CCNA Network Infrastructure and Connectivity Practice Test 16 — 15 Questions

Question 1

A network engineer is troubleshooting a link between two Cisco switches that are connected via a 1000BASE-LX SFP transceiver. Hosts on VLAN 10 on Switch A cannot ping the default gateway on Switch B. The interface on Switch A is up, but the engineer notices CRC errors incrementing. What should the engineer do to resolve this issue?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Use a mode-conditioning patch cable between the SFP and the fiber patch panel. The 1000BASE-LX SFP transceiver operates at 1310 nm over single-mode fiber (SMF). When connected to multimode fiber (MMF), the larger core diameter causes excessive modal dispersion, leading to CRC errors. A mode-conditioning patch cable (mode-conditioning patch cord) launches the laser off-center into the MMF core, reducing differential mode delay and restoring proper signal integrity. This is a known Cisco best practice for LX transceivers on MMF links.

Answer

Replace the SFP with a 1000BASE-SX transceiver

Answer

Configure the same VLAN on both switch interfaces

Answer

Replace the fiber cable with a single-mode fiber cable

Question 2

Which TWO statements about SFP transceivers and fiber optic cabling are correct?

Accepted Answer

1000BASE-SX SFP transceivers are designed for multimode fiber and typically support distances up to 550 meters.. 1000BASE-SX SFP transceivers are designed for multimode fiber (MMF) and use short-wavelength lasers (850 nm). Over 50/125 µm MMF, they support up to 550 meters. Option D is correct because 1000BASE-LX SFP transceivers are designed for single-mode fiber (SMF) and support distances up to 5 km according to the IEEE 802.3 standard (not 10 km, which is typically a vendor-specific LH extension). Option A is false because SFPs are hot-swappable pluggable modules, not permanently installed. Option C is false because multimode fiber typically uses LED or VCSEL transmitters for short distances, not lasers for long-haul. Option E is false because single-mode fiber has a smaller core diameter (8-10 µm) than multimode fiber (50-62.5 µm), which reduces modal dispersion and allows longer distances.

Answer

SFP transceivers are permanently installed on the switch motherboard and cannot be replaced.

Answer

Multimode fiber typically uses laser-based transmitters for long-distance transmission.

Answer

Single-mode fiber has a larger core diameter than multimode fiber, allowing longer distances.

Question 3

Which TWO statements accurately describe characteristics of copper and fiber optic cabling used in modern Ethernet networks?

Accepted Answer

Fiber optic cables are immune to electromagnetic interference (EMI).. Fiber optic cables transmit data as light pulses through glass or plastic cores, which are completely unaffected by electromagnetic interference (EMI), unlike copper cables that rely on electrical signals and are susceptible to EMI. Option D is correct because single-mode fiber uses a narrow core (typically 9 microns) and laser transmitters to support long-distance transmission (up to tens of kilometers) with low signal loss. Option A is wrong because copper UTP cables are limited to 100 meters without a repeater, not 500 meters. Option C is wrong because multi-mode fiber typically uses LED or VCSEL transmitters for short-range communication, while laser-based transmitters are used with single-mode fiber. Option E is wrong because fiber optic cabling is generally more expensive per meter than copper cabling, though installation and equipment costs may differ.

Answer

Copper UTP cables can reliably transmit data up to 500 meters without a repeater.

Answer

Multi-mode fiber typically uses laser-based transmitters for short-range communication.

Answer

Fiber optic cabling is generally less expensive per meter than copper cabling.

Question 4

Drag and drop the cable types and transceivers on the left to their corresponding distance limits or interface diagnostics on the right.

Accepted Answer

Cat5e: 100 meters. Each cable type or transceiver has a specified maximum distance based on IEEE standards and fiber-optic characteristics. Cat5e UTP supporting 1000BASE-T is limited to 100 meters due to signal attenuation and the 1000BASE-T standard. Multimode fiber OM3 with 1000BASE-SX (short wavelength) reaches up to 550 meters because of modal dispersion and the SX transceiver's power budget. Singlemode fiber with 1000BASE-LX (long wavelength) can transmit up to 5 kilometers due to lower attenuation and reduced dispersion in single-mode fiber. The SFP-10G-SR (short-reach 10 Gigabit) transceiver over OM3 multimode fiber has a maximum distance of 300 meters per the 10GBASE-SR standard. The 'show interfaces' command displays critical interface diagnostics such as input/output errors, speed, duplex settings, and CRC errors, which are essential for troubleshooting link issues.

Question 5

A network technician is troubleshooting a connectivity issue between two hosts on different subnets. During the analysis, the technician captures packets and observes that the data link layer frames are being stripped and rebuilt at each router hop. Which layer of the OSI model is responsible for encapsulating the original data into segments before transmission from the source host?

Accepted Answer

Transport layer. The Transport layer (Layer 4) is responsible for encapsulating the original data into segments. Protocols such as TCP (RFC 793) or UDP (RFC 768) add a header containing source and destination port numbers, sequence numbers, and other control information to form a segment. This segmentation occurs at the source host before the data is passed down to the Network layer for routing.

Answer

Network layer

Answer

Data Link layer

Answer

Application layer

Question 6

A network technician is troubleshooting a connectivity issue between two hosts. Host A sends a web request to Host B. The technician captures packets on the link between the two hosts and sees the data as '01010101...'. At which layer of the OSI model is this data being transmitted, and what is the correct PDU name for this layer?

Accepted Answer

Physical layer; bits. The data shown as '01010101...' represents raw binary bits being transmitted over the physical medium. At the Physical layer (Layer 1), data is encoded as electrical signals, light pulses, or radio waves, and the PDU is called bits. This matches the description of the captured data.

Answer

Data Link layer; frames

Answer

Network layer; packets

Answer

Transport layer; segments

Question 7

Which TWO statements correctly describe the encapsulation and de-encapsulation process at the transport layer of the OSI model?

Accepted Answer

During encapsulation, the transport layer adds a header containing source and destination port numbers.. During encapsulation at the transport layer, the TCP or UDP header is added, which includes source and destination port numbers. These port numbers identify the specific application-layer processes on the sending and receiving hosts, enabling proper demultiplexing of data. Option D is correct because during de-encapsulation, the transport layer removes its own header (e.g., TCP or UDP header) and passes the remaining payload up to the session layer (or directly to the application layer in a simplified model).

Answer

During encapsulation, the transport layer adds a header to form a packet.

Answer

During de-encapsulation, the transport layer removes the IP header to extract the segment.

Answer

During encapsulation, the transport layer adds a trailer for error detection.

Question 8

Which TWO statements accurately describe the encapsulation process in the TCP/IP model as data moves from the application layer to the network access layer?

Accepted Answer

At the transport layer, the PDU is called a segment (for TCP) and includes source and destination port numbers.. At the transport layer, TCP creates segments that include source and destination port numbers (B correct). At the network layer, the PDU is a packet containing source and destination IP addresses (D correct). Option A is wrong because the application layer generates data, not segments, and transport headers are added later. Option C mislabels the network layer PDU; it is a packet, not a frame, and MAC addresses belong to frames. Option E is wrong because the data link layer PDU is a frame, not a packet, and it uses MAC addresses, not IP addresses.

Answer

At the application layer, the PDU is called a segment and includes a transport layer header.

Answer

At the network layer, the PDU is called a frame and includes source and destination MAC addresses.

Answer

At the data link layer, the PDU is called a packet and includes source and destination IP addresses.

Question 9

A network administrator notices that a workstation connected to a Cisco switch port cannot communicate with other devices on the same VLAN. The switch port is up/up, but the workstation reports slow performance and intermittent connectivity. What is the most likely cause of this issue?

Accepted Answer

A duplex mismatch between the switch port and the workstation.. A duplex mismatch occurs when one end of the link is set to full-duplex and the other to half-duplex. The half-duplex end detects collisions and the full-duplex end does not, causing late collisions, CRC errors, and retransmissions. This results in slow performance and intermittent connectivity even though the port is operationally up.

Answer

Replace the faulty Ethernet cable between the switch and the workstation.

Answer

Assign the switch port to the correct VLAN.

Answer

Disable spanning-tree on the port to prevent frequent topology changes.

Question 10

A network technician is troubleshooting connectivity between two directly connected Cisco switches. Hosts on VLAN 10 connected to SwitchA cannot ping the default gateway on SwitchB. The interface on SwitchB shows up/up, but the interface on SwitchA shows up/down. The technician examines the interface configuration and status on SwitchA. What is the most likely cause of this issue?

Accepted Answer

Configure both interfaces with the same duplex and speed settings, either both auto or both manually set to full-duplex and 1000 Mbps.. The interface on SwitchA shows up/down, meaning Layer 1 is active but the line protocol is down. This is commonly caused by a speed mismatch between the two ends. A duplex mismatch, in contrast, typically results in both interfaces showing up/up with CRC errors. Therefore, the most likely cause is that the speed settings differ—for example, one interface is set to auto-negotiate while the other is hard-coded to a specific speed. Configuring both interfaces with identical speed and duplex settings, either both auto or both manually configured, resolves the issue.

Answer

Replace the Ethernet cable because it is faulty.

Answer

Issue the 'shutdown' and 'no shutdown' commands on the interface to recover from err-disabled state.

Answer

Check the VLAN configuration on SwitchA because the interface is administratively down.

Question 11

A network administrator is troubleshooting connectivity issues between two switches. Hosts connected to Switch A cannot ping hosts on Switch B. The link between the switches shows as up/up on both ends, but interface error counters (CRC, runts) are increasing rapidly. What should the administrator do to resolve the issue?

Accepted Answer

Change the duplex setting on SwitchA's interface to auto-negotiation.. The increasing CRC and runts errors on an up/up link indicate a duplex mismatch, where one side is using full duplex and the other half duplex. Assuming SwitchB is using auto-negotiation (the default on Cisco switches), changing SwitchA's interface to auto-negotiation will allow both ends to negotiate the correct duplex setting, resolving the mismatch and stopping the errors.

Answer

Replace the faulty cable between the two switches.

Answer

Replace the SFP module on SwitchA's GigabitEthernet0/1 port.

Answer

Enable the interface with 'no shutdown' command.

Question 12

A network administrator is troubleshooting connectivity between two directly connected Cisco switches. Hosts on VLAN 10 connected to Switch A cannot ping the default gateway on Switch B. The interface on Switch A shows 'up/up' but there are excessive CRC errors and runts. The administrator checks the interface configuration on both switches. What is the most likely cause of the issue?

Accepted Answer

Mismatched duplex and speed settings between the interfaces.. The presence of excessive CRC errors and runts on an interface that is 'up/up' strongly indicates a Layer 1 or Layer 2 duplex mismatch. When one switch is set to full-duplex and the other to half-duplex (or auto-negotiation fails), the half-duplex side will detect collisions and retransmit, while the full-duplex side will not, leading to frame corruption (CRC errors) and truncated frames (runts). Configuring both interfaces with the same duplex and speed settings (e.g., full-duplex and 1000 Mbps) resolves this mismatch, restoring proper connectivity for VLAN 10 traffic to the default gateway.

Answer

Replace the faulty Ethernet cable.

Answer

Disable spanning tree on both interfaces to prevent loop prevention from blocking traffic.

Answer

Assign the interfaces to the same VLAN to ensure Layer 2 connectivity.

Question 13

A network technician is troubleshooting a connectivity issue between two directly connected switches, SW1 and SW2. Hosts on VLAN 10 connected to SW1 can ping each other but cannot ping the default gateway or any host on VLAN 10 connected to SW2. The interface on SW1 is up/up, but the interface on SW2 is up/down. What is the most likely cause of the problem?

Accepted Answer

Ensure both switches are configured for the same duplex setting, preferably by enabling autonegotiation on both interfaces.. The interface on SW2 is up/down, which typically indicates a Layer 1 issue such as a duplex mismatch. Duplex mismatch occurs when one switch is manually set to full duplex and the other to half duplex or auto-negotiation fails, causing the side expecting full duplex to report up/down due to excessive errors. Option A is incorrect because MTU mismatch would cause connectivity issues but not an up/down interface state. Option C is incorrect because a faulty cable would likely cause both interfaces to be down/down, not up/down. Option D is incorrect because late collisions are a symptom of duplex mismatch, not a separate cause; increasing collision window size is not a standard troubleshooting step. The correct solution is to ensure both switches use the same duplex setting, preferably via autonegotiation (IEEE 802.3u).

Answer

Configure the interface on SW2 to use a different MTU value.

Answer

Replace the Ethernet cable connecting SW1 and SW2.

Answer

Check for late collisions on the interface and increase the collision window size.

Question 14

Which TWO interface issues can be identified by analyzing the output of the 'show interfaces' command?

Accepted Answer

Duplex mismatch. The 'show interfaces' command displays interface statistics and operational status, including duplex and speed settings. A duplex mismatch occurs when one end of a link is set to full-duplex and the other to half-duplex, leading to collisions and CRC errors visible in the output. Speed mismatch is also detectable because the interface will show the negotiated speed or errors like 'input errors' if the speeds do not match.

Answer

Routing protocol misconfiguration

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VLAN mismatch

Answer

STP topology change

Question 15

Which TWO symptoms are most likely to appear in the output of 'show interfaces' when a duplex mismatch exists between a switch port and a connected host?

Accepted Answer

Excessive collisions and CRC errors on the interface. A duplex mismatch causes collisions on the half-duplex side, resulting in excessive collisions and CRC errors (option A). On the full-duplex side, the host receives truncated frames from the half-duplex side's collisions, leading to runts and frame errors (option B). Option C is incorrect because 'Auto-negotiation failed' would appear only if negotiation itself failed, not from a mismatch after successful negotiation. Option D is wrong because a duplex mismatch typically reduces throughput and causes errors, not a high input rate. Option E is incorrect because the line protocol remains up; duplex mismatch does not bring the line protocol down.

Answer

Auto-negotiation failed message in the interface output

Answer

High input rate on the interface

Answer

Line protocol is down