ISC2 CC Network Security Practice Question
Which protocol operates at the Transport layer of the OSI model and is connectionless and unreliable?
⚠ Common exam trap
Candidates often confuse the OSI layers: candidates might think IP is Transport layer because it's connectionless, or assume TCP is unreliable because it's often compared to UDP. Remember: UDP is the connectionless, unreliable Transport layer protocol.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
UDP
UDP (User Datagram Protocol) is a Transport layer (Layer 4) protocol that is connectionless and unreliable. It does not establish a connection before sending data, and it does not guarantee delivery, ordering, or error recovery. This makes it suitable for applications that prioritize speed over reliability, such as streaming or DNS.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
TCP
Why it's wrong here
TCP is connection-oriented and reliable, using handshakes, sequence numbers and acknowledgements to guarantee delivery. UDP is the connectionless, unreliable Transport layer protocol the question describes. TCP is tempting because it also operates at the Transport layer, so it matches the layer requirement while failing the connectionless and unreliable characteristics.
- ✗
HTTP
Why it's wrong here
HTTP operates at the Application layer, not the Transport layer, and it relies on TCP for delivery. UDP is the connectionless, unreliable Transport layer protocol. HTTP is tempting because it is a widely recognised protocol associated with network communication, but it sits above the Transport layer and provides no transport-level addressing or multiplexing.
- ✗
IP
Why it's wrong here
IP operates at the Network layer, handling logical addressing and routing between networks, not transport-layer multiplexing. UDP is the connectionless, unreliable Transport layer protocol. IP is tempting because it is connectionless and unreliable, matching those adjectives, but it belongs to Layer 3 rather than Layer 4.
- ✓
UDP
Why this is correct
UDP operates at the Transport layer and is connectionless, sending datagrams without handshaking, acknowledgement, or retransmission, so delivery is unreliable. TCP, the alternative Transport protocol, establishes connections and guarantees ordered, reliable delivery, which contradicts both stated constraints.
Go deeper
Related to this question
Learn chapter
Business Continuity and Disaster Recovery
Key term
Recovery
Recovery is the process of restoring systems, data, and operations after a security incident, failure, or disaster to return to normal functioning.
Key term
DNS
DNS is the system that translates human-friendly domain names like example.com into machine-readable IP addresses so computers can find each other on a network.
About these practice questions
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official ISC2 exam blueprint
This CC practice question is part of Courseiva's free ISC2 certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CC exam.