Computer Networking: Applications George Blankenship. Applications George Blankenship 1

Transcription

1 CSCI 232 Computer Networking: Applications i George Blankenship Applications George Blankenship 1

2 TCP/IP Applications The user of TCP/IP transport (TCP/UDP) is an application, the top level lof the TCP/IP protocol stack. User interface or application program (end user) Example applications DNS SNMP SMTP HTTP Applications George Blankenship 2

3 Application/transport Interface Application known by transport SAP (TCP port) Application makes itself known by publishing its connection port (passive open, listening gp port) service port Application user connects to service port The connection is know by the combination of service port and service request port Applications George Blankenship 3

4 TCP Applications Application attaches to TCP Application performs passive open (waiting for requestor) server, service Paired application (requestor) performs active open client, service requestor Server processes all opens received on listening port Applications George Blankenship 4

5 UDP Application Behaves much like TCP application Attaches to TCP Establishes a passive open (listening port) as a server application Client applications send message to server application (may or may not respond) Server processes all messages received on listening port Applications George Blankenship 5

6 DNS Domain Name System Rationale IP address structure is difficult to use No apparent relationship between individual addresses No method to predict addresses Name to lookup is full search of address space Hierarchical address structure limits search space Applications George Blankenship 6

7 Domain Name Structure Name space constructed from assignment domains Each domain is able to define names within the domain Name format is <child>.<parent> Root administers com, edu, mil, org, gov.edu administers i gwu, marymount,.gwu administers seas Applications George Blankenship 7

8 Naming Objective Each name is mapped to an IP address To obtain an IP address associated with a name one searches the name space Search performed from leaf to root, then from root to leaf ending with authoritative source Search starts with known spot and works back to root (usually shared parent) Search results can be cached to shorten lookup Applications George Blankenship 8

9 Search Examples gwiz.circ.gwu.edu system looking for seas.gwu.edu Look to circ.gwu.edu for location Request would move to gwu.edu (authority) saic.com looking for seas.gwu.edu Look to com Request would move to root Request would move to edu Response would be sent from gwu.edu Applications George Blankenship 9

10 Resolution Process User Program Resolver Parent Parent local names Name Server Name Server cache Zone Zone External Name Server Zone Applications George Blankenship 10

11 Resource Records <name> <type> <class> <ttl> <data> Type A address NS name server CNAME alias SOA start of authority MX mail server PTR (name is address) domain name Applications George Blankenship 11

12 Query Query ID Q/R, Opcode, AA, TC, RD, RA, Rcode TC truncated RD/RA recursion denied/available Rcode response status (error code) QDcount, ANcount, NScount, ARcount Size of question, answer, name server, and additional information sections Applications George Blankenship 12

13 Transport Usage Uses UDP port 53 Maximum message size is 512 octets with truncated indicated in message Large transfers (zone updates/refreshes) use TCP port 53 Applications George Blankenship 13

14 SNMP Simple Network Management Protocol Management of a distributed network is difficult Identification of failed component is difficult Prediction of network problems is difficult Network information collected in a MIB Actual protocol result of work done in ISO community Applications George Blankenship 14

15 Information Collection Each network entity maintains a MIB of information (performance data) on the local l system Remote management system collects the data from the individual MIBs (to a central MIB) There must be a balance between the retrieval of data and network traffic Applications George Blankenship 15

16 Traffic Balance Network managers can poll the network devices for MIBd data Continuous view of entity performance Constant flow of performance data (impacting network performance) Network entities can send MIB data when it exceeds tolerances (traps) Erratic view of performance View of errors Applications George Blankenship 16

17 Traffic Encoding Based on ISO encoding ASN.1 Typical accusation is wordiness (CPU hog ) Virtualizes representation to accommodate different machine formats (flexibility, extensibility) BNF type of definition Header defined encoding Tag identifies data type Length length of data value Value machine independent format Applications George Blankenship 17

18 SNMP (MIB System Information) Applications George Blankenship 18

19 SNMP (System Information) Applications George Blankenship 19

20 SNMP (MIB Interfaces) Applications George Blankenship 20

21 SNMP (Interfaces) Applications George Blankenship 21

22 SNMP (MIB IP Data) Applications George Blankenship 22

23 SNMP IP Information Applications George Blankenship 23

24 SNMP (MIB TCP Data) Applications George Blankenship 24

25 SNMP (TCP Information) Applications George Blankenship 25

26 SMTP is exchanged as plain text (ascii) data Mail format is broken down into two general areas. Message headers Message body Applications George Blankenship 26

27 SMTP Headers To: Cc: (additional recipients) Bcc: (recipients hidden from to & cc) From: (author) Sender: (actual sender) Received: (audit of message path) Return-Path: (return address) Applications George Blankenship 27

28 SMTP Commands HELO <SP> <domain> <CRLF> MAIL <SP> FROM:<reverse-path> <CRLF> RCPT <SP> TO:<forward-path> <CRLF> DATA <CRLF> RSET <CRLF> SEND <SP> FROM:<reverse-path> <CRLF> SOML <SP> FROM:<reverse-path> <CRLF> SAML <SP> FROM:<reverse-path> <CRLF> VRFY <SP> <string> <CRLF> EXPN <SP> <string> <CRLF> HELP [<SP> <string>] <CRLF> NOOP <CRLF> QUIT <CRLF> TURN <CRLF> Applications George Blankenship 28

29 SMTP Replies 211 System status, or system help reply 214 Help message 220 <domain> Service ready 221 <domain> Service closing transmission i channel 250 Requested mail action okay, completed 251 User not local; will forward to <forward-path> 4xx <domain> Service error 5xx Syntax error Applications George Blankenship 29

30 SMTP Exchanges CONNECTION ESTABLISHMENT Success: 220 Fail: 421 HELO Success: 250 Error: 500, 501, 504, 421 MAIL Success: 250 Fail: 552, 451, 452 Error: 500, 501, 421 Applications George Blankenship 30

31 SMTP Exchanges DATA Intermediate: t 354 (send data) Success: 250 Fail: 552, 554, 451, 452 Fail: 451, 554 Error: 500, 501, 503, 421 SEND Success: 250 Fail: 552, 451, 452 Error: 500, 501, 502, 421 Applications George Blankenship 31

32 HTTP URL (Uniform Resource Locator) name/file Applications George Blankenship 32

33 HTTP (DNS - Request) Applications George Blankenship 33

34 HTTP (DNS Response) Applications George Blankenship 34

35 HTTP (Socket Open) Applications George Blankenship 35

36 HTTP (Socket Accepted) Applications George Blankenship 36

37 HTTP (Socket Opened) Applications George Blankenship 37

38 HTTP (Initial GET) Applications George Blankenship 38

39 HTTP (Initial GET raw) Applications George Blankenship 39

40 HTTP (GET Response) Applications George Blankenship 40

41 HTTP Methods (Commands) GET Request for a web page HEAD Request for a web page header PUT Request to store a web page POST Append to a resource (response) DELETE Request to delete a web page LINK Request tto connect web pages UNLINK Request to break a connection Applications George Blankenship 41

42 HTTP Sequences Request GET <file> <version> <CR><LF> File location of web page Version version of HTML supported Response HTTP/<version> <response code> <CR><LF> Response code code (2xx is success) Applications George Blankenship 42

43 Protocol Examples Wireshark DNS ARP (NS), Query, Response HTTP GET of first page Applications George Blankenship 43

44 ARP Request for Name Server Applications George Blankenship 44

45 ARP Response for Name Server Applications George Blankenship 45

46 DNS (Request) Applications George Blankenship 46

47 DNS (Response) Applications George Blankenship 47

48 HTTP (Get) Applications George Blankenship 48

49 HTTP (Page Displayed) Applications George Blankenship 49

50 Bad Page DNS ARP (Query, Error page Applications George Blankenship 50

51 Bad DNS (Many Tries) Applications George Blankenship 51

52 Bad DNS (NS No Such Name) Applications George Blankenship 52

53 Browser Generate Error Page Applications George Blankenship 53