Outline. à Basic principles à Domain name and server hierarchy à Name resolution à Message format à DNS extensions

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1 Domain Name System

2 Outline à Basic principles à Domain name and server hierarchy à Name resolution à Message format à DNS extensions

3 BASIC PRINCIPLES

4 Names and Addresses à Name is more user friendly à Meant for users à Address is used to route packets à Meant for computers

5 Names and Addresses à One address multiple names à Multiple services on one server (FTP, WWW)

6 Names and Addresses à One name multiple addresses à Load balancing à Content caching

7 Local Mapping à File /etc/hosts in unix-like hosts à 127.O.O.1 localhost à alpha à beta à gamma delta à Impractical for large network à Not scalable

8 Hierarchical Solution à Scalable à Name syntax à Name assignment à Authorities à Name resolution à Servers

9 A Distributed Database à Name hierarchy used to locate information in server hierarchy à Independent of network (addressing and routing) hierarchy

10 DOMAIN NAME AND SERVER HIERARCHY

11 Fully Qualified Domain Name (FQDN) à Variable number of hierarchical naming levels host department organization nation

12 Domain Name Syntax à ASCII encoding for internationalized names

13 Top Level Domain (TLD) à Country Code TLD (cctld) à.it,.fr,.uk, à Generic TLD (gtld) à Unrestricted à com net org info à Restricted (sponsored) à gov edu aero coop

14 Second Level Domain à Organization/corporation in some TLDs à.polito.it, apple.com à (Organizational) characterization for others à.bt.co.uk ucl.ac.uk

15 Name Assignment à IANA: Internet Assigned Numbers Authority à Decides on TLDs à Delegates à Assignment à Domain server

16 Server Hierarchy à One server per domain à Addresses of hosts in domain à Addresses of servers for lower domain à Same hierarcy as names à Manual configuration

17 Root Server à [a-m].root-server.net à Managed by IANA à Address of first level domain servers à cctlds: it fr uk à gtlds: com gov aero

18 TLD Servers à Address of next level servers à rai.it co.uk nwu.edu

19 Second Level Servers à Host names à ftp.nasa.com à Next level domain servers à cs.rice.edu technion.ac.il

20 Root edu il it com Server Hierarchy edu it com il ucla njit polito polito cnr eni eni gs cnn kodak bn ac ac co mi co www netgroup pop www ftp mail haifa technion lynx icq

21 Logical Hierarchy à Server might be hosted by multiple machines à Machine might host several servers à Synchronization with primary server

22 DNS Hosting à Machine hosting DNS server does not need to be close to hosts à Service provider supports with domain registration à Offers DNS server

23 NAME RESOLUTION

24 Client à Address of one or more servers à Can be anywhere à Usually close à Usually responsible for client domain à Default domain (opt)

25 Name Resolution 2 ftp.technion.ac.il? polito 9 it polito cnr eni Root edu il it com eni com gs cnn bn ftp.technion.ac.il? 8 ac 7 il ac co mi 3 co 1 www pop www ftp mail haifa technion 4 lynx icq technion tilie.polito.it www ftp mail

26 Name Caching à Answers are cached à Also in client à Expedite queries à Non-authoritative answers à Address of auth server à Iterative resolution

27 DNS Record Type à A à host name to address à MX à mail domain to mail server address à CNAME à alias to canonical name à NS à domain name to server address

28 DNS Record Type à Query specifies the type of record polito.it (A)? polito.it (MX)? pop.polito.it

29 Inverse Resolution à Given an IP address, find primary name à Same procedure and server hierarchy à PTR (pointer) records à Fake domain name x.y.z.t.in-addr.arpa

30 Inverse Resolution à E.g., 13O query (PTR) O.in-addr.arpa à At polito.it assignment à DNS server (13O ) à Address range (13O. 192.O.O)

31 Inverse Resolution A giove PTR giove Root arpa il it com IANA manages in-addr.arpa it arpa polito polito cnr eni in-addr in-addr www netgroup

32 MESSAGE FORMAT

33 Message Format Identification Parameter Number of Questions Number of Authority Number of Answers Number of Additional Question Section... Answer Section... Authority Section... Additional Information Section...

34 Parameter Field 0 1 O QT A T D R RT à O-operation (O=query, 1= response) à QT-query type à O: standard à 1: inverse à A-autorithative answer

35 Parameter Field 0 1 O QT A T D R RT à T-Truncated à D-Recursion desired à R-Recursion available à G-Reserved

36 Parameter Field 0 1 O QT A T D R RT à RT-Response type à O: no error à 1: format error in query à 2: server failure à 3: name does not exist

37 Lifetime à Attached to each piece of information à Used to manage ageing in caches

38 DNS EXTENSIONS

39 Dynamic DNS (DDNS) à Automatic update of DNS servers à Useful with dynamic host configuration à Host lets server know its address à Potential security threat

40 DNS Security Extensions (DNSSEC) à Protect from DNS-based attacks à E.g., cache poisoning à Forged DNS data à Authentication of responses à No encryption

41 DNS Security Extensions (DNSSEC) à Digital signature of records à Public key cryptography à Digital certificates à DNSSEC specific records

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