How To Use Telnet To Test Open Ports (Windows, Linux, and MacOSX)?

The telnet is an application protocol used to connect remote devices over the network. Telnet provides text-oriented communication between local and remote hosts. Even the telnet is created to manage devices remotely via the command line interface it is also used to test open ports. As the telnet protocol and command use the TCP it can be used to test open ports remotely.

Install Telnet For Windows Operating System

Windows operating systems provide the telnet client but it is not installed by default. The telnet client for Windows operating system can install different ways which are described in detail.

Install Telnet For Linux Operating System

All major Linux distributions provide the telnet client but should be installed via the package managers like apt or dnf .

Install Telnet For Ubuntu, Debian, Mint, Kali:

$ sudo apt install telnet

Install Telnet For Fedora, CentOS, RHEL:

$ sudo dnf install telnet

Test Open Port Using IP Address

The telnet command is very simple it can accept the remote IP address and remote port we want to connect. The syntax of the telnet command is like below.

telnet IP PORT
  • IP is the remote system IP address.
  • PORT is the remote system TCP port we want to check if it is open.

In the following example, we check the HTTP port of the remote system with IP address

$ telnet 80
Connected to
Escape character is '^]'.
Connection closed by foreign host.

The output consists of 4 lines with the following meaning.

  • Trying…” line means the telnet try to connect remote IP address
  • Connected to” line means the port is open and connected succesfully.
  • Escape character is ‘^]’.” line is hust a simple information not related with the port connectivity.
  • Connection closed by foreign host.” line means the connection is closed by the remote host because every network protocol has a timeout value to close port automatically after specified of time.

Test Open Port Using Domain Name

The remote host can be also specified with the domain name or hostname. The syntax is the same with the IP address where the domain name is specified instead of the IP address. In the following example, we check the hostname port number 443 .

$ telnet 443
Test Open Port Using Domain Name
Telnet Port Check CommandDescription
telnet 80Check remote HTTP (80) port
telnet 443Check remote HTTPS (443) port
telnet 23Check remote Telnet(23) port
telnet 21Check remote FTP(21) port
telnet 25Check remote SMTP(25) port
telnet 143Check remote IMAP(143) port
telnet 3389Check remote RDP(3389) port
telnet 22Check remote SSH(22) port
Telnet Port Check

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