CCNA Mock Exam 79 — 25 Questions

Question 1

Which command output would be the best next step to verify whether the port-channel is operational after configuration changes?

Accepted Answer

show etherchannel summary. The best next step is to check EtherChannel status directly. In practical terms, after fixing the member-link configuration, the quickest verification is to inspect the summary output that shows whether the bundle exists and whether the member ports are actively participating. That is more direct than checking unrelated switching or routing tables.

This is a simulation-style 'what do you verify next' question, which is important for realistic CCNA prep.

Answer

show ip ospf neighbor

Answer

show ip route

Answer

show access-lists

Question 2

A switchport connected to another switch should carry VLANs 10, 20, and 30. The interface is operational, but only VLAN 10 works. VLANs 20 and 30 fail. Which explanation is most likely if the port was accidentally configured as an access port in VLAN 10?

Accepted Answer

The interface is carrying only VLAN 10 because an access port does not transport multiple VLANs like a trunk.. The correct answer is A because an access port is limited to a single VLAN, so only VLAN 10 traverses the link. Option B is incorrect: IP subnet masks are irrelevant on switchports that operate at Layer 2. Option C is incorrect: inter-switch links typically use trunk ports, not routed ports. Option D is incorrect: STP does not block based on VLAN IDs; it blocks redundant paths, not specific VLANs.

Answer

VLAN 20 and 30 require different IP subnet masks on the switches.

Answer

Every inter-switch link must use a routed port instead of a trunk.

Answer

STP blocks all VLANs except VLAN 10 by design.

Question 3

Which two statements about ARP on an IPv4 Ethernet network are correct? (Choose two.)

Accepted Answer

An ARP request is sent as a Layer 2 broadcast.. ARP resolves an IPv4 address to a MAC address on the local segment. ARP requests are broadcast; ARP replies are typically unicast.

Answer

ARP is used to map IPv6 addresses to MAC addresses.

Answer

ARP is forwarded by routers across subnets by default.

Question 4

A switch administrator enters the following commands on interface GigabitEthernet1/0/10:

interface g1/0/10
 switchport mode access
 switchport access vlan 30
 spanning-tree portfast
 spanning-tree bpduguard enable

A user connects a small managed switch to this port, and the access port immediately changes to an err-disabled state.

Which feature caused the port to shut down?

Accepted Answer

BPDU Guard. BPDU Guard is the feature that caused the shutdown. This question is really about separating two features that are often configured together on user-facing ports: PortFast and BPDU Guard. PortFast helps an edge port come up quickly, which is useful for PCs and phones. BPDU Guard adds protection by watching for BPDUs on that same port. If a switch is connected where only an end device should exist, the newly connected switch may send BPDUs. The local switch interprets that as a topology risk and disables the port to protect the Layer 2 network. The clues are the err-disabled state and the fact that another switch was connected. VLAN assignment and access mode are normal here and do not explain the shutdown.

Answer

PortFast

Answer

Access VLAN 30 assignment

Answer

The interface being in access mode

Question 5

Exhibit: A script sends an API request and receives HTTP status code 401. What does that code indicate?

Accepted Answer

The client is not authenticated successfully. HTTP 401 means the request was not accepted because authentication is required or the provided credentials or token were invalid. In practice, the first thing to check is the token, username, password, or auth header format.

Answer

The requested resource was not found

Answer

The server completed the request successfully

Answer

The server rejected the request because the JSON body was too large

Question 6

An EtherChannel between two switches is configured for LACP. One switch shows the member interfaces as bundled, while the other shows them as individual interfaces. Which explanation is most likely if both sides are using LACP?

Accepted Answer

The member interface settings do not match closely enough for bundling, even though both sides use LACP.. The most likely explanation is that some other interface settings do not match, even though both sides are using the same EtherChannel protocol. In practical terms, LACP alone is not enough. The candidate member interfaces also need to agree on characteristics such as speed, duplex, switchport mode, allowed VLANs where relevant, and other channel-related settings. If they do not, one side may treat the links as separate instead of bundling them.

This is a common troubleshooting pattern because it tests whether you know that EtherChannel success depends on more than just the negotiation protocol name.

Answer

LACP always requires one side to use PAgP as a backup.

Answer

EtherChannel cannot operate on switch trunks.

Answer

One switch must disable STP before EtherChannel can form.

Question 7

R1 and R2 are directly connected and running OSPF. The IP addressing is correct and both routers are in area 0, but they do not form an adjacency. What is the most likely cause?

Accepted Answer

The OSPF MTU values do not match on the connected interfaces.. The most likely cause is an MTU mismatch between the two interfaces. During the OSPF database exchange process, neighbors must agree on the MTU value to successfully exchange DBD packets; a mismatch typically causes the adjacency to become stuck in the ExStart or Exchange state. Basic connectivity (e.g., ping) often still works because ICMP packets are small, but the OSPF adjacency fails due to the MTU discrepancy.

Answer

The routers must use identical hostnames before OSPF can form neighbors.

Answer

The routers must use VLAN 1 for OSPF to operate.

Answer

The interfaces need to be configured as trunks instead of routed ports.

Question 8

Two switches, SW1 and SW2, are connected via a trunk link. Hosts in VLAN 50 on SW1 cannot communicate with hosts in VLAN 50 on SW2, while hosts in other VLANs communicate normally. What is the most likely cause?

Accepted Answer

VLAN 50 is not allowed on the trunk from SW1.. The strongest explanation is that VLAN 50 is missing from the allowed VLAN list on one side of the trunk. In practical terms, the trunk is up and carrying other VLANs, so the problem is selective rather than total. When one VLAN is omitted from the allowed list, only that VLAN fails while others continue to work normally.

This is a high-value switching troubleshooting pattern because it rewards careful reading of operational output rather than generic trunk theory.

Answer

The native VLAN must be changed to 50 on both switches.

Answer

The trunk must be changed to an access port.

Answer

The switches must run PPP on the uplink.

Question 9

Based on the exhibit, what is the most likely reason the PPP link is failing to authenticate?

Accepted Answer

The PPP authentication credentials do not match between the two sides.. The most likely reason is a credentials mismatch between the two sides of the PPP authentication setup. In practical terms, PPP authentication requires the peers to agree on the relevant identity and secret information. If those values do not align, the link may come up physically but authentication fails and the logical connection does not establish properly.

This is a very exam-relevant WAN troubleshooting scenario because it focuses on a realistic failure after the transport is already present.

Answer

The interfaces must use HDLC instead of PPP before authentication can work.

Answer

CHAP requires the routers to be in different IPv4 subnets.

Answer

PPP authentication works only over GRE tunnels.

Question 10

Drag and drop the following steps into the correct order to configure AAA with a RADIUS server and enable 802.1X port authentication on a Cisco IOS-XE switch.

Accepted Answer

Enter global configuration mode, define the RADIUS server, configure AAA authentication, enable 802.1X globally, apply per-interface 802.1X settings.. First enter global config, then define the RADIUS server, then configure AAA authentication, then enable 802.1X globally, and finally apply per-interface 802.1X settings.

Answer

Enter global configuration mode, enable 802.1X globally, define the RADIUS server, configure AAA authentication, apply per-interface 802.1X settings.

Answer

Enter global configuration mode, configure AAA authentication, define the RADIUS server, enable 802.1X globally, apply per-interface 802.1X settings.

Answer

Enter global configuration mode, define the RADIUS server, enable 802.1X globally, configure AAA authentication, apply per-interface 802.1X settings.

Question 11

Drag and drop the following steps into the correct order to configure a Cisco IOS-XE router as a DHCP server for a local subnet and enable a DHCP relay agent on a different interface to forward client requests to that server.

Accepted Answer

Configure the DHCP server on the local subnet, then configure the DHCP relay agent on the remote interface, and finally verify both server and relay functionality.. The DHCP server must be configured first on the local subnet, then the relay agent on the remote interface to forward requests; verification ensures both server and relay function correctly.

Answer

Configure the DHCP relay agent on the remote interface, then configure the DHCP server on the local subnet, and finally verify both server and relay functionality.

Answer

Configure the DHCP server on the local subnet, then verify functionality, and finally configure the DHCP relay agent on the remote interface.

Answer

Configure the DHCP relay agent on the remote interface, then verify functionality, and finally configure the DHCP server on the local subnet.

Question 12

Drag and drop the following steps into the correct order to implement an AI/ML-based network operations workflow for proactive anomaly detection and automated remediation on a Cisco IOS-XE device.

Accepted Answer

Data Collection. The workflow starts with data collection, then streaming, model training, deployment, and finally automated remediation based on detection.

Answer

Model Training

Answer

Automated Remediation

Answer

Data Streaming

Question 13

Drag and drop the following steps into the correct order to trace the DNS resolution process from a client query to receiving an A-record response.

Accepted Answer

Client sends DNS query to recursive resolver. The client first sends its query to a recursive resolver (often provided by the ISP or a public DNS service). The resolver then queries a root name server to find the TLD server for the domain's top-level domain (e.g., .com). Next, the resolver queries the TLD server to learn the authoritative name server for the specific domain. Finally, the resolver queries that authoritative server, which responds with the A record containing the IP address. Each step depends on the previous one because higher-level servers only delegate to lower levels, not store final records. The resolver then caches the response and returns it to the client, completing the process. Nslookup and dig are diagnostic tools used after this resolution if records are missing or incorrect, but they are not part of the resolution steps themselves.

Question 14

Drag and drop the following steps into the correct order to configure a Cisco IOS-XE router as a DHCP server for a VLAN 10 subnet and enable DHCP relay for a remote client on VLAN 20.

Accepted Answer

1. Exclude addresses from the pool. 2. Configure the DHCP pool for VLAN 10 with network, default-router, and DNS. 3. Enable DHCP relay on the VLAN 20 interface. 4. Verify DHCP operations.. The correct sequence is to globally exclude IP addresses first, preventing the DHCP server from assigning reserved addresses. Then define the DHCP pool for VLAN 10 with network parameters, enable DHCP relay on the VLAN 20 interface so it forwards requests to the server, and finally verify the service is functioning. Options that place relay before pool or exclusions after pool misorder these essential configuration steps and deviate from recommended practice.

Answer

1. Enable DHCP relay on the VLAN 20 interface. 2. Configure the DHCP pool for VLAN 10. 3. Exclude addresses from the pool. 4. Verify DHCP operations.

Answer

1. Exclude addresses from the pool. 2. Enable DHCP relay on the VLAN 20 interface. 3. Configure the DHCP pool for VLAN 10. 4. Verify DHCP operations.

Answer

1. Configure the DHCP pool for VLAN 10. 2. Enable DHCP relay on the VLAN 20 interface. 3. Exclude addresses from the pool. 4. Verify DHCP operations.

Question 15

Drag and drop the following steps into the correct order for an agentic AI system to remediate a network performance issue using Cisco IOS-XE CLI commands.

Accepted Answer

Enter global configuration mode, diagnose interface with 'show interfaces', apply QoS policy, enable SNMP monitoring, verify with 'show running-config'.. The agent first enters configuration mode, then diagnoses the interface, applies QoS, enables monitoring, and finally verifies the changes.

Answer

Enable SNMP monitoring, enter global configuration mode, apply QoS policy, diagnose interface with 'show interfaces', verify with 'show running-config'.

Answer

Apply QoS policy, enter global configuration mode, diagnose interface with 'show interfaces', enable SNMP monitoring, verify with 'show running-config'.

Answer

Enter global configuration mode, apply QoS policy, diagnose interface with 'show interfaces', enable SNMP monitoring, verify with 'show running-config'.

Question 16

Drag and drop the following steps into the correct order to configure gRPC streaming telemetry subscription on a Cisco IOS-XE device, from initial setup to data collection.

Accepted Answer

Enter global configuration mode, enable telemetry, define subscription with encoding and filter, specify receiver, verify data collection.. The correct order starts with entering global config, then enabling telemetry, defining subscription details (encoding and filter), specifying the receiver, and finally verifying data collection.

Answer

Enable telemetry, define subscription, specify receiver, enter global config, verify data collection.

Answer

Define subscription with encoding and filter, enable telemetry, specify receiver, enter global config, verify data collection.

Answer

Specify receiver, define subscription, enable telemetry, enter global config, verify data collection.

Question 17

Drag and drop the ACL commands and concepts on the left to their correct descriptions on the right.

Accepted Answer

Standard ACL. Standard ACLs filter only by source IP. Extended ACLs offer more granular filtering. Named ACLs use names for identification. Implicit deny is the default deny-all at the end. Inbound ACLs process traffic before routing, outbound after routing.

Answer

Extended ACL

Answer

Named ACL

Answer

Implicit deny

Question 18

Drag and drop the AI/automation concepts on the left to the correct descriptions on the right.

Accepted Answer

Machine learning is a broad subset of AI. Deep learning uses multi-layer neural networks. NLP deals with human language. Computer Vision interprets visual data. Reinforcement learning uses rewards. Supervised learning uses labeled data.. AI Agent is correctly matched because it is defined as an autonomous entity that perceives its environment and takes actions to achieve goals. Tool-calling enables AI agents to invoke external functions or APIs, which aligns with the given description. Closed-loop remediation is accurately paired with the workflow that automatically detects, diagnoses, and corrects network issues without human intervention. Retrieval-Augmented Generation (RAG) is the technique that combines large language models with external knowledge retrieval to produce more accurate responses. Intent-based Networking (IBN) translates high-level business intent into network configuration and assurance, matching the description. Finally, Reinforcement Learning (RL) is the training method where an agent learns optimal actions through rewards and penalties, which perfectly fits its definition.

Answer

Machine learning uses multi-layer neural networks. Deep learning is a broad subset of AI. NLP interprets visual data. Computer Vision deals with human language. Reinforcement learning uses labeled data. Supervised learning uses rewards.

Answer

Machine learning uses rewards. Deep learning uses labeled data. NLP is a broad subset of AI. Computer Vision uses multi-layer neural networks. Reinforcement learning deals with human language. Supervised learning interprets visual data.

Answer

Machine learning interprets visual data. Deep learning deals with human language. NLP uses multi-layer neural networks. Computer Vision uses rewards. Reinforcement learning uses labeled data. Supervised learning is a broad subset of AI.

Question 19

You are connected to R1. The link between R1 and R2 is experiencing packet loss and slow performance. Examine the following partial show interface output:

R1# show interfaces gigabitEthernet 0/0
GigabitEthernet0/0 is up, line protocol is up
  Duplex: Full, Speed: Auto, 100Mb/s
  Input errors: 12345, CRC: 5000, frame: 0, overrun: 0, ignored: 0

R2# show interfaces gigabitEthernet 0/0
GigabitEthernet0/0 is up, line protocol is up
  Duplex: Half, Speed: Auto, 100Mb/s
  Input errors: 0, CRC: 0, collisions: 5000, late collisions: 0

Identify the root cause of the issue, and apply the necessary fix on R1 to resolve the problem.

Accepted Answer

Configure the interface with 'duplex half' to match the half-duplex setting on R2.. The output reveals a duplex mismatch. R1 is operating in full‑duplex mode, while R2 is in half‑duplex mode. On the full‑duplex side (R1), simultaneous transmissions from both ends result in corrupted frames, visible as a high count of CRC errors. On the half‑duplex side (R2), ordinary collisions occur because R2 uses CSMA/CD, but no CRC errors are seen because it detects collisions and retransmits. The only immediate fix from R1—since R2 is fixed at half‑duplex—is to change R1's interface to half‑duplex using the command 'duplex half', which matches the settings and stops the corrupted frames. (Long‑term, both sides should ideally be set to full‑duplex, but that requires access to R2.)

Answer

Configure the interface with 'speed 100' to force the link speed to 100 Mbps.

Answer

Replace the Ethernet cable with a new one to fix the physical layer issue.

Answer

Configure the interface with 'no shutdown' to bring the interface up.

Question 20

You are troubleshooting connectivity between R1 and R2. R1's Gi0/0 interface is connected to R2's Gi0/0. R1 can ping its own IP but cannot ping R2's IP. Examine the provided 'show interfaces' output on R1 and identify the root cause. Then, apply the necessary configuration command(s) on R1 to resolve the issue.

Accepted Answer

interface GigabitEthernet0/0
 duplex full
 speed 1000. The 'line protocol is down' on R1's Gi0/0 interface indicates a Layer 2 issue. Since the interface is up but line protocol is down, the most common cause is a duplex mismatch or a keepalive issue. In this scenario, the interface is configured as 'full-duplex' but the far-end R2 might be set to half-duplex, causing a mismatch. The fix is to set the duplex to 'full' and speed to 1000 on R1's interface, or to use 'auto' for both. However, the correct command to resolve a duplex mismatch is to set both sides to the same setting, typically 'full' for GigabitEthernet. The command 'duplex full' under the interface will ensure R1 uses full-duplex, and if R2 is also set to full-duplex, the line protocol should come up.

Answer

interface GigabitEthernet0/0
 no shutdown

Answer

interface GigabitEthernet0/0
 ip address 192.168.1.1 255.255.255.0

Answer

interface GigabitEthernet0/0
 no keepalive