Flashcards
Telnet, SSH & FTP Services
Cards in this deck (45)
- 1What is a port numberA port number uniquely identifies an application running on a client or a server
- 2Why do different services have port numbersSo a computer can run multiple services using the same physical network connection
- 3What are the two transport protocols used with port numbersTCP & UDP
- 4Are TCP & UDP port numbers separate?Yes
- 5Are the TCP & UDP port numbers used for the same purpose?Yes
- 6What is a socket ?It's a combination of:
*An IP Address
*A transport protocol(TCP or UDP)
*A port number
It uniquely identifies a particular service on a particular computer - 7Name the 5 most common port numbers and their services*HTTP – TCP port 80
*SMTP – TCP port 25
*FTP – TCP ports 20 & 21
HTTPS – TCP port 443 - 8What is the telnet protocol?Telnet provides a command-line interface for control of a remote host
- 9What port number does the telnet protocol usePort 23
- 10How do users use the telnet protocol?The user uses a command line to control and send commands to the telnet server which executes the instruction as if the user were logged on locally and sends the output back to the client computer
- 11Can telnet have multiple clients?Yes they can they create a slave server for each client and tracks which one it is communicating with using the clients port numbers
- 12Is telnet secure ?No but there are options provided by windows to make it safer
- 13What is the network terminal and why is it usedIt's a set of commands both the server and client send to one another to communicate for certain actions and it used to make sure that a client and server can communicate with the needs of compatibility in terms of OS etc
- 14What are the different format characters? How many bits are they both? What do they begin with so you can tell the difference?Data and control, they are 8 bits long and the data begins with 0 and control begins with 1
- 15What are 7-bit ASCII charactersThey're characters on a keyboard that are labeled with either:
*Decimal
*Hex
*Octave
*Char - 16What does the data control function EC mean?Erase character
- 17Explain what is going on hereThe user has typed in an incorrect character so they use the 2 control commands to remove the last character and enter in the new character for the server to accept the password
- 18What are the 2 issues with telnet*It doesn't encrypt ant data between the client and server i.e login info is clear
*It doesn't authenticate the client or server so its can be vulnerable to a man in the middle attack - 19What should telnet not be used for and what is the solution for itIt shouldn't be used for remote login and the solution is SSH
- 20What does SSH stand for?Secure Shell
- 21What is SSH?It uses public key cryptography to achieve security
- 22What port does SSH work on?TCP Port 22
- 23How does SSH protect data?It generates a key pair private and public and then encrypts them rather than the data; it then uses symmetric encryption i.e ceaser shift to encrypt the packet to prevent the process from being resourcesively expensive
- 24How does the client and server use SSH for password authentication in 5 steps1) Both the client and server generate a public-private key pair
2) Server and client generate a shared session key based on the server’s key pair
3) Client encrypts username & password and sends an authentication request to the server
4) Server decrypts username & password and authenticates user
5) Client sends encrypted commands. Server decrypts, executes and sends encrypted result to be decrypted and displayed by client - 25For password authentication does the client need a key pair?No
- 26Why is public key authentication better than password authenticationBecause it avoids sending passwords
- 27Do both the client and server have a key pair with Public key AuthenticationYes
- 28How does the client and server use SSH for public key authentication in 5 steps1) Server generates a public-private key pair
2) Server and client generate a shared session key based on the server’s key pair
3) Client sends username in a public key authentication request, signed with its private key to the server
4) Server uses client’s public key to verify origin of request and authenticates client
5) Client sends encrypted commands. Server decrypts, executes and sends encrypted result to be decrypted and displayed by client - 29What else can SSH be used for?tunnelling
- 30What is tunnelling?Sending traffic through an SSH connection, which then provides protection for otherwise unprotected activities such as file transfer
- 31What does tunnelling need in order for it to work?A listener to be set up on the client (to capture traffic) and forwarding to be set up on the server (to redirect it at the other end)
- 32Can tunnelling cause any harm?Yes because it can bypass firewalls
- 33What is the FTP protocolIt allows file transfers between a client and a remote server
- 34Name the 3 steps involved in FTP between the client and server1) Client connects to the FTP server and the user is authenticated using TCP port 21 (anonymous authentication may be allowed)
2) Client browses through the folder structure, finds the desired file & sends a file transfer command to TCP port 21
3) Server opens TCP port 20 and uses this for data transfer. Connection is closed when transfer is complete - 35What the TCP ports 20 & 21 used forData requests and responses come to/from TCP port 20 on the server but control and command information are sent to/from TCP port 21.
- 36What is the status of the information sent using port 20 & 21 and what does it useThis information is said to be out-of-band, and uses the Telnet NVT format
- 37Why must the FTP server maintain server ? Does this affect the FTP server ?To know where the client currently is in the directory structure and the authentication information provided earlier
and it restricts the number of simultaneous FTP sessions the server can support - 38Is FTP secure and why?No because it sends traffic in clear traffic
- 39What are more secure protocols of FTP?SFTP & FTPS
- 40What are the difference modes FTP can operate in and what issue do they cause?Active or passive and they cause issues for the firewall
- 41What is Active (traditional) mode ?The handshake is inititiated by the client to TCP port 21 on the server;
The data transfer is initiated by the server from TCP port 20 - 42What is Passive (modern) mode ?The handshake is inititiated by the client to TCP port 21 on the server, and the server tells the client what port to use for data transfer (not 20);
The data transfer is initiated by the client to the nominate port on the server - 43Explain what is happening here and a potential issuesThe client is sending data to the FTP server using port 21 and is then downloading data using port 20
The potential issue is the clients firewall may block the connection between data exchange since the port numbers are not the same on the client end
- 44Explain what is happening here in passive mode and a potential issuesThe client is in control of both connections so it can upload and download from the FTP server while being able to trust itself.
The potential issue is that the server may not recognise a port and use its firewall to block its upload from the client
- 45Give the range for the following: 1) Well-known port numbers; 2) Registered ports; 3) Dynamic, private and ephermeral ports.1) Well-known port numbers – 1-1023;
2) Registered ports – 1024-49151;
3) Dynamic, private and ephermeral ports – 49152-65535.
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- System Admin Semester 2 Flashcards on Telnet, SSH & FTP Services, created by Tunds on 05/03/2015.
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- Tunds
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