PuTTy and Protocols

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SSH, Telnet and Rlogin are three ways of doing the same thing: logging in to a multi-user computer from another computer, over a network.

Using this type of interface, there is no need for you to be sitting at the same machine you are typing commands to. The commands, and responses, can be sent over a network, so you can sit at one computer and give commands to another one, or even to more than one.

SSH, Telnet and Rlogin are network protocols that allow you to do this. On the computer you sit at, you run a client, which makes a network connection to the other computer (the server). The network connection carries your keystrokes and commands from the client to the server, and carries the server's responses back to you.

These protocols can also be used for other types of keyboard-based interactive session. In particular, there are a lot of bulletin boards, talker systems and MUDs (Multi-User Dungeons) which support access using Telnet. There are even a few that support SSH.


Unix software utility that allows users to log in on another host via a network, communicating via TCP port 513. It was first distributed as part of the 4.2BSD release. rlogin is also the name of the application layer protocol used by the software, part of the TCP/IP protocol suite.

SSH and Rlogin both allow you to log in to the server without having to type a password. (Rlogin's method of doing this is insecure, and can allow an attacker to access your account on the server. SSH's method is much more secure, and typically breaking the security requires the attacker to have gained access to your actual client machine.)


Secure SHell (SSH) is a cryptographically protected remote login protocol designed to replace the insecure telnet and rlogin protocols. SSH provides strong protection against password sniffing and third party session monitoring, better protecting your authentication credentials and privacy. In addition to protecting your passwords and your privacy, SSH offers additional authentication methods that are considered more secure than passwords, such as public key authentication, and extensive protection against spoofing.

Putty SSH[edit]


  • PuTTY.exe — Secure Shell client
  • PuTTYgen.exe — SSH public/private key generator
  • Pagent.exe — SSH key agent
  • PSCP.exe — Secure Copy from command line
  • PSFTP.exe — Secure Copy with FTP-like interface

Internet Protocol Suite[edit]

Internet protocol suite is the set of communications protocols that implement the protocol stack on which the Internet and most commercial networks run. It is sometimes called the TCP/IP protocol suite, after the two most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), which were also the first two defined.

TCP/IP provides end-to-end connectivity specifying how data should be formatted, addressed, transmitted, routed and received at the destination. It has four abstraction layers which are used to sort all Internet protocols. From hight to low they are:

  1. Application Layer protocols for specific data communications services on a process-to-process level.
  2. Transport Layer handles host-to-host communication
  3. Internet Layer connects local networks, thus establishing internetworking.
  4. Link Layer communication technologies for a local network.

Application Layer[edit]

Application Layer Description
BGP Border Gateway Protocol is the protocol which is used to make core routing decisions on the Internet; it involves a table of IP networks or "prefixes" which designate network reachability among autonomous systems (AS)
DHCP Dynamic Host Configuration Protocol is a network protocol to configure devices connected to a network for communication on an IP network.
DNS Domain Name System is a hierarchical distributed naming system for computers/services/resources connected to the internet or a private network.
FTP File Transfer Protocol (FTP) is a standard network protocol used to transfer files from one host or to another host over a TCP-based network, such as the Internet.
HTTP Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, hypermedia information systems. Hypertext is a multi-linear set of objects, building a network by using logical links (the so-called hyperlinks) between the nodes (e.g. text or words). HTTP is the protocol to exchange or transfer hypertext.
IMAP Internet Message Access Protocol is an Application Layer Internet protocol that allows an e-mail client to access e-mail on a remote mail server.
IRC Internet Relay Chat is a protocol for live interactive Internet text messaging (chat) or synchronous conferencing.
LDAP The Lightweight Directory Access Protocol is an application protocol for accessing and maintaining distributed directory information services over an Internet Protocol (IP) network.
MGCP Media Gateway Control Protocol is one of the implementations of the Media Gateway Control Protocol Architecture for controlling media gateways on Internet Protocol (IP) networks and the public switched telephone network (PSTN).
NNTP Network News Transfer Protocol is an application protocol used for transporting Usenet news articles (netnews) between news servers and for reading and posting articles by end user client applications.
POP Post Office Protocol (POP) is an application-layer Internet standard protocol used by local e-mail clients to retrieve e-mail from a remote server over a TCP/IP connection.
NTP Network Time Protocol is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks.
RPC Remote Procedure Call is an inter-process communication that allows a computer program to cause a subroutine or procedure to execute in another address space (commonly on another computer on a shared network) without the programmer explicitly coding the details for this remote interaction.
RTP Real-time Transport Protocol defines a standardized packet format for delivering audio and video over IP networks.
RTSP Real Time Streaming Protocol is a network control protocol designed for use in entertainment and communications systems to control streaming media servers.
RIP Routing Information Protocol is a distance-vector routing protocol, which employs the hop count as a routing metric
SIP Session Initiation Protocol is an IETF-defined signaling protocol widely used for controlling communication sessions such as voice and video calls over Internet Protocol (IP). The protocol can be used for creating, modifying and terminating two-party (unicast) or multiparty (multicast) sessions. Sessions may consist of one or several media streams.
SMTP Simple Mail Transfer Protocol is an Internet standard for electronic mail (e-mail) transmission across Internet Protocol (IP) networks.
SNMP Simple Network Management Protocol (SNMP) is an "Internet-standard protocol for managing devices on IP networks".
SOCKS SOCKet Secure (SOCKS) is an Internet protocol that routes network packets between a client and server through a proxy server. SOCKS5 additionally provides authentication so only authorized users may access a server. Practically, a SOCKS server will proxy TCP connections to an arbitrary IP address as well as providing a means for UDP packets to be forwarded.
SSH Secure Shell is a cryptographic network protocol for secure data communication, remote shell services or command execution and other secure network services between two networked computers that connects, via a secure channel over an insecure network, a server and a client (running SSH server and SSH client programs, respectively). The protocol specification distinguishes between two major versions that are referred to as SSH-1 and SSH-2.
Telnet Telnet is a network protocol used on the Internet or local area networks to provide a bidirectional interactive text-oriented communication facility using a virtual terminal connection. User data is interspersed in-band with Telnet control information in an 8-bit byte oriented data connection over the Transmission Control Protocol (TCP).
TLS/SSL Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL), are cryptographic protocols that provide communication security over the Internet. TLS and SSL encrypt the segments of network connections at the Application Layer for the Transport Layer, using asymmetric cryptography for key exchange, symmetric encryption for confidentiality and message authentication codes for message integrity.
XMPP Extensible Messaging and Presence Protocol (XMPP) is a communications protocol for message-oriented middleware based on XML (Extensible Markup Language).[1] The protocol was originally named Jabber.

Transport Layer[edit]

Transport Layer Description
DCCP Datagram Congestion Control Protocol
RSVP Resource Reservation Protocol
SCTP Stream Control Transmission Protocol
TCP Transmission Control Protocol is one of the core protocols of the Internet protocol suite. TCP is one of the two original components of the suite, complementing the Internet Protocol (IP), and therefore the entire suite is commonly referred to as TCP/IP. TCP provides reliable, ordered delivery of a stream of octets from a program on one computer to another program on another computer. TCP is the protocol used by major Internet applications such as the World Wide Web, email, remote administration and file transfer. Other applications, which do not require reliable data stream service, may use the User Datagram Protocol (UDP), which provides a datagram service that emphasizes reduced latency over reliability.
UDP User Datagram Protocol is one of the core members of the Internet protocol suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol (IP) network without prior communications to set up special transmission channels or data paths.

Internet Layer[edit]

Internet Layer Description
ECN Explicit Congestion Notification is an extension to the Internet Protocol and to the Transmission Control Protocol and is defined in RFC 3168 (2001). ECN allows end-to-end notification of network congestion without dropping packets. ECN is an optional feature that is only used when both endpoints support it and are willing to use it. It is only effective when supported by the underlying network.
ICMP Internet Control Message Protocol is one of the core protocols of the Internet Protocol Suite. It is used by the operating systems of networked computers to send error messages indicating, for example, that a requested service is not available or that a host or router could not be reached. ICMP can also be used to relay query messages.
IGMP Internet Group Management Protocol is a communications protocol used by hosts and adjacent routers on IP networks to establish multicast group memberships. IGMP is an integral part of IP multicast.
IP Internet Protocol is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. This function of routing enables internetworking, and essentially establishes the Internet.
IP is the primary protocol in the Internet layer of the Internet protocol suite and has the task of delivering packets from the source host to the destination host solely based on the IP addresses.
For this purpose, IP defines datagram structures that encapsulate the data to be delivered. It also defines addressing methods that are used to label the datagram source and destination.
IPsec Internet Protocol Security is a protocol suite for securing Internet Protocol (IP) communications by authenticating and encrypting each IP packet of a communication session. IPsec also includes protocols for establishing mutual authentication between agents at the beginning of the session and negotiation of cryptographic keys to be used during the session.

Link Layer[edit]

Link Layer Description
ARP Address Resolution Protocol (ARP) is a telecommunications protocol used for resolution of network layer addresses into link layer addresses, a critical function in multiple-access networks.
ARP has been implemented in many combinations of network and overlaying internetwork technologies, such as IPv4, Chaosnet, DECnet and Xerox PARC Universal Packet (PUP) using IEEE 802 standards, FDDI, X.25, Frame Relay and Asynchronous Transfer Mode (ATM), IPv4 over IEEE 802.3 and IEEE 802.11 being the most common cases.
In Internet Protocol Version 6 (IPv6) networks, the functionality of ARP is provided by the Neighbor Discovery Protocol (NDP).
DSL Digital subscriber line (DSL, originally digital subscriber loop) is a family of technologies that provide Internet access by transmitting digital data over the wires of a local telephone network. In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line (ADSL), the most commonly installed DSL technology. DSL service is delivered simultaneously with wired telephone service on the same telephone line. This is possible because DSL uses higher frequency bands for data. On the customer premises, a DSL filter on each non-DSL outlet blocks any high frequency interference, to enable simultaneous use of the voice and DSL services.
Ethernet Ethernet is a family of computer networking technologies for local area networks (LANs). Ethernet was commercially introduced in 1980 and standardized in 1985 as IEEE 802.3. Ethernet has largely replaced competing wired LAN technologies.
The Ethernet standards comprise several wiring and signaling variants of the OSI physical layer in use with Ethernet. The original 10BASE5 Ethernet used coaxial cable as a shared medium. Later the coaxial cables were replaced by twisted pair and fiber optic links in conjunction with hubs or switches.
FDDI Fibre Distributed Data Interface (FDDI) provides a 100 Mbit/s optical standard for data transmission in a local area network that can extend in range up to 200 kilometers (120 mi). Although FDDI logical topology is a ring-based token network, it does not use the IEEE 802.5 token ring protocol as its basis;
ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network.
Token ring Token ring local area network (LAN) technology is a protocol which resides at the data link layer (DLL) of the OSI model. It uses a special three-byte frame called a token that travels around the ring.


The oldest and most insecure way. Use it only when nothing else is available.


  • PuTTY, A free SSH, Telnet and Rlogin client for 32-bit Windows systems.
  • WinSCP, Open Source Freeware SFTP GUI client for Windows using SSH.

See also[edit]



In this article the Putty manual by Simon Tatham has been used frequently.


  • Internet Protocol Suite, Wikipedia information on TCP/IP.
  • PuTTy Manual, Tartarus Putty Manual by Simon Tatham creator of PuTTy.
  • Unix Wiz Putty OpenSSH, Tech Tip details how to use the free PuTTY SSH client to connect to a Linux system running the OpenSSH server, all while using public key encryption and SSH agent support.
  • Wikipedia, List of HTTP status codes,
    • 1xx Informational, Request received, continuing process.
    • 2xx Success, Indicates the action requested by the client was received, understood, accepted and processed successfully.
    • 3xx Redirection, indicates that further action needs to be taken by the user agent to fulfil the request. The action required may be carried out by the user agent without interaction with the user if and only if the method used in the second request is GET or HEAD
    • 4xx Client Error, intended for cases in which the client seems to have erred.
    • 5xx Server Error, The server failed to fulfill an apparently valid request
  • Wikipedia, List of common media types.
  • W3Org, rfc2616
  • DataTrackers httpbis
  • Mozilla Live HTTP headers.