What is an example of Telnet?
A terminal emulation that enables a user to connect to a remote host or device using a telnet client, usually over port 23. In the image to the right, is an example of a telnet session. As can be seen from this example, a telnet session is a command line interface.
Telnet is a user command and an underlying TCP/IP protocol for accessing remote computers. Through Telnet, an administrator or another user can access someone else's computer remotely.
- Typically, this protocol is used to establish a connection to Transmission Control Protocol (TCP) port number 23, where a Telnet server application (telnetd) is listening. Telnet, however, predates TCP/IP and was originally run over Network Control Program (NCP) protocols.
- Telnet is a protocol that allows you to connect to remote computers (called hosts) over a TCP/IP network (such as the internet). Using telnet client software on your computer, you can make a connection to a telnet server (i.e., the remote host).
- You can configure the port numbers to use for SSH and Telnet connections: The default port for SSH client connections is 22; to change this default, enter a port number between 1024 and 32,767. The default port for Telnet client connections is 23; to change this default, enter a port number between 1024 and 32,767.
Telnet is a simple, text-based network protocol that is used for accessing remote computers over TCP/IP networks like the Internet. Telnet was created and launched in 1969 and, historically speaking, you can say that it was the first Internet.
- Transport - Corresponds to the transport layer and includes the TCP and UDP protocols. Application - Corresponds to the OSI Session, Presentation and Application layers and includes FTP, Telnet, ping, Rlogin, rsh, TFTP, SMTP, SNMP, DNS, your program, etc.
- The 5-Layer Model (the TCP Model)
Layer Name 4 Transport 3 Internet (sometimes called the Network Layer) 2 Network (sometimes called the Data Link Layer) 1 Physical
- HTTP is an application layer protocol designed within the framework of the Internet protocol suite. Its definition presumes an underlying and reliable transport layer protocol, and Transmission Control Protocol (TCP) is commonly used.
The encryption in telnet is based upon a shared secret key, not a public/private key system. The shared secret is established with kerberos authentication. If you do not have valid kerberos tickets, you can not establish a secure and encrypted connection with our current telnet client or telnet server programs.
- In security parlance, the term open port is used to mean a TCP or UDP port number that is configured to accept packets. In contrast, a port which rejects connections or ignores all packets directed at it is called a closed port. Ports can be "closed" (in this context, filtered) through the use of a firewall.
- The reality is that DNS queries can also use TCP port 53 if UDP port 53 is not accepted. Now with the impending deployment of DNSSEC and the eventual addition of IPv6 we will need to allow our firewalls for forward both TCP and UDP port 53 packets.
- HTTPS can run over any reliable stream transport protocol. Normally that's TCP, but it could also be SCTP. It is NOT expected to run over UDP, which is an unreliable datagram protocol (in fact, while that's not its official name, that's a good way to remember what it is).
Updated: 2nd October 2019