops are; about 94 Mbps is typical real-world throughput on Fast Ethernet. Jitter affects timing for real-time traffic, not a steady ceiling on bulk transfer speed.

Answer: A. Toner and probe

A toner places a signal on the cable at the jack, and the probe picks it up at the patch panel to identify the right port. A cable tester checks wiring and continuity, but you need to know both ends first, and a visual fault locator is for fiber.

Answer: B. show mac-address-table

The MAC address table maps learned MAC addresses to switch ports and VLANs, so it shows exactly where the device is plugged in. show arp maps IP addresses to MAC addresses but doesn't show the physical switch port.