CCNA Network Infra Connectivity Questions

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.

The workstation likely has DHCP enabled, but the switch's SVI being down prevents DHCP discovery from reaching a server.

A VLAN mismatch would likely result in a different IP address or no connectivity, but the SVI being down is a more direct cause.

The absence of a DHCP server is a possible cause, but the exhibit clearly shows the SVI is administratively down, which is a more specific and immediate issue.

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.

The specific factual error is that subinterfaces do not have an independent line protocol state; they depend on the physical interface. The problem is likely a physical layer issue like duplex mismatch.

The specific factual error is that the SVI is not involved in this scenario; the router's subinterface handles routing for VLAN 10. The link between R1 and SW1 is the bottleneck.

The specific factual error is that native VLAN mismatch causes different symptoms (e.g., CDP/STP issues) and does not cause line protocol down or CRC errors.

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.

Candidates often believe that a missing FIB adjacency is the root cause, but in this scenario both paths are reachable and installed; the issue lies in how CEF weights the paths, which is influenced by interface parameters.

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.

Area mismatch is a valid cause but not supported by the given data; the IP addresses are on different subnets, which logically precedes area negotiation.

MTU is not shown; candidates may recall that mismatched MTU can cause OSPF problems but the scenario explicitly reveals an IP addressing inconsistency.

Authentication issues are common OSPF traps, but they are not indicated here; the IP address difference is explicitly observed.

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.

Candidates often think connectivity problems are caused by gateway misconfiguration, ignoring the subnet mask mismatch that actually prevents Layer 2 communication.

Candidates may glance at the output and assume an access list is blocking traffic, but the output clearly shows no ACL is applied.

A common troubleshooting mistake is to assume an interface is down, but the state is clearly shown as up in the exhibit.

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.

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.

The address 10.1.1.31 is incorrect as a broadcast address for the subnet 10.1.1.34/30; the correct broadcast address is 10.1.1.35, derived from the subnet mask which allows for only 4 IP addresses (10.1.1.34 to 10.1.1.37).

The address 10.1.1.32 is not the broadcast address for the subnet 10.1.1.34/30; instead, it is the network address for the subnet, which is 10.1.1.32 to 10.1.1.35.

The address 10.1.1.36 is incorrect because it exceeds the valid range for a /30 subnet, which only allows for four IP addresses (two usable hosts, one network, and one broadcast). The broadcast address for the subnet 10.1.1.34/30 is 10.1.1.35.

The symptom is err-disabled, not a speed or duplex mismatch; cable type is not the issue.

The port is a built-in copper port, not an SFP-based interface; distance is not the issue.

The err-disabled state is due to BPDU guard, not speed/duplex mismatch; manual settings would not fix the root cause.

The exhibit confirms consistent speed and duplex settings.

The modules are correctly identified and match the fiber type.

There is no evidence of the cable length in the exhibit, and the low power is more indicative of a physical fault rather than simply exceeding distance limits.

The specific factual error: Disabling PMF entirely is not necessary; PMF can be set to Optional to allow both PMF-capable and non-PMF clients.

The specific factual error: Disabling PMF alone does not allow a WPA2-only client to associate with a WPA3-only WLAN; the WLAN must also support WPA2.

The specific factual error: PMF Required is only supported with WPA3; WPA2 only supports PMF Optional. Additionally, this configuration would not support WPA3 clients.

A single cable fault is only one of many possibilities; more testing is needed before concluding physical layer failure.

Timed-out hops in tracert do not directly prove the router is down; it may simply not be generating ICMP Time Exceeded messages.

These commands do not guarantee a lease; the DHCP server must be operational and reachable.

This statement is false because SFP slots are designed for modular, replaceable transceivers.

Laser transmitters are used in single-mode fiber for longer distances; multimode uses LED/VCSEL.

Single-mode fiber has a smaller core, not larger. The smaller core reduces dispersion and allows longer reach.

The Data Link layer encapsulates packets into frames, not bits; bits are the PDU of the Physical layer.

The Session layer handles session management and does not perform encapsulation into 'sessions'; encapsulation at this layer is not defined.

The Physical layer transmits frames as bits but does not encapsulate frames into bits; encapsulation ends at Layer 2.

Option B incorrectly includes the network address (172.16.20.128) and broadcast address (172.16.20.191) as usable hosts, which are reserved and cannot be assigned to devices, making this option invalid.

Option C excludes the first usable host address (172.16.20.129) and incorrectly includes the broadcast address (172.16.20.191), which is not assignable to hosts, thus making it an incorrect range.

Option D lists a range starting at 172.16.20.193, which belongs to the next subnet block (192–255) and does not include the IP 172.16.20.190, so it is unrelated and incorrect for this question.

Option A (192.168.10.16/28) is incorrect because it represents a different subnet, specifically the range 192.168.10.16 to 192.168.10.31, which does not include the host 192.168.10.33.

Option C is wrong because the host IP 192.168.10.33/28 falls within the subnet range of 192.168.10.32 to 192.168.10.47, making 192.168.10.48/28 an entirely different subnet that does not include the host.

Option D (192.168.10.0/28) is incorrect because it represents a different subnet than the one containing the host 192.168.10.33. The subnet for 192.168.10.33/28 is 192.168.10.32/28, which includes IPs from 192.168.10.32 to 192.168.10.47.

The specific factual error is that reapplying the same manual settings does not resolve a duplex mismatch; it may even perpetuate the mismatch if the remote side is set to auto-negotiation.

The specific factual error is that 'no shutdown' is used to enable an interface that is administratively down, but the interface is already up.

The specific factual error is that forcing half-duplex is unlikely to resolve the issue; it may worsen performance and still cause errors if the remote side is full-duplex.

Option B is incorrect because the broadcast address for the subnet 192.168.30.0/26 is 192.168.30.63, not 192.168.30.64. The address 192.168.30.64 is actually the first address of the next subnet (192.168.30.64/26).

The address 192.168.30.255 is incorrect as the broadcast address for the subnet 192.168.30.0/26, which only spans IPs from 192.168.30.0 to 192.168.30.63. The broadcast address for this subnet is 192.168.30.63.

Option D, 192.168.30.31, is incorrect because it represents the last usable IP address in the subnet 192.168.30.0/26, not the broadcast address. The broadcast address for this subnet is 192.168.30.63.

The specific factual error: Excluding 10 addresses does not exhaust the pool; the pool still has 244 addresses available.

The specific factual error: The pool configuration is already correct; modifying it does not address the disabled DHCP service.

The specific factual error: 'ip helper-address' is for DHCP relay across subnets; it is not needed when the server is local.

The specific factual error is that manually setting speed/duplex does not guarantee compatibility with the remote end and does not address the SFP distance limitation.

The specific factual error is that 1000BASE-SX is for multimode fiber and short distances, not single-mode fiber at 40 km.

The specific factual error is that the SFP distance limitation is not addressed; auto-negotiation alone does not change the physical layer capability.

Using SX would not fix the issue because the fiber is multimode and LX is designed for longer distances; the problem is the cable type mismatch, not the transceiver type.

The interface is up/up, so VLAN mismatch is not the issue.

Although replacing with single-mode fiber would work, the exhibit does not show CRC errors, so the problem is more likely a mode-conditioning issue.

MU-MIMO is a feature of 802.11ac and 802.11ax, but 802.11ax primarily relies on OFDMA for multi-user support.

Overlapping channels reduce performance due to co-channel interference, not maximize non-overlapping channels.

Console port is used for initial configuration or troubleshooting, not for routine management.