Protocols and Servers

1. Telnet: application layer protocol used to connect to a virtual terminal of another computer -access console to run programs, start batch processes and perform system admin tasks remotely -login using username and password -not encrypted -uses telnet protocol to listen for incoming connections on port 23 eg: telnet [IP] -not reliable for access to remote system bc all data is sent in clear text

2. HTTP: protocol used to transfer web pages. -connects to the webserver and uses HTTP to request HTML pages and images, submit forms, upload files etc -sends and receives data as cleartext (not encrypted) -need HTTP server(webserver) and an HTTP client (web browser) to use HTTP protocol -Three Popular HTTP servers (Apache, Internet Information Services(IIS), Nginx) -Web browsers (Chrome, Edge, Firefox, Safari)

3. FTP: File Transfer Protocol -created to make transfer of files between different computers efficient -sends and receives data as cleartext -default port 21

4. connect to an FTP server using Telnet client

5. provide user and pass usefull commands:

• ‘STAT’ - provide some added information
• ‘SYST’ - shows the system type of the target
• ‘PASV’ - switches mode to passive
• ‘TYPE A’ - switches file transfer to ASCII
• ‘TYPE I’ - switches file transfer mode to binary Active mode - data is sent over a separate channel originating from the FTP server’s port 20 Passive mode - data is sent over a separate channel originating from an FTP client’s port above port 1023 After logged in: ‘ftp>’ - execute various commands ‘ls’ - list files ‘get [FILE NAME]’ - client and server extablish another channel for file transfer

4. SMTP: Simple Mail Transfer Protocol -Email system can be used to allow local users to exchange emails with each other without access to the internet -multiple components

5. Mail Submmision Agent (MSA) - has email to be sent, connects to MUA to send message, checks for errors before passing to MTA

6. Mail Transfer Agent (MTA) - send the emamil message to MTA of the recipient

7. Mail Delivery Agent (MDA) - passed to MDA to deliver to email client

8. Mail User Agent (MUA) - agent send the mail Two protocols

9. Simple Mail Transfer Protocol (SMTP)

10. Post Office Protocol Version 3 (POP3) or Internet Message Access Protocol (IMAP) SMTP - communicate using an MTA server -cleartext -default port 25 by default steps:

11. telnet [IP] 25

12. helo [hostname]

13. mail from:

14. rcpt to:

15. data

16. -ENTER ’.’ Enter to send

17. Post Office Protocol 3 (POP3) -used to download email messages from a mail delivery agent (MDA) -default port 110 -steps:

18. telnet [IP] 110

19. USER [username]

20. PASS [password]

21. ‘STAT’ —reply +OK nn mm— nn: number of email messages in the inbox mm: size of the inbox in octates (byte)

22. ‘LIST’ -list of messages on server-

23. ‘RETR [number]’ —retrive message from list—

24. Internet Message Access Protocol (IMAP) -more synchronized than POP3 -keep email syncronized across multiple devices and mail clients -default port: 143 -IMAP requires each command to be preceded by a random string to be able to track the reply, c1, c2, etc -List mail folders: ‘LIST "" ”*”’ -steps:

25. telnet [IP] 143

26. c1 LOGIN [username] [password]

27. c2 LIST "" ”*”

Protocol TCP Port Application(s) Data Security FTP 21 File Transfer Cleartext HTTP 80 Worldwide Web Cleartext IMAP 143 Email (MDA) Cleartext POP3 110 Email (MDA) Cleartext SMTP 25 Email (MTA) Cleartext Telnet 23 Remote Access Cleartext