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CompTIA Network+ study materials
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CompTIA Network+ practice questions

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Question 1Networking concepts

A router makes forwarding decisions based on IP addresses. At which OSI model layer does it primarily operate?

  1. Layer 3 Correct answer.
  2. Layer 1
  3. Layer 2
  4. Layer 4

Explanation

Routers operate at the network layer (Layer 3), where logical addressing and path selection occur. They examine destination IP addresses to forward packets between networks.

Question 2Networking concepts

Which TCP port is used by default for HTTPS?

  1. 443 Correct answer.
  2. 80
  3. 20
  4. 25

Explanation

HTTPS uses TCP 443 by default to carry HTTP over TLS. Other well-known ports include 80 for HTTP, 20/21 for FTP, and 25 for SMTP.

Question 3Networking concepts

Which device forwards frames based on destination MAC addresses?

  1. Firewall
  2. Router
  3. Hub
  4. Switch Correct answer.

Explanation

A switch learns MAC addresses and forwards frames only to the port where the destination MAC resides. Routers use IP addresses, hubs repeat to all ports, and firewalls filter by policy.

Question 4Networking concepts

Which address block is reserved for private use by RFC 1918?

  1. 11.0.0.0/8
  2. 172.15.0.0/16
  3. 172.16.0.0/12 Correct answer.
  4. 12.0.0.0/8

Explanation

RFC 1918 defines 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 as private ranges. The 172.16.0.0/12 block spans 172.16.0.0 through 172.31.255.255.

Question 5Networking concepts

What is the primary function of DNS?

  1. Resolves names to IP addresses Correct answer.
  2. Routes packets between subnets
  3. Encrypts web traffic
  4. Assigns addresses automatically

Explanation

DNS is a hierarchical naming system that maps host names to IP addresses so clients can locate services. Address assignment is handled by DHCP, encryption by TLS, and routing by routers.

Question 6Networking concepts

Which value tells a host where to send traffic destined for a different network?

  1. The interface MAC address
  2. The default gateway Correct answer.
  3. The local subnet mask
  4. The preferred DNS server

Explanation

The default gateway is the router address a host uses when the destination lies outside its own subnet. The subnet mask distinguishes local from remote destinations, DNS resolves names, and MAC addresses are used only on the local link.

Question 7Networking concepts

What is the maximum throughput and distance supported by Cat 6a twisted-pair cable?

  1. 10 Gbps at 100 m Correct answer.
  2. 10 Gbps at 55 m
  3. 1 Gbps at 100 m
  4. 100 Mbps at 100 m

Explanation

Cat 6a is rated for 10 Gbps over 100 meters and has improved shielding to reduce crosstalk. Cat 6 reaches 10 Gbps only to 55 m, and Cat 5e supports 1 Gbps to 100 m.

Question 8Networking concepts

What does DHCP provide to network clients?

  1. Provides domain name resolution for clients
  2. Resolves MAC to IP addresses
  3. Filters traffic by TCP port
  4. Assigns IP settings automatically Correct answer.

Explanation

DHCP automatically delivers an IP address, subnet mask, default gateway, and DNS settings to clients through a lease. Name resolution is DNS, MAC-to-IP mapping is ARP, and port filtering is a firewall function.

Question 9Networking concepts

How many usable host addresses does a /27 IPv4 subnet provide?

  1. 14
  2. 30 Correct answer.
  3. 62
  4. 32

Explanation

A /27 leaves five host bits, producing 2^5 = 32 total addresses. Subtracting the network and broadcast addresses leaves 30 usable host addresses.

Question 10Networking concepts

What is the primary effect of placing switch ports into different VLANs?

  1. They increase the link speed
  2. They assign IP addresses automatically
  3. They isolate broadcast domains Correct answer.
  4. They encrypt traffic between ports

Explanation

Each VLAN is a separate Layer 2 broadcast domain, so broadcast traffic stays within its VLAN. Link speed is a physical property, encryption requires protocols such as IPsec or MACsec, and IP assignment is done by DHCP.

Question 11Networking concepts

A home router maps many internal private addresses to a single public address. Which technology performs this?

  1. VLAN
  2. PAT Correct answer.
  3. Static NAT
  4. ARP

Explanation

Port Address Translation, also called NAT overload, uses source port numbers to distinguish multiple internal sessions sharing one public IP address. Static NAT is one-to-one, ARP resolves MAC addresses, and VLANs segment Layer 2 traffic.

Question 12Networking concepts

How does traceroute identify each router along a path?

  1. DNS reverse lookups for each hop
  2. ARP cache inspection
  3. TTL expiration with ICMP Correct answer.
  4. TCP window scaling

Explanation

Traceroute sends packets with incrementally increasing TTL values, and each router that decrements the TTL to zero returns an ICMP Time Exceeded message identifying itself. DNS lookups may label hops but do not discover them.

Question 13Networking concepts

What is the role of ARP on an IPv4 network?

  1. Assigns IP addresses dynamically to hosts
  2. Resolves names to IP addresses
  3. Maps IPv4 addresses to MAC addresses Correct answer.
  4. Encrypts data between hosts

Explanation

ARP broadcasts a request for the MAC address that owns a given IPv4 address, and the reply is cached so frames can be delivered on the local link. DHCP assigns addresses, DNS resolves names, and encryption is unrelated.

Question 14Networking concepts

Compared with 2.4 GHz, which characteristic applies to the 5 GHz Wi-Fi band?

  1. Support for legacy 802.11b only
  2. Shorter range, more channels Correct answer.
  3. Higher microwave interference
  4. Longer range, better wall penetration

Explanation

Higher frequencies attenuate faster, so 5 GHz offers shorter range and poorer wall penetration but many more non-overlapping channels. The 2.4 GHz band is more susceptible to microwave and Bluetooth interference and is the only band used by 802.11b.

Question 15Networking concepts

Which protocol provides encrypted remote CLI access over TCP port 22?

  1. SNMP
  2. SSH Correct answer.
  3. RDP
  4. Telnet

Explanation

SSH uses TCP 22 and encrypts the session, replacing cleartext Telnet on TCP 23. SNMP uses UDP 161 and 162, while RDP uses TCP 3389.

Question 16Networking concepts

A packet exceeds the interface MTU and the DF bit is set. What happens?

  1. An ICMP error is returned Correct answer.
  2. It is converted to a broadcast
  3. It is dropped with no notification
  4. It is queued indefinitely

Explanation

With the DF bit set, the router cannot fragment the packet, so it drops it and returns an ICMP Destination Unreachable with Fragmentation Needed to the source. This message supports path MTU discovery.

Question 17Networking concepts

Which routing protocol is a link-state interior gateway protocol that uses the Dijkstra algorithm?

  1. BGP
  2. RIP
  3. EIGRP
  4. OSPF Correct answer.

Explanation

OSPF builds a topology database from link-state advertisements and runs the SPF (Dijkstra) algorithm to compute shortest paths. RIP is distance-vector, BGP is an exterior path-vector protocol, and EIGRP is an advanced distance-vector protocol.

Question 18Networking concepts

A switch port shows late collisions, CRC errors, and poor throughput. Which cause is most likely?

  1. Wrong subnet mask
  2. Incorrect DNS server
  3. Expired DHCP lease
  4. Duplex mismatch Correct answer.

Explanation

A duplex mismatch, where one side is full-duplex and the other half-duplex, produces collisions and CRC errors and severely reduces throughput. The other issues affect addressing or name resolution and do not cause frame errors.

Question 19Networking concepts

Which cloud service model delivers virtual machines and storage that the customer configures and manages?

  1. IaaS Correct answer.
  2. PaaS
  3. SaaS
  4. FaaS

Explanation

Infrastructure as a Service provides virtualized compute, storage, and networking, while the customer manages the operating system and applications. SaaS delivers finished applications, PaaS provides a managed runtime, and FaaS runs individual functions.

Question 20Networking concepts

A host has the address 169.254.10.5. What does this indicate?

  1. It received a manually assigned address
  2. It has a valid DHCP lease
  3. No DHCP server was reachable Correct answer.
  4. It is using a public address

Explanation

The 169.254.0.0/16 range is the link-local APIPA range that a host self-assigns when DHCP fails. Such an address permits only local communication and is not routable.

Question 21Networking concepts

What is the broadcast address of the subnet 172.16.4.0/22?

  1. 172.16.8.255
  2. 172.16.7.255 Correct answer.
  3. 172.16.4.255
  4. 172.16.5.255

Explanation

A /22 has a block size of 4 in the third octet, so the subnet spans 172.16.4.0 through 172.16.7.255. The broadcast address is the last address in that range, 172.16.7.255.

Question 22Networking concepts

How is the root bridge elected in Spanning Tree Protocol?

  1. By the highest port priority
  2. By the highest MAC address
  3. By the lowest IP address
  4. By the lowest bridge ID Correct answer.

Explanation

The bridge with the lowest bridge ID, which combines priority and MAC address, becomes the root bridge. Port priority influences which port forwards, and STP does not use IP addresses for election.

Question 23Networking concepts

Which statement describes BGP?

  1. It uses hop count as its primary metric
  2. It is an interior link-state protocol
  3. It is a distance-vector IGP
  4. It is an exterior path-vector protocol Correct answer.

Explanation

BGP is the exterior gateway protocol used between autonomous systems, and it selects paths using attributes rather than hop count. It is classified as a path-vector protocol.

Question 24Networking concepts

Which IPv6 prefix identifies link-local addresses?

  1. 2000::/3
  2. fe80::/10 Correct answer.
  3. fc00::/7
  4. ff00::/8

Explanation

IPv6 link-local addresses use the fe80::/10 prefix and are valid only on a single link. Global unicast uses 2000::/3, unique local uses fc00::/7, and multicast uses ff00::/8.

Question 25Networking concepts

In a software-defined network, what is the main function of the controller?

  1. It translates private addresses
  2. It centralizes control logic Correct answer.
  3. It forwards packets at line rate
  4. It supplies power to access points

Explanation

SDN separates the control plane from the data plane, and the controller computes and programs forwarding policy across the network. Switches perform the actual data-plane forwarding, while PoE and NAT are unrelated functions.

Question 26Networking concepts

A router forwards a packet toward a remote network by examining the destination IP address and choosing a path. Which OSI layer performs this function?

  1. Transport layer (Layer 4)
  2. Session layer (Layer 5)
  3. Network layer (Layer 3) Correct answer.
  4. Data link layer (Layer 2)

Explanation

Logical addressing and path selection between networks are handled at the network layer, where routers operate on IP addresses. Layer 2 deals with local frame delivery by MAC address, while layers 4 and 5 handle end-to-end transport and session management.

Question 27Networking concepts

Which address block is reserved for private use and is not routed across the public internet?

  1. 198.51.100.0/24
  2. 192.0.2.0/24
  3. 203.0.113.0/24
  4. 172.16.0.0/12 Correct answer.

Explanation

RFC 1918 defines three private ranges: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. Traffic using these addresses must be translated before it can reach the internet. The other blocks shown are documentation ranges, not private addressing.

Question 28Networking concepts

A client sends a name resolution query to a DNS server. Which transport port does the server listen on by default?

  1. TCP 389
  2. UDP 161
  3. UDP 53 Correct answer.
  4. TCP 123

Explanation

DNS listens on port 53 and uses UDP for standard queries and TCP for large responses and zone transfers. Port 123 belongs to NTP, 161 to SNMP, and 389 to LDAP.

Question 29Networking concepts

In a star topology, every host connects to a central switch. Which statement describes a key characteristic of this design?

  1. Traffic passes from host to host around a closed loop until it reaches the sender.
  2. Every host has a direct physical link to every other host on the segment.
  3. A central device failure isolates every connected host. Correct answer.
  4. All hosts share one coaxial backbone cable with terminators at both ends.

Explanation

In a star, each endpoint depends on the central device for connectivity, so a failure there disconnects the whole segment while individual cable faults affect only one host. Full-mesh designs link every host to every other host, and ring or bus designs use the other described layouts.

Question 30Networking concepts

Which of these protocols relies on UDP as its transport?

  1. HTTPS
  2. SSH
  3. FTP
  4. TFTP Correct answer.

Explanation

TFTP uses UDP port 69 because it favors low overhead over reliability and handles retransmission itself. SSH, HTTPS, and FTP all require the ordered, reliable byte stream that TCP provides.

Question 31Networking concepts

What is the purpose of NTP on a network?

  1. Maps MAC addresses to IP addresses on the local link
  2. Resolves host names into IP addresses
  3. Keeps device clocks synchronized to a common time source Correct answer.
  4. Assigns IP addresses to hosts on a local segment

Explanation

NTP exchanges timestamps over UDP port 123 so routers, servers, and clients agree on time, which keeps logs and certificates consistent. Address assignment belongs to DHCP, name resolution to DNS, and MAC-to-IP mapping to ARP.

Question 32Networking concepts

Which sequence is used to establish a TCP connection?

  1. SYN, SYN-ACK, ACK Correct answer.
  2. ACK, SYN, FIN
  3. SYN, FIN, ACK
  4. SYN, ACK, RST

Explanation

The three-way handshake begins with a SYN carrying the client's initial sequence number, is answered by a SYN-ACK from the server, and is completed by an ACK from the client. Data transfer begins only after this exchange completes.

Question 33Networking concepts

A trunk link between two switches carries traffic for several VLANs. Which standard inserts a VLAN identifier into the Ethernet frame?

  1. 802.1X
  2. 802.1Q Correct answer.
  3. 802.3ad
  4. 802.11

Explanation

802.1Q adds a four-byte tag containing a 12-bit VLAN ID so a single link can carry multiple VLANs. 802.1X handles port-based access control, 802.3ad covers link aggregation, and 802.11 covers wireless LANs.

Question 34Networking concepts

A network is addressed as 192.168.10.0/24. How many equal-sized /26 subnets can be created from it?

  1. 16
  2. 8
  3. 2
  4. 4 Correct answer.

Explanation

Borrowing two bits (from /24 to /26) yields 2^2 = 4 subnets, each with 64 addresses. Each step of two in the prefix length multiplies the subnet count by four.

Question 35Networking concepts

Which characteristic applies to single-mode fiber cabling?

  1. It is the least expensive option for links under 100 meters.
  2. It uses a core diameter of 50 or 62.5 micrometers.
  3. It carries one light path and supports links of many kilometers. Correct answer.
  4. It uses an LED light source and is limited to short building runs.

Explanation

Single-mode fiber has a small core that admits one propagation path, so laser signals travel long distances with little dispersion. Multimode fiber uses the larger 50 or 62.5 micrometer cores and LED or VCSEL sources for shorter runs within a building.

Question 36Networking concepts

A switch receives a frame whose destination MAC address is not present in its MAC address table. How does the switch handle it?

  1. It floods the frame out every other port in the VLAN. Correct answer.
  2. It holds the frame until the destination host sends a broadcast.
  3. It drops the frame and returns an ICMP unreachable error.
  4. It sends the frame back out the port on which it arrived.

Explanation

Unknown unicast frames are flooded within the ingress VLAN so the destination can respond and be learned; later frames are forwarded only to the learned port. The switch does not generate ICMP errors, and it never forwards a frame back out its ingress port.

Question 37Networking concepts

Which DNS record type identifies the mail servers that accept email for a domain?

  1. A
  2. PTR
  3. MX Correct answer.
  4. CNAME

Explanation

MX records list the hosts responsible for mail delivery for a domain, along with a preference value used to order them. A records map names to addresses, CNAMEs create aliases, and PTR records support reverse lookups.

Question 38Networking concepts

Which IEEE wireless standard operates only in the 5 GHz band?

  1. 802.11ac Correct answer.
  2. 802.11g
  3. 802.11n
  4. 802.11b

Explanation

802.11ac was defined solely for 5 GHz operation, while 802.11n can use either 2.4 GHz or 5 GHz. 802.11b and 802.11g operate only in 2.4 GHz.

Question 39Networking concepts

Which IEEE standard supplies roughly 30 watts of Power over Ethernet per port?

  1. 802.3af
  2. 802.3ad
  3. 802.3bz
  4. 802.3at Correct answer.

Explanation

802.3at, commonly called PoE+, delivers about 30 watts at the source port, roughly double the 15.4 watts of 802.3af. 802.3ad defines link aggregation and 802.3bz covers 2.5G/5G Ethernet.

Question 40Networking concepts

Which IPv6 prefix is reserved for unique local addressing?

  1. ff00::/8
  2. fc00::/7 Correct answer.
  3. 2000::/3
  4. 2001:db8::/32

Explanation

Unique local addresses use fc00::/7 and serve the same role as RFC 1918 private IPv4 space, remaining unroutable on the public internet. 2000::/3 is global unicast, ff00::/8 is multicast, and 2001:db8::/32 is reserved for documentation.

Question 41Networking concepts

A cloud service automatically adds virtual machines when demand rises and removes them as demand falls. Which characteristic does this describe?

  1. Multitenancy
  2. Elasticity Correct answer.
  3. High availability
  4. Measured service

Explanation

Elasticity is the ability to scale resources out and back in automatically as workload changes. High availability keeps services reachable during failures, multitenancy shares infrastructure among customers, and measured service refers to metered billing.

Question 42Networking concepts

Two switches are joined by four links bundled into one logical link with LACP. What is the primary benefit of this configuration?

  1. A single broadcast domain spanning both switches
  2. Automatic assignment of IP addresses on the link
  3. Increased aggregate bandwidth and link redundancy Correct answer.
  4. Encryption of the traffic between the two switches

Explanation

Link aggregation combines parallel links into one logical interface, so throughput scales with the number of member links and traffic continues if a member fails. It does not encrypt traffic or provide addressing, and broadcast domains are determined by VLAN configuration.

Question 43Networking concepts

A router has an OSPF route (administrative distance 110), a static route (administrative distance 1), and an eBGP route (administrative distance 20) toward the same destination prefix. Which route is installed in the routing table?

  1. The static route Correct answer.
  2. The eBGP route
  3. The OSPF route
  4. All three routes, shared equally

Explanation

When multiple sources offer the same prefix, the router prefers the lowest administrative distance, which ranks source trustworthiness. A static route with an AD of 1 beats eBGP at 20 and OSPF at 110, so only it is installed.

Question 44Networking concepts

Which summary route covers the four subnets 10.1.4.0/24 through 10.1.7.0/24?

  1. 10.1.0.0/21
  2. 10.1.4.0/23
  3. 10.1.6.0/23
  4. 10.1.4.0/22 Correct answer.

Explanation

The four /24 networks occupy the 10.1.4.0 to 10.1.7.255 range, which is a single block of 1024 addresses aligned on a /22 boundary. A /22 contains exactly four /24s, so 10.1.4.0/22 summarizes all of them.

Question 45Networking concepts

A receiving host advertises a TCP window size of zero. What does this signal to the sender?

  1. The next segment must be resent with a smaller MSS.
  2. The sender may continue at full rate until an ACK arrives.
  3. The receiver buffer is full and the sender must pause. Correct answer.
  4. The connection should be reset and re-established.

Explanation

The window field tells the sender how much buffer space remains, so a zero window means no data can be accepted and transmission stops until a window update arrives. It is part of flow control, distinct from congestion control and from connection teardown.

Question 46Networking concepts

A subnet must support at least 500 usable host addresses. Which prefix length satisfies the requirement with the least wasted address space?

  1. /23 Correct answer.
  2. /24
  3. /22
  4. /21

Explanation

Usable hosts equal 2^h - 2, so a /23 provides 512 addresses minus 2, or 510 usable hosts, which meets the requirement with the smallest block. A /24 provides only 254 usable addresses and would fall short.

Question 47Network implementation

Which IEEE standard defines 10 Gbps Ethernet over twisted-pair copper cabling?

  1. 10GBASE-ER
  2. 10GBASE-T Correct answer.
  3. 10GBASE-SR
  4. 10GBASE-LR

Explanation

10GBASE-T carries 10 Gbps over four pairs of twisted-pair copper, typically Cat 6 or Cat 6a, for distances up to 100 meters. The other designations in this family use optical fiber rather than copper.

Question 48Network implementation

Which frequency band is used by IEEE 802.11ac?

  1. 6 GHz only
  2. Both 2.4 GHz and 5 GHz
  3. 5 GHz only Correct answer.
  4. 2.4 GHz only

Explanation

802.11ac (Wi-Fi 5) is specified only for the 5 GHz band, which is why it offers wider channels and higher throughput than 2.4 GHz designs. Operation in 2.4 GHz comes from 802.11b/g/n, and 6 GHz support was added with 802.11ax (Wi-Fi 6E).

Question 49Network implementation

Which UDP ports does a DHCP server use to receive client requests and send replies?

  1. 161 and 162
  2. 68 and 69
  3. 53 and 67
  4. 67 and 68 Correct answer.

Explanation

DHCP servers listen on UDP port 67 and DHCP clients listen on UDP port 68, with relay agents forwarding messages between the two. Port 53 is used by DNS, and ports 161/162 by SNMP.

Question 50Network implementation

Which PoE standard provides up to 15.4 watts of power at the PSE port?

  1. 802.3bt Type 4
  2. 802.3at
  3. 802.3af Correct answer.
  4. 802.3bt Type 3

Explanation

802.3af, also called PoE Type 1, delivers up to 15.4 W at the power sourcing equipment and about 12.95 W at the powered device. 802.3at (Type 2) raises this to 30 W, while 802.3bt types provide 60 W or more.