Telnet (Teletype Network) is an application layer protocol that was developed in 1969. It provides text‑based, bidirectional communication. Similar to SSH, it also allows users to access the CLI remotely. However, because Telnet was developed before the internet, security was not considered necessary, so it transmits all data including usernames and passwords in plain text. Nowadays, if anyone intercepts network traffic, they can easily read sensitive data. Therefore, for security reasons, Telnet should only be used over trusted networks. SSH provides secure login by encrypting transmitted data. Due to this vulnerability, Telnet is now primarily used for testing whether a specific TCP port is open and accepting connections.

Telnet vs. Ping

Telnet establishes a remote text session and is also used for testing specific TCP services. It is an application layer protocol that relies on the transport layer protocol TCP. It operates on port 23 by establishing a connection using the TCP three‑way handshake.

Ping tests basic host reachability and measures round‑trip latency. It works with the network layer protocol ICMP. Since ICMP operates below the transport layer, it does not require a port. It functions without establishing a connection.

Conclusion

In real-life network diagnosis, the best approach is to use both tools. First, check basic connectivity using ping. If it fails, the target host is either down, disconnected, or the firewall is blocking ICMP traffic. If it responds to ping, the next step is to check service availability using telnet. Even when a host responds to ping, an application running on a specific port may still be unable to communicate. By running the command telnet targetAddress port, you can verify whether the application service itself is listening and accepting TCP handshakes.