DNS: Domain Name System

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1 DNS: Domain Name System People: many identifiers: SSN, name, passport # Internet hosts, routers: IP address (32 bit) - used for addressing datagrams name, e.g., ww.yahoo.com - used by humans Q: map between IP addresses and name? Domain Name System: distributed database implemented in hierarchy of many name servers application-layer protocol host, routers, name servers to communicate to resolve names (address/name translation) note: core Internet function, implemented as application-layer protocol complexity at network s edge H. Fauconnier M2-Internet 1

2 DNS DNS services hostname to IP address translation host aliasing Canonical, alias names mail server aliasing load distribution replicated Web servers: set of IP addresses for one canonical name Why not centralize DNS? single point of failure traffic volume distant centralized database maintenance doesn t scale! H. Fauconnier M2-Internet 2

3 Distributed, Hierarchical Database Root DNS Servers com DNS servers org DNS servers edu DNS servers yahoo.com DNS servers amazon.com DNS servers pbs.org DNS servers poly.edu umass.edu DNS servers DNS servers Client wants IP for 1 st approx: client queries a root server to find com DNS server client queries com DNS server to get amazon.com DNS server client queries amazon.com DNS server to get IP address for H. Fauconnier M2-Internet 3

4 DNS: Root name servers contacted by local name server that can not resolve name root name server: contacts authoritative name server if name mapping not known gets mapping returns mapping to local name server e NASA Mt View, CA f Internet Software C. Palo Alto, CA (and 36 other locations) a Verisign, Dulles, VA c Cogent, Herndon, VA (also LA) d U Maryland College Park, MD g US DoD Vienna, VA h ARL Aberdeen, MD j Verisign, ( 21 locations) k RIPE London (also 16 other locations) i Autonomica, Stockholm (plus 28 other locations) m WIDE Tokyo (also Seoul, Paris, SF) b USC-ISI Marina del Rey, CA l ICANN Los Angeles, CA 13 root name servers worldwide H. Fauconnier M2-Internet 4

5 TLD and Authoritative Servers Top-level domain (TLD) servers: responsible for com, org, net, edu, etc, and all top-level country domains uk, fr, ca, jp. Network Solutions maintains servers for com TLD Educause for edu TLD Authoritative DNS servers: organization s DNS servers, providing authoritative hostname to IP mappings for organization s servers (e.g., Web, mail). can be maintained by organization or service provider H. Fauconnier M2-Internet 5

6 Local Name Server does not strictly belong to hierarchy each ISP (residential ISP, company, university) has one. also called default name server when host makes DNS query, query is sent to its local DNS server acts as proxy, forwards query into hierarchy H. Fauconnier M2-Internet 6

7 DNS name resolution example root DNS server Host at cis.poly.edu wants IP address for gaia.cs.umass.edu TLD DNS server iterated query: contacted server replies with name of server to contact I don t know this name, but ask this server local DNS server dns.poly.edu 1 8 requesting host cis.poly.edu 7 6 authoritative DNS server dns.cs.umass.edu gaia.cs.umass.edu H. Fauconnier M2-Internet 7

8 DNS name resolution example root DNS server recursive query: puts burden of name resolution on contacted name server heavy load? 2 local DNS server dns.poly.edu TLD DNS server 1 8 requesting host cis.poly.edu authoritative DNS server dns.cs.umass.edu gaia.cs.umass.edu H. Fauconnier M2-Internet 8

9 DNS: caching and updating records once (any) name server learns mapping, it caches mapping cache entries timeout (disappear) after some time TLD servers typically cached in local name servers Thus root name servers not often visited update/notify mechanisms under design by IETF RFC H. Fauconnier M2-Internet 9

10 DNS records DNS: distributed db storing resource records (RR) RR format: (name, value, type, ttl) Type=A name is hostname value is IP address Type=NS name is domain (e.g. foo.com) value is hostname of authoritative name server for this domain Type=CNAME name is alias name for some canonical (the real) name is really servereast.backup2.ibm.com value is canonical name Type=MX value is name of mailserver associated with name H. Fauconnier M2-Internet 10

11 DNS protocol, messages DNS protocol : query and reply messages, both with same message format msg header identification: 16 bit # for query, reply to query uses same # flags: query or reply recursion desired recursion available reply is authoritative H. Fauconnier M2-Internet 11

12 DNS protocol, messages Name, type fields for a query RRs in response to query records for authoritative servers additional helpful info that may be used H. Fauconnier M2-Internet 12

13 Inserting records into DNS example: new startup Network Utopia register name networkuptopia.com at DNS registrar (e.g., Network Solutions) provide names, IP addresses of authoritative name server (primary and secondary) registrar inserts two RRs into com TLD server: (networkutopia.com, dns1.networkutopia.com, NS) (dns1.networkutopia.com, , A) create authoritative server Type A record for Type MX record for networkutopia.com How do people get IP address of your Web site? H. Fauconnier M2-Internet 13

14 Quelques compléments Java réseaux 14

15 Sommaire URL et URI html et swing URLconnections URLStreamHandler URLStreamHandlerFactory ContentHandler ContentHandlerFactory 15

16 URL la classe URL permet d'utiliser les URL les classes URLDecoder et URLEncoder permettent de traiter les formulaires HTML Une URI (Uniform ressource Identifier), est une sorte de généralisation des URL qui inclut de Uniform Resource Location (URL) mais aussi de Uniform Ressource Names (URN) exemples tel: =_hdbc (la classe URLConnection sera décrite plus loin) 16

17 URI URI: URL (location) designfaq.html#28 ou URN (name): Syntaxe: Général: [scheme:]scheme-specific-part[#fragment] Hiérarchique: [scheme:][//authority][path][?query][#fragment] Authorité: 1-17

18 URL isbn=56888#toc stuff protocol port authority chemin référence requête user 18

19 Construire une URL public URL(String url) throws MalformedURLException public URL(String protocol, String hostname, String file) throws MalformedURLException public URL(String protocol, String host, int port, String file) throws MalformedURLException public URL(URL base, String relative) throws MalformedURLException 19

20 Remarques tous les protocoles ne sont pas compris par la machine virtuelle exception MalFormedURLException 20

21 Exemple: Quels protocoles? import java.net.*; public class ProtocolTester { public static void main(string[] args) { testprotocol("http://www.adc.org"); testprotocol("https://www.amazon.com/exec/obidos/order2/"); testprotocol("ftp://metalab.unc.edu/pub/languages/java/javafaq/"); testprotocol("telnet://dibner.poly.edu/"); testprotocol("file:///etc/passwd"); testprotocol("gopher://gopher.anc.org.za/"); testprotocol( "ldap://ldap.itd.umich.edu/o=university%20of%20michigan,c=us? postaladdress"); testprotocol( "jar:http://cafeaulait.org/books/javaio/ioexamples/javaio.jar!" +"/com/macfaq/io/streamcopier.class"); testprotocol("nfs://utopia.poly.edu/usr/tmp/"); testprotocol("jdbc:mysql://luna.metalab.unc.edu:3306/news"); testprotocol("rmi://metalab.unc.edu/renderengine"); testprotocol("doc:/usersguide/release.html"); testprotocol("netdoc:/usersguide/release.html"); testprotocol("systemresource://www.adc.org/+/index.html"); testprotocol("verbatim:http://www.adc.org/"); 21

22 Quels protocoles (suite) private static void testprotocol(string url) { try { URL u = new URL(url); System.out.println(u.getProtocol() + " is supported"); catch (MalformedURLException ex) { String protocol = url.substring(0,url.indexof(':')); System.out.println(protocol + " is not supported"); http is supported https is supported ftp is supported mailto is supported telnet is not supported file is supported gopher is supported ldap is not supported jar is supported nfs is not supported jdbc is not supported rmi is not supported doc is supported netdoc is supported systemresource is supported verbatim is supported 22

23 Décomposer l'url public static void decomposeurl(string st) { try{ URL u = new URL(st); System.out.println("URL :" + u); System.out.println("Protocole : " + u.getprotocol( )); System.out.println("UserInfo :" + u.getuserinfo( )); String host = u.gethost( ); if (host!= null) { int atsign = if (atsign!= -1) host = host.substring(atsign+1); System.out.println("hôte " + host); else { System.out.println("hôte null."); 23

24 suite System.out.println("Port :" + u.getport( )); System.out.println("Path : " + u.getpath( )); System.out.println("Ref : " + u.getref( )); System.out.println("Query: " + u.getquery( )); catch (MalformedURLException ex) {System.err.println(st + " URL malformée"); 24

25 Résultat isbn=56888#toc URL :http://www.bib.org:80/javafaq/book/ index.html?isbn=56888#toc Protocole : http UserInfo :null hôte Port :80 Path : /javafaq/book/index.html Ref : toc Query: isbn=

26 Obtenir des données public InputStream openstream( ) throws IOException public URLConnection openconnection( ) throws IOException public URLConnection openconnection(proxy proxy) throws IOException public Object getcontent( ) throws IOException public Object getcontent(class[] classes) throws IOException 26

27 Charger le contenu d'une URL public static void chargerfichier(string url) { try { URL u = new URL(url); InputStream in = u.openstream(); in = new BufferedInputStream(in); Reader r = new InputStreamReader(in); int c; while ((c = r.read())!= -1) { System.out.print((char) c); catch (MalformedURLException ex) { System.err.println(url + " mauvaise URL"); catch (IOException e) { System.err.println(e + " problème de lecture url " + url); 27

28 Type du contenu public static void typeobjeturl(string st) { try { URL u = new URL(st); try { Object o = u.getcontent(); System.out.println("L'objet est un " + o.getclass().getname()); catch (IOException ex) {System.err.println(ex); catch (MalformedURLException ex) { System.err.println(st + " URL malformée"); L'objet est un sun.net.www.protocol.http.httpurlconnection $HttpInputStream 28

29 Et encore URLEncoder URLDecoder 29

30 URLEncode: Exemple public class QueryString { private StringBuffer query = new StringBuffer(); public QueryString(String name, String value) { encode(name, value); public synchronized void add(string name, String value) { query.append('&'); encode(name, value); private synchronized void encode(string name, String value){ try { query.append(urlencoder.encode(name, "UTF-8")); query.append('='); query.append(urlencoder.encode(value, "UTF-8")); catch (UnsupportedEncodingException ex) { throw new RuntimeException("??"); //... 30

31 Exemple (suite) / public String getquery() { return query.tostring(); public String tostring() { return getquery(); 31

32 Authentication Classe (abstraite) Authenticator PasswordAuthentication représente un couple password + user Méthode getpasswordauthentication() à redéfinir pour obtenir un PasswordAuthenitcation Méthode setdefault(authenticator) définit l'authenticator pour le système C'est à lui que s'adressera le système à chaque fois que nécessaire 32

33 Pour apache: Fichier.htaccess: (il faut aussi un AllowOverride AuthConfig dans httpd.conf) AuthType Basic AuthName "restreint" AuthUserFile /Users/hf/Sites/.psswd Require user hf.psswd est le fichier des mots de passe htpasswd c /Users/hf/Sites/.passwd hf 33

34 Exemple 34

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