CCNA Network Infrastructure and Connectivity Practice Test 14 — 15 Questions

Question 1

A network engineer notices that users on VLAN 100 are experiencing intermittent connectivity to the server farm. The switch connecting these users shows no errors on the uplink interface, but the server farm switch reports a high number of input errors on its connected interface. The engineer runs 'show controllers' on the server farm switch. What is the most likely cause of the issue?

Accepted Answer

The SFP module is faulty or incompatible with the cable type.. The 'show controllers' command on the server farm switch reveals physical-layer issues such as framing errors, CRC errors, or alignment errors, which are often caused by faulty or incompatible SFP modules. Since the uplink interface on the user switch shows no errors, the problem is isolated to the server farm switch's interface, and a faulty SFP can introduce signal degradation or electrical issues without necessarily causing complete link failure. Option B is correct because SFP incompatibility or defects commonly produce input errors at the physical layer, even when the link appears up.

Answer

The interface is configured with the wrong duplex setting.

Answer

The cable is too long, causing attenuation.

Answer

Auto-negotiation is disabled, causing a speed mismatch.

Question 2

Which TWO of the following are valid interpretations of errors seen in the output of the 'show interface' command?

Accepted Answer

CRC errors indicate that frames were received with an invalid checksum, often due to cabling issues.. CRC errors (option A) indicate frames with an invalid checksum, often due to cabling issues, which is correct. Option D is also correct: 'Input errors' is a cumulative counter that includes runts, giants, CRC errors, and frame errors. Option B is wrong because runts are frames smaller than 64 bytes, not larger. Option C is wrong because giants are frames larger than the maximum allowed size (typically 1518 bytes), not smaller than 64 bytes. Option E is wrong because 'flaps' refer to an interface going up and down repeatedly, not necessarily physically disconnected; it could be due to duplex mismatch or other reasons.

Answer

Runts are frames that are larger than the maximum allowed size.

Answer

Giants are frames that are smaller than 64 bytes.

Answer

Flaps indicate that the interface is physically disconnected.

Question 3

Which TWO interface errors are most likely caused by a mismatch in duplex settings between two connected switches?

Accepted Answer

Runts. A duplex mismatch occurs when one switch operates at full duplex while the other operates at half duplex. On the half-duplex side, frames arriving while the interface is transmitting are considered collisions, causing the frame to be truncated into fragments (runts). On the full-duplex side, the switch does not detect collisions but may receive incomplete frames, which are counted as runts if they are less than 64 bytes. CRC errors also spike because the truncated or corrupted frames fail the Frame Check Sequence (FCS) validation.

Answer

Giants

Answer

Input errors

Answer

Output errors

Answer

Flaps

Question 4

Which TWO statements correctly describe the causes or implications of CRC errors, runts, giants, or output errors as seen in the output of 'show interface' or 'show interface status'?

Accepted Answer

A high number of runts on an interface typically indicates excessive collisions or a faulty NIC.. Option B is correct because runts—frames smaller than 64 bytes—often result from collisions truncating frames on half-duplex links or a faulty NIC. Option D is correct because duplex mismatch can cause late collisions, which appear as output errors in 'show interface'; a device on one side full-duplex and the other half-duplex leads to collisions and framing errors. Option A is wrong because CRC errors can stem from faulty cabling, interference, or a mismatched NIC, not exclusively a bad switch port. Option C is wrong because giants (frames over maximum MTU) may be forwarded if the interface is configured with jumbo frames or the switch is set to accept oversize frames. Option E is wrong because 'show controllers' displays frame-size errors like runts and giants, including details beyond CRC errors.

Answer

CRC errors are always caused by a faulty switch port and require port replacement.

Answer

Giants are frames that exceed the maximum transmission unit (MTU) and are always discarded by the switch.

Answer

The 'show controllers' command provides a detailed view of CRC errors but does not show runts or giants.

Question 5

Drag and drop the interface error types on the left to the corresponding descriptions on the right.

Accepted Answer

CRC errors. CRC errors occur when a frame fails the cyclic redundancy check (checksum mismatch) due to noise or faulty cabling. Runts are frames smaller than 64 bytes, typically caused by collisions. Giants are frames exceeding the maximum frame size, often from a faulty NIC. Flaps are repeated link up/down transitions, usually from loose cables or hardware issues. Input errors is a catch-all counter for all receive-side errors including CRC, runts, giants, and framing errors. Each match is correct because the description aligns with the standard definition; for example, CRC errors specifically involve checksum failure, not frame size or link flapping.

Answer

Runts

Answer

Giants

Answer

Late collisions

Question 6

Drag and drop the cable issue symptoms on the left to the correct descriptions on the right.

Accepted Answer

Crosstalk: Interference caused by electromagnetic coupling between adjacent cables.. Each interface counter describes a specific type of packet failure. CRC errors occur when the frame check sequence fails, pointing to physical issues like bad cabling or interference. Input errors is a broader counter that sums all receive-side anomalies, including CRC errors, runts, and giants. Output errors represents transmit-side failures, often from collisions, buffer overruns, or late collisions. Runts are frames shorter than the 64-byte minimum, commonly caused by collisions or defective hardware, while giants exceed the maximum frame size and usually indicate a duplex mismatch or faulty NIC. Understanding these categories helps pinpoint whether the problem is receive-side, transmit-side, or due to physical layer faults.

Answer

Attenuation: Loss of signal strength over the length of the cable.

Answer

Impedance mismatch: Reflection of signals due to inconsistent cable impedance.

Answer

Split pair: Incorrect wire pairing causing excessive crosstalk.

Question 7

A network engineer is troubleshooting an issue where a Windows 10 workstation (Host-A) cannot reach the internet, but can ping the local default gateway. The engineer runs 'ipconfig /all' on Host-A and reviews the output. What is the most likely cause of the problem?

Accepted Answer

The DNS server is configured as a public DNS server that may be unreachable due to network policy or firewall.. Host-A can ping the default gateway, which confirms that Layer 3 connectivity to the local network is working and that the subnet mask and default gateway are correctly configured. The inability to reach the internet despite this connectivity points to a name resolution failure, likely caused by an incorrect or unreachable DNS server. A public DNS server (e.g., 8.8.8.8) may be blocked by corporate firewall policy, preventing Host-A from resolving internet domain names.

Answer

The subnet mask is incorrect.

Answer

The default gateway is missing or incorrect.

Answer

The host has obtained an APIPA address (169.254.x.x).

Question 8

A network administrator is troubleshooting an IPv6 connectivity issue on a newly deployed router. The router's G0/0/0 interface is configured with an IPv6 address using EUI-64, but hosts on that subnet cannot reach the router's link-local address. The administrator runs 'show ipv6 interface g0/0/0' and sees that the interface is up/up but the IPv6 address is not in the expected format. What is the most likely cause of the problem?

Accepted Answer

The IPv6 address was not configured correctly; the 'ipv6 address' command was likely omitted or misconfigured.. The router's G0/0/0 interface is up/up, but the IPv6 address is not in the expected EUI-64 format. This indicates that the 'ipv6 address' command was likely omitted entirely, because if it were simply misconfigured (e.g., without the `eui-64` keyword), the router would still automatically generate a link-local address, and hosts would be able to reach it. Since hosts cannot reach the link-local address, IPv6 is not enabled on the interface at all. The correct configuration requires the `ipv6 address` command with the appropriate prefix and the `eui-64` keyword.

Answer

The interface is administratively down.

Answer

The MAC address of the interface is invalid, preventing EUI-64 from generating a proper address.

Answer

The router is not sending Router Advertisements, so hosts cannot autoconfigure.

Question 9

A network engineer is troubleshooting a workstation that cannot access the internet. The workstation is connected to a switch port configured for access VLAN 10. The switch is a Cisco 2960-X running IOS-XE. The engineer runs 'ipconfig /all' on the workstation and sees an IPv4 address of 169.254.123.45 with a subnet mask of 255.255.0.0. The engineer then connects to the switch and issues 'show interfaces vlan 10'. What is the most likely cause of the issue?

Accepted Answer

The switch's VLAN 10 SVI is administratively down.. The workstation has an APIPA address (169.254.x.x), which indicates it failed to obtain a DHCP lease. Since the switch's VLAN 10 SVI is administratively down, the workstation cannot reach the DHCP server (which may be on a different subnet or the SVI itself), causing the DHCP request to time out and the workstation to self-assign an APIPA address. Option B is correct because an administratively down SVI breaks Layer 3 connectivity for that VLAN, preventing DHCP traffic from being routed.

Answer

The workstation is not configured to use DHCP.

Answer

The switch port connecting the workstation is in a different VLAN.

Answer

The DHCP server is not configured on the network.

Question 10

Which TWO statements correctly describe IPv4 and IPv6 host configuration?

Accepted Answer

APIPA assigns an IPv4 address in the 169.254.0.0/16 range when a DHCP server is unavailable.. Option A is correct because APIPA (Automatic Private IP Addressing) automatically assigns an IPv4 address from the 169.254.0.0/16 range when a DHCP server is unavailable, enabling local subnet communication without manual configuration. Option E is correct because the ipconfig command on Windows displays both IPv4 and IPv6 addresses, subnet masks, default gateways, and DNS servers. Option B is incorrect because while IPv6 link-local addresses start with FE80::/10, they are not always assigned using EUI-64; they can also be randomly generated (privacy extensions) or manually configured. Option C is incorrect because EUI-64 generates the interface identifier (host portion) of an IPv6 address from the MAC address, not the network prefix — the prefix is provided via SLAAC, DHCPv6, or manual configuration. Option D is incorrect because a host can have multiple default gateways configured for redundancy, though only one is active at a time per routing table; additionally, IPv4 and IPv6 default gateways are independent and can coexist.

Answer

IPv6 link-local addresses are always assigned using EUI-64 and start with FE80::/10.

Answer

EUI-64 is used to generate the network prefix of an IPv6 address from the interface's MAC address.

Answer

A host can have only one default gateway configured at a time for both IPv4 and IPv6.

Question 11

Which TWO statements are true about IPv6 link-local addresses?

Accepted Answer

They are automatically configured on all IPv6-enabled interfaces.. Option A is correct because IPv6 link-local addresses (fe80::/10) are automatically generated on every IPv6-enabled interface using Stateless Address Autoconfiguration (SLAAC) as defined in RFC 4862. This ensures that each interface has a unique local address for neighbor discovery and other link-local operations without requiring manual configuration or a DHCPv6 server.

Answer

They are routable across the entire IPv6 internet.

Answer

They always use the EUI-64 format for the interface ID.

Answer

They are used as the default gateway address for IPv6 hosts.

Question 12

A network administrator is troubleshooting a Windows 10 workstation that cannot access the internet. The workstation receives an IPv4 address starting with 169.254.x.x. The network uses DHCP, and other workstations on the same subnet are working correctly. What is the most likely cause of this issue?

Accepted Answer

The workstation's network cable is unplugged or faulty, preventing DHCP communication.. The 169.254.x.x address is an Automatic Private IP Addressing (APIPA) address assigned by Windows when DHCP fails. Since other workstations on the same subnet work correctly, the DHCP server and network are functional, isolating the issue to the specific workstation. A faulty or unplugged network cable would prevent the workstation from sending DHCP Discover messages, causing it to fall back to APIPA.

Answer

The workstation's DNS server settings are incorrect.

Answer

The DHCP server has exhausted its address pool.

Answer

The workstation's default gateway is misconfigured.

Question 13

A network administrator is configuring a new Windows 10 workstation on a network that uses DHCP. The workstation receives an IPv4 address of 169.254.10.20 with a subnet mask of 255.255.0.0 and no default gateway. The user cannot access the internet or other subnets. What is the most likely cause of this issue?

Accepted Answer

The DHCP server is unreachable or not responding.. The IP address 169.254.10.20 with a /16 subnet mask is an Automatic Private IP Addressing (APIPA) address, which Windows assigns when a DHCP discovery broadcast (DHCPDISCOVER) fails to receive a response from a DHCP server. Without a valid DHCP lease, the workstation has no default gateway, so it cannot communicate outside its local subnet, explaining the lack of internet or inter-subnet access. The most likely cause is that the DHCP server is unreachable or not responding, forcing the client to self-assign an APIPA address.

Answer

The workstation has a duplicate IP address conflict.

Answer

The workstation's DNS server configuration is incorrect.

Answer

The workstation's subnet mask is misconfigured.

Question 14

A network engineer is troubleshooting a wireless performance issue in a dense office environment. Clients on the 5 GHz band are experiencing low throughput even though they are close to the AP. The AP is a Cisco 9130AXI running IOS-XE 17.9. What is the most likely cause of the poor performance?

Accepted Answer

The AP is operating in 802.11ac mode instead of 802.11ax, and the 80 MHz channel bonding is causing high interference in the dense environment.. Option B is correct because in a dense office environment, using 80 MHz channel bonding with 802.11ac (Wave 2) increases the likelihood of co-channel interference and overlapping basic service sets (OBSS), which degrades throughput despite strong signal. The Cisco 9130AXI supports 802.11ax (Wi-Fi 6), which includes OFDMA and better spatial reuse, but if the AP is configured for 802.11ac mode, it loses these efficiency gains and suffers from the wide channel's interference penalty.

Answer

The AP is using an incorrect channel width of 80 MHz, which is not supported by 802.11ac.

Answer

The AP has DFS non-compliance, which prevents it from using channel 36 and causes the radio to operate at reduced power.

Answer

The AP is using WPA2-PSK instead of WPA3, which causes lower throughput due to weaker encryption.

Question 15

Which TWO statements correctly describe differences between 802.11ac (Wi-Fi 5) and 802.11ax (Wi-Fi 6)?

Accepted Answer

802.11ax supports 1024-QAM modulation, whereas 802.11ac supports up to 256-QAM.. Options B and D are correct. 802.11ax (Wi-Fi 6) introduces 1024-QAM for higher data rates (B), while 802.11ac maxes at 256-QAM. Additionally, 802.11ax supports both 2.4 GHz and 5 GHz bands, whereas 802.11ac is limited to 5 GHz only (D). Option A is incorrect because it reverses the roles: 802.11ac uses OFDM, and 802.11ax uses OFDMA. Option C is incorrect because 802.11ax also operates in 2.4 GHz. Option E is incorrect because Target Wake Time (TWT) is introduced in 802.11ax, not 802.11ac.

Answer

802.11ac uses OFDMA, while 802.11ax uses only OFDM.

Answer

Both 802.11ac and 802.11ax operate exclusively in the 5 GHz band.

Answer

802.11ac introduces target wake time (TWT) for improved power saving, but 802.11ax does not support it.

CCNA Network Infrastructure and Connectivity Practice Test 14 — 15 Questions

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CCNA Network Infrastructure and Connectivity Practice Test 14 — 15 Questions

Exhibit