CompTIA N10-009 Practice Test 1

Question 1

A network team observes: A switch port has no optical receive power even though its configuration is correct and the peer is active. What is the MOST appropriate corrective action or technical decision?

Inspect transceiver compatibility and measure the fiber path before replacing the defective physical component.
Increase the switch-port MTU and run an IP throughput test before investigating the missing receive-light signal.
Recreate the access VLAN to repair Layer 2 forwarding while leaving the optical receive path untested.
Change the negotiated Ethernet speed while ignoring transceiver type, fiber cleanliness, and optical receive levels.

Explanation

Correct Answer

No optical receive power is a physical-layer symptom. Verify transceiver compatibility and optical levels, then inspect or clean the fiber path and replace the defective optic or cable component indicated by measurement.

Incorrect Answers

MTU and IP throughput tests operate above the physical signal path; they cannot restore received optical power when no light reaches the port.

VLAN configuration influences Layer 2 forwarding after link establishment. It does not create light at the optical receiver.

Speed negotiation cannot compensate for an incompatible or failed optic, disconnected fiber, or dirty connector. Measure optical power and inspect the path.

Question 2

After reseating a fiber optic uplink, both transceivers report supported optics and the switch sees stable light levels. What test most directly confirms that the previous Layer 1 failure is resolved?

Check only the host DHCP lease expiration time.
Verify the interface is operational, optical receive power is within the transceiver specification, and error counters remain stable under traffic.
Change the local switch’s DNS resolver while leaving the optical port untested.
Open an HTTPS page once and ignore transceiver telemetry and counters.

Explanation

Correct Answer

Layer 1 restoration should be verified at the port and optical signal before concluding that higher-layer connectivity is healthy.

Incorrect Answers

A DHCP lease is a Layer 3 addressing detail and does not prove optical signal quality on the repaired uplink.

DNS can fail independently of fiber link integrity, so editing it does not validate the physical repair.

One successful application request does not establish that optical signal levels and error rates are stable.

Question 3

A network team observes: Two hosts in the same VLAN have healthy physical links but their switch learns no source MAC address on the access port. What is the MOST appropriate corrective action or technical decision?

Change the hosts’ IP subnet masks until the interface appears in the correct IP network, without checking the switch MAC table.
Add a new default route on each host, even though the communication is between stations in the same VLAN.
Inspect the access VLAN port state and MAC-learning controls rather than changing IP routes.
Increase switch uplink bandwidth without inspecting whether this access port is forwarding or authorized.

Explanation

Correct Answer

A switch learns source MAC addresses from frames admitted on the access port. When link is up but learning is absent, check VLAN membership, security/802.1X authorization, forwarding state and MAC-learning controls before IP routing.

Incorrect Answers

An IP subnet mask affects Layer 3 reachability but does not explain why the switch learns no source MAC from frames arriving on its port.

Same-VLAN frame forwarding does not require a default route. A routing change will not enable a port that is discarding or failing to learn source frames.

Extra uplink capacity cannot restore MAC learning on a local access port that is blocked, misassigned or not accepting frames.

Question 4

Two endpoints share a VLAN, but the switch learns no source MAC from a device despite link lights. A packet capture confirms frames leave that device, yet the switch port shows ingress discards. Which evidence is most useful next?

Focus only on the remote DNS server because hostnames might be slow to resolve.
Adjust the host’s web browser proxy and then recheck the ARP cache only.
Enable a BGP routing session between unrelated uplink routers before checking the port.
Inspect the port’s error and discard counters, VLAN membership, security restrictions, and frame admission behavior while repeating a controlled test.

Explanation

Correct Answer

Frame learning requires accepted ingress frames with a source MAC. Port discards, VLAN policy or security controls may prevent learning despite a physical link.

Incorrect Answers

DNS resolution does not explain missing source MAC learning on locally received Ethernet frames.

Browser proxy selection is unrelated to Layer 2 frame admission and CAM learning on the access switch.

Dynamic routing is not required for MAC learning between hosts within the same access VLAN.

Question 5

Two endpoints in the same access VLAN show link lights, but packet capture at the source shows outgoing broadcast frames while the attached switch learns no source MAC on that port. What should be investigated first?

Port admission, security/802.1X state, VLAN membership and whether MAC learning or frame forwarding is blocked.
The IP default gateway, because a same-VLAN broadcast must first traverse the default route.
The DHCP lease duration, because a shorter lease normally prevents the switch from learning Ethernet source addresses.
The application TLS cipher suite, because it decides whether an Ethernet switch records a sender MAC.

Explanation

Correct Answer

Broadcast frames entering a forwarding switch port should present a source MAC for learning. An access-port security, authorization, VLAN or forwarding condition can prevent that admission; those controls are the first place to inspect.

Incorrect Answers

Local broadcast frames do not go through a default gateway. Default routing occurs at Layer 3 and is unrelated to the switch learning the incoming frame source address.

DHCP lease time controls IP address validity, not the Layer 2 learning operation for a broadcast frame with a source MAC.

TLS negotiation occurs inside IP/TCP sessions above Ethernet; a switch learns source MACs from frames without inspecting TLS.

Question 6

A network team observes: A client reaches its local gateway but every destination on another subnet fails and the gateway lacks a matching route. What is the MOST appropriate corrective action or technical decision?

Review the application session lifecycle and idle-timeout settings.
Install or correct a Layer 3 route with valid next-hop reachability.
Check TCP listener state and transport filtering before changing HTTP headers.
Standardize the negotiated character encoding and serialization format.

Explanation

Correct Answer

IP routers select paths using destination prefixes and next hops. Network-layer forwarding has no route to the remote prefix.

Incorrect Answers

Network-layer forwarding has no route to the remote prefix.

Checking TCP listener state and transport filtering would not install or correct a Layer 3 route with valid next-hop reachability.

Standardizing the negotiated character encoding and serialization format would not install or correct a Layer 3 route with valid next-hop reachability.

Question 7

A network team addresses this situation: A client reaches its local gateway but every destination on another subnet fails and the gateway lacks a matching route. After the corrective action, which test or result BEST verifies that the problem is resolved?

Compare raw bytes and decoded text using the agreed Unicode encoding.
Capture a SYN followed by SYN-ACK and ACK for the destination port.
Inspect the route table and trace packets through the expected next hop.
Reproduce idle-time expiry and confirm a valid session resume or reauthentication.

Explanation

Correct Answer

A matching route and progressing hops prove Layer 3 forwarding.

Incorrect Answers

Matching decoding proves the presentation translation is consistent. That check cannot demonstrate a valid Layer 3 route toward the remote subnet.

Three-way handshake packets verify the transport path. That check cannot demonstrate a valid Layer 3 route toward the remote subnet.

Session token state distinguishes session failure from packet loss. That check cannot demonstrate a valid Layer 3 route toward the remote subnet.

Question 8

A network specialist investigates this evidence: A client reaches its local gateway but every destination on another subnet fails and the gateway lacks a matching route. Which underlying condition BEST explains the observed failure or requirement?

The requested application resource no longer exists at that URI.
The peers disagree on character representation.
The data-link frame path is not being learned or forwarded.
Network-layer forwarding has no route to the remote prefix.

Explanation

Correct Answer

Network-layer forwarding has no route to the remote prefix. IP routers select paths using destination prefixes and next hops.

Incorrect Answers

An HTTP 404 after a successful TCP connection indicates an application resource or path mismatch. That does not establish a valid Layer 3 route toward the remote subnet.

Both endpoints must agree on character encoding for transmitted bytes to produce readable text. That does not establish a valid Layer 3 route toward the remote subnet.

The data-link frame path is not being learned or forwarded.

Question 9

A network team observes: A web host resolves correctly and answers ICMP, but SYN retransmissions receive no SYN-ACK on TCP 443. What is the MOST appropriate corrective action or technical decision?

Check TCP listener state and transport filtering before changing HTTP headers.
Inspect transceiver compatibility and measure the fiber path before replacing the defective physical component.
Install or correct a Layer 3 route with valid next-hop reachability.
Standardize the negotiated character encoding and serialization format.

Explanation

Correct Answer

TCP handshakes must succeed before application traffic can be exchanged. The transport-layer tcp handshake is not completing.

Incorrect Answers

Inspecting transceiver compatibility and measuring the fiber path would not check TCP listener state and transport filtering.

Installing or correct a Layer 3 route with valid next-hop reachability would not check TCP listener state and transport filtering.

Standardizing the negotiated character encoding and serialization format would not check TCP listener state and transport filtering.

Question 10

A network team addresses this situation: A web host resolves correctly and answers ICMP, but SYN retransmissions receive no SYN-ACK on TCP 443. After the corrective action, which test or result BEST verifies that the problem is resolved?

Measure received optical power and confirm link comes up using a known-good optic and patch.
Capture a SYN followed by SYN-ACK and ACK for the destination port.
Compare raw bytes and decoded text using the agreed Unicode encoding.
Confirm MAC table learning and successful same-subnet frame exchange.

Explanation

Correct Answer

Three-way handshake packets verify the transport path.

Incorrect Answers

Optical transceiver compatibility and receive-light measurements diagnose the physical signal path before higher-layer work. That check cannot demonstrate completion of the TCP three-way handshake.

Matching decoding proves the presentation translation is consistent. That check cannot demonstrate completion of the TCP three-way handshake.

Ethernet switching learns source MAC addresses from admitted frames on a forwarding VLAN port. That check cannot demonstrate completion of the TCP three-way handshake.