TCP vs UDP
TCP and UDP are the two transport-layer protocols. TCP trades speed for reliability; UDP trades reliability for speed. Knowing which services use each, and the TCP handshake, shows up across the SY0-701 networking objectives.
Last updated August 2026
| Aspect | TCP | UDP |
|---|---|---|
| Connection | Connection-oriented (three-way handshake) | Connectionless |
| Reliability | Reliable: guarantees delivery and order | Best-effort: no delivery guarantee |
| Ordering | Reassembles packets in order | No ordering |
| Overhead | Higher, slower | Lower, faster |
| Error handling | Acknowledgements and retransmission | None: lost packets are not resent |
| Header size | 20 bytes minimum | 8 bytes |
| Typical uses | HTTP/HTTPS, SMTP, SSH, file transfer | DNS, DHCP, VoIP, streaming, SNMP, TFTP |
The bottom line
TCP uses a handshake, acknowledgements, and ordering to guarantee delivery; UDP skips all of that for speed. Choose TCP when every byte must arrive intact, and UDP when speed matters more than the occasional lost packet.
Lock it in with practice
Reading the difference is a start. SecPlus Mastery drills it with over 1,000 practice questions, timed mock exams, and spaced review across all five SY0-701 domains, so it sticks for exam day.
New accounts get 30% off both plans for 7 days: the 90-Day Pass is $27.30 instead of $39.
FAQ
Why does DNS use UDP?
DNS queries are small and fast, so the low overhead of UDP fits. DNS switches to TCP for zone transfers and for responses too large for a single UDP packet.What is the TCP three-way handshake?
SYN, SYN-ACK, ACK. The client and server exchange these to establish a connection before data flows. It also underlies the SYN flood attack, so know the sequence.
More Security+ comparisons
Compare Security+ to other certifications
Written to the CompTIA Security+ SY0-701 objectives. CompTIA and Security+ are trademarks of CompTIA, used here for identification only.