m2-internet 1 dns: domain name system people: many identifiers: ssn, name, passport # internet...
TRANSCRIPT
M2-Internet 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 2
DNS
Why not centralize DNS? single point of failure traffic volume distant centralized
database maintenance
doesn’t scale!
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
H. Fauconnier
M2-Internet 3
Root DNS Servers
com DNS servers org DNS servers edu DNS servers
poly.eduDNS servers
umass.eduDNS servers
yahoo.comDNS servers
amazon.comDNS servers
pbs.orgDNS servers
Distributed, Hierarchical Database
Client wants IP for www.amazon.com; 1st 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 www.amazon.comH. Fauconnier
M2-Internet 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
13 root name servers worldwideb USC-ISI Marina del Rey, CA
l ICANN Los Angeles, CA
e NASA Mt View, CAf Internet Software C. Palo Alto, CA (and 36 other locations)
i Autonomica, Stockholm (plus 28 other locations)
k RIPE London (also 16 other locations)
m WIDE Tokyo (also Seoul, Paris, SF)
a Verisign, Dulles, VAc Cogent, Herndon, VA (also LA)d U Maryland College Park, MDg US DoD Vienna, VAh ARL Aberdeen, MDj Verisign, ( 21 locations)
H. Fauconnier
M2-Internet 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 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 7
requesting hostcis.poly.edu
gaia.cs.umass.edu
root DNS server
local DNS serverdns.poly.edu
1
23
4
5
6
authoritative DNS serverdns.cs.umass.edu
78
TLD DNS server
DNS name resolution example
Host at cis.poly.edu wants IP address for gaia.cs.umass.edu
iterated query: contacted server
replies with name of server to contact
“I don’t know this name, but ask this server”
H. Fauconnier
M2-Internet 8
requesting hostcis.poly.edu
gaia.cs.umass.edu
root DNS server
local DNS serverdns.poly.edu
1
2
45
6
authoritative DNS serverdns.cs.umass.edu
7
8
TLD DNS server
3recursive query: puts burden of
name resolution on contacted name server
heavy load?
DNS name resolution example
H. Fauconnier
M2-Internet 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 2136 http://www.ietf.org/html.charters/dnsind-charter.html
H. Fauconnier
M2-Internet 10
DNS records
DNS: distributed db storing resource records (RR)
Type=NS name is domain (e.g.
foo.com) value is hostname of
authoritative name server for this domain
RR format: (name, value, type, ttl)
Type=A name is hostname value is IP address
Type=CNAME name is alias name for some
“canonical” (the real) name www.ibm.com is really servereast.backup2.ibm.com value is canonical name
Type=MX value is name of
mailserver associated with name
H. Fauconnier
M2-Internet 11
DNS protocol, messagesDNS 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 12
DNS protocol, messages
Name, type fields for a query
RRs in responseto query
records forauthoritative servers
additional “helpful”info that may be used
H. Fauconnier
M2-Internet 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, 212.212.212.1, A)
create authoritative server Type A record for www.networkuptopia.com; Type MX record for networkutopia.com
How do people get IP address of your Web site?
H. Fauconnier
Sommaire
URL et URI html et swing URLconnections
URLStreamHandler URLStreamHandlerFactory
ContentHandler ContentHandlerFactory
15H. Fauconnier M2-Internet
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:1-800-9988-9938• http://www.xml.comp/pub/stax.html#id =_hdbc
(la classe URLConnection sera décrite plus loin)
16H. Fauconnier M2-Internet
URI URI:
URL (location) http://java.sun.com/j2se/1.3/docs/guide/collections/
designfaq.html#28 ou URN (name):
mailto:[email protected]
Syntaxe: Général:
[scheme:]scheme-specific-part[#fragment] Hiérarchique:
[scheme:][//authority][path][?query][#fragment]Authorité: [user-info@]host[:port]
H. Fauconnier M2-Internet 1-17
URL
http://www.bib.org:80/javafaq/book/index.html?isbn=56888#toc
ftp://anonymous:[email protected]/c%3a/stuff protocol port authority chemin référence requête user
18H. Fauconnier M2-Internet
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
19H. Fauconnier M2-Internet
Remarques
tous les protocoles ne sont pas compris par la machine virtuelle…
exception MalFormedURLException
20H. Fauconnier M2-Internet
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("mailto:[email protected]"); 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/"); }
21H. Fauconnier M2-Internet
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 supportedhttps is supportedftp is supportedmailto is supportedtelnet is not supportedfile is supportedgopher is supportedldap is not supportedjar is supportednfs is not supportedjdbc is not supportedrmi is not supporteddoc is supportednetdoc is supportedsystemresource is supportedverbatim is supported
22H. Fauconnier M2-Internet
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 = host.indexOf('@'); if (atSign != -1) host = host.substring(atSign+1); System.out.println("hôte " + host); } else { System.out.println("hôte null."); }
23H. Fauconnier M2-Internet
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"); } }
24H. Fauconnier M2-Internet
Résultat
http://www.bib.org:80/javafaq/book/index.html?isbn=56888#toc
URL :http://www.bib.org:80/javafaq/book/index.html?isbn=56888#toc
Protocole : httpUserInfo :nullhôte www.bib.orgPort :80Path : /javafaq/book/index.htmlRef : tocQuery: isbn=56888
25H. Fauconnier M2-Internet
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
26H. Fauconnier M2-Internet
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); } }
27H. Fauconnier M2-Internet
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"); } }http://www.liafa.jussieu.frL'objet est un sun.net.www.protocol.http.HttpURLConnection$HttpInputStream
28H. Fauconnier M2-Internet
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("??"); }//...
30H. Fauconnier M2-Internet
Exemple (suite)
/… public String getQuery() { return query.toString(); } public String toString() { return getQuery(); }}
31H. Fauconnier M2-Internet
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
32H. Fauconnier M2-Internet
Pour apache:
Fichier .htaccess: (il faut aussi un AllowOverride AuthConfig dans httpd.conf)
AuthType BasicAuthName "restreint"AuthUserFile /Users/hf/Sites/.psswdRequire user hf
.psswd est le fichier des mots de passe htpasswd –c /Users/hf/Sites/.passwd hf
33H. Fauconnier M2-Internet