Internet Applications II

Transcription

1 Internet Applications II รศ.ดร. อน นต ผลเพ ม Asso. Prof. Anan Phonphoem, Ph.D. Computer Engineering Department Kasetsart University, Bangkok, Thailand 1

2 Application Layer Examples Hypertext Transfer Protocol (HTTP) Domain Name System (DNS) Telnet SSH File Transfer Protocol (FTP) Trivial File Transfer Protocol (TFTP) Simple Mail Transport Protocol (SMTP) Simple Network Management Protocol (SNMP) 2

3 Telnet Telecommunications Network Protocol Standard communication for terminals to remote host Character-based command interface General purpose client-server 3

4 Local Login 4

5 Remote Login 5

6 Network Virtual Terminal Differences of character sets Example 1: IBM used EBCDIC (A =0xC1) Others used ASCII (A = 0x41) Example 2: PC (eol = carriage return +line feed) Unix server (eol = only line feed) Need Translation! 6

7 Network Virtual Terminal (NVT) perform translation between its own character set and NVT format 7

8 Telnet Operation Server listens on TCP port 23 Normally, client transmits when enter is pressed Sever sends back in blocks of lines Control command embedded in character flow 8

9 Control Command IAC: Interrupt As Command (0xFF) indicate that next char is control command followed by one or more characters DO: Request other party to perform (0xFD) DON T: Demand other party to stop (0xFE) SB: Subnegotiation (0xFA) SE: End subnegotiation (0xF0) 9

10 Example: Telnet Exchange 18 FB FF FF FD 18 10

11 Example 11

12 telnet example 12

13 Application Layer Examples Hypertext Transfer Protocol (HTTP) Domain Name System (DNS) Telnet SSH File Transfer Protocol (FTP) Trivial File Transfer Protocol (TFTP) Simple Mail Transport Protocol (SMTP) Simple Network Management Protocol (SNMP) 13

14 Secure Shell (SSH) Another remote login application More secure than TELNET 14

15 SSH 15

16 ssh example 16

17 Application Layer Examples Hypertext Transfer Protocol (HTTP) Domain Name System (DNS) Telnet SSH File Transfer Protocol (FTP) Trivial File Transfer Protocol (TFTP) Simple Mail Transport Protocol (SMTP) Simple Network Management Protocol (SNMP) 17

18 File Transfer Protocol (FTP) FTP usages download files from remote host to local host upload files from local host to remote host Differences in file names and types Need two TCP connections well-known port 21 for control connection well-known port 20 for data connection Text mode / graphic mode 18

19 FTP Please give examples of FTP s client program! 19

20 Using FTP program open command (specify domain name of remote host) Form a TCP control connection Supply login name and password anonymous login name with guest password (or address) after authorization establish a new data connection for each file file transfer can start in either direction control connection remains open after finished, close command 20

21 Creating Data Connection 21

22 FTP Commands dir: remote host sends directory listing to local host get <file-name>: remote host sends <file-name> to local host put <file-name>: local host sends <filename> to remote host cd <directory-name>: change directory of remote host to <directory-name> 22

23 Example 23

24 Example Test Server: test.talia.net Reply code 24

25 Example Reply code 25

26 FTP characteristics FTP is complex protocol FTP uses TCP (heavyweight) for large file transfer not suitable for simple/small transactions 26

27 Application Layer Examples Hypertext Transfer Protocol (HTTP) Domain Name System (DNS) Telnet SSH File Transfer Protocol (FTP) Trivial File Transfer Protocol (TFTP) Simple Mail Transport Protocol (SMTP) Simple Network Management Protocol (SNMP) 27

28 Trivial FTP (TFTP) Lightweight protocol Only support file transfer (no interaction) No authorization Use only subset of FTP command connect, get, put, ascii, and binary Use UDP with port 69 less reliable but low overhead Usage bootstrap (diskless HW) e.g. Router only need network connection and small ROM 28

29 TFTP Connection 29

30 TFTP Connection UDP Source port 50,100 Dest port 69 write file2, netascii UDP Source port 60,000 Dest port 50,100 Ack block =0 UDP Source port 50,100 Dest port 60,000 Data block = 1 UDP Source port 60,000 Dest port 50,100 Ack block =1 30

31 Application Layer Examples Hypertext Transfer Protocol (HTTP) Domain Name System (DNS) Telnet SSH File Transfer Protocol (FTP) Trivial File Transfer Protocol (TFTP) Simple Mail Transport Protocol (SMTP) Simple Network Management Protocol (SNMP) 31

32 Electronic Mail uses several application protocols: SMTP: to exchange messages between Servers and to send from your PC to an server. POP or IMAP: to retrieve messages from your server to your PC. MIME: to structure the content of the message 32

33 Simple Mail Transfer Protocol (SMTP) 33

34 User Agent (UA) and Mail Transfer Agent (MTA) create/read/store mail find path/delivery mail 34

35 Electronic Mail Sending host server IP Network server receiver Receiving host Sending host server server host User Agent Mail Transfer Agent Mail Transfer Agent User Agent SMTP SMTP SMTP SMTP POP3 or IMAP POP3 or IMAP Transport Service Provider Transport Service Provider Transport Service Provider 35

36 User Agent (UA) Format 36

37 Relay MTA Store-and-forward Store mail while not connect Security: one point of connection to outside 37

38 Mail Gateway 38

39 Example % telnet mailgw.acn.org. 25 Trying Connected to mailgw.acn.org. Escape character is '^]'. 220 mailgw.acn.org ESMTP Sendmail 8.8.5; Sat, 15 Aug :55:31 39

40 System 40

41 Alias Expansion One-to-Many Many-to-One 41

42 MIME: Multipurpose Internet Mail Extensions wants to send anything: ASCII/Binary 42

43 Non-ASCII ASCII 43

44 MINE Header 44

45 Delivery 45

46 Mail Access Protocol POP3: Post Office Protocol IMAP: Internet Message Access Protocol POP: TCP 110 IMAP: TCP

47 Application Layer Examples Hypertext Transfer Protocol (HTTP) Domain Name System (DNS) Telnet SSH File Transfer Protocol (FTP) Trivial File Transfer Protocol (TFTP) Simple Mail Transport Protocol (SMTP) Simple Network Management Protocol (SNMP) 47

48 SNMP : Simple Network Management Protocol SNMP Component แมเนเจอร Packet Format ข อความเอสเอ นเอ มพ ไอพ เฮดเดอร ย ด พ เฮดเดอร เฮดเดอร พ ด ย เอเจนต เอเจนต เอเจนต เอเจนต UDP 161/162 48

49 Other Applications DHCP NTP: Network Time Protocol (UDP 113) finger (TCP 79) whois (TCP 43) LDAP: Lightweight Directory Access Protocol 49

50 DHCP: Dynamic Host Configuration Protocol ด เอชซ พ เซ ร ฟเวอร ตอบกล บ ร องขอ ด เอชซ พ ไคลเอ นต 50

51 Summary Hypertext Transfer Protocol (HTTP) Domain Name System (DNS) Telnet SSH File Transfer Protocol (FTP) Trivial File Transfer Protocol (TFTP) Simple Mail Transport Protocol (SMTP) Simple Network Management Protocol (SNMP) 51