CCNA Network Infrastructure and Connectivity Practice Test 17 — 15 Questions

Question 1

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?

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

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

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Network layer; packets

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Transport layer; segments

Question 2

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.

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

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

Question 3

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 4

Drag and drop the PDU names on the left to the correct OSI model layers on the right.

Accepted Answer

Application: Message, Transport: Segment, Network: Packet, Data Link: Frame, Physical: Bit, Session: Data. In the OSI model, each layer processes a specific Protocol Data Unit (PDU). The Application layer (Layer 7) uses 'Message', the Transport layer (Layer 4) uses 'Segment', the Network layer (Layer 3) uses 'Packet', the Data Link layer (Layer 2) uses 'Frame', the Physical layer (Layer 1) uses 'Bit', and the Session layer (Layer 5) uses 'Data'. This pairing follows the correct OSI terminology as shown in Option A.

Answer

Application: Data, Transport: Segment, Network: Packet, Data Link: Frame, Physical: Bit, Session: Message

Answer

Application: Message, Transport: Packet, Network: Segment, Data Link: Frame, Physical: Bit, Session: Data

Answer

Application: Data, Transport: Segment, Network: Packet, Data Link: Frame, Physical: Bit, Session: Message

Question 5

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.

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Assign the switch port to the correct VLAN.

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

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?

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

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.

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

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

Question 7

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.

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

Answer

Enable the interface with 'no shutdown' command.

Question 8

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 9

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?

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

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.

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

Question 10

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

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STP topology change

Question 11

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

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High input rate on the interface

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Line protocol is down

Question 12

A user on VLAN 10 reports that they cannot ping the default gateway at 192.168.10.1 from their PC with IP 192.168.10.50/24. The switch interface connecting to the PC is up/up, and the PC shows a valid IP configuration. What is the most likely cause of this connectivity failure?

Accepted Answer

Configure an SVI for VLAN 10 with an IP address in the 192.168.10.0/24 subnet.. The PC and default gateway are on the same subnet (192.168.10.0/24), but the switch lacks a Layer 3 interface for VLAN 10. Without an SVI (Switch Virtual Interface) configured with an IP address in that subnet, the switch cannot route traffic to the gateway or respond to ARP requests from the PC, breaking connectivity even though the access port is up/up.

Answer

Change the switchport mode to trunk to allow VLAN 10 traffic.

Answer

Change the PC's IP address to a different subnet, such as 192.168.20.0/24.

Answer

Recreate VLAN 10 and reassign the port to it.

Question 13

A network engineer is troubleshooting connectivity issues for hosts in VLAN 10. Hosts in VLAN 10 are unable to ping the default gateway at 192.168.10.1. The engineer checks the switch configuration and notices that the SVI for VLAN 10 is configured with an IP address, but the interface is in a down/down state. What is the most likely cause of this issue?

Accepted Answer

VLAN 10 does not exist in the VLAN database.. An SVI (Switch Virtual Interface) will remain in a down/down state if the corresponding VLAN does not exist in the switch's VLAN database. Even if the SVI is configured with an IP address, the interface cannot come up because there is no Layer 2 VLAN to associate with it. This is a common cause of SVI down/down issues when the VLAN has not been created or has been deleted.

Answer

The interface is administratively shut down.

Answer

The IP address is not in the correct subnet for VLAN 10.

Answer

The switch does not have a default gateway configured.

Question 14

Which TWO statements correctly describe the configuration and verification of IPv4 and IPv6 parameters for host connectivity, including default gateway, DNS, and subnet masks?

Accepted Answer

The default gateway must be on the same subnet as the host's IP address.. A host's default gateway must be on the same subnet to be reachable at Layer 2; otherwise, a circular dependency occurs. Option D is correct because the 'ipconfig /all' command displays both IPv4 and IPv6 configuration details, including IP address, subnet mask, default gateway, and DNS servers. Option A is wrong because the subnet mask determines the network and host portions of an IP address, not the DNS server address. Option C is wrong because IPv6 hosts can obtain their IP address via SLAAC, DHCPv6, or static configuration; the phrase 'can only' makes it incorrect. Option E is wrong because the default gateway must be reachable (on the same subnet) and configured with an IP address that belongs to a router interface on that subnet, not just any IP address.

Answer

The subnet mask determines the DNS server address used by the host.

Answer

IPv6 hosts can only obtain their IP address via DHCPv6.

Answer

A host can reach any remote network if its default gateway is configured with any IP address.

Question 15

Which TWO statements correctly describe the configuration and verification of IPv4 and IPv6 parameters for host connectivity?

Accepted Answer

On a Windows host, the default gateway IPv4 address must be on the same subnet as the host's IPv4 address.. For a host to reach outside its subnet, the default gateway's IP must be in the same subnet; otherwise the host cannot ARP for the gateway's MAC and traffic will fail. Option D is correct because DNS server addresses can be set manually or assigned via DHCP. Option B is wrong because IPv6 gateways must be on the same local link, not any global unicast address on the internet. Option C is wrong because the subnet mask defines the network/subnet portion of an IPv4 address, not the host portion. Option E is wrong because DNS is used for name resolution; local IP communication on the same subnet works without DNS.

Answer

The IPv6 default gateway can be any global unicast address on the internet.

Answer

The subnet mask is used to define the host portion of an IPv4 address.

Answer

Configuring a DNS server is mandatory for a host to communicate with any other device on the same subnet.