CompTIA Network+
N10-009
OSI Model, Networking Concepts, Protocols, Security & Troubleshooting
Exam Code: N10-009 | 60 Questions & Verified Answers
Covers All Official Exam Objectives
,Domain 1: Networking Concepts
OSI Model & TCP/IP
Q1. Which layer of the OSI model is responsible for end-to-end communication, error detection,
and flow control?
A. Network Layer (Layer 3)
B. Data Link Layer (Layer 2)
C. Transport Layer (Layer 4)
D. Session Layer (Layer 5)
Answer: C. Transport Layer (Layer 4)
The Transport Layer handles end-to-end communication between hosts, segmentation, reassembly,
flow control, and error recovery.
Key protocols: TCP (reliable, connection-oriented) and UDP (fast, connectionless).
TCP uses the 3-way handshake: SYN → SYN-ACK → ACK.
Q2. A network technician needs to identify which OSI layer a router operates at. What is the
correct answer?
A. Layer 1 — Physical
B. Layer 2 — Data Link
C. Layer 3 — Network
D. Layer 4 — Transport
Answer: C. Layer 3 — Network
Routers operate at Layer 3 and forward packets based on IP addresses.
Switches operate at Layer 2 using MAC addresses. Hubs operate at Layer 1.
Memory tip: 1=Physical(hub), 2=Data Link(switch), 3=Network(router), 4=Transport(TCP/UDP)
Q3. What is the correct order of the TCP three-way handshake?
A. SYN, ACK, SYN-ACK
B. SYN, SYN-ACK, ACK
C. ACK, SYN, SYN-ACK
D. SYN-ACK, SYN, ACK
Answer: B. SYN, SYN-ACK, ACK
Client sends SYN (synchronize) → Server responds SYN-ACK → Client sends ACK.
This establishes a TCP connection before data transfer begins.
The 4-way teardown uses FIN and ACK to close the connection.
Q4. Which protocol operates at Layer 7 (Application) and is used to send email?
A. IMAP
B. HTTP
C. SMTP
D. FTP
, Answer: C. SMTP
SMTP (Simple Mail Transfer Protocol) on port 25 sends email from client to server and between
mail servers.
IMAP (port 143/993) and POP3 (port 110/995) retrieve email from a server.
IMAP keeps mail on the server (syncs). POP3 downloads and typically deletes from server.
Q5. What does the acronym ARP stand for and what does it do?
A. Address Resolution Protocol — maps IP addresses to MAC addresses
B. Advanced Routing Protocol — finds the fastest route
C. Automatic Request Protocol — requests IP addresses
D. Address Registration Protocol — registers domain names
Answer: A. Address Resolution Protocol — maps IP addresses to MAC addresses
ARP resolves a known IP address to an unknown MAC address on the local network.
A device broadcasts 'Who has IP 192.168.1.5?' and the owner responds with its MAC address.
ARP table (cache) stores recent IP-to-MAC mappings to reduce broadcast traffic.
Q6. Which IPv4 address class supports the MOST host addresses per network?
A. Class A
B. Class B
C. Class C
D. Class D
Answer: A. Class A
Class A: 1.0.0.0–126.255.255.255. First octet = network (8 bits), remaining 24 bits = hosts.
Supports ~16 million hosts per network.
Class B: 128–191. 16-bit network, 16-bit host. ~65,000 hosts per network.
Class C: 192–223. 24-bit network, 8-bit host. 254 hosts per network.
Q7. A host is configured with IP 192.168.10.50 and subnet mask 255.255.255.0. What is the
network address?
A. 192.168.10.1
B. 192.168.10.0
C. 192.168.0.0
D. 192.168.10.255
Answer: B. 192.168.10.0
With a /24 mask (255.255.255.0), the first three octets are the network portion.
Network address: 192.168.10.0 (all host bits set to 0).
Broadcast address: 192.168.10.255 (all host bits set to 1). Usable hosts: .1 to .254.
Q8. How many usable host addresses does a /28 subnet provide?
A. 14
B. 16
N10-009
OSI Model, Networking Concepts, Protocols, Security & Troubleshooting
Exam Code: N10-009 | 60 Questions & Verified Answers
Covers All Official Exam Objectives
,Domain 1: Networking Concepts
OSI Model & TCP/IP
Q1. Which layer of the OSI model is responsible for end-to-end communication, error detection,
and flow control?
A. Network Layer (Layer 3)
B. Data Link Layer (Layer 2)
C. Transport Layer (Layer 4)
D. Session Layer (Layer 5)
Answer: C. Transport Layer (Layer 4)
The Transport Layer handles end-to-end communication between hosts, segmentation, reassembly,
flow control, and error recovery.
Key protocols: TCP (reliable, connection-oriented) and UDP (fast, connectionless).
TCP uses the 3-way handshake: SYN → SYN-ACK → ACK.
Q2. A network technician needs to identify which OSI layer a router operates at. What is the
correct answer?
A. Layer 1 — Physical
B. Layer 2 — Data Link
C. Layer 3 — Network
D. Layer 4 — Transport
Answer: C. Layer 3 — Network
Routers operate at Layer 3 and forward packets based on IP addresses.
Switches operate at Layer 2 using MAC addresses. Hubs operate at Layer 1.
Memory tip: 1=Physical(hub), 2=Data Link(switch), 3=Network(router), 4=Transport(TCP/UDP)
Q3. What is the correct order of the TCP three-way handshake?
A. SYN, ACK, SYN-ACK
B. SYN, SYN-ACK, ACK
C. ACK, SYN, SYN-ACK
D. SYN-ACK, SYN, ACK
Answer: B. SYN, SYN-ACK, ACK
Client sends SYN (synchronize) → Server responds SYN-ACK → Client sends ACK.
This establishes a TCP connection before data transfer begins.
The 4-way teardown uses FIN and ACK to close the connection.
Q4. Which protocol operates at Layer 7 (Application) and is used to send email?
A. IMAP
B. HTTP
C. SMTP
D. FTP
, Answer: C. SMTP
SMTP (Simple Mail Transfer Protocol) on port 25 sends email from client to server and between
mail servers.
IMAP (port 143/993) and POP3 (port 110/995) retrieve email from a server.
IMAP keeps mail on the server (syncs). POP3 downloads and typically deletes from server.
Q5. What does the acronym ARP stand for and what does it do?
A. Address Resolution Protocol — maps IP addresses to MAC addresses
B. Advanced Routing Protocol — finds the fastest route
C. Automatic Request Protocol — requests IP addresses
D. Address Registration Protocol — registers domain names
Answer: A. Address Resolution Protocol — maps IP addresses to MAC addresses
ARP resolves a known IP address to an unknown MAC address on the local network.
A device broadcasts 'Who has IP 192.168.1.5?' and the owner responds with its MAC address.
ARP table (cache) stores recent IP-to-MAC mappings to reduce broadcast traffic.
Q6. Which IPv4 address class supports the MOST host addresses per network?
A. Class A
B. Class B
C. Class C
D. Class D
Answer: A. Class A
Class A: 1.0.0.0–126.255.255.255. First octet = network (8 bits), remaining 24 bits = hosts.
Supports ~16 million hosts per network.
Class B: 128–191. 16-bit network, 16-bit host. ~65,000 hosts per network.
Class C: 192–223. 24-bit network, 8-bit host. 254 hosts per network.
Q7. A host is configured with IP 192.168.10.50 and subnet mask 255.255.255.0. What is the
network address?
A. 192.168.10.1
B. 192.168.10.0
C. 192.168.0.0
D. 192.168.10.255
Answer: B. 192.168.10.0
With a /24 mask (255.255.255.0), the first three octets are the network portion.
Network address: 192.168.10.0 (all host bits set to 0).
Broadcast address: 192.168.10.255 (all host bits set to 1). Usable hosts: .1 to .254.
Q8. How many usable host addresses does a /28 subnet provide?
A. 14
B. 16
