Application Protocols

1. Application Protocols

2. Domain Name Service • http://topicmaps.bond.edu.au/mda/internet/dns/@/users/rho/InTechI/ • defines a hierarchical naming standard for the Internet (1980s) • Relies on a Database • Root servers • Distributed over 13 key computers

3. DNS Domain? Part of IP add are same? Your Domain needs Internet Recognition? Go register with one of ICANN’s accredet registers No other parties in the world can use your domain for their machines

4. DNS • top-level-domains (TLDs) • "old-style" .com, .edu, .net, .mil, .gov • ccTLDs .au, .us, .gb • "new generic" TLDs .info, .biz • second-level-domains • company.com, com.au • third-level-domains • bond.edu.au

5. TLD • ARPA – Reverse lookup domain • COM- Commercial • EDU- Educational • GOV- Government • ORG- Non commercial organization • NET- Network such as ISP • INT- International Treaty organization

6. TLD • MIL- U.S. Military Organization • BIZ- Business • INFO- Unrestricted use • AERO- Air-transport industry • COOP- Cooperatives • MUSEUM- Museums • NAME- Individuals • PRO- Professionals such as doctors, lawyers and engineers

7. DNS • maps domain names to IP addresses • eg. kirk.bond.edu.au -> A 131.244.1.1 • 'A record' holds address information in database • Name Space? database of Internet IP adds and their associated names

8. DNS • Divided into components for routing efficiently • 1. Resolvers: any host on the internet that needs to look up domain name info & associate that info with an IP add. It is build into TCP/IP applications such as Telnet, HTTP and FTP. Example: when you type cnn.com, your workstation initiates a resolver to associate the host name (cnn.com) with the correct IP. If you have connected b4, the info may exist in the temp memory & retrieved quickly. Otherwise the resolver service queries your machine’s name server to get the IP for cnn.com

9. DNS • 2. Name servers: also known as DNS servers. They contain database of names and their associated IPs. It supplies a resolver the info queried. • Hierarchy: if a name server cannot resolve the IP, query is passed on to higher level name server

10. DNS Name Server example: look for cnn.com via your browser what happens first? Who tries to serve the query first? your company’s DNS server if you are browsing from your company if it cannot find the IP, query goes to the higher level name server of the company’s ISP

11. DNS • If ISP’s name server cannot resolve -> passes to another name server • Each name server manages a group of devices, collectively called a zone • In a company DNS server-> include all the pcs and their ips • At the highest level ->root server • Every name server holds a piece of the DNS name space

12. DNS Database • database contains zones • everything what is known about a domain • host names, IP addresses, subdomains.... • every zone is made up by records • 'A records' for addresses • IN records' Internet record class • every record has TTL (time-to-live) for caching

13. DNS • fault tolerance • more than one name server for a zone • caching, replication • relaxed consistency, things "converge eventually"

14. Port? • Logical address on a host where an application makes itself available to incoming data • TCP/IP service is associated with a port number • Example: 23 for Telnet • 128.9.33.67:23

15. Telnet • http://topicmaps.bond.edu.au/mda/internet/telnet-ssh/@/users/rho/InTechI/ • for interactive access to a remote machine • "Internet terminal" • e.g. telnet pac.carl.org • Colorado Alliance of Research Libraries • TCP-based protocol, default server port 23 • Application: telnet <host> [<port>]

16. user login shell pseudo terminal driver terminal driver telnet client telnet server tcp/ip stack tcp/ip stack Telnet process model telnet shell.it.bond.edu.au Green Hat Linux release 5.5 (Manhattan) login: jruser Password: tcsh>

17. Telnet's pros and cons • Standardized (RFC 854) • Application useful to debug text-based protocols (HTTP, SMTP, NNTP, POP, ....) • Data and Passwords in the clear • like most other remote login tools • simple to eavesdrop • don't use it for interactive work! • use SSH for that

18. SSH (packet-based binary protocol) • interactive access to a remote computer, like TELNET • but encrypted data transfer • password not sniffable • not fully standardized • not as widespread yet, less applications and servers • no replacement for TELNET as a debugging tool

19. File Transfer Protocol • Application layer, between TCP/IP hosts • Bi-directional file transfer • ftp <host> (default port: 21) • Interactive access (file, directory commands) • Authentication via username/password • Anonymous FTP: • login as anonymous/<email address>

20. FTP sample session > ftp mirror.aarnet.edu.au Connected to .... 220 AARNet Mirror FTP server ready. Name (mirror.aarnet.edu.au:az): ftp 331 Anonymous login ok Password: az@bond.edu.au 230 Anonymous access granted, restrictions apply. ftp> ls 150 Opening ASCII mode data connection for file list drwxr-xr-x 13 mirror mirror 4096 May 26 21:17 pub drwxr-xr-x 7 root root 512 Feb 28 00:47 raid 226 Transfer complete. ftp> bye 221 Goodbye.

21. FTP commands • User commands, understood by the client app. • ascii-sets file transfer mode to ASCII • binary-sets file transfer mode to Binary • cd- changes working directory • Delete-delets a file from host • get- transfer a file from host to client • help- exmp type ‘help ls’ • ls, open, put, quit

22. FTP replies • 3-digit code (ASCII) + optional message • Example replies: • 125 Data connection already open; transfer starting. • 200 Command OK. • 331 Username OK, password required. • 425 Can'topen data connection. • 500 Syntax error (unrecognized command). • QUIT -> 221 Goodbye

23. FTP's pros and cons • Pro: • Standardized (RFC 959) • Anonymous FTP • Contra: Very hard to get through a firewall securely

24. Protocols involved in email • Simple Mail Transfer Protocol (SMTP) • TCP protocol, port 25 • Post Office Protocol (POP) • retrieve mail from a mail drop • TCP , port 110 (POP3) • Internet Message Access Protocol (IMAP) • access and manage remote mail drop • TCP, port 143 (IMAP4)

25. SMTP • Operates on application layer • Relies on TCP at transport layer • Port 25 • Simple protocol-incapable of doing anything more than transporting mail or holding it in a queue • Acts as a mail carrier • Just delivers mail

26. SMTP • If undeliverable, simply holds on to it • Does not attempt to figure out what went wrong • If you use DNS-> do not have to identify IP address of the SMTP server, only the name • Example: jodie@postoffice.com, SMTP server is probably called postoffice.com

27. SMTP commands • Minimal SMTP command set (RFC 2821) • HELO: client identification • MAIL FROM: identify sender • RCPT TO : identify receiver • DATA: start taking the message • QUIT: terminate mail exchange • RSET: abort current mail transaction, reset • VRFY: verify recipient address • NOOP: do nothing

28. SMTP replies • 3-digit code (ASCII) + optional message • Example replies: • 250 <address>... Sender ok • 354 Enter mail, end with "." on a line by itself • 421 <domain> Service not available, closing transmission channel • 500 Syntax error (unrecognized command). • 221 <domain> closing connection (after QUIT)

29. local store user maildrop user agent user POP server Post Office Protocol • Retrieve mail from a mail drop • Default port: 110 (POP3) client server TCP connection client POP interface

30. POP • Provides centralized storage for e-mail messages • Application layer protocol • Relies on SMTP • Post office that holds mail until it is delivered • User need an SMTP compliant mail program to connect to their POP server and download mail from storage • POP does not allow users to store mail on the server after they download it • Problem->if user move from machine to machine

31. POP • Solution -> 1. store user’s mail on a LAN server or • 2. provide users with Web browser interface, allowing them to read messages without downloading them • More thorough solution has been provided by IMAP

32. Internet Message Access Protocol • POP’s shortcomings • transfers mail to local system • network access ? Mail scattered on several computers. • leave mail on POP server • unstructured • IMAP • supports access and management of email on a mail server (RFC 2060)

33. IMAP • Common: Version 4, IMAP4 • Allows users to store messages on the mail server, rather than downloading to local machine • Benefits if your are moving machine to machine • Features: • Users can retrieve all or a portion of message, remainder on the mail server, good->if you have slow connection or low hard drive space • Users can review and delete msg on the server-> preserves bandwidth, major advantage over POP

34. IMAP • Users can create sophisticated methods of organizing messages on the server, for instance building a system of folders to contain messages with similar content • Users can share a mailbox in a central location. If several maintenance personnel who use different PCs need to receive the same messages from the Facilities Department head but do not need email for any other purpose, they all log on with the same ID and share the same mailbox on the server. If POP were used->only one member could read then he had to forward or copy it to his colleagues

35. IMAP • Better security than POP because it supports authentication. Disadvantages IMAP servers require more storage space and processing resources than POP servers Network admins have to watch so that the users are not exceeding their storage limit install software like disk quota manager what if IMAP server fails? No access

36. IMAP Recently most popular email programs were used to use with POP servers only. However, Eudora Pro, GroupWise, Lotus notes, Netscape, Microsoft Outlook all support IMAP4. but not all ISPs have configured their mail servers to use IMAP