Telnet/SSHConnecting to Hosts

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What is Telnet? Method for connecting to hosts

Enables remote login (rlogin) to computers on the Internet• One computer can connect to another to use its services• Like Window’s Remote Desktop

Establishes a “dumb terminal” session• No processing on the client side once connected• Local terminal appears to be a terminal at the remote system.• Simple input/output device

Client-Server Application Users (clients) connect to multiuser computers (servers) Uses telnet protocol (port 23) over Internet (TCP/IP) One of the first Internet applications (1968)

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Why Telnet? Before PC became popular

People used terminals physically connected to big computers (e.g., mainframes)

Problems• Need a terminal per machine per user

→ 3 mainframes & 5 users = 15 terminals→ Like having 10 TVs to view 10 channels

• Difficult to access over distance

Telnet protocol made possible “terminal emulation”

• i.e., virtual terminal regardless of location & hardware

⇓• any computer running telnet client• can connect to & use any computer

running telnet server• over Internet (TCP/IP, physical layer)

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Telnet: Client-Server Architecture

Telnet Server The actual server is software that runs typically on larger computers

• with multi-user, multi-tasking operating systems like Unix &• a full-time/direct/high-speed connection to Internet

May provide dumb terminal access to• external data & services

→ library database or commercial service

• internal data & applications→ files on disk, shell account

Telnet Client The software that initiates a telnet connection Provides the interface and a set of features for the end user

• e.g., allow user to use custom fonts/colors

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Telnet: How to Use

telnet HOSTNAME PORTNUMBER HOSTNAME = host name or IP address PORTNUMBER = port

• Default telnet (login) port = 23• Web server port = 80

Examples• telnet widit.knu.ac.kr 80

→ Connect to WIDIT Web Server• telnet rainmaker.wunderground.com

→ Access weather information• telnet sdf.lonestar.org

→ Create a shell account at SDF Public Access Unix System

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Telnet: Weakness

Telnet suffers from a major security problem Communication is done in plain text

• Data from/to client and server can be captured by a LAN computer using a snooper software

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Telnet Client 1

Telnet Server

Snooper

ID, password

Telnet Client 2

Banking info

SecureSHell Overview Replacement for Telnet

Communication between computers using encryption • Encryption = transform data in unreadable form• Communication is encrypted over a secure channel

Current standard for remote login (port 22)• Secure command shell (remote execution of commands)

History Originated from an academic project in Finland Commercialized in 1998 by SSH Communications Security SSH1 expired in May 1995 because of security flaws SSH2 is currently used

Client Software SSH Client MobaXterm PuTTY

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SSH: Client-Server Architecture

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SSH ClientInitiates a Connection

SSH ServerWaits & Responds to

Incoming Connections

Client Application Server Applicationprogram running on

client machine(e.g., Putty, SSH Secure Shell)

Application Protocol(SSH)

203.247.16.240 155.230.194.245

program running on server machine

(e.g., Open SSH Server )Encrypted Data

FTP/SFTPTransferring Files

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FTP Overview Used to transfer files from one computer to another

Port 20, 21 - one to send data and one to send commands

A basic Internet service (like telnet and email)

Works with all types of computers (Unix, pc, mac, etc.) &all types of files (“binary” and “text”)

One of the first Internet applications (1971)

Involves Navigation on both client and server User authentication

• Exception: Anonymous FTP→ Allows access to “public” FTP sites→ Only allows access to specific directories→ e.g., login ID=anonymous, password=email address

Suffers from security problem similar to Telnet

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SFTP Overview Stands for

SSH File Transfer Protocol

Provides Secure data transfer by data encryption over an SSH session Replacement for FTP

SFTP Clients GUI Interactive file transfer programs Perform all operations over an encrypted transport Examples

• SSH Secure File Transfer (includes SSH client: SSH Secure Shell)• WinSCP – supports SFTP & SCP

• FileZilla – cross platform (Windows, Linux, Mac OS)

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SSH & SFT ClientsPuTTY & SSH Secure File Transfer

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SSH Client: PuTTY

PuTTY configuration1. Download and double click PuTTY2. Type in the Host Name (e.g. widit.knu.ac.kr) and click Open3. Login

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SSH Client: PuTTY PuTTY configuration (continued)

4. Right-click the top blue bar of the PuTTY window5. Select “Change Settings”6. Select “Translation” under Window Category7. Set Character set translation to “UTF-8”

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SSH Client: PuTTY PuTTY configuration (continued)

8. Select “Appearance” under Window Category9. Set Font settings to desired font if needed10. Select “Colors” under Window Category11. Set Default Foreground and Default Background to desired colors if needed12. Click Apply to apply the current settings.

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SSH Client: PuTTY PuTTY configuration (continued)

13. Click the “Session” category14. Type in a name for the current configuration (e.g., widit) in the “Saved Sessions” box15. Click Save to save the current settings 16. Next time, you can right-Click the top blue bar and select Saved Sessions to choose the appropriate

session (e.g. widit)

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SFTP Client: FileZillaDownload & install FileZilla.

In the FileZilla’s main menu,1. Click File and 2. select Site Manager.

In the Site Manager window,1. Click New Site2. Type in the Remote Host Name

(e.g. widit.knu.ac.kr)3. Select SFTP Protocol4. Select Ask for password Logon

Type5. Type in your User Name

(leave the password blank)6. Click the Rename button7. Type in a site name

(e.g., widit)8. Click Connect

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SFTP Client: FileZilla

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SFTP Client: FileZilla

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Adding Bookmarks:

1. Go to target directories by typing in the path in the site address box (A) or traversing the directory tree (B).

2. Click Bookmarks and 3. Select Add bookmark.

4. Select Site-specific bookmark and5. Type in the bookmark name

→ The saved bookmark should appear under the Bookmarks menu.

SFTP Client: FileZilla

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displays saved site profile toggles the display of the message log toggles the display of the local directory tree toggles the display of the remote directory tree toggles the display of the transfer queue Refreshes the file and folder lists

SFTP Client: FileZilla

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Using Quickconnect:

In the Quickconnect bar, Type in Host name, Username, Password, Port value of 22, Click the Quickconnect button, and Click OK to connect.

Click File in the Menu bar, and Select Copy current connection to Site Manager.

In the Site Manager window, Type in the site name and Click OK.→ The saved connection should appear

in the Site Manager.