CompTIA Network+ Practice Test

Câu hỏi luyện tập mẫu

Một vài câu hỏi thực tế từ ngân hàng miễn phí này, kèm giải thích đầy đủ. Dùng công cụ luyện tập ở trên cho toàn bộ.

1. 1. Networking Concepts

   Which layer of the OSI model is responsible for logical addressing and determining the best path for packets across an internetwork?

   • a.Layer 1 (Physical)
   • b.Layer 4 (Transport)
   • c.Layer 3 (Network)
   • d.Layer 2 (Data Link)

   Đáp án: c

   Giải thích: Layer 3, the Network layer, handles logical addressing such as IP and makes routing decisions to move packets between networks. The Data Link layer uses physical MAC addresses for local delivery, while the Transport layer manages end-to-end segmentation. Routers operate primarily at Layer 3.

2. 2. Network Operations

   Which protocol allows network devices to be monitored and managed by collecting metrics such as interface counters and CPU usage?

   • a.TFTP
   • b.NTP
   • c.SNMP
   • d.SMTP

   Đáp án: c

   Giải thích: SNMP (Simple Network Management Protocol) polls and collects metrics like interface statistics and CPU usage from managed devices. SNMPv3 adds authentication and encryption over earlier versions. It is a foundational tool for network monitoring systems.

3. 3. Network Troubleshooting

   Which command displays a host's current IP configuration, including address, subnet mask, and default gateway, on Windows?

   • a.ipconfig
   • b.ping
   • c.route add
   • d.telnet

   Đáp án: a

   Giải thích: The ipconfig command on Windows displays the host's IP address, subnet mask, and default gateway, with /all showing DNS and DHCP details. The equivalent on Linux is ifconfig or ip addr. It is a first step in verifying local configuration.

4. 4. Networking Concepts

   The subnet mask 255.255.255.240 corresponds to which CIDR prefix length?

   • a./27
   • b./29
   • c./28
   • d./26

   Đáp án: c

   Giải thích: The last octet 240 is 11110000 in binary, which is four network bits added to the 24 in the first three octets, totaling 28. So 255.255.255.240 equals /28. Each /28 subnet provides 14 usable hosts.

5. 5. Networking Concepts

   Which UDP port pair does DHCP use for server and client communication?

   • a.80 and 8080
   • b.53 and 54
   • c.67 and 68
   • d.137 and 138

   Đáp án: c

   Giải thích: DHCP servers listen on UDP port 67 and clients receive on UDP port 68. These ports are essential to allow through firewalls or configure in DHCP relays. Knowing them helps diagnose why clients fail to obtain addresses.

6. 6. Network Implementation

   For seamless roaming as a user walks between two access points, how should the APs be configured?

   • a.Hidden SSIDs with static client IPs
   • b.Different SSIDs and the same channel
   • c.The same SSID on non-overlapping channels
   • d.The same SSID and the same channel

   Đáp án: c

   Giải thích: Seamless roaming needs the same SSID across APs so clients see one network, with each AP on a non-overlapping channel to avoid co-channel interference. Matching channels would cause interference in overlapping coverage. Consistent security settings are also required for smooth handoff.

7. 7. Network Security

   Which remote-access method lets a user reach internal web applications through an HTTPS portal without installing a dedicated VPN client?

   • a.Clientless SSL/TLS VPN
   • b.GRE tunnel
   • c.IPsec site-to-site VPN
   • d.L2TP tunnel

   Đáp án: a

   Giải thích: A clientless SSL/TLS VPN provides access to internal web applications through a standard browser over HTTPS, with no dedicated client software. It is convenient for occasional access from untrusted devices. Full VPN clients are still preferred for broad, native network access.

8. 8. Network Operations

   A facility must keep critical network gear running through a multi-hour utility power outage. Beyond battery backup, which resource provides sustained power?

   • a.A backup generator
   • b.A redundant cooling unit
   • c.A second internet circuit
   • d.A single uninterruptible power supply on its own

   Đáp án: a

   Giải thích: A backup generator supplies sustained power during extended utility outages, well beyond the minutes a UPS battery provides. The UPS bridges the gap while the generator starts. Together they form a layered power-resilience strategy.

9. 9. Network Operations

   A team wants every device configuration stored in version control so changes are tracked and any prior known-good version can be restored. Which practice provides this?

   • a.Disabling remote management to prevent changes
   • b.Configuration management with version control
   • c.Manually retyping commands on each device
   • d.Relying on each device's factory defaults

   Đáp án: b

   Giải thích: Configuration management with version control tracks every change to device configs and lets teams roll back to a known-good version. It reveals who changed what and when, and detects drift from the baseline. Automation tools often enforce it at scale.

10. 10. Network Troubleshooting

    A technician wants a single tool that both traces the path to a destination and, over time, measures packet loss at each hop. Which utility combines these?

    • a.arp
    • b.pathping/mtr
    • c.ipconfig
    • d.nslookup, used to query DNS record types

    Đáp án: b

    Giải thích: Pathping (Windows) and mtr (Unix) combine traceroute with continuous statistics, reporting per-hop latency and packet loss over time. This pinpoints the hop where loss originates. It is more diagnostic than a single traceroute pass.