Network+ N10-009 Domain 1: Networking Concepts — 12 practice questions with answers

Domain 1 is 23% of the CompTIA Network+ (N10-009) exam, which works out to roughly 21of the up to 90 questions on the real test. Below are study notes for the domain's objectives, then every question from our free Network+ N10-009 practice test that targets this domain, with the correct answer and the reasoning behind it. Try to answer each one before reading the explanation.

Objectives in this domain

1.1 Explain concepts related to the OSI reference model
1.2 Compare and contrast networking appliances, applications, and functions
1.3 Summarize cloud concepts and connectivity options
1.4 Explain common networking ports, protocols, services, and traffic types
1.5 Compare and contrast transmission media and transceivers
1.6 Compare and contrast network topologies, architectures, and types
1.7 Given a scenario, use appropriate IPv4 network addressing
1.8 Summarize evolving use cases for modern network environments

What to focus on

Networking Concepts is the broadest domain and the foundation for the troubleshooting questions later on. Two skills carry the most marks: placing a device, protocol or header field at the right OSI layer, and recalling port numbers without hesitation. Learn ports in pairs with their secure replacements, such as Telnet 23 with SSH 22, HTTP 80 with HTTPS 443, and LDAP 389 with LDAPS 636.

Subnetting (1.7) must be fast. A /26 has 64 addresses and 62 usable hosts; a /20 mask (255.255.240.0) steps through the third octet in blocks of 16, so 10.1.45.7/20 sits in 10.1.32.0, whose broadcast address is 10.1.47.255. Recognise the private ranges (10/8, 172.16/12, 192.168/16), APIPA (169.254/16) and loopback (127/8) on sight.

The newer objectives in 1.8 cover SDN and SD-WAN, VXLAN, zero trust architecture, SASE and SSE, infrastructure as code, and IPv6 addressing and transition. Media and transceivers (1.5) are about matching a requirement to a cable or optic: copper Ethernet is limited to 100 m per segment, while single-mode fibre covers long building-to-building runs.

Practice questions and explanations

1. A switch forwards a frame to a port based on the destination MAC address in the frame header. At which OSI layer is the switch making this decision?
1. A) Layer 1 — Physical
2. B) Layer 2 — Data Link
3. C) Layer 3 — Network
4. D) Layer 4 — Transport
Answer: B — Layer 2 — Data Link
MAC addresses live in the frame header, which is a Layer 2 (Data Link) construct, so a switch forwarding on MAC addresses is a Layer 2 device. Layer 3 forwarding uses IP addresses (routers), Layer 4 uses TCP/UDP ports, and Layer 1 is bits on the wire with no addressing at all. (Objective 1.1)
2. A network administrator needs to allow a web server to accept encrypted HTTPS connections. Which port must be open on the firewall by default?
1. A) TCP 80
2. B) TCP 443
3. C) TCP 22
4. D) UDP 53
Answer: B — TCP 443
HTTPS uses TCP 443 by default. TCP 80 is unencrypted HTTP, TCP 22 is SSH, and UDP 53 is DNS. Port numbers are tested heavily on N10-009, and HTTPS/443 is one of the most common. (Objective 1.4)
3. Which protocol uses UDP port 123 to keep clocks on network devices synchronised?
1. A) SNMP
2. B) NTP
3. C) Syslog
4. D) LDAP
Answer: B — NTP
NTP (Network Time Protocol) uses UDP 123. SNMP uses UDP 161/162, Syslog uses UDP 514, and LDAP uses TCP/UDP 389. Accurate time matters for log correlation and certificate validation, which is why NTP appears in both the concepts and operations domains. (Objective 1.4)
4. A host has the IP address 172.16.45.10 with a subnet mask of 255.255.240.0. What is the network address of the subnet this host belongs to?
1. A) 172.16.0.0
2. B) 172.16.32.0
3. C) 172.16.45.0
4. D) 172.16.48.0
Answer: B — 172.16.32.0
A /20 mask (255.255.240.0) creates subnets in blocks of 16 in the third octet: 0, 16, 32, 48… The third octet 45 falls in the 32–47 block, so the network address is 172.16.32.0. 172.16.48.0 is the next subnet, and 172.16.45.0 would only be correct with a /24 mask. (Objective 1.7)
5. How many usable host addresses are available in a /26 IPv4 subnet?
1. A) 30
2. B) 62
3. C) 64
4. D) 126
Answer: B — 62
A /26 leaves 6 host bits, giving 2^6 = 64 addresses. Subtracting the network and broadcast addresses leaves 62 usable hosts. 64 forgets to subtract the two reserved addresses, 30 is a /27, and 126 is a /25. (Objective 1.7)
6. A workstation that cannot reach a DHCP server has assigned itself the address 169.254.37.201. What does this address indicate?
1. A) A valid lease from a backup DHCP server
2. B) An APIPA (link-local) address assigned by the client itself
3. C) A statically configured public address
4. D) A loopback address
Answer: B — An APIPA (link-local) address assigned by the client itself
169.254.0.0/16 is the APIPA (Automatic Private IP Addressing) range, which a Windows or similar client assigns itself when no DHCP server answers. It allows local link communication only, so it is a classic symptom of a DHCP failure. The loopback range is 127.0.0.0/8, and APIPA addresses are never public or statically planned. (Objective 1.7)
7. Which IPv6 address type is automatically configured on every IPv6-enabled interface and is only valid on the local link?
1. A) Global unicast (2000::/3)
2. B) Link-local (fe80::/10)
3. C) Unique local (fc00::/7)
4. D) Multicast (ff00::/8)
Answer: B — Link-local (fe80::/10)
Every IPv6 interface automatically derives a link-local address in fe80::/10, used for neighbour discovery and routing-protocol traffic on that link only. Global unicast addresses are internet-routable, unique local addresses are the IPv6 equivalent of private addressing, and multicast addresses identify groups rather than interfaces. (Objective 1.8)
8. A company wants to run several isolated Layer 2 networks over a shared Layer 3 data-centre fabric, exceeding the 4,094-VLAN limit. Which technology is designed for this?
1. A) 802.1Q trunking
2. B) VXLAN
3. C) Spanning Tree Protocol
4. D) NAT
Answer: B — VXLAN
VXLAN encapsulates Layer 2 frames inside UDP/IP packets and uses a 24-bit network identifier, allowing about 16 million segments across a routed underlay. 802.1Q is standard VLAN tagging limited to 4,094 VLANs, STP prevents loops, and NAT translates addresses. (Objective 1.8)
9. Which cloud deployment characteristic describes a company that keeps a database on its own servers but runs its web front end in a public cloud?
1. A) Private cloud
2. B) Hybrid cloud
3. C) Community cloud
4. D) Multitenancy
Answer: B — Hybrid cloud
A hybrid cloud combines on-premises (or private cloud) resources with public cloud resources that work together. A private cloud is entirely dedicated to one organisation, a community cloud is shared by organisations with common requirements, and multitenancy describes multiple customers sharing the same cloud infrastructure. (Objective 1.3)
10. A technician must run a cable 180 metres between two buildings across an area with heavy electrical interference. Which medium is MOST appropriate?
1. A) Cat 6a UTP
2. B) Coaxial
3. C) Single-mode fibre
4. D) Cat 5e STP
Answer: C — Single-mode fibre
Fibre carries light, so it is immune to electromagnetic interference and easily spans 180 m (twisted-pair Ethernet is limited to 100 m per segment). Single-mode fibre is the standard choice for building-to-building runs. Shielded twisted pair reduces interference but still cannot exceed 100 m, and coaxial is not used for modern LAN links. (Objective 1.5)
11. In a three-tier hierarchical network design, which layer provides high-speed, resilient transport between distribution switches and contains no end-user policy?
1. A) Access layer
2. B) Distribution layer
3. C) Core layer
4. D) Spine layer
Answer: C — Core layer
The core layer is the high-speed backbone that moves traffic between distribution blocks as fast as possible; policy (ACLs, routing between VLANs) belongs at the distribution layer and end-device connectivity at the access layer. Spine and leaf are terms from the two-tier data-centre architecture, not the three-tier campus model. (Objective 1.6)
12. Which traffic type sends a single stream of packets that is delivered to a selected group of interested receivers, such as IPTV viewers?
1. A) Unicast
2. B) Broadcast
3. C) Multicast
4. D) Anycast
Answer: C — Multicast
Multicast delivers one stream to a group of hosts that have joined the group (via IGMP in IPv4), which is how IPTV and some routing protocols conserve bandwidth. Unicast is one-to-one, broadcast reaches every host on the segment whether interested or not, and anycast delivers to the nearest one of several hosts sharing an address. (Objective 1.4)

Reading answers is not the same as recalling them. When you have worked through every domain, take the timed Network+ N10-009 practice test: it shuffles the questions and options and scores you by domain, so you can see whether this one still needs work.

Network+ N10-009 Domain 1: Networking Concepts — 12 practice questions with answers

Objectives in this domain

What to focus on

Practice questions and explanations

1. A switch forwards a frame to a port based on the destination MAC address in the frame header. At which OSI layer is the switch making this decision?

2. A network administrator needs to allow a web server to accept encrypted HTTPS connections. Which port must be open on the firewall by default?

3. Which protocol uses UDP port 123 to keep clocks on network devices synchronised?

4. A host has the IP address 172.16.45.10 with a subnet mask of 255.255.240.0. What is the network address of the subnet this host belongs to?

5. How many usable host addresses are available in a /26 IPv4 subnet?

6. A workstation that cannot reach a DHCP server has assigned itself the address 169.254.37.201. What does this address indicate?

7. Which IPv6 address type is automatically configured on every IPv6-enabled interface and is only valid on the local link?

8. A company wants to run several isolated Layer 2 networks over a shared Layer 3 data-centre fabric, exceeding the 4,094-VLAN limit. Which technology is designed for this?

9. Which cloud deployment characteristic describes a company that keeps a database on its own servers but runs its web front end in a public cloud?

10. A technician must run a cable 180 metres between two buildings across an area with heavy electrical interference. Which medium is MOST appropriate?

11. In a three-tier hierarchical network design, which layer provides high-speed, resilient transport between distribution switches and contains no end-user policy?

12. Which traffic type sends a single stream of packets that is delivered to a selected group of interested receivers, such as IPTV viewers?