Network Troubleshooting
Free CompTIA Network+ practice — 6 questions on Network Troubleshooting, with explanations. No sign-up. Full 12-question mixed test →
A fiber link between two buildings has been experiencing intermittent high error rates. A technician suspects a micro-bend or a partial break somewhere along the 2 km run and needs to pinpoint the exact distance to the fault from the near end. Which tool should be used?
An OTDR sends light pulses down the fiber and measures reflected/backscattered light to calculate the exact distance to breaks, bends, or connector faults — essential for locating faults on long fiber runs.
Hosts on VLAN 20 can successfully ping hosts on VLAN 10, and packet captures on VLAN 10 confirm the ICMP echo requests arrive and echo replies are sent. However, VLAN 20 hosts report the pings time out. A stateful firewall sits between the VLANs, and each VLAN's traffic takes a different physical path to and from the firewall. What is the MOST likely cause?
Because each direction of traffic follows a different path, the stateful firewall only sees the reply and never saw the matching outbound request in its session table, so it treats the reply as unsolicited and drops it — a classic asymmetric routing problem.
A server connected to a switch port configured for 1000 Mbps/Full duplex is experiencing intermittent slow throughput. The engineer wants definitive proof that a duplex mismatch (one side running full duplex while the other runs half duplex) is the root cause. Which approach will BEST confirm this?
Late collisions and CRC/FCS errors captured in a protocol analyzer trace are the hallmark symptom of a duplex mismatch — one side is transmitting while the other is also transmitting because it doesn't believe collision detection is needed, corrupting frames.
A network originally provisioned with a DHCP scope of 192.168.1.100–192.168.1.150 supported 50 devices. The office has since grown to 300 devices, and new devices are now receiving 169.254.x.x addresses while existing devices keep working. What is the BEST long-term solution?
The 169.254.x.x (APIPA) addresses indicate the scope is fully exhausted; expanding the scope (or adding a supplemental scope/subnet) permanently resolves the shortage for a network that has genuinely outgrown its original address pool.
In a high-density Wi-Fi 6 deployment with many closely spaced access points, users report high latency and excessive retransmissions even though RSSI readings show strong signal everywhere. What is the MOST likely cause, and what tool should be used to confirm it?
Strong RSSI with high latency/retransmissions in a dense deployment is the classic signature of co-channel interference (multiple APs sharing the same channel causing contention); a Wi-Fi analyzer showing channel utilization and overlapping BSSIDs on the same channel confirms this.
While troubleshooting a name resolution issue, a technician runs 'dig www.example.com' against a public DNS server and receives a response containing 'flags: qr rd ra;' (notably missing the 'aa' flag) along with a populated ANSWER SECTION. What does the absence of the 'aa' flag indicate?
The 'aa' (authoritative answer) flag is set only when the responding server is authoritative for the queried zone. Its absence, combined with 'ra' (recursion available) and a populated answer, indicates a recursive resolver is returning a cached, non-authoritative answer on behalf of the authoritative server.
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