CCNA Network Infrastructure and Connectivity Questions

192.168.14.207 is the broadcast address of the previous /28 subnet (192.168.14.192/28), not the subnet containing 192.168.14.222.

192.168.14.208 is the network address (subnet ID) of the /28 subnet containing .222, not the broadcast address.

192.168.14.224 is the network address of the next /28 subnet (192.168.14.224/28), not the broadcast of the current subnet.

Incorrect DNS settings prevent name resolution but do not affect IP address assignment. The workstation would still receive a valid IP from DHCP, not an APIPA address.

If the DHCP pool were exhausted, all workstations would fail to obtain addresses and use APIPA. The scenario states other workstations are working correctly, so pool exhaustion is not the cause.

A misconfigured default gateway would prevent internet access but the workstation would still receive a valid IP from DHCP. APIPA addresses are only assigned when DHCP fails entirely.

Subnet masks are used solely for IP addressing and routing purposes, not for name resolution. Hostname-to-IP-address resolution is performed by the Domain Name System (DNS), which is a completely different protocol and service.

Subnet masks do not provide any encryption or security functionality. Encryption of packets is performed by protocols such as IPsec, TLS, or other cryptographic mechanisms, which operate independently of subnet masking.

A default gateway is still required for any traffic destined to a different subnet. The subnet mask only defines the local network boundary; it does not provide routing to other networks. Without a default gateway, a host cannot send packets off its subnet.

192.168.50.159 is the broadcast address for the 192.168.50.128/27 subnet, not the network address. The broadcast address is used to send packets to all hosts in the subnet and cannot be assigned to a host.

192.168.50.160 is the network address of the next /27 subnet (160-191), not the subnet containing 158. The /27 mask creates subnets with a block size of 32, so the subnet boundaries are multiples of 32.

192.168.50.96 is the network address of the 96-127 /27 subnet, which is an earlier subnet. The address 158 falls in the 128-159 range, not the 96-127 range.

Manually configuring a link-local address with the eui-64 keyword is invalid; link-local addresses are automatically generated.

This option does not include the required ipv6 enable command, so it does not satisfy the explicit scenario requirement.

Uses a static host address (::1/64) instead of the eui-64 keyword, so the interface ID will not be generated from the MAC address.

Candidates might fixate on the up/down status and assume encapsulation mismatch without considering the explicitly stated troubleshooting steps.

Students often associate up/down with missing clock rate, but the question precludes this by confirming correct configuration.

Some learners confuse Layer 3 problems (IP issues) with the line protocol status that reflects Layer 2 health.

The interface status shows 'up, line protocol is down', which indicates a Layer 2 issue, not a physical cable fault. Additionally, no CRC, runts, giants, or collisions are reported, so the cable is likely not faulty.

The interface status is 'up, line protocol is down', not 'err-disabled'. The err-disabled state would show 'err-disabled' in the interface status, and a shutdown/no shutdown would be appropriate only for err-disabled recovery.

The interface status is 'up', not 'administratively down'. An administratively down interface would show 'administratively down, line protocol is down'. VLAN configuration issues typically cause the interface to be up/up but unable to forward traffic, not up/down.

192.168.50.127 is the broadcast address for the lower /25 subnet (192.168.50.0/25), not the subnet containing 192.168.50.130. Since the host IP is in the upper subnet, this option is incorrect.

192.168.50.128 is the network address of the upper /25 subnet (192.168.50.128/25), not the broadcast address. Network addresses cannot be assigned to hosts or used as broadcast addresses, so this option is incorrect.

192.168.50.254 is a valid usable host address within the upper /25 subnet. It is not the broadcast address, so this option is incorrect.

The specific factual error: The 'clock rate' command configures the clocking rate on a DCE serial interface, not the administrative state.

The specific factual error: The encapsulation command changes the Layer 2 protocol but does not affect the administrative state of the interface.

The specific factual error: The 'clear interface' command does not enable an administratively down interface; it only resets statistics.

Many candidates assume that a Layer 2 protocol down on a serial link is always caused by an encapsulation mismatch, overlooking the explicit clocking issue displayed in the output.

Novice engineers might misinterpret 'line protocol is down' as an indication that the interface is disabled, without reading the full status line.

The trap: candidates see 'line protocol is down' and immediately think of a physical problem, missing the clear distinction that the interface itself is 'up'.

192.168.88.32 is the network address of the previous /27 subnet (32-63). Since the host address 192.168.88.66 falls in the 64-95 range, the correct network address is 192.168.88.64, not 192.168.88.32.

192.168.88.95 is the broadcast address for the /27 subnet that starts at 192.168.88.64. The broadcast address is the last address in the subnet, used to send packets to all hosts in that subnet, not the network address.

192.168.88.96 is the network address of the next /27 subnet (96-127). The host 192.168.88.66 is not in that range; it belongs to the subnet starting at 192.168.88.64.

Routers do not modify packet payloads to add hostnames during normal forwarding. Traceroute relies on ICMP Time Exceeded messages generated by routers when TTL expires, not on payload modifications. Adding hostnames would violate IP packet integrity and is not a standard function.

ARP (Address Resolution Protocol) operates only within a local network segment to map IP addresses to MAC addresses. It is not used for path discovery across multiple routed hops. Traceroute uses TTL expiry to trigger ICMP responses, not ARP replies.

Switches operate at Layer 2 and do not decrement TTL or generate ICMP Time Exceeded messages for traceroute. Syslog is a logging protocol used for network device event reporting, not for hop-by-hop path discovery. Traceroute relies on ICMP or UDP/TCP probes, not syslog messages.

The specific factual error is that manually setting half-duplex does not resolve a mismatch; it may create a new mismatch or degrade performance further.

The specific factual error is that GigabitEthernet interfaces usually operate at 1000 Mbps; setting speed to 100 may cause the interface to not come up or to underperform.

The specific factual error is that clearing counters is a diagnostic step, not a fix. The root cause (duplex mismatch) remains unaddressed.

Single-mode fiber has a smaller core diameter (typically 9 microns) than multimode (50 or 62.5 microns), so this reverses the relationship.

Multimode fiber’s larger core introduces modal dispersion, limiting it to shorter distances; long-distance links use single-mode fiber.

IEEE 1000BASE-LX specifies a maximum distance of 5 km over single-mode fiber; 10 km is beyond the standard CCNA curriculum.

192.168.1.7 is the broadcast address for the /29 block 0–7, which does not contain host .14. The host .14 is in the block 8–15, so its broadcast is .15.

192.168.1.14 is the host address itself, not the broadcast address. The broadcast address is always the last address in the subnet, which is .15 for the block 8–15.

192.168.1.16 is the network address of the next /29 block (16–23), not the broadcast address for the block containing .14. The broadcast address must be the last address in the same block as the host.

The specific factual error is that WPA3-only security may not be supported by the client, and changing the management interface IP does not resolve the client VLAN assignment issue.

The specific factual errors are: WPA3 may not be compatible, disabling SSID broadcast hides the network, and DHCP scope must be on the same VLAN as the client (VLAN 100).

The specific factual errors are: SSID broadcast must be enabled for client discovery, and the WLAN interface must be mapped to VLAN 100, not VLAN 1.

The subnet mask 255.255.255.0 is correct for a /24 network, so it is not the cause of the problem.

The default gateway is correctly set to 192.168.1.1, and the host can ping it, so the gateway is not missing or incorrect.

The IPv4 address is 192.168.1.100, which is a valid private address, not an APIPA address (169.254.x.x). APIPA addresses are used when DHCP fails, but here the host has a proper address.

Replacing the cable does not solve a duplex/speed mismatch because the errors are caused by configuration, not physical layer damage.

Disabling autonegotiation alone does not guarantee the interface will use the correct speed and duplex; it still requires manual configuration of the correct values.

Increasing the MTU addresses fragmentation issues, not CRC errors resulting from duplex or speed mismatches.

The specific factual error: 'interface reset' is not a real command; the correct command to reset counters is 'clear counters'.

The specific factual error: speed mismatch causes line protocol issues but not administrative down state.

The specific factual error: 'no keepalive' affects line protocol detection but does not change administrative state.

Switches do not operate at Layer 1; hubs and repeaters do.

While some multilayer switches can route, the basic switch in this scenario operates at Layer 2.

Segments are used by transport layer protocols, not by switches.

Option A (/28) is incorrect because a /28 subnet provides only 16 total addresses, which results in 14 usable host addresses after subtracting the network and broadcast addresses. This is insufficient to support 30 hosts.

Option C (/26) is incorrect because although it supports 62 usable hosts, it is larger than necessary for 30 hosts, leading to inefficient IP address allocation.

Option D (/25) is incorrect because it provides 126 usable host addresses, which is far more than required, resulting in significant address space waste.

Auto-negotiation cannot match a hardcoded speed/duplex; 1000BASE-SX is for short distances (up to 550 m).

Gigabit Ethernet does not support half duplex; 1000BASE-LX maximum distance is 10 km.

Speed mismatch (100 vs 1000) will cause link failure; 1000BASE-EX is not an IEEE standard (ZX is used for extended reach).

The specific factual error: WPA2-PSK is not compatible with clients expecting WPA3-Personal, and hiding the SSID prevents clients from seeing it.

The specific factual error: VLAN 1 is the default and often discouraged for management; the issue is not firmware-related but configuration-based.

The specific factual error: WPA3-Enterprise is not appropriate without a RADIUS server, and DHCP for management can lead to unreliable access.

The specific factual error is that WPA2-Personal with TKIP does not meet the WPA3-Personal requirement; WPA3 mandates AES-CCMP.

The specific factual error is that the radio policy must be set to 5 GHz only, not 'All', to restrict access to 5 GHz clients.

The specific factual error is that the WLAN remains disabled, so clients cannot associate even if other settings are correct.

Cable issues would manifest as input errors or interface flapping, but the counters show zero errors.

No errors are reported, so the SFP is functioning correctly.

The 'show interface' output clearly shows the interface is up, so no shutdown is not needed.

The Transport layer uses port numbers, not IP addresses. IP addresses are added during Network layer encapsulation.

MAC addresses are used for local delivery on a network segment and are part of Layer 2 encapsulation.

The Physical layer handles the actual transmission of raw bits over the network medium.

DHCPv6 is not a protocol that replaces ARP; instead, it is used for assigning IP addresses and configuration information to IPv6 devices. ARP is replaced by the Neighbor Discovery Protocol in IPv6, which performs similar functions for address resolution.

EUI-64 is not a protocol but a method for generating IPv6 interface identifiers. It does not perform the function of resolving link-layer addresses like ARP does in IPv4.

SLAAC (Stateless Address Autoconfiguration) is a method for automatically configuring IPv6 addresses but does not perform the function of resolving link-layer addresses like ARP does in IPv4. Therefore, it cannot replace ARP in IPv6.

Option A is incorrect because the subnet mask 255.255.254.0 corresponds to a prefix length of /23, not /22. A /22 prefix would indicate a subnet mask of 255.255.252.0.

The subnet mask 255.255.254.0 corresponds to a prefix length of /23, not /24. A /24 prefix length would indicate a subnet mask of 255.255.255.0, which allows for fewer hosts per subnet.

Option D is incorrect because a subnet mask of 255.255.254.0 corresponds to a prefix length of /23, not /25. A /25 subnet mask would allow for only 128 IP addresses, which is not applicable here.

The running-config shows 'no shutdown', so this is not the cause.

The IP address and subnet mask are correctly configured for the VLAN.

The SVI status is not affected by the presence or absence of a default gateway.

10.20.30.32 is incorrect because the host IP 10.20.30.95 does not fall within the 32–63 subnet block. This address belongs to a different subnet block and cannot be the network address for the given host.

10.20.30.95 is incorrect because it is the host IP address itself, not the network address. The network address must be the first address in the subnet block, not a host address.

10.20.30.96 is incorrect because it is the first address of the next subnet block (96–127). The host IP 10.20.30.95 belongs to the previous block, so 10.20.30.96 cannot be its network address.

Duplex mismatch would cause CRC errors and late collisions, which are not present in the exhibit.

VLAN mismatch does not cause runts or giants; it causes Layer 2 issues like no connectivity.

Speed mismatch would prevent the link from coming up or cause CRC errors, but the link is up at 1000 Mb/s.

The transceiver diagnostics show no fault flags, and the module is reporting nominal bit rate and other values within range.

The distance itself is within spec; the issue is the receive power being too low, not the distance exceeding the limit.

This is a configuration mismatch, but it does not directly cause CRC errors. The CRC errors are due to low receive power.

IPv6 unicast-routing is already enabled; the problem is at the interface level.

The requirement specifies EUI-64; omitting it results in a static address that does not match the intended configuration.

The VLAN configuration is correct; no change is needed.

Option B, 172.16.32.0/23, is incorrect because it only summarizes two of the four provided routes (172.16.32.0/24 and 172.16.33.0/24), failing to include the other two routes (172.16.34.0/24 and 172.16.35.0/24).

Option C (172.16.32.0/21) includes a broader range of addresses than necessary, covering 172.16.32.0 to 172.16.39.255, which exceeds the specified routes and could lead to incorrect routing information being advertised.

Option D is incorrect because the summary route 172.16.34.0/22 would only cover the addresses from 172.16.34.0 to 172.16.35.255, missing the routes 172.16.32.0/24 and 172.16.33.0/24.

The statement incorrectly claims that link-local addresses are always assigned using EUI-64.

The statement confuses the role of EUI-64; it creates the interface ID, not the network prefix.

The statement is too restrictive; multiple default gateways can be configured, especially in multi-homed hosts.

The issue is with the IP addresses, which are not handled at Layer 1.

The MAC addresses are correct, so the Data Link Layer is functioning properly.

IP addresses are not part of the Transport Layer header; they belong to the Network Layer.

Option A (192.0.2.80) is incorrect because the subnet mask /28 indicates a block size of 16, making the valid network addresses range from 192.0.2.96 to 192.0.2.111. The network address for this subnet is 192.0.2.96.

The address 192.0.2.111 is not a valid network address for the subnet defined by 192.0.2.97/28, as it falls outside the range of usable addresses for that subnet, which spans from 192.0.2.96 to 192.0.2.111.

Option D, 192.0.2.112, is wrong because it does not represent the network address for the subnet defined by the IP address 192.0.2.97/28. The correct network address is 192.0.2.96, which is the first address in the subnet range.

Exam‑takers may confuse verifying the symptom with identifying the root cause. Seeing only one interface transmitting confirms the problem but offers no corrective insight.

A common reflex is to re‑verify the obvious; however, the question states the routes are present and next‑hops are reachable, so revisiting the RIB is redundant.

Option A states 12 usable hosts, which is incorrect because a /28 subnet provides 16 total addresses. Subtracting the network and broadcast addresses leaves 14 usable hosts, not 12. This option underestimates the host capacity.

Option C claims 16 usable hosts, which is incorrect because 16 represents the total number of addresses in the subnet, including network and broadcast addresses. Usable hosts must exclude these two reserved addresses.

Option D suggests 30 usable hosts, which corresponds to a /27 subnet mask (255.255.255.224), not /28. This overestimates the host count for the given subnet mask and is therefore incorrect.

While a faulty cable could cause CRC errors, it would likely produce other error types and might not exhibit the specific pattern of only runts and CRC errors with no collisions. This pattern strongly points to a duplex mismatch.

A speed mismatch would generally cause the link to fail entirely; you wouldn't see interface errors because there would be no connectivity. The scenario describes connectivity with errors, so this is unlikely.

Outdated drivers may cause performance problems, but they do not produce the specific interface error counters on the switch. The recorded runts and CRC errors point to a physical or data-link layer issue, not a driver problem.

The technician sees raw bits before framing, so this is not the Data Link layer.

The Network layer deals with logical addressing and routing, not the physical transmission of bits.

The Transport layer is above the Physical layer and does not deal with bit-level transmission.

16 would be the total addresses for a /28 mask (4 host bits), not the /27 mask specified.

30 is the number of usable host addresses (total addresses minus network and broadcast), not the total addresses.

64 would be the total addresses for a /26 mask (6 host bits), not the /27 mask specified.

This statement reverses the technologies: 802.11ac uses OFDM, and 802.11ax uses OFDMA.

802.11ax adds 2.4 GHz support for backward compatibility and better range.

TWT is a feature of 802.11ax, not 802.11ac.

This option is incorrect because IPv6 gateways do not have to be global unicast; link-local addresses are valid for routing within the local network segment. The host can use the link-local address of the router as the next hop for packets destined to other networks.

This option is incorrect because a host with a link-local next hop can still reach global unicast addresses, as link-local addresses are used only for communication within the same local network segment.

This option is wrong because a router advertisement does not need to provide a MAC address for the next-hop link-local address to be valid; link-local addresses are inherently usable for local communication without MAC address specification.

WPA3 mandates AES encryption and does not include TKIP for any compatibility; TKIP was deprecated in WPA2.

WPA3-Personal uses SAE, not 802.1X/EAP; only WPA3-Enterprise relies on 802.1X.

GCMP-256 is only mandated in the optional WPA3-Enterprise 192-bit mode; standard WPA3 uses GCMP with 128-bit keys.

Protected Management Frames (PMF) are required, not optional, in WPA3 to mitigate management frame attacks.

The specific factual error is that speed mismatch does not cause the high input error count without CRC errors; duplex mismatch does.

The specific factual error is that cable issues produce CRC errors, not just input errors; the absence of CRC errors rules out cable problems.

The specific factual error is that 'no shutdown' is used to enable an interface that is administratively down; here the interface is up and passing traffic.

The default gateway must be the IP address of the directly connected neighbor (R2's G0/0), which is 10.0.0.2, not 10.0.0.1.

The IP address 10.0.0.6/30 is in the same subnet as R2's G0/1 (10.0.0.5/30), so it does not resolve the duplicate address conflict. A different subnet must be used.

The destination is local to the same /26 subnet, so it does not need to go through the default gateway.

The subnet directed broadcast is 172.16.50.191 (the last address in the .128/26 range), not .190.

The source address 172.16.50.130 is a usable host address, not the network address of the subnet.

Single-mode fiber supports much longer distances (up to 10 km or more) than multimode fiber (typically up to 550 m for 10 Gbps).

SFP is limited to 1 Gbps; for 10 Gbps, SFP+ is required.

This describes single-mode fiber, not multimode.

A /27 subnet provides only 30 usable host addresses (32 total minus 2 for network and broadcast), which does not meet the requirement of at least 62 usable addresses.

Option C: /25 provides 126 usable host addresses, which exceeds the requirement of at least 62 usable addresses. However, it is not the smallest prefix that meets the requirement, as /26 suffices with 62 usable addresses.

Option D: /24 provides 256 total addresses, with 254 usable, which exceeds the requirement of at least 62 usable addresses. However, it is not the smallest prefix that meets the requirement.

Duplicate IP conflicts typically result in a warning but do not cause the system to assign a 169.254.x.x address.

DNS issues do not affect IP address assignment via DHCP.

The subnet mask is correct for the APIPA range; the problem is the lack of a DHCP server response.

A /24 subnet provides only 256 usable host addresses, which is insufficient for the requirement of at least 500 usable addresses. Therefore, it cannot be the correct answer.

Option C (/22) provides 1022 usable addresses, which exceeds the requirement of 500 usable addresses, but it is not the smallest prefix that meets the requirement. The correct answer is /23, which provides exactly 510 usable addresses.

Option D: /25 provides only 126 usable host addresses, which is insufficient for a requirement of at least 500 usable addresses in a single subnet.

Best-effort delivery with no acknowledgments is a characteristic of UDP, not TCP. TCP provides reliable delivery with acknowledgments and retransmission.

TCP has higher overhead because it maintains session state (sequence numbers, acknowledgments, etc.), while UDP is stateless and has lower overhead. The question asks for characteristics of TCP, not UDP.

Option A (192.168.5.63) is incorrect because it does not fall within the subnet defined by the address 192.168.5.126/25, which has a valid range of 192.168.5.128 to 192.168.5.255 for host addresses.

The address 192.168.5.128 is incorrect because it falls outside the subnet defined by 192.168.5.126/25, which includes addresses from 192.168.5.0 to 192.168.5.127. The broadcast address for this subnet is 192.168.5.127.

Option D, 192.168.5.255, is incorrect because it is the broadcast address for the entire 192.168.5.0/24 subnet, not the /25 subnet specified in the question.

Option A (192.168.20.159) is incorrect because the broadcast address for the subnet 192.168.20.128/26 is 192.168.20.191, calculated as the highest address in the subnet range from 192.168.20.128 to 192.168.20.191.

The option C, 192.168.20.192, is incorrect because it falls outside the range of the subnet defined by 192.168.20.128/26, which has a valid broadcast address of 192.168.20.191.

The broadcast address for the subnet 192.168.20.128/26 is 192.168.20.191, not 192.168.20.255. The address 192.168.20.255 is the broadcast address for the entire 192.168.20.0/24 network, which is not relevant to the specified subnet.

Trunk ports are used to carry multiple VLANs between switches, not to assign a single workstation to a specific VLAN.

Trunk ports are designed to carry multiple VLANs and are typically used between switches, not for end-user devices.

DTP modes control whether a port becomes a trunk or remains an access port; they do not change the access VLAN.

A /27 subnet provides only 30 usable host addresses, which is insufficient for the requirement of 50 usable addresses. Therefore, it does not meet the needs of the branch LAN.

Option C: /25 provides 126 usable addresses, which exceeds the requirement of 50 usable addresses. However, it is not the smallest prefix that meets the requirement.

Option D, /24, provides 256 total addresses, which exceeds the requirement of 50 usable addresses. However, it is not the smallest prefix that meets the requirement, as /26 provides 64 addresses, which is sufficient and more efficient.

A speed mismatch would show 'up, line protocol down' and possibly increased input errors, but the interface here is 'administratively down'—manually disabled.

A duplex mismatch would cause late collisions or CRC errors, not an 'administratively down' status, which indicates a shutdown state.

Disabling keepalives has no effect on 'administratively down' because the interface is disabled at the administrative level, not because of a keepalive failure.