Topic 02 Practice Test 1 covers Physical Interfaces, Ethernet Issues, and TCP/UDP for Cisco Certified Network Associate 200-301 CCNA and maps to objectives 1.3–1.5. For broader exam preparation, review the Cisco CCNA 200-301 Exam Dumps. Every option includes focused technical reasoning explaining both the networking concept and its fit to the scenario.
Question 1
A campus must connect two buildings several kilometers apart with an optical link, and the selected transceivers support long reach. Which medium is the best fit? Choose ONE.
- Single-mode fiber
- Multimode fiber
- Copper twisted-pair Ethernet
- Point-to-point Ethernet link
Correct Answer: A
Correct Answer
Answer A is correct because Single-mode fiber uses a small core that carries one propagation mode and is commonly paired with optics designed for comparatively long reach. The task requires a long-distance optical Ethernet run. The distance requirement favors the optical medium commonly used for long-reach transceiver options. It is the appropriate choice.
Incorrect Answers
Answer B is incorrect because Multimode fiber carries multiple light modes and is commonly paired with short-reach optics for links inside buildings or data centers. It fits shorter optical runs where MMF cabling and matching transceivers are available. Here, the task is a long-distance optical Ethernet run. The distance requirement favors the optical medium commonly used for long-reach transceiver options. That option misses the required function.
Answer C is incorrect because It fits ordinary access runs that need electrical Ethernet and possibly PoE within supported distance. Copper twisted-pair Ethernet uses electrical signaling over balanced pairs and can also carry Power over Ethernet on compatible links. The case instead needs a long-distance optical Ethernet run. The distance requirement favors the optical medium commonly used for long-reach transceiver options. The roles differ.
Answer D is incorrect because A point-to-point Ethernet link connects exactly two endpoints across one link; modern switched full-duplex links do not form a shared collision domain. Its proper use differs: It fits a dedicated switched connection with only two participating endpoints. This case needs a long-distance optical Ethernet run. The distance requirement favors the optical medium commonly used for long-reach transceiver options. It therefore fails here.
Question 2
A data center needs a short optical connection between switches in adjacent rows using 850-nm short-reach optics. Which medium is appropriate? Choose ONE.
- Copper twisted-pair Ethernet
- Single-mode fiber
- Shared Ethernet media
- Multimode fiber
Correct Answer: D
Correct Answer
Answer D is correct because MMF has a larger core that supports multiple propagation modes and is widely used with short-range optical Ethernet transceivers. The selected optics and short in-building distance align with multimode fiber. Required outcome: a short-reach optical data-center link. This option fits.
Incorrect Answers
Answer B is incorrect because Choose SMF when reach is the dominant requirement and compatible long-range transceivers are available. SMF minimizes modal dispersion by supporting one propagation mode, making it the normal choice for longer optical Ethernet links with suitable transceivers. The case instead needs a short-reach optical data-center link. The selected optics and short in-building distance align with multimode fiber. The roles differ.
Answer A is incorrect because Twisted-pair copper provides electrical Ethernet connectivity and, with supported equipment, can deliver PoE over the same cabling. Its proper use differs: Choose copper when the design requires a standard twisted-pair access link, especially where PoE is needed. This case needs a short-reach optical data-center link. The selected optics and short in-building distance align with multimode fiber. It therefore fails here.
Answer C is incorrect because Shared Ethernet media puts multiple stations in one collision domain, historically requiring half-duplex contention mechanisms such as CSMA/CD. It describes a common-medium segment, unlike a dedicated modern switched connection. Here, the task is a short-reach optical data-center link. The selected optics and short in-building distance align with multimode fiber. That option misses the required function.
Question 3
An access switch must provide both Ethernet data and PoE to an IP phone over one cable. Which physical medium supports that requirement? Choose ONE.
- Single-mode fiber
- Copper twisted-pair Ethernet
- Point-to-point Ethernet link
- Multimode fiber
Correct Answer: B
Correct Answer
Answer B is correct because PoE requires copper conductors in the Ethernet cable to carry DC power. Access Ethernet over copper sends data as electrical signals through twisted pairs; compatible cabling and ports can simultaneously provide DC power. The required outcome is electrical Ethernet plus PoE on the same access run. The role matches.
Incorrect Answers
Answer A is incorrect because Long-reach Ethernet optics commonly use single-mode fiber, whose small core supports a single light path over distances beyond typical multimode links. Its proper use differs: It is appropriate for longer optical paths, not simply because a link happens to use fiber. This case needs electrical Ethernet plus PoE on the same access run. PoE requires copper conductors in the Ethernet cable to carry DC power. It therefore fails here.
Answer D is incorrect because Short-reach data-center optical links often use multimode fiber with compatible optics, accepting modal dispersion over the intended shorter distance. It is appropriate when the installed fiber and optic specification call for MMF at the required distance. Here, the task is electrical Ethernet plus PoE on the same access run. PoE requires copper conductors in the Ethernet cable to carry DC power. That option misses the required function.
Answer C is incorrect because Choose it for direct switch-to-device or switch-to-switch links rather than hub-style shared segments. Dedicated switch-to-host or switch-to-switch Ethernet connections are point-to-point because only the two attached interfaces participate on that link. The case instead needs electrical Ethernet plus PoE on the same access run. PoE requires copper conductors in the Ethernet cable to carry DC power. The roles differ.
Question 4
An old hub-based Ethernet segment places all attached devices in one collision domain. What type of Ethernet connection is this? Choose ONE.
- Single-mode fiber
- Shared Ethernet media
- Point-to-point Ethernet link
- Copper twisted-pair Ethernet
Correct Answer: B
Correct Answer
Answer B is correct because On a shared Ethernet segment, attached devices contend for a common medium instead of receiving isolated full-duplex switch links. The task requires multiple stations contending on one common medium. The hub creates a shared collision domain rather than isolated switched links. It is the appropriate choice.
Incorrect Answers
Answer C is incorrect because Point-to-point Ethernet gives two interfaces a dedicated link instead of placing multiple stations on one shared transmission medium. It is appropriate when the link is isolated between a pair of interfaces. Here, the task is multiple stations contending on one common medium. The hub creates a shared collision domain rather than isolated switched links. That option misses the required function.
Answer D is incorrect because It fits ordinary access runs that need electrical Ethernet and possibly PoE within supported distance. Copper twisted-pair Ethernet uses electrical signaling over balanced pairs and can also carry Power over Ethernet on compatible links. The case instead needs multiple stations contending on one common medium. The hub creates a shared collision domain rather than isolated switched links. The roles differ.
Answer A is incorrect because Single-mode fiber uses a small core that carries one propagation mode and is commonly paired with optics designed for comparatively long reach. Its proper use differs: It fits long building-to-building or provider-style optical runs when the optics support the required distance. This case needs multiple stations contending on one common medium. The hub creates a shared collision domain rather than isolated switched links. It therefore fails here.
Question 5
A workstation has a dedicated full-duplex Ethernet connection to one switch port. How should that connection be characterized? Choose ONE.
- Point-to-point Ethernet link
- Multimode fiber
- Shared Ethernet media
- Layer 3 routing problem
Correct Answer: A
Correct Answer
Answer A is correct because A point-to-point Ethernet link connects exactly two endpoints across one link; modern switched full-duplex links do not form a shared collision domain. Only the workstation and switch interface participate on the link, so it is point-to-point. Required outcome: a dedicated two-endpoint Ethernet link. This option fits.
Incorrect Answers
Answer C is incorrect because It fits hub-style half-duplex behavior rather than an isolated two-endpoint Ethernet link. Hub-based or otherwise shared Ethernet exposes several stations to the same collision domain and shared transmission resource. The case instead needs a dedicated two-endpoint Ethernet link. Only the workstation and switch interface participate on the link, so it is point-to-point. The roles differ.
Answer B is incorrect because Multimode fiber carries multiple light modes and is commonly paired with short-reach optics for links inside buildings or data centers. Its proper use differs: It fits shorter optical runs where MMF cabling and matching transceivers are available. This case needs a dedicated two-endpoint Ethernet link. Only the workstation and switch interface participate on the link, so it is point-to-point. It therefore fails here.
Answer D is incorrect because A Layer 3 routing problem affects IP path selection or reachability between networks rather than the electrical or optical integrity of the Ethernet link. Investigate routing when Layer 1/2 counters are clean but IP forwarding or route information is wrong. Here, the task is a dedicated two-endpoint Ethernet link. Only the workstation and switch interface participate on the link, so it is point-to-point. That option misses the required function.
Question 6
A fiber design needs the greatest practical reach among the listed media choices for a building-to-building uplink. Which choice should be evaluated first? Choose ONE.
- Copper twisted-pair Ethernet
- Shared Ethernet media
- Multimode fiber
- Single-mode fiber
Correct Answer: D
Correct Answer
Answer D is correct because Single-mode designs support long-reach optic families that exceed typical multimode and copper distances. SMF minimizes modal dispersion by supporting one propagation mode, making it the normal choice for longer optical Ethernet links with suitable transceivers. The required outcome is the optical medium normally selected for longer reach. The role matches.
Incorrect Answers
Answer C is incorrect because MMF has a larger core that supports multiple propagation modes and is widely used with short-range optical Ethernet transceivers. Its proper use differs: Choose multimode for appropriate short-reach optical links rather than long-haul fiber requirements. This case needs the optical medium normally selected for longer reach. Single-mode designs support long-reach optic families that exceed typical multimode and copper distances. It therefore fails here.
Answer A is incorrect because Twisted-pair copper provides electrical Ethernet connectivity and, with supported equipment, can deliver PoE over the same cabling. Choose copper when the design requires a standard twisted-pair access link, especially where PoE is needed. Here, the task is the optical medium normally selected for longer reach. Single-mode designs support long-reach optic families that exceed typical multimode and copper distances. That option misses the required function.
Answer B is incorrect because It describes a common-medium segment, unlike a dedicated modern switched connection. Shared Ethernet media puts multiple stations in one collision domain, historically requiring half-duplex contention mechanisms such as CSMA/CD. The case instead needs the optical medium normally selected for longer reach. Single-mode designs support long-reach optic families that exceed typical multimode and copper distances. The roles differ.
Question 7
A server rack uses short optical patching between top-of-rack and aggregation equipment, and the installed plant is OM4. Which medium is being used? Choose ONE.
- Point-to-point Ethernet link
- Copper twisted-pair Ethernet
- Multimode fiber
- Single-mode fiber
Correct Answer: C
Correct Answer
Answer C is correct because Short-reach data-center optical links often use multimode fiber with compatible optics, accepting modal dispersion over the intended shorter distance. The task requires short-reach optical connectivity over OM4 cabling. OM4 is a multimode fiber category intended for multimode optical links. It is the appropriate choice.
Incorrect Answers
Answer D is incorrect because Long-reach Ethernet optics commonly use single-mode fiber, whose small core supports a single light path over distances beyond typical multimode links. It is appropriate for longer optical paths, not simply because a link happens to use fiber. Here, the task is short-reach optical connectivity over OM4 cabling. OM4 is a multimode fiber category intended for multimode optical links. That option misses the required function.
Answer B is incorrect because It is appropriate for supported local Ethernet cable runs rather than a fiber-only distance requirement. Access Ethernet over copper sends data as electrical signals through twisted pairs; compatible cabling and ports can simultaneously provide DC power. The case instead needs short-reach optical connectivity over OM4 cabling. OM4 is a multimode fiber category intended for multimode optical links. The roles differ.
Answer A is incorrect because Dedicated switch-to-host or switch-to-switch Ethernet connections are point-to-point because only the two attached interfaces participate on that link. Its proper use differs: Choose it for direct switch-to-device or switch-to-switch links rather than hub-style shared segments. This case needs short-reach optical connectivity over OM4 cabling. OM4 is a multimode fiber category intended for multimode optical links. It therefore fails here.
Question 8
A desktop link uses 1000BASE-T and terminates on an RJ-45 access switch port. Which medium is involved? Choose ONE.
- Single-mode fiber
- Shared Ethernet media
- Multimode fiber
- Copper twisted-pair Ethernet
Correct Answer: D
Correct Answer
Answer D is correct because Copper twisted-pair Ethernet uses electrical signaling over balanced pairs and can also carry Power over Ethernet on compatible links. 1000BASE-T is copper twisted-pair Ethernet rather than an optical medium. Required outcome: electrical twisted-pair Ethernet access cabling. This option fits.
Incorrect Answers
Answer A is incorrect because It fits long building-to-building or provider-style optical runs when the optics support the required distance. Single-mode fiber uses a small core that carries one propagation mode and is commonly paired with optics designed for comparatively long reach. The case instead needs electrical twisted-pair Ethernet access cabling. 1000BASE-T is copper twisted-pair Ethernet rather than an optical medium. The roles differ.
Answer C is incorrect because Multimode fiber carries multiple light modes and is commonly paired with short-reach optics for links inside buildings or data centers. Its proper use differs: It fits shorter optical runs where MMF cabling and matching transceivers are available. This case needs electrical twisted-pair Ethernet access cabling. 1000BASE-T is copper twisted-pair Ethernet rather than an optical medium. It therefore fails here.
Answer B is incorrect because On a shared Ethernet segment, attached devices contend for a common medium instead of receiving isolated full-duplex switch links. Choose shared media when multiple stations contend within one collision domain. Here, the task is electrical twisted-pair Ethernet access cabling. 1000BASE-T is copper twisted-pair Ethernet rather than an optical medium. That option misses the required function.
Question 9
A network engineer compares a hub segment with a modern switched full-duplex segment. Which term best describes the hub segment? Choose ONE.
- Single-mode fiber
- Point-to-point Ethernet link
- Shared Ethernet media
- Layer 3 routing problem
Correct Answer: C
Correct Answer
Answer C is correct because Hub-connected devices share the collision domain and medium access. Hub-based or otherwise shared Ethernet exposes several stations to the same collision domain and shared transmission resource. The required outcome is a common Ethernet medium shared by several stations. The role matches.
Incorrect Answers
Answer B is incorrect because Point-to-point Ethernet gives two interfaces a dedicated link instead of placing multiple stations on one shared transmission medium. Its proper use differs: It is appropriate when the link is isolated between a pair of interfaces. This case needs a common Ethernet medium shared by several stations. Hub-connected devices share the collision domain and medium access. It therefore fails here.
Answer A is incorrect because SMF minimizes modal dispersion by supporting one propagation mode, making it the normal choice for longer optical Ethernet links with suitable transceivers. Choose SMF when reach is the dominant requirement and compatible long-range transceivers are available. Here, the task is a common Ethernet medium shared by several stations. Hub-connected devices share the collision domain and medium access. That option misses the required function.
Answer D is incorrect because Choose Layer 3 troubleshooting when the interface is healthy yet destination prefixes are unreachable due to path information. Routing faults occur above the physical link and involve missing, incorrect, or unusable IP forwarding information. The case instead needs a common Ethernet medium shared by several stations. Hub-connected devices share the collision domain and medium access. The roles differ.
Question 10
A switch-to-router Ethernet link has exactly two attached interfaces and is configured full duplex. Which connection model applies? Choose ONE.
- Duplex mismatch
- Point-to-point Ethernet link
- Copper twisted-pair Ethernet
- Shared Ethernet media
Correct Answer: B
Correct Answer
Answer B is correct because A point-to-point Ethernet link connects exactly two endpoints across one link; modern switched full-duplex links do not form a shared collision domain. The task requires a two-node dedicated Ethernet segment. The link is dedicated between two interfaces rather than shared among multiple stations. It is the appropriate choice.
Incorrect Answers
Answer D is incorrect because Shared Ethernet media puts multiple stations in one collision domain, historically requiring half-duplex contention mechanisms such as CSMA/CD. It describes a common-medium segment, unlike a dedicated modern switched connection. Here, the task is a two-node dedicated Ethernet segment. The link is dedicated between two interfaces rather than shared among multiple stations. That option misses the required function.
Answer A is incorrect because It is a strong diagnosis when the link remains up but collision/error counters and performance are poor. A duplex mismatch occurs when one Ethernet side operates full duplex and the other half duplex, often producing poor throughput, collisions, and FCS errors. The case instead needs a two-node dedicated Ethernet segment. The link is dedicated between two interfaces rather than shared among multiple stations. The roles differ.
Answer C is incorrect because Twisted-pair copper provides electrical Ethernet connectivity and, with supported equipment, can deliver PoE over the same cabling. Its proper use differs: Choose copper when the design requires a standard twisted-pair access link, especially where PoE is needed. This case needs a two-node dedicated Ethernet segment. The link is dedicated between two interfaces rather than shared among multiple stations. It therefore fails here.
Question 11
Users report very slow file transfers. The switch side is full duplex, the attached device is half duplex, and collision/FCS counters increase. What is the most likely cause? Choose ONE.
- Layer 3 routing problem
- Duplex mismatch
- Speed or autonegotiation mismatch
- Damaged cable, optic, port, or NIC
Correct Answer: B
Correct Answer
Answer B is correct because When Ethernet peers disagree on duplex, the half-duplex side may report collisions while the full-duplex side sees errors or severe performance degradation. The asymmetric half/full configuration and collision symptoms are classic duplex-mismatch evidence. Required outcome: a mismatch between the duplex settings at the two ends. This option fits.
Incorrect Answers
Answer C is incorrect because It fits symptoms centered on link negotiation or link-up failure rather than Layer 3 forwarding. A speed or autonegotiation mismatch occurs when Ethernet peers cannot establish compatible link-speed or negotiation settings. The case instead needs a mismatch between the duplex settings at the two ends. The asymmetric half/full configuration and collision symptoms are classic duplex-mismatch evidence. The roles differ.
Answer D is incorrect because Damaged cabling, optics, connectors, ports, or NIC hardware can corrupt frames and appear as CRC/FCS errors, link flaps, or intermittent Layer 1 faults. It should be investigated when physical error counters rise or the interface repeatedly flaps. This case needs a mismatch between the duplex settings at the two ends. That mismatch rules it out.
Answer A is incorrect because Layer 3 path problems can prevent remote-network reachability even while interface state and Ethernet error counters remain normal. It fits IP reachability failures driven by routes, not symptoms that directly identify cabling or Ethernet negotiation. Here, the task is a mismatch between the duplex settings at the two ends. The asymmetric half/full configuration and collision symptoms are classic duplex-mismatch evidence. That option misses the required function.
Question 12
A newly installed Ethernet link remains down because one side is manually fixed to a speed the peer does not support. Which issue should be corrected? Choose ONE.
- TCP
- Duplex mismatch
- Layer 3 routing problem
- Speed or autonegotiation mismatch
Correct Answer: D
Correct Answer
Answer D is correct because The failure occurs during link negotiation before Layer 3 or transport protocols matter. Incompatible speed or autonegotiation configuration can prevent an Ethernet link from coming up or make physical connectivity unstable. The required outcome is incompatible interface speed or negotiation settings. The role matches.
Incorrect Answers
Answer B is incorrect because Mismatched half/full-duplex settings can leave link up while causing intermittent delivery, late collisions, CRC/FCS errors, and unexpectedly low throughput. Its proper use differs: It fits error-heavy, slow Ethernet caused by half/full-duplex disagreement, not an IP route-selection problem. This case needs incompatible interface speed or negotiation settings. The failure occurs during link negotiation before Layer 3 or transport protocols matter. It therefore fails here.
Answer C is incorrect because An IP routing issue concerns next-hop and prefix selection; it does not inherently create CRC errors, collisions, or loss of physical carrier. Use this diagnosis when packets lack a valid Layer 3 path despite otherwise normal physical connectivity. Here, the task is incompatible interface speed or negotiation settings. The failure occurs during link negotiation before Layer 3 or transport protocols matter. That option misses the required function.
Answer A is incorrect because It fits applications that require reliable ordered delivery and can accept the extra transport overhead. TCP is connection-oriented and uses sequencing, acknowledgments, retransmission, and flow control to provide reliable ordered byte-stream delivery. The case instead needs incompatible interface speed or negotiation settings. The failure occurs during link negotiation before Layer 3 or transport protocols matter. The roles differ.
Question 13
A full-duplex switch port suddenly accumulates CRC errors after a patch cable is pinched under furniture. What should be suspected first? Choose ONE.
- TCP
- Damaged cable, optic, port, or NIC
- Speed or autonegotiation mismatch
- Layer 3 routing problem
Correct Answer: B
Correct Answer
Answer B is correct because Physical media and transceiver defects commonly drive rising CRC/FCS counters or repeated up/down transitions even when IP configuration is unchanged. The task requires a physical-link fault causing frame corruption. The damaged cable and CRC increase directly implicate the physical path. It is the appropriate choice.
Incorrect Answers
Answer D is incorrect because A Layer 3 routing problem affects IP path selection or reachability between networks rather than the electrical or optical integrity of the Ethernet link. Investigate routing when Layer 1/2 counters are clean but IP forwarding or route information is wrong. Here, the task is a physical-link fault causing frame corruption. The damaged cable and CRC increase directly implicate the physical path. That option misses the required function.
Answer C is incorrect because It is appropriate when the problem begins at Ethernet parameter negotiation, before IP routing or applications are involved. Ethernet interfaces must agree on supported signaling parameters; a forced or incompatible speed setting can break link establishment or negotiation. The case instead needs a physical-link fault causing frame corruption. The damaged cable and CRC increase directly implicate the physical path. The roles differ.
Answer A is incorrect because Transmission Control Protocol establishes a connection and tracks sequence/acknowledgment state so lost data can be retransmitted and delivered in order. Its proper use differs: Choose TCP when delivery correctness, sequencing, and recovery from loss matter more than minimal latency. This case needs a physical-link fault causing frame corruption. The damaged cable and CRC increase directly implicate the physical path. It therefore fails here.
Question 14
A link stays up, but one side is hard-coded full duplex while the peer falls back to half duplex. Which condition explains intermittent performance and collision errors? Choose ONE.
- Duplex mismatch
- UDP
- Damaged cable, optic, port, or NIC
- Speed or autonegotiation mismatch
Correct Answer: A
Correct Answer
Answer A is correct because A duplex mismatch occurs when one Ethernet side operates full duplex and the other half duplex, often producing poor throughput, collisions, and FCS errors. The mismatch allows connectivity while producing poor performance and error counters. Required outcome: opposite duplex modes on the two link partners. This option fits.
Incorrect Answers
Answer D is incorrect because It fits symptoms centered on link negotiation or link-up failure rather than Layer 3 forwarding. A speed or autonegotiation mismatch occurs when Ethernet peers cannot establish compatible link-speed or negotiation settings. The case instead needs opposite duplex modes on the two link partners. The mismatch allows connectivity while producing poor performance and error counters. The roles differ.
Answer C is incorrect because A faulty cable, optic, connector, switch port, or NIC can introduce bit errors or loss of signal, producing frame-check errors and unstable links. Its proper use differs: It fits faults tied to media, optics, connectors, ports, or NICs rather than route or application logic. This case needs opposite duplex modes on the two link partners. The mismatch allows connectivity while producing poor performance and error counters. It therefore fails here.
Answer B is incorrect because UDP is connectionless and provides lightweight datagram transport without built-in acknowledgments, retransmission, or ordered-delivery guarantees. It fits latency-sensitive or simple request/response traffic that can tolerate loss or handle reliability elsewhere. Here, the task is opposite duplex modes on the two link partners. The mismatch allows connectivity while producing poor performance and error counters. That option misses the required function.
Question 15
Two Gigabit Ethernet ports are manually configured to incompatible speeds and no carrier is established. Which problem best matches? Choose ONE.
- Speed or autonegotiation mismatch
- Damaged cable, optic, port, or NIC
- Duplex mismatch
- Layer 3 routing problem
Correct Answer: A
Correct Answer
Answer A is correct because The incompatible configured rates prevent the interfaces from forming a normal Ethernet link. Incompatible speed or autonegotiation configuration can prevent an Ethernet link from coming up or make physical connectivity unstable. The required outcome is a speed configuration mismatch preventing link establishment. The role matches.
Incorrect Answers
Answer C is incorrect because When Ethernet peers disagree on duplex, the half-duplex side may report collisions while the full-duplex side sees errors or severe performance degradation. Its proper use differs: Choose it when symptoms specifically combine an operational link with collisions or asymmetric duplex behavior. This case needs a speed configuration mismatch preventing link establishment. The incompatible configured rates prevent the interfaces from forming a normal Ethernet link. It therefore fails here.
Answer D is incorrect because Routing faults occur above the physical link and involve missing, incorrect, or unusable IP forwarding information. Choose Layer 3 troubleshooting when the interface is healthy yet destination prefixes are unreachable due to path information. Here, the task is a speed configuration mismatch preventing link establishment. The incompatible configured rates prevent the interfaces from forming a normal Ethernet link. That option misses the required function.
Answer B is incorrect because It should be investigated when physical error counters rise or the interface repeatedly flaps. Damaged cabling, optics, connectors, ports, or NIC hardware can corrupt frames and appear as CRC/FCS errors, link flaps, or intermittent Layer 1 faults. The case instead needs a speed configuration mismatch preventing link establishment. The incompatible configured rates prevent the interfaces from forming a normal Ethernet link. The roles differ.
Question 16
An interface shows rapidly increasing FCS/CRC counters on a full-duplex link. Replacing the cable clears the errors. Which root-cause category was confirmed? Choose ONE.
- UDP
- Layer 3 routing problem
- Duplex mismatch
- Damaged cable, optic, port, or NIC
Correct Answer: D
Correct Answer
Answer D is correct because Physical media and transceiver defects commonly drive rising CRC/FCS counters or repeated up/down transitions even when IP configuration is unchanged. The task requires a faulty physical component in the Ethernet path. The error disappears when the physical medium is replaced, confirming a physical-layer cause. It is the appropriate choice.
Incorrect Answers
Answer C is incorrect because Mismatched half/full-duplex settings can leave link up while causing intermittent delivery, late collisions, CRC/FCS errors, and unexpectedly low throughput. It fits error-heavy, slow Ethernet caused by half/full-duplex disagreement, not an IP route-selection problem. Here, the task is a faulty physical component in the Ethernet path. The error disappears when the physical medium is replaced, confirming a physical-layer cause. That option misses the required function.
Answer B is incorrect because It fits IP reachability failures driven by routes, not symptoms that directly identify cabling or Ethernet negotiation. Layer 3 path problems can prevent remote-network reachability even while interface state and Ethernet error counters remain normal. The case instead needs a faulty physical component in the Ethernet path. The error disappears when the physical medium is replaced, confirming a physical-layer cause. The roles differ.
Answer A is incorrect because User Datagram Protocol sends independent datagrams with minimal transport state; reliability and ordering are not supplied by UDP itself. Its proper use differs: Choose UDP when low overhead is preferred and the application does not require TCP-style retransmission or ordering. This case needs a faulty physical component in the Ethernet path. The error disappears when the physical medium is replaced, confirming a physical-layer cause. It therefore fails here.
Question 17
An application must deliver a byte stream reliably and in order, retransmitting lost data when necessary. Which transport protocol fits? Choose ONE.
- Layer 3 routing problem
- DNS application behavior
- TCP
- UDP
Correct Answer: C
Correct Answer
Answer C is correct because TCP trades additional connection and recovery overhead for reliable, ordered transport with acknowledgments and retransmissions. TCP provides the connection state, acknowledgments, sequencing, and recovery the application requires. Required outcome: reliable ordered transport with retransmission. This option fits.
Incorrect Answers
Answer D is incorrect because It is appropriate for best-effort datagrams where timeliness or simplicity outweighs built-in reliable delivery. UDP avoids connection setup and retransmission mechanisms, reducing overhead at the cost of guaranteed delivery and ordering. The case instead needs reliable ordered transport with retransmission. TCP provides the connection state, acknowledgments, sequencing, and recovery the application requires. The roles differ.
Answer A is incorrect because An IP routing issue concerns next-hop and prefix selection; it does not inherently create CRC errors, collisions, or loss of physical carrier. Its proper use differs: Use this diagnosis when packets lack a valid Layer 3 path despite otherwise normal physical connectivity. This case needs reliable ordered transport with retransmission. TCP provides the connection state, acknowledgments, sequencing, and recovery the application requires. It therefore fails here.
Answer B is incorrect because DNS normally uses UDP for ordinary queries and responses, while TCP is used for particular cases such as zone transfers or other transport needs. It shows that the application operation determines whether TCP or UDP is appropriate. Here, the task is reliable ordered transport with retransmission. TCP provides the connection state, acknowledgments, sequencing, and recovery the application requires. That option misses the required function.
Question 18
A real-time telemetry sender prioritizes low overhead and can tolerate occasional datagram loss without retransmission. Which transport protocol fits? Choose ONE.
- DNS application behavior
- TCP
- UDP
- Layer 3 routing problem
Correct Answer: C
Correct Answer
Answer C is correct because UDP avoids connection setup and built-in recovery, matching the latency-focused requirement. UDP is connectionless and provides lightweight datagram transport without built-in acknowledgments, retransmission, or ordered-delivery guarantees. The required outcome is connectionless low-overhead datagram delivery. The role matches.
Incorrect Answers
Answer B is incorrect because TCP is connection-oriented and uses sequencing, acknowledgments, retransmission, and flow control to provide reliable ordered byte-stream delivery. Its proper use differs: It fits applications that require reliable ordered delivery and can accept the extra transport overhead. This case needs connectionless low-overhead datagram delivery. UDP avoids connection setup and built-in recovery, matching the latency-focused requirement. It therefore fails here.
Answer D is incorrect because A Layer 3 routing problem affects IP path selection or reachability between networks rather than the electrical or optical integrity of the Ethernet link. Investigate routing when Layer 1/2 counters are clean but IP forwarding or route information is wrong. Here, the task is connectionless low-overhead datagram delivery. UDP avoids connection setup and built-in recovery, matching the latency-focused requirement. That option misses the required function.
Answer A is incorrect because Choose DNS behavior when the question is about which transport a name-service operation normally uses. Domain Name System traffic commonly uses UDP for simple lookups, with TCP available when the operation requires a connection-oriented exchange. The case instead needs connectionless low-overhead datagram delivery. UDP avoids connection setup and built-in recovery, matching the latency-focused requirement. The roles differ.
Question 19
A file-transfer application cannot accept missing segments and relies on transport-layer acknowledgments and retransmissions. Which protocol should it use? Choose ONE.
- Layer 3 routing problem
- TCP
- UDP
- Shared Ethernet media
Correct Answer: B
Correct Answer
Answer B is correct because Transmission Control Protocol establishes a connection and tracks sequence/acknowledgment state so lost data can be retransmitted and delivered in order. The task requires transport-level reliability and loss recovery. TCP supplies reliable ordered delivery and retransmission behavior. It is the appropriate choice.
Incorrect Answers
Answer C is incorrect because User Datagram Protocol sends independent datagrams with minimal transport state; reliability and ordering are not supplied by UDP itself. Choose UDP when low overhead is preferred and the application does not require TCP-style retransmission or ordering. Here, the task is transport-level reliability and loss recovery. TCP supplies reliable ordered delivery and retransmission behavior. That option misses the required function.
Answer D is incorrect because Choose shared media when multiple stations contend within one collision domain. On a shared Ethernet segment, attached devices contend for a common medium instead of receiving isolated full-duplex switch links. The case instead needs transport-level reliability and loss recovery. TCP supplies reliable ordered delivery and retransmission behavior. The roles differ.
Answer A is incorrect because Routing faults occur above the physical link and involve missing, incorrect, or unusable IP forwarding information. Its proper use differs: Choose Layer 3 troubleshooting when the interface is healthy yet destination prefixes are unreachable due to path information. This case needs transport-level reliability and loss recovery. TCP supplies reliable ordered delivery and retransmission behavior. It therefore fails here.
Question 20
A voice media stream prefers timely delivery over retransmitting late packets that would no longer be useful. Which transport protocol is typically the better fit? Choose ONE.
- TCP
- Damaged cable, optic, port, or NIC
- Layer 3 routing problem
- UDP
Correct Answer: D
Correct Answer
Answer D is correct because UDP avoids connection setup and retransmission mechanisms, reducing overhead at the cost of guaranteed delivery and ordering. UDP’s minimal transport behavior suits real-time media that handles loss without waiting for retransmissions. Required outcome: low-latency delivery where late retransmissions are undesirable. This option fits.
Incorrect Answers
Answer A is incorrect because It is appropriate when the application expects a reliable byte stream rather than best-effort datagrams. TCP trades additional connection and recovery overhead for reliable, ordered transport with acknowledgments and retransmissions. The case instead needs low-latency delivery where late retransmissions are undesirable. UDP’s minimal transport behavior suits real-time media that handles loss without waiting for retransmissions. The roles differ.
Answer C is incorrect because Layer 3 path problems can prevent remote-network reachability even while interface state and Ethernet error counters remain normal. Its proper use differs: It fits IP reachability failures driven by routes, not symptoms that directly identify cabling or Ethernet negotiation. This case needs low-latency delivery where late retransmissions are undesirable. UDP’s minimal transport behavior suits real-time media that handles loss without waiting for retransmissions. It therefore fails here.
Answer B is incorrect because A faulty cable, optic, connector, switch port, or NIC can introduce bit errors or loss of signal, producing frame-check errors and unstable links. It fits faults tied to media, optics, connectors, ports, or NICs rather than route or application logic. Here, the task is low-latency delivery where late retransmissions are undesirable. That mismatch rules it out.
