Terminal Access Protocols ============================== These protocols play key roles in network communication by establishing sessions and enabling secure or remote access to devices and systems. .. toctree:: :maxdepth: 1 :hidden: :includehidden: Telnet rlogin rsh mosh .. list-table:: :widths: 20 60 20 :header-rows: 1 * - Protocol - Description - Use Case * - Telnet - A legacy protocol that provides remote command-line access over TCP port 23. Telnet transmits data—including usernames and passwords—in plaintext, making it vulnerable to interception. *Due to lack of encryption, Telnet is mostly replaced by SSH in secure environments.* - Remote management of legacy devices and network equipment, mainly in trusted or isolated networks. * - rlogin (Remote Login) - A legacy protocol that provides remote terminal access over TCP port 513. It enables a user to log in to another UNIX host. Authentication is based on trusted hosts or `.rhosts` files, making it insecure for untrusted networks. *Often replaced by SSH due to lack of encryption.* - Remote shell access between UNIX systems in trusted networks. * - rsh (Remote Shell) - Allows remote command execution without interactive login. Uses TCP port 514. Like rlogin, it depends on `.rhosts` trust, which poses security risks. *Replaced by SSH in most modern systems.* - Automating commands across trusted UNIX systems. * - mosh (Mobile Shell) - A modern remote terminal application designed for intermittent and roaming network conditions. Unlike SSH, it maintains session state when IP addresses or connectivity change. *Uses UDP and provides encryption.* - Remote shell access over unreliable or mobile networks. .. tab-set:: .. tab-item:: Telnet **Main Features** - Provides remote command-line access over TCP port 23 - Transmits data, including usernames and passwords, in plaintext - Simple and widely supported on legacy devices - Does not provide encryption or strong authentication **RFC References** - RFC 854 – Telnet Protocol Specification - RFC 855 – Telnet Options **Use Cases** - Remote management of legacy network devices - Access in trusted or isolated network environments - Basic command-line access where security is not a concern **Alternative Protocols** - SSH – Encrypted remote shell access - Console access via serial or out-of-band management - Remote desktop protocols for GUI access (RDP, VNC) .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: What You Will Learn in This Section **Let us learn more about Telnet:** * :ref:`Learnings in this section ` * :ref:`Terminology ` * :ref:`Version Info ` * :ref:`Telnet Version&RFC Details ` * :ref:`Telnet Basic Setup on Ubuntu using IPv4 ` * :ref:`Telnet Basic Setup on Ubuntu using IPv6 ` * :ref:`Telnet Protocol Packet Details ` * :ref:`Telnet Usecases ` * :ref:`Telnet Basic Features ` * :ref:`Telnet Feature : Text based Communication ` * :ref:`Telnet Feature : Remote Login ` * :ref:`Telnet Feature : Port Based Access ` * :ref:`Telnet Feature : Network Virtual Terminal ` * :ref:`Telnet Feature : Option Negotiation ` * :ref:`Telnet Feature : Subnegotiation support ` * :ref:`Telnet Feature : Cross Platform Compatiblity ` * :ref:`Telnet Feature : Simple Protocol structure ` * :ref:`Reference links ` .. button-link:: ./Telnet.html :color: primary :shadow: :expand: Jump to "Telnet" .. tab-set:: .. tab-item:: rlogin (Remote Login) **Main Features** - Provides remote login over TCP port 513 - Relies on `.rhosts` for host/user trust relationships - No encryption; data is sent in plaintext - Interactive login shell on remote systems **RFC References** - Not formalized in a standalone RFC but described in BSD UNIX documentation **Use Cases** - Logging into UNIX systems across trusted LANs - Administrative access in non-critical environments **Alternative Protocols** - SSH – Secure replacement with encrypted communication - Telnet – Similar legacy protocol, also insecure .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: What You Will Learn in This Section **Let us learn more about rlogin:** * :ref:`Learnings in this section ` * :ref:`Terminology ` * :ref:`Version Info ` * :ref:`rlogin Version&IEEE Details ` * :ref:`rlogin Basic Setup on Ubuntu using IPv4 ` * :ref:`rlogin Basic Setup on Ubuntu using IPv6 ` * :ref:`rlogin Protocol Packet Details ` * :ref:`rlogin Usecases ` * :ref:`rlogin Basic Features ` * :ref:`Reference links ` .. button-link:: ./rlogin.html :color: primary :shadow: :expand: Jump to "rlogin" .. tab-set:: .. tab-item:: rsh (Remote Shell) **Main Features** - Executes commands on a remote machine over TCP port 514 - Does not require interactive login - Insecure: relies on `.rhosts` for access control - Sends credentials and data unencrypted **RFC References** - No official RFC; defined in BSD UNIX specifications **Use Cases** - Running batch jobs or commands remotely - Scripts requiring remote execution on trusted systems **Alternative Protocols** - SSH – Secure remote command execution - SCP/SFTP – For secure file transfers and scripts .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: What You Will Learn in This Section **Let us learn more about rsh:** * :ref:`Learnings in this section ` * :ref:`Terminology ` * :ref:`Version Info ` * :ref:`rsh Version&IEEE Details ` * :ref:`rsh Basic Setup on Ubuntu using IPv4 ` * :ref:`rsh Basic Setup on Ubuntu using IPv6 ` * :ref:`rsh Protocol Packet Details ` * :ref:`rsh Usecases ` * :ref:`rsh Basic Features ` .. button-link:: ./rsh.html :color: primary :shadow: :expand: Jump to "rsh" .. tab-set:: .. tab-item:: mosh (Mobile Shell) **Main Features** - Designed for mobile/roaming environments - Uses UDP for communication (default port 60000+) - Supports intermittent connectivity and IP changes - Encrypted sessions using AES-CTR and client-side prediction **RFC References** - No RFC; open-source protocol developed by MIT **Use Cases** - Connecting to remote systems from mobile networks - Stable terminal access in poor or changing connectivity - SSH alternative for mobile workers **Alternative Protocols** - SSH – Reliable but less tolerant to IP changes - Tmate – For collaborative remote sessions .. panels:: :container: container pb-4 :column: col-lg-12 p-2 :card: What You Will Learn in This Section **Let us learn more about mosh:** * :ref:`Learnings in this section ` * :ref:`Terminology ` * :ref:`Version Info ` * :ref:`mosh Version&IEEE Details ` * :ref:`mosh Basic Setup on Ubuntu using IPv4 ` * :ref:`mosh Basic Setup on Ubuntu using IPv6 ` * :ref:`mosh Protocol Packet Details ` * :ref:`mosh Usecases ` * :ref:`mosh Basic Features ` * :ref:`Reference links ` .. button-link:: ./mosh.html :color: primary :shadow: :expand: Jump to "mosh"