Which layer 4 protocol is used for a Telnet connection?

The appropriate layer 4 protocol for a Telnet connection is TCP (Transmission Control Protocol). Telnet is a protocol used to provide a command-line interface for communication with remote devices. This is crucial for tasks such as remote server management or accessing network devices.

TCP is chosen because it offers reliable, ordered, and error-checked delivery of data between applications. This is essential for Telnet communications, as the user expects a consistent, reliable session without data loss or duplication. TCP establishes a connection-oriented session, ensuring that all packets are delivered correctly and in sequence, making it ideal for interactive sessions such as those facilitated by Telnet.

Other protocols mentioned may not fulfill the requirements for a Telnet connection. For example, IP is a layer 3 protocol responsible for routing packets but does not manage data flow or reliability. TCP/IP refers to a suite of protocols where TCP plays the role at layer 4, but it does not directly refer to a specific layer 4 protocol like Telnet requires. UDP, another layer 4 protocol, is connectionless and does not guarantee delivery, making it unsuitable for the interactive and reliable nature of Telnet.