Transport Protocol Identification — Which Services Use TCP? From the services listed below, select the subset that uses Transmission Control Protocol (TCP) rather than UDP. DHCP 2) SMTP 3) HTTP 4) TFTP 5) FTP

Introduction / Context:
Recognizing which applications ride over TCP versus UDP is crucial for firewall rules, troubleshooting, and performance expectations. TCP provides connection-oriented delivery, sequencing, and reliability, while UDP is connectionless with minimal overhead and no built-in reliability.

Given Data / Assumptions:

• Services in question: DHCP, SMTP, HTTP, TFTP, FTP.
• We assume standard, well-known port behavior.
• We need to choose only those that use TCP.

Concept / Approach:
SMTP uses TCP port 25 (and 587/465 variants). HTTP uses TCP port 80 (and HTTPS uses TCP 443). FTP uses TCP ports 20/21 for data/control in active/passive modes. DHCP uses UDP ports 67/68 for lightweight broadcast/relay exchanges; TFTP uses UDP port 69 for simple file transfers without session state. Therefore, the TCP trio is SMTP, HTTP, and FTP (2, 3, 5).

Step-by-Step Solution:
Classify each service by transport: SMTP → TCP, HTTP → TCP, FTP → TCP.Classify the remaining services: DHCP → UDP, TFTP → UDP.Select the set that includes 2, 3, and 5 only.Confirm ports if needed using standard IANA assignments.

Verification / Alternative check:
Network traces (for example, with Wireshark) clearly show 3-way handshakes for SMTP/HTTP/FTP and no such handshake for DHCP/TFTP which use UDP.

Why Other Options Are Wrong:

• Options including 1 (DHCP) or 4 (TFTP) are incorrect because both use UDP.
• Any pair or trio that omits one of SMTP/HTTP/FTP fails to capture the full TCP set among the provided services.

Common Pitfalls:
Assuming TFTP is TCP because FTP is; despite similar names, TFTP is UDP-based and intentionally minimal.

Final Answer:
2, 3 and 5