Application Protocols

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

2 Outline Client-Server DNS 2

3 TCP/IP Protocol Suite (Internet Model) Applications Transport Network Data Link Physical User service and interface Process delivery + Error (TCP/UDP) Reliable end-to-end (whole message) Move packets from source to destination Packet end-to-end (across network) Provide frames Node-to-node (same network segment) Transmission bit streams (mechanical and electrical spec) 3

4 Responsibilities of Application Layer Identifying and establishing the availability of intended communication partners Synchronizing cooperating applications Establishing agreement on procedures for error recovery Controlling data integrity 4

5 Application Definition Programs run on behalf of users serve specific service requests Application types self-contained (take input show output) remote interaction (send-receive info.) client receive instruction from user server react/service as requested 5

6 Client-Server Architecture Most network application Server use well-known port numbers run all the time Client use an ephemeral port number terminate after the service. If a client requests a service on a port number associated with no server In UDP, return ICMP port unreachable error to client In TCP, the TCP connection is reset 6

7 Client-Server Client Application Client Application Daemon Server Application Client Internet Server Client Application Connection: TCP or UDP and Ports 7

8 Connectionless Iterative Server Legend Datagram from client 1 Datagram from client 2 Datagram from client 3 8

9 Connection-Oriented Concurrent Server 9

10 TCP/IP protocol suite and OS 10

11 Sockets Basic Concepts 11

12 Sockets Basic Concepts 12

13 Connectionless Iterative: using UDP 13

14 Connection-Oriented Concurrent: TCP Client Server 14

15 Connection-Oriented Concurrent: TCP Client Server Connection handshake 15

16 Connection-Oriented Concurrent: TCP Client Server 16

17 Parent / Child Process 17

18 Application Layer Examples Domain Name System (DNS) Telnet File Transfer Protocol (FTP) Trivial File Transfer Protocol (TFTP) Hypertext Transfer Protocol (HTTP) Simple Mail Transport Protocol (SMTP) Simple Network Management Protocol (SNMP) 18

19 Domain Name System (DNS) 19

20 Naming Purpose Addresses are used to locate objects Names are easier to remember than numbers To get to the address or other objects prefer using a name 20

21 Domain Name System (DNS) System used for translating names of domains into IP addresses using lookup mechanism Domain names comprise a hierarchy (tree) unique easy to remember DNS can use the services of UDP or TCP using the well-known port

22 DNS Mapping Process User 1 Host name 2 Host name 6 IP address Transport layer 5 IP address 3 Query Response 4 22

23 IP Address Mapping Example name server 2 สอบถามช อโดเมน nontri.ku.ac.th ผ ใช 1 ใช ช อโดเมน telnet nontri.ku.ac.th TELNET ตอบไอพ แอดเดรส TCP IP 23

24 DNS Features A globally distributed maintain data locally, but retrievable globally No single computer has all DNS data Loosely coherent replicate changes (timing set by the zone admin) Scalable not limited size not limited # of query Reliable (data replicate) Dynamic database 24

25 DNS Concept Domain names can be mapped to a tree New branches at the dots No restriction to the amount of branches www ftp ripe ws1 disi net ws2 isi edu sun com www tislabs moon google 25

26 Domain Name Space Hierarchy th 26

27 DNS in Internet ราก arpa com edu gov int mil net org de th uk in-addr mit usu ac go or cc ku mua nectec โดเมนท วไป nontri mis nucleus cc.usu.edu. 2 โดเมนผกผ น nontri.ku.ac.th. nucleus.nectec.or.th. โดเมนระด บประเทศ in-addr.arpa. = ม ต นไม ย อยได อ ก 27

28 Standard Name Space (Top Level) com edu gov mil net org th commercial education goverment military network operator organization country New.aero.biz.coop.info.name.pro 28

29 Inverse Domain in-addr arpa ราก in-addr.arpa nontri.ku.ac.th 29

30 Hostname Structure Sequence of labels separated by periods each label can be up to 63 characters total name can be at most 255 characters Examples: iwing.cpe.ku.ac.th 30

31 Domain Name and Label Absolute Domain Name challenger.atc.fhda.edu. Relative Domain Name atc atc.fhda.edu. 31

32 Domain Concept 32

33 Hierarchy of Name Servers 33

34 Domain ku.ac.th ราก th Node ku.ac.th go ac Domain ku.ac.th ku 34

35 Sub-Domain ราก th Domain cpc.ku.ac.th go ac ku Domain ku.ac.th Domain sci.ku.ac.th cpc eng lib sci Domain eng.ku.ac.th ce ie me Domain lib.ku.ac.th 35

36 Delegation Administrator can create sub-domains according to geography, affiliation or other criterion Domain Admin may delegate responsibility for managing a sub-domain Parent domain retains links to delegated sub-domain parent domain remembers who it delegated the sub-domain to 36

37 Zones and Domains 37

38 Zones and Delegations Zones are administrative spaces Zone administrators are responsible for portion of a domain s name space Authority is delegated from a parent and to a child net zone net domain ripe.net zone disi.ripe.net zone ripe net www disi ftp ws2 edu isi ws1 com sun moon google tislabs www 38

39 Zone and Domain ราก th go ac ku Zone ku Domain ku cpc eng lib sci ce ie me 39

40 Zone and Domain ราก th go ac ku Zone ku Domain ku Domain eng Zone eng cpc ce ie eng me lib sci Domain lib Zone lib 40

41 Name Servers Name servers answer DNS questions Several types of name servers Authoritative servers master (primary) slave (secondary) (Caching) recursive servers also caching forwarders Mixture of functionality 41

42 Authoritative Name Servers Give authoritative answers for one or more zones Master server loads data from zone file Slave server replicates data from master via a zone transfer slave master slave 42

43 Recursive Name Server Perform actual lookups ask questions to DNS on behalf of clients Answers are obtained from authoritative servers but answers forwarded to clients are marked as not authoritative Answers are stored for future reference in cache 43

44 Resolver Ask questions to DNS system on behalf of the application Normally implemented in a system library (e.g, libc) gethostbyname (char *name); gethostbyaddr (char *addr, int len, type); 44

45 Recursive Resolution

46 Iterative Resolution

47 Resolving process & Cache Question: A A? root-server Resolver A? Caching forwarder (recursive) A? Ask net X.gtld-servers.net (+ glue) gtld-server Ask ripe ns.ripe.net (+ glue) Add to cache A? ripe-server Type A = indicate that VALUE is an IP Add 47

48 Resolving process jaguar.lcs.mit.edu 2 ร ทเนมเซ ร ฟเวอร ไคลเอ นต nontri.ku.ac.th 1 jaguar.lcs.mit.edu w20ns.mit.edu, jaguar.lcs.mit.edu 4 mintaka.lcs.mit.edu, ns.ku.ac.th เนมเซ ร ฟเวอร mit.edu w20ns.mit.edu jaguar.lcs.mit.edu 6 7 jaguar.lcs.mit.edu, เนมเซ ร ฟเวอร lcs.mit.edu mintaka.lcs.mit.edu

49 DNS Message 49

50 Header Format 50

51 Query Record Format (Question) admin.atc.fhda.edu. 51

52 Resource Record Format (Answer) 52

53 DNS Exchange ftp.nectec.or.th เนมเซ ร ฟเวอร 1 2 ku.or.th ftp.nectec.or.th เนมเซ ร ฟเวอร nectec.or.th nontri.ku.ac.th ftp.nectec.or.th, 4 ns.ku.ac.th ns.nectec.or.th

54 nontri.ku.ac.th ns.ku.ac.th ไอพ เฮดเดอร (บางส วน) destination= identification=10 source= query, standard, recursive ด เอ นเอสเฮดเดอร number of questions = 1 number of answers RRs = 0 number of authority RRs = 0 numberof additional RRs = 0 ส วนค าถาม name=ftp.nectec.or.th., type=a, class=in Type A = indicate that VALUE is an IP Add Class IN = indicate Internet 54

55 ns.ku.ac.th ns.nectec.or.th destination= identification=20 source= query, standard, recursive ด เอ นเอสเฮดเดอร number of questions = 1 number of answers RRs = 0 number of authority RRs = 0 numberof additional RRs = 0 ส วนค าถาม name=ftp.nectec.or.th., type=a, class=in 55

56 DNS File Example BIND (Berkeley Internet Name Domain) Unix use demon named ns มาสเตอร เนมเซ ร ฟเวอร /etc/named.conf /usr/local//named/db.ku /usr/local/named/db.rev /usr/local/named/db.local /usr/local/named/db.cache ns2 สเลฟเนมเซ ร ฟเวอร /etc/named.conf /usr/local/named/db.ku * /usr/local/named/db.rev * /usr/local/named/db.local /usr/local/named/db.cache www mail nontri omega sigma 56

57 nslookup Interactive resolver allows user to communicate directly with a DNS server 57

58 dig 58

59 References TCP/IP Protocol Suite, 2nd Edition, Behrouz A. Forouzan Introduction to the DNS system, Olaf M. Kolkman CCNA 1 v3.0 Module 11 TCP/IP Transport and Application Layers, cisco.com Address Conversion Functions and The Domain Name System, Anonymous ส รศ กด สงวนพงษ, ท ซ พ ไอพ 59

Internet Applications

Internet Applications รศ.ดร. อน นต ผลเพ ม Assoc. Prof. Anan Phonphoem, Ph.D. anan.p@ku.ac.th http://www.cpe.ku.ac.th/~anan Computer Engineering Department Kasetsart University, Bangkok, Thailand 1 Outline