CCNA Network Infrastructure and Connectivity Practice Test 19 — 15 Questions

Question 1

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 2

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.. 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 3

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 4

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 5

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.. 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 6

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

Accepted Answer

They are automatically configured on all IPv6-enabled interfaces.. 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 7

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 8

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 9

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.. 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 10

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.

Question 11

Drag and drop the wireless terms on the left to the correct descriptions on the right.

Options:
A: SSID: The network name broadcast by an access point to identify the wireless network.
B: BSSID: The MAC address of the access point's radio interface, used to uniquely identify a BSS.
C: RSSI: A measurement of the power level of the received radio signal, indicating signal strength.
D: DFS: A mechanism that allows wireless devices to avoid interference with radar systems by dynamically selecting channels.

Accepted Answer

SSID: The network name broadcast by an access point to identify the wireless network.. SSID (Service Set Identifier) is the network name broadcast by an access point to identify the wireless network, allowing clients to distinguish between different networks. BSSID (Basic Service Set Identifier) is the MAC address of the AP's radio interface, uniquely identifying a specific BSS. RSSI (Received Signal Strength Indicator) measures the power level of the received radio signal, indicating signal strength. DFS (Dynamic Frequency Selection) is a mechanism that allows wireless devices to avoid interference with radar systems by dynamically selecting channels. Each term correctly matches the provided description.

Question 12

A network technician is troubleshooting a connectivity issue for a PC connected to switch port Gi1/0/12. The PC can ping its default gateway (192.168.10.1) but cannot ping a server at 192.168.20.10. The switch is configured with VLAN 10 for the access port and is connected to a router-on-a-stick. The technician runs 'show vlan brief' and 'show interfaces trunk' on the switch. What is the most likely cause of the problem?

Accepted Answer

The router is missing a subinterface for VLAN 20.. The PC can ping its default gateway (192.168.10.1) but not the server at 192.168.20.10, indicating Layer 3 routing is failing between VLANs. Since the switch is configured with VLAN 10 for the access port and uses a router-on-a-stick, the router must have a subinterface for VLAN 20 to route traffic to the server's subnet. The absence of a subinterface for VLAN 20 prevents the router from forwarding packets from VLAN 10 to VLAN 20, making option B correct.

Answer

The trunk port Gi1/0/24 is not in trunking mode.

Answer

The switch port Gi1/0/12 is not assigned to VLAN 10.

Answer

The PC has a duplicate IP address with the server.

Question 13

Which TWO commands would a network administrator use to verify that a client has received a valid IP address from a DHCP server and can resolve domain names to IP addresses?

Accepted Answer

ipconfig /all. (ipconfig /all) is correct because it displays the full TCP/IP configuration for all network adapters, including whether DHCP is enabled, the assigned IP address, subnet mask, default gateway, and the DHCP server address. This allows the administrator to confirm that the client received a valid IP address from the DHCP server. Option D (nslookup www.courseiva.com) is correct because it queries the configured DNS server to resolve the domain name to an IP address, verifying that name resolution is working. Option B (ping 127.0.0.1) only tests the local TCP/IP stack and does not verify DHCP assignment or DNS resolution. Option C (tracert 8.8.8.8) uses an IP address directly and does not test domain-name resolution. Option E (arp -a) displays the ARP cache, which is unrelated to DHCP or DNS.

Answer

ping 127.0.0.1

Answer

tracert 8.8.8.8

Answer

arp -a

Question 14

Which TWO commands would a network engineer use to verify that a Windows client has received an IP address from a DHCP server and can resolve a domain name to an IP address?

Accepted Answer

ipconfig /all. `ipconfig /all` displays the full TCP/IP configuration for all adapters, including whether the IP address was obtained from a DHCP server (the DHCP Enabled and DHCP Server fields). Option D is correct because `nslookup www.courseiva.com` queries the configured DNS server to resolve the domain name to an IP address, confirming DNS resolution works.

Answer

ping 8.8.8.8

Answer

tracert www.courseiva.com

Answer

arp -a

Question 15

Which command or tool would a network engineer use to verify if a client has a duplicate IP address conflict on the local subnet?

Accepted Answer

arp -a. The two tools to verify a duplicate IP conflict are arp -a and ping. The arp -a command displays the ARP cache; if a duplicate IP exists, the ARP table may show multiple MAC addresses for the same IP or rapid changes. Ping can be used to send traffic to the local IP address; if a reply is received from a different MAC address than expected, it indicates a conflict. Together, these commands help network engineers confirm IP address duplication. Other commands like ipconfig /all, nslookup, and tracert do not directly reveal such conflicts.

Answer

ipconfig /all

Answer

nslookup

Answer

tracert