CCNA Practice Exam 51 — 20 Questions

Question 1

Why is NTP especially useful when devices send logs to a centralized Syslog server?

Accepted Answer

It helps align device clocks so centralized log timestamps can be correlated more accurately.. NTP is especially useful because synchronized clocks make the log timestamps more meaningful and easier to correlate. In plain language, if each device thinks the current time is different, the sequence of events in the centralized log becomes confusing. NTP helps align time across devices so the logs tell a more accurate story.

This is an operational best practice. Syslog collects the messages, and NTP makes their timing consistent. The correct answer is the one focused on timestamp correlation.

Answer

It assigns the Syslog server an IP address.

Answer

It replaces the need for a Syslog server.

Answer

It encrypts every Syslog message automatically.

Question 2

Which rule does a router apply first when selecting a route for a destination packet?

Accepted Answer

Longest prefix match. Routers first look for the most specific matching prefix. Administrative distance and metrics matter when competing routes exist for the same destination prefix length.

Answer

Lowest metric across all protocols

Answer

Oldest route in the routing table

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Default route if one exists

Question 3

Hosts in VLAN 10 need to communicate with hosts in VLAN 20. What is required for that communication to work?

Accepted Answer

A Layer 3 routing function. Traffic between VLANs must be routed. A router or multilayer switch provides the Layer 3 function needed for inter-VLAN communication.

Answer

A DHCP server

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A DNS server

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A second access switch

Question 4

Which three options accurately describe characteristics of OSPFv2 in a single area? (Choose three.)

Accepted Answer

The designated router (DR) is elected on broadcast multiaccess networks to reduce LSAs flooding.. OSPFv2 uses cost as its metric, derived from interface bandwidth using the formula cost = reference bandwidth / interface bandwidth (default reference bandwidth is 100 Mbps). Hello packets are used to discover neighbors, maintain adjacencies, and act as keepalives (default every 10 seconds on broadcast networks). The designated router (DR) is elected only on broadcast multiaccess networks (e.g., Ethernet) to reduce LSA flooding. The incorrect options: OSPFv2 does not natively support IPv6 (OSPFv3 is needed for IPv6); LSAs are refreshed every 30 minutes, not 30 seconds; router IDs must be unique across the OSPF domain, not the same in an area.

Answer

OSPFv2 supports IPv6 routing natively without any additional configuration.

Answer

Link-state advertisements (LSAs) are sent periodically every 30 seconds by default.

Answer

OSPF routers in the same area must be configured with the same router ID.

Question 5

Why is an extended ACL usually placed close to the source of the traffic being filtered?

Accepted Answer

To stop unwanted traffic earlier and conserve bandwidth. Extended ACLs can filter by source, destination, and protocol. Placing them near the source drops unwanted traffic before it crosses more of the network.

Answer

Because standard ACLs cannot be applied near the destination

Answer

To make NAT translation easier on inside interfaces

Answer

Because extended ACLs only work inbound on access interfaces

Question 6

Drag and drop the items on the left to the correct descriptions on the right.

Accepted Answer

show interface transceiver: Outputs Digital Optical Monitoring (DOM) data such as temperature, voltage, and Tx/Rx power for installed transceivers.. show interface transceiver outputs Digital Optical Monitoring (DOM) data such as temperature, voltage, and Tx/Rx power for installed transceivers. show controllers ethernet-controller phy displays physical layer diagnostics including cable length estimates, MDI/MDI-X status, pair swaps, and link quality counters. SFP-10G-SR is a multimode fiber transceiver supporting 10 Gigabit Ethernet at 850nm over distances up to 300 meters. Cat6a is enhanced copper twisted-pair cabling rated for 10GBASE-T up to 100 meters with improved alien crosstalk performance. LC connectors are the small form-factor duplex fiber connectors commonly used with SFP and SFP+ optical modules.

Answer

show interface transceiver: Displays physical layer diagnostics including cable length estimates, MDI/MDI-X status, pair swaps, and link quality counters.

Answer

Cat6a: Multimode fiber transceiver supporting 10 Gigabit Ethernet at 850nm over distances up to 300 meters.

Question 7

Which three of the following statements about Network Address Translation (NAT) are correct? (Choose three.)

Accepted Answer

Static NAT provides a one-to-one mapping between a private IP and a public IP.. Static NAT provides a one-to-one mapping between a private IP and a public IP, ensuring that a specific internal host always uses the same public address. Dynamic NAT uses a pool of public IP addresses assigned on a first-come, first-served basis, so internal hosts compete for available addresses. PAT (Port Address Translation) allows multiple internal hosts to share a single public IP by differentiating sessions via unique port numbers, which is the most common form of NAT used in home and small office routers.

Answer

Dynamic NAT always assigns the same public IP to a given internal host.

Answer

NAT eliminates the need for any routing in a network.

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PAT requires a unique public IP for every concurrent session.

Question 8

Which three of the following are characteristics of Layer 2 Ethernet switches that support VLANs? (Choose three.)

Accepted Answer

They forward frames based on the destination MAC address.. Layer 2 Ethernet switches that support VLANs forward frames based on the destination MAC address, which is the fundamental switching decision. They can segment a LAN into multiple broadcast domains because each VLAN creates its own isolated broadcast domain, preventing unnecessary traffic propagation. They use the Spanning Tree Protocol (STP) to prevent Layer 2 loops by dynamically blocking redundant paths, ensuring a loop-free topology.

Answer

They forward frames based on the destination IP address.

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They use ARP to resolve IP addresses to MAC addresses.

Answer

They perform routing between VLANs without a router.

Question 9

Which four of the following are best practices for securing network services and devices? (Choose four.)

Accepted Answer

Keep device firmware and operating systems up to date with security patches.. Disabling unused ports, implementing role-based access control (RBAC), enabling logging, and keeping firmware updated are all critical security best practices: they reduce the attack surface, limit user permissions, detect threats, and patch known vulnerabilities. Using Telnet is insecure because it transmits data in cleartext, unlike SSH. Placing all devices on the same VLAN undermines network segmentation and allows lateral movement by attackers.

Answer

Place all network devices on the same VLAN to simplify security policy enforcement.

Answer

Use Telnet for remote management because it is simpler to configure than SSH.

Question 10

Which three of the following are key benefits of integrating AI into network operations? (Choose three.)

Accepted Answer

Real-time traffic classification and policy enforcement using machine learning models. The three correct answers highlight practical AI benefits: anomaly detection correlates diverse telemetry (NetFlow, SNMP) to identify issues faster; real-time traffic classification uses ML models for dynamic policy enforcement without manual rule updates; predictive maintenance analyzes historical data to forecast failures, enabling proactive intervention. The wrong options are unrealistic: AI cannot eliminate all human administrators (complex troubleshooting still needs humans), cannot guarantee 100% uptime (failures still occur), and cannot automatically reconfigure physical cabling (that requires physical access).

Answer

Guaranteed 100% network uptime through self-healing algorithms

Answer

Automatic reconfiguration of physical cabling without manual intervention

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Complete elimination of the need for human network administrators

Question 11

A network engineer notices that users on VLAN 100 are experiencing intermittent connectivity to the server farm. The switch connecting these users shows no errors on the uplink interface, but the server farm switch reports a high number of input errors on its connected interface. The engineer runs 'show controllers' on the server farm switch. What is the most likely cause of the issue?

Accepted Answer

The SFP module is faulty or incompatible with the cable type.. The 'show controllers' command on the server farm switch reveals physical-layer issues such as framing errors, CRC errors, or alignment errors, which are often caused by faulty or incompatible SFP modules. Since the uplink interface on the user switch shows no errors, the problem is isolated to the server farm switch's interface, and a faulty SFP can introduce signal degradation or electrical issues without necessarily causing complete link failure. Option B is correct because SFP incompatibility or defects commonly produce input errors at the physical layer, even when the link appears up.

Answer

The interface is configured with the wrong duplex setting.

Answer

The cable is too long, causing attenuation.

Answer

Auto-negotiation is disabled, causing a speed mismatch.

Question 12

Drag and drop the following steps into the correct order to describe the data encapsulation process as it flows down the OSI model from the source host.

Accepted Answer

Application data is generated and passed to the Transport layer.. Encapsulation proceeds from the top OSI layers to the bottom. First, the application generates data (Step 1). The Transport layer then adds a header (TCP or UDP) to create a segment (Step 2) because this is the first step in preparing data for reliable delivery. The Network layer adds an IP header to form a packet (Step 3), which provides logical addressing and routing information. The Data Link layer adds a frame header and trailer to create a frame (Step 4), enabling physical addressing (MAC) and error detection. Finally, the Physical layer converts the frame to bits for transmission (Step 5), as it is the layer that ultimately puts signals on the wire.

Question 13

Why is a default route often described as a route of last resort?

Accepted Answer

Because it is used only when no more specific route matches.. It is described that way because it is used only when no more specific route matches the destination. In practical terms, the router checks for connected, static, or dynamic routes that describe the destination more precisely. If it finds none, the default route becomes the fallback path.

This phrase captures the default route’s purpose exactly. It is not the fastest route or the most specific route. It is simply the catch-all route for otherwise unknown destinations.

Answer

Because it always has the lowest bandwidth.

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Because it is more specific than any other route.

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Because it can be learned only through OSPF.

Question 14

Drag and drop the 802.11 standards on the left to their correct frequency band and maximum throughput on the right.

Accepted Answer

802.11b: 2.4 GHz, 11 Mbps. Each 802.11 standard operates in specific frequency bands and has a maximum theoretical throughput. 802.11a uses 5 GHz at 54 Mbps, 802.11b uses 2.4 GHz at 11 Mbps, 802.11g uses 2.4 GHz at 54 Mbps, 802.11n uses both 2.4 and 5 GHz up to 600 Mbps, 802.11ac uses 5 GHz up to 6.9 Gbps, and 802.11ax uses 2.4, 5, and 6 GHz up to 9.6 Gbps.

Question 15

Drag and drop the following steps into the correct order to describe the encapsulation of data as it passes down the TCP/IP stack for transmission.

Accepted Answer

Application data is generated by the user application.. The encapsulation process starts with the application layer generating data. The transport layer packages data into segments (TCP) or datagrams (UDP). The network layer adds an IP header, creating a packet. The data link layer adds a frame header and trailer (frame). Finally, the physical layer converts the frame into bits for transmission.

Question 16

A network engineer is troubleshooting a connectivity issue between two hosts on different subnets. The sending host has constructed a packet with a destination IP address of 192.168.2.10. As the packet travels down the OSI model layers on the sending host, which Protocol Data Unit (PDU) name is assigned to the data at the Transport layer after TCP segments are created, and at which layer does the IP address get encapsulated?

Accepted Answer

PDU is a segment; IP address is added at the Network layer.. At the Transport layer, TCP divides data into segments, so the PDU is called a segment, making B correct. The destination IP address (192.168.2.10) is added at the Network layer, where the IP header encapsulates the segment into a packet. Option A is wrong because a frame is a Data Link layer PDU, and IP addresses are not added at that layer. Option C is wrong because the PDU at the Transport layer is a segment, not a packet, and IP addresses are added at the Network layer, not the Transport layer. Option D is wrong because 'datagram' typically refers to UDP’s Transport layer PDU (not TCP), and IP addresses are not added at the Transport layer.

Answer

PDU is a frame; IP address is added at the Data Link layer.

Answer

PDU is a packet; IP address is added at the Transport layer.

Answer

PDU is a datagram; IP address is added at the Transport layer.

Question 17

Drag and drop the following steps into the correct order to troubleshoot a Windows client that is unable to reach a remote server.

Accepted Answer

Run ipconfig /all to check IP configuration, subnet mask, default gateway, and DNS servers.. The correct troubleshooting order starts with verifying the client's IP configuration using ipconfig /all (A) to ensure the device has proper addressing. Next, test the TCP/IP stack by pinging the loopback address 127.0.0.1 (B). Then, ping the client's own IP address (C) to confirm the network interface card is operational. After that, ping the default gateway (D) to verify local network connectivity. If successful, ping the remote server (E) to test end-to-end connectivity. If that fails, use tracert (F) to identify where the path breaks. This bottom-up approach isolates the problem starting from the local host outwards.

Question 18

Drag and drop the following steps into the correct order to configure a router-on-a-stick topology for inter-VLAN routing between VLANs 10 and 20, using 802.1Q trunking with native VLAN 99 for management traffic.

Accepted Answer

Create VLANs 10, 20, and 99 on the switch.. The sequence follows Cisco's best practices: VLANs are created first, then access ports are assigned to them. The switch trunk is configured with 802.1Q encapsulation and the native VLAN set to 99 before the router end. On the router, the physical interface must be enabled before subinterfaces can operate. The native VLAN subinterface is created first to handle untagged frames, then the data VLAN subinterfaces are configured. This order avoids errors such as missing VLANs, incorrect encapsulation, and physical link down state.

Question 19

Drag and drop the following steps into the correct order to retrieve the operational status of interface GigabitEthernet0/0 using NETCONF and the ietf-interfaces YANG model.

Accepted Answer

Establish an SSH connection to the network device on TCP port 830, the standard NETCONF port.. First, establish an SSH connection to the device's NETCONF subsystem (TCP port 830). The NETCONF protocol then performs a capability exchange via messages to ensure both sides support the required YANG models. Next, a RPC with an XPath filter is sent to request the specific interface status. The server replies with containing the XML data. The client parses the XML to extract the desired value. Finally, the NETCONF session is closed by a RPC, and the SSH connection is terminated. This order ensures a proper NETCONF transaction lifecycle.

Question 20

Drag and drop the following steps into the correct order to configure a Windows 10 host with a static IPv4 address, subnet mask, and default gateway.

Accepted Answer

Open Control Panel and navigate to Network and Sharing Center.. The correct order begins with opening Network and Sharing Center to access network settings. Then, you must click 'Change adapter settings' to see the list of network connections. Right-clicking the appropriate adapter and selecting Properties opens its configuration. Selecting IPv4 and clicking Properties allows you to set the IP parameters. Choosing 'Use the following IP address' enables the fields for static input. Finally, entering the IP address, subnet mask, and default gateway followed by OK/Close applies the configuration. This sequence follows the logical navigation of the Windows GUI to reach the static IP assignment interface.