Telnet vs SSH

Last Updated on Wed, 28 Jun 2023 | Firewall Fundamentals

Telnet is an unencrypted network communication protocol that is typically used to provide remote access to systems and other devices. Telnet is originally defined in RFC 854 and was developed long before the Internet was in its current formwhen networks were much smaller. Not much consideration was given in the Telnet protocol design to confidentiality in the data being transmitted using the protocol. Therefore, all data transmitted using the Telnet protocol is subject to eavesdropping and susceptible to capture.

SSH provides for cryptographic protection of data as well as authentication and ensures that the integrity and confidentiality of the communication is secured. If a device can support SSH as an access method to the command line, it should be preferred over Telnet. Alternatively, if the device's GUI is accessible within a secure network and it is necessary to remotely manage the device across an insecure network and an SSH connection can be established, it is possible to tunnel the connection through SSH. To establish an SSH tunnel between two hosts, you need to use port forwarding. In the example shown in Figure 11-6 the client establishes an SSH connection through to the SSH server on TCP port 22 (the standard SSH port). However, the client uses the port-forwarding capability to forward his localhost TCP port 1025 and redirects it to the Telnet port of on the router. To access the Telnet port of the router through the tunnel, the client need only telnet to his localhost TCP port 1025 and he will automatically be redirected, through the SSH tunnel, to the router's Telnet port.

Figure 11-6. SSH Forwarding Across an Insecure Network

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Insecure Network I Secure Network

Figure 11-6. SSH Forwarding Across an Insecure Network

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Insecure Network I Secure Network

This way the traffic goes through an encrypted SSH session between the client and the SSH server and then the traffic can be forwarded using an insecure protocol such as Telnet.

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Readers' Questions

  • madison
    What is the difference between telnet and ssh?
    8 months ago
    • Telnet is an unencrypted protocol for remote access, whereas SSH (Secure Shell) is a secure encrypted protocol for remote access. Telnet does not provide any data encryption, so it is considered less secure than SSH. Furthermore, SSH allows for strong authentication using public keys, making it much more difficult for malicious actors to access servers.
    • Berylla
      Why is ssh preferred over telnet for remote connections?
      8 months ago
      • SSH (Secure Shell) is preferred over telnet for remote connections because it provides a secure encrypted connection, while telnet does not encrypt its data. Furthermore, SSH provides stronger authentication mechanisms than telnet, which makes it more resistant to remote hacking. Additionally, SSH is more versatile than telnet, as SSH can forward arbitrary network protocols, while telnet is limited to just terminal access.