Cisco Certified Network Associate (CCNA) Practice Exam 2026 - Free CCNA Practice Questions and Study Guide

The protocol that uses TCP port 25 is SMTP, which stands for Simple Mail Transfer Protocol. This protocol is primarily used for sending email messages between servers. When an email is sent from a client to a server or between servers, it commonly communicates over TCP port 25, allowing for reliable transmission of email data.

SMTP is designed to handle the routing of emails, and port 25 is designated for this purpose in the specifications related to email transmission protocols. This distinguishes it from other protocols, each of which operates on different designated ports. For instance, DNS (Domain Name System) typically uses UDP port 53 for name resolution, FTP (File Transfer Protocol) uses TCP ports 20 and 21 for transferring files, and HTTP (Hypertext Transfer Protocol) usually communicates over TCP port 80 for transferring web pages.

Understanding that SMTP is essential for email delivery and operates over port 25 highlights the specific role it plays in network communications, particularly in the context of sending and receiving email.