Which network protocol is connectionless and unreliable?

Answer: UDP (User Datagram Protocol)

Explanation: UDP is a transport-layer protocol that is connectionless and does not guarantee delivery, ordering, or protection against duplicates.

• Connectionless: Each UDP datagram is sent independently without a handshake or session setup.

• Unreliable: UDP does not provide acknowledgments, retransmission, or ordering guarantees; lost or out-of-order packets are not corrected by UDP.

• Contrast with TCP: TCP is connection-oriented and provides reliability through connection establishment, acknowledgments, retransmission, and flow control.

• Notes on other protocols mentioned: IP is a network-layer protocol that handles addressing and routing; ARP resolves IP addresses to MAC addresses on a local network. These are different layers and roles from UDP.

• Common uses of UDP: DNS queries, VoIP, live video streaming, and online gaming—applications that favor low latency over guaranteed delivery.