Telnet/SSH: Connecting to Hosts Internet Technology1.
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Transcript of Telnet/SSH: Connecting to Hosts Internet Technology1.
Telnet/SSH:Connecting to Hosts
Internet Technology 1
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)
Internet Technology 2
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)
Internet Technology 3
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
Internet Technology 4
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 kiyang.kmu.ac.kr
Connect to KMU Web hosting services (login required)• telnet www.kmu.ac.kr 80
Connect to KMU Web Server• telnet sdf.lonestar.org
Create a shell account at SDF Public Access Unix System
Internet Technology 5
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
Internet Technology 6
Telnet Client 1
Telnet Server
Snooper
ID, password
Telnet Client 2
Banking info
SecureSHell Overview Replacement for Telnet
► Communicate with other computers using encryption • Encryption = transform data in unreadable form
► Current standard for remote login• Secure command shell (remote execution of commands)• Secure file transfer
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► PuTTY
Internet Technology 7
Internet Technology
SSH ClientInitiates a Connection
SSH Server Waits & Responds to Incoming Connections
Client Application Server Applicationprogram running on
client machine(e.g., Putty, SSH Secure Shell)
Application Protocol(SSH)
SSH: Client-Server Architecture
203.247.16.240 203.247.16.248
program running on server machine
(e.g., Open SSH Server )
8
Encrypted Data
FTP/SFTP: Transferring Files
Internet Technology 9
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 login ID=anonymous, password=email address
Suffers from security problem similar to Telnet
Internet Technology 10
SFTP Overview Stands for
► Secure File Transfer Protocol or SSH File Transfer Protocol
Provides ► Secure data transfer by data encryption► Replacement for FTP
SFTP Clients► GUI Interactive file transfer programs► Perform all operations over an encrypted transport► SSH Secure File Transfer (includes SSH client: SSH Secure Shell)
Internet Technology 11
SSH & SFT Clients:PuTTY & SSH Secure File Transfer
Internet Technology 12
SSH Client: PuTTY PuTTY configuration
1. Download and double click PuTTY 2. Type in the Host Name (e.g. widit.knu.ac.kr) and click Open3. Login
Internet Technology 13
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”
Internet Technology 14
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.
Internet Technology 15
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)
Internet Technology 16
SFTP Client: SSH Secure File Transfer SSH Secure File Transfer (includes SSH client)
1. Click File, and select Connect2. Type in the Remote Host Name (e.g. widit.kmu.ac.kr), User Name, and click Connect3. Type in Password
Internet Technology 17
SFTP Client: SSH SFTP SSH Secure File Transfer (continued)
1. Click Profiles, and select Add Profile2. Type in the profile name (e.g. widit-ftp) and click Add to Profiles3. Next time, Click Profiles and select the saved profile name to connect
Internet Technology 18