CCNA Practice Test 16 — 15 Questions

Question 1

You are connected to R1, a multilayer switch acting as a DNS client for internal name resolution. The network uses a private DNS server at 192.168.1.100. Users report that resolving the hostname 'server01.courseiva.local' fails intermittently. Diagnose and fix the DNS resolution issue by examining the current configuration and using appropriate show commands to verify.

Accepted Answer

Re-enter the 'ip name-server 192.168.1.100' command and verify with 'show ip dns'.. The 'ip name-server' command was missing from the configuration, causing the switch to use broadcast DNS queries (to 255.255.255.255) instead of a specific server. Broadcast queries may occasionally succeed if a DNS server on the network answers them, producing the reported intermittent failures. Re-entering the 'ip name-server 192.168.1.100' command forces directed queries, ensuring reliable resolution. After configuration, a 'ping server01.courseiva.local' will trigger DNS and confirm success if the server is reachable.

Answer

Configure 'ip domain lookup' to enable DNS resolution on the switch.

Answer

Change the 'ip domain name' to 'courseiva.local' to match the hostname being resolved.

Answer

Use 'debug ip dns' to monitor DNS queries and identify the problem.

Question 2

A network operations team is implementing an automated system to detect and remediate interface flapping on core switches. The system must be able to query the network device for interface status and execute commands to disable or reconfigure the interface if a pattern of flapping is detected. Which protocol or technology enables the system to programmatically interact with the network device for both monitoring and configuration changes?

Accepted Answer

NETCONF. NETCONF is the correct choice because it is a standardized network configuration protocol that allows automated systems to retrieve operational data and push configuration changes securely. In this scenario, the system would use NETCONF to query interface status and then apply remediation configurations. SNMP can monitor but has limited configuration capabilities, CLI scripting is non-programmatic and error-prone, and Syslog is only for logging.

Answer

SNMP

Answer

CLI scripting

Answer

Syslog

Question 3

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 4

A multilayer switch must route traffic between VLAN 10 and VLAN 20. Which condition is required for that to happen?

Accepted Answer

SVIs for the VLANs plus Layer 3 routing enabled on the switch. Inter-VLAN routing on a multilayer switch depends on having functional Layer 3 gateway interfaces for the VLANs and routing enabled on the switch. In plain language, the switch needs a routed brain for each VLAN, usually in the form of SVIs, and it must actually be operating as a Layer 3 device rather than only as a pure Layer 2 switch. Without those conditions, traffic may switch inside a VLAN but cannot be routed between different VLANs.

This is a core CCNA design idea because people often assume creating VLANs alone automatically gives them inter-VLAN communication. In reality, VLANs create separation, and routing is what reconnects them under controlled conditions. A trunk between switches can carry VLAN traffic, but it does not itself perform Layer 3 routing between the VLANs. The correct answer is the requirement that makes the switch act as the gateway between VLANs.

Answer

All ports in both VLANs configured as trunks

Answer

A separate OSPF process on every access port

Answer

Port security disabled on every edge port

Question 5

A trunk between two switches is up, but users in VLAN 40 cannot communicate across it. The output shows both sides allow VLAN 40. What is another likely trunk-related cause to check next?

Accepted Answer

Native VLAN mismatch between the two trunk ends. If VLAN 40 is allowed on both ends and the trunk is up, a native VLAN mismatch is still worth checking because trunk problems are not limited to the allowed VLAN list. In plain language, the link may be carrying traffic, but if the two switches disagree on how untagged traffic should be treated, behavior can still become unpredictable. Native VLAN mismatches are a well-known source of warnings and unexpected traffic handling on 802.1Q trunks.

That does not mean every VLAN problem is caused by the native VLAN, but once the obvious allowed-list issue has been ruled out, it becomes a logical next trunk-specific item to verify.

Answer

Missing router ID in OSPF

Answer

Incorrect NTP source interface

Answer

Lack of PAT overload on the WAN router

Question 6

You are troubleshooting a link between R1 (G0/0) and R2 (G0/0). The link is up but experiencing packet loss. You suspect an interface speed/duplex mismatch or SFP issue. Configure R1's interface to match the correct speed and duplex, and replace the SFP module if necessary to support a required distance of 40 km over single-mode fiber.

Accepted Answer

Remove manual speed/duplex settings, enable auto-negotiation, and replace the SFP with a long-reach module (e.g., 1000BASE-ZX) that supports 40 km over single-mode fiber.. The link is experiencing packet loss, likely due to a speed/duplex mismatch between the manually configured interface and the peer (which may use auto-negotiation) and/or an SFP module that cannot support the required 40 km distance over single-mode fiber. To resolve both potential issues, remove any manual speed and duplex settings to restore default auto-negotiation (using 'no speed' and 'no duplex'), and replace the SFP with a module rated for 40 km or more on SMF, such as a 1000BASE-ZX (or 1000BASE-EX) transceiver. Standard 1000BASE-LX/LH only reaches up to 10 km on SMF, so it is insufficient for this scenario.

Answer

Change the duplex to full and speed to 1000 Mbps manually, and keep the existing SFP.

Answer

Keep the manual speed/duplex settings but replace the SFP with a 1000BASE-SX module.

Answer

Enable auto-negotiation on both ends but keep the existing SFP.

Question 7

You are troubleshooting a network connectivity issue on R1. The network 192.168.10.0/24 behind R2 must be reachable from R1 via the primary path through R2 (192.0.2.2). A backup path via R3 (198.51.100.2) should automatically take over if the primary fails. Currently, traffic to 192.168.10.0/24 is incorrectly using the backup path even though the primary path is operational. Analyze the routing table and configuration, then fix the issue so that the primary path is preferred when available.

Accepted Answer

Remove the static route to 192.168.10.0/24 via 198.51.100.2 and add a floating static route via 198.51.100.2 with AD 200. Ensure the primary route via 192.0.2.2 uses default AD 1.. The routing table shows a static route to 192.168.10.0/24 via 198.51.100.2 with Administrative Distance (AD) 1, which is the default for static routes. The intended primary path via 192.0.2.2 was configured with AD 200 (floating static), but because the default AD (1) is lower than 200, the backup route is preferred. The fix is to reconfigure the primary path with the default AD (1) and the backup path with a higher AD (e.g., 200). This ensures the primary path is used when available and the backup takes over only if the primary fails.

Answer

Change the AD of the static route via 192.0.2.2 to 200 and the AD of the route via 198.51.100.2 to 1.

Answer

Add a static route to 192.168.10.0/24 via 192.0.2.2 with AD 1 and remove the existing route via 198.51.100.2.

Answer

Configure a policy-based route to prefer the next-hop 192.0.2.2 for traffic to 192.168.10.0/24.

Question 8

A switch port should allow an IP phone and attached PC to operate correctly. The phone should place voice traffic in VLAN 200 while the PC remains in VLAN 20. Which configuration approach best supports that design?

Accepted Answer

Configure the port with an access VLAN for data and a voice VLAN for the phone. The best approach is to configure the access VLAN for user data and the voice VLAN separately. In plain language, the PC should remain a normal untagged data endpoint in VLAN 20, while the phone can tag its own voice traffic for VLAN 200. Cisco access-port designs support this exact use case and allow the switch to keep voice and user traffic logically separated without requiring two physical ports.

This is a classic CCNA edge-port design. It is not a general trunking problem, and it does not require EtherChannel or router subinterfaces. The important idea is that one switchport can support an access VLAN and a voice VLAN together in a way designed specifically for IP phones with downstream PCs.

Answer

Configure the port as a routed port with no switchport

Answer

Configure the port as an EtherChannel member

Answer

Use a native VLAN only and disable all tagging

Question 9

A network engineer is troubleshooting a link between two Cisco switches that are connected via a 1000BASE-LX SFP transceiver. Hosts on VLAN 10 on Switch A cannot ping the default gateway on Switch B. The interface on Switch A is up, but the engineer notices CRC errors incrementing. What should the engineer do to resolve this issue?

Accepted Answer

Use a mode-conditioning patch cable between the SFP and the fiber patch panel. The 1000BASE-LX SFP transceiver operates at 1310 nm over single-mode fiber (SMF). When connected to multimode fiber (MMF), the larger core diameter causes excessive modal dispersion, leading to CRC errors. A mode-conditioning patch cable (mode-conditioning patch cord) launches the laser off-center into the MMF core, reducing differential mode delay and restoring proper signal integrity. This is a known Cisco best practice for LX transceivers on MMF links.

Answer

Replace the SFP with a 1000BASE-SX transceiver

Answer

Configure the same VLAN on both switch interfaces

Answer

Replace the fiber cable with a single-mode fiber cable

Question 10

A switch interface connects to a user PC and should belong only to VLAN 30. Which command assigns that VLAN after the interface is in access mode?

Accepted Answer

switchport access vlan 30. After an interface is placed into access mode, the command used to assign its VLAN is `switchport access vlan 30`. In plain language, this tells the switch which VLAN the endpoint traffic on that access port belongs to. Access mode defines the role of the interface, and the access VLAN command defines the specific VLAN membership for that role.

This distinction matters because some commands change the port’s behavior while others set the VLAN it uses. The correct answer is the one that directly assigns VLAN 30 to the access port rather than modifying a trunk or a native VLAN setting.

Answer

switchport trunk allowed vlan 30

Answer

encapsulation dot1Q 30

Answer

ip helper-address 30

Question 11

Two switches are connected by a trunk. VLAN 50 exists on both switches, but traffic still fails across the link. The allowed VLAN list is correct. Which additional item should be checked next?

Accepted Answer

Check for a trunk mismatch such as native VLAN inconsistency or other trunk-parameter problems.. After confirming that the VLAN exists on both switches and is allowed on the trunk, another important item to verify is whether the trunk itself is actually operational with the expected encapsulation and whether there is a native VLAN or other trunk inconsistency. In plain language, just because the VLAN is listed does not guarantee the trunk is healthy in every relevant way. Trunking problems can still occur because of broader configuration mismatches.

This question is about disciplined troubleshooting. Once the obvious allowed-list issue is ruled out, the next step is to keep checking other trunk-related characteristics rather than jumping immediately to unrelated routing or service features. The correct answer is the one that stays grounded in trunk-specific verification.

Answer

Reset OSPF process IDs on both switches.

Answer

Add ip helper-address under every access interface.

Answer

Disable the MAC address table.

Question 12

R1 and R2 are connected via a shared Ethernet segment. Both routers are configured in OSPF area 0 and are on the same IP subnet. OSPF authentication is enabled on both interfaces, but the adjacency is not forming. What is the most likely reason?

Accepted Answer

The OSPF authentication key does not match on the two routers.. The most likely reason is an OSPF authentication mismatch. In practical terms, both routers are on the same IP subnet and in the same area, but they are not using the same authentication key on the shared link. OSPF neighbors must agree on key authentication parameters before they will trust each other enough to form an adjacency.

This is a classic CCNA troubleshooting pattern because the configuration looks almost correct until you compare the security settings carefully.

Answer

The routers must use different OSPF areas to become neighbors.

Answer

OSPF message-digest authentication can be used only on serial links.

Answer

The routers must remove IP addressing before OSPF can form.

Question 13

A switchport connected to another switch is configured with `switchport mode dynamic auto` on both ends. What is the most likely outcome if neither side actively negotiates trunking?

Accepted Answer

The link is likely to remain non-trunking because both sides are waiting passively.. If both ends are set to dynamic auto, the most likely outcome is that the link does not become a trunk automatically. In plain language, both interfaces are waiting passively for the other side to initiate the negotiation. Since neither side is actively trying to form the trunk, the link typically remains non-trunking unless one side is changed to a more active mode or trunk is configured directly.

This is a classic DTP behavior question because it tests whether you understand the difference between active and passive negotiation roles. The correct answer is the one that reflects the passive nature of dynamic auto on both sides.

Answer

The link always becomes a trunk immediately.

Answer

The link becomes a routed Layer 3 link.

Answer

All VLANs are deleted from both switches.

Question 14

An administrator wants a switchport connected to an end device to move to forwarding quickly but does not want that setting used on inter-switch links. Which feature is intended for that edge-port behavior?

Accepted Answer

PortFast. PortFast is intended for that exact edge-port behavior: it allows a host-facing access port to skip the usual listening and learning delays and transition directly to forwarding, enabling end devices to come online quickly. Root guard is used to protect the root bridge election by restricting which ports can become root ports; it is not designed for edge ports. Loop guard prevents alternate or root ports from becoming designated in the absence of BPDUs, which is a different STP protection mechanism. UDLD aggressive mode detects and disables unidirectional links on point-to-point links, typically between switches, not for end-device connections. Therefore, only PortFast meets the requirement for fast forwarding on an edge port without affecting inter-switch links.

Answer

Root guard

Answer

Loop guard

Answer

UDLD aggressive

Question 15

A router has a static route to 10.30.5.128/25, an OSPF route to 10.30.5.0/24, and a default route 0.0.0.0/0 in its routing table. Which route will the router use for destination 10.30.5.130?

Accepted Answer

The static route to 10.30.5.128/25. The router selects the route with the longest prefix match between the destination IP and the prefixes in the routing table. 10.30.5.130 matches both 10.30.5.0/24 (prefix length 24) and 10.30.5.128/25 (prefix length 25); the /25 is more specific and wins. Option D is wrong because 10.30.5.130 falls within the subnet range of 10.30.5.128/25 (hosts .129–.254), so a valid route does exist.

Answer

The OSPF route to 10.30.5.0/24

Answer

The default route

Answer

No route, because the destination is outside all prefixes shown.

CCNA Practice Test 16 — 15 Questions

Exhibit

CCNA Practice Test 16 — 15 Questions

Exhibit