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Einführung in Domain Name System DNS und Bind

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Thema: DNS - Domain Name System, eine Einführung in die Theorie von DNS und die Konfiguration von Bind
Ort / Anlass: LugBE Off-Event im Restaurant Beaulieu Bern
Datum: 20. Oktober 2005

Published in: Technology
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Einführung in Domain Name System DNS und Bind

  1. 1. DNS – Domain Name System Das Domain Name System, eine Einführung Thomas Deutsch <thomas@tuxpeople.org> 20. Oktober 2005 Restaurant Beaulieu, Bern
  2. 2. Inhalt <ul><li>Was ist DNS </li></ul><ul><li>Warum ein DNS? </li></ul><ul><li>Geschichte des DNS </li></ul><ul><li>Wie funktioniert DNS </li></ul><ul><li>Konfiguration des Clients </li></ul><ul><li>Konfiguration eines Servers </li></ul><ul><li>Nicht Inhalt dieses Vortrages: </li></ul><ul><li>Konfiguration eines Servers für rekursive Auflösung </li></ul>
  3. 3. Was ist DNS? <ul><li>„unsichtbarer“ Helfer im Hintergrund </li></ul><ul><li>Notwendiger Wegweiser </li></ul><ul><li>Telefonbuch </li></ul><ul><li>Hirarchisch und dezentral </li></ul><ul><li>Unverzichtbar für surfen und mailen </li></ul>
  4. 4. Was ist DNS? Grafik © Denic.de
  5. 5. Die Domain <ul><li>students.informatik.uni-ffm.de. </li></ul><ul><li>. Root </li></ul><ul><li>de Top-Level-Domain (TLD) </li></ul><ul><li>uni-ffm Second-Level-Domain </li></ul><ul><li>informatik Third-Level-Domain </li></ul><ul><li>students Hostname </li></ul>
  6. 6. Rootserver <ul><li>13 Rootserver „A“ - „M“ </li></ul><ul><li>Zentrale Rolle: A-Server </li></ul><ul><ul><li>Datenbasis für alle Rootserver </li></ul></ul><ul><ul><li>Sync 2x pro Tag </li></ul></ul><ul><li>Aus technischen Gründen nicht mehr möglich </li></ul><ul><li>Trick: Anycast </li></ul><ul><ul><li>5 Rootserver nutzen Anycast z.B. </li></ul></ul><ul><ul><li>F-Server: 19 Server auf 5 Kontinenten </li></ul></ul><ul><ul><li>K-Server: 16 Server auf 4 Kontinenten </li></ul></ul><ul><ul><li>Genf: I + K </li></ul></ul><ul><li>5 alternative Rootserver-Netzwerke </li></ul>
  7. 7. Die Topleveldomains <ul><li>Es gibt über 200 TLDs </li></ul><ul><li>Unterschieden werden: </li></ul><ul><ul><li>Allgemeine Top Level Domains </li></ul></ul><ul><ul><li>Länderspezifische Top Level Domains </li></ul></ul><ul><ul><li>Sonderfälle </li></ul></ul>
  8. 8. Allgemeine TLDs <ul><li>.aero: aeronautics(weltweit) </li></ul><ul><li>.arpa: Arpanet </li></ul><ul><li>.biz: business (weltweit) </li></ul><ul><li>.com: commercial (weltweit, *) </li></ul><ul><li>.coop: cooperatives (weltweit) </li></ul><ul><li>.edu: educational (*) </li></ul><ul><li>.gov: government (*) </li></ul><ul><li>.info: Informationsanbieter (weltweit) </li></ul><ul><li>.int: Internationale Regierungsorganisationen </li></ul><ul><li>*=Ursprüngliche TLDs </li></ul><ul><li>.mil: military (*) </li></ul><ul><li>.museum: Museen (weltweit) </li></ul><ul><li>.name: nur für natürliche Personen oder Familien (Privatpersonen, weltweit) </li></ul><ul><li>.net: Netzverwaltungseinrichtung (weltweit, *) </li></ul><ul><li>.org: organization (weltweit, *) </li></ul><ul><li>.pro: professions (Anwälte, Steuerberater, Ärzte), nur für genannte Berufsgruppen der USA </li></ul><ul><li>.travel: für die Reiseindustrie </li></ul>
  9. 9. Länderspezifische TLDs <ul><li>Es gibt über 200 ccTLDs. Jedes Land besitzt genau einen Zwei-Buchstaben Code nach ISO 3166. </li></ul><ul><li>Ausnahmen: </li></ul><ul><ul><li>das Vereinigte Königreich besitzt die TLDs .uk und .gb </li></ul></ul><ul><ul><li>Ascension hat eine eigene TLD .ac, obwohl es nicht auf der ISO-Liste steht, sondern zu St. Helena (.sh) gehört. </li></ul></ul><ul><ul><li>Des weiteren sind noch vier obsolete TLDs aus Gründen der Erreichbarkeit aktiv: </li></ul></ul><ul><ul><ul><li>Serbien und Montenegro besitzt die TLDs .cs und .yu </li></ul></ul></ul><ul><ul><ul><li>In der Russischen Föderation wird neben .ru auch noch .su betrieben </li></ul></ul></ul><ul><ul><ul><li>Ost-Timor wechselt momentan von .tp auf .tl und betreibt für eine Übergangszeit beide TLDs </li></ul></ul></ul><ul><ul><ul><li>.zr für Zaire wurde 2004 aus den Root-Servern entfernt (jetzt .cd) </li></ul></ul></ul>
  10. 10. Sonderfälle <ul><li>.eu </li></ul><ul><ul><li>Ist weder eine Länderspezifiche Domin (Die EU ist kein Land) noch eine Allgemeine TLD da sie auf ein bestimmtes Gebiet beschränkt ist. </li></ul></ul><ul><li>.arpa </li></ul><ul><ul><li>Gedacht als Temporäre Lösung bei der Einführung von DNS </li></ul></ul><ul><ul><li>Subdomain in-addr.arpa ist weltweit im Einsatz, um das Auflösen einer IP-Adresse in einen Domainnamen (reverse lookup) zu ermöglichen </li></ul></ul><ul><ul><li>Subdomain e164.arpa wird für ENUM, die Adressierung von Internet-Diensten über Telefonnummern verwendet. </li></ul></ul>
  11. 11. Warum ein DNS? <ul><li>Namen kann man besser merken als Zahlen </li></ul><ul><li>Werbewirksammer </li></ul><ul><li>Virtuelle Hosts nur dank DNS möglich </li></ul><ul><li>Alternativen: </li></ul><ul><li>IP-Adressen auswendig lernen </li></ul><ul><li>/etc/hosts </li></ul>
  12. 12. Geschichte des DNS <ul><li>Ende der 60er: </li></ul><ul><ul><li>Advanced Research Projects Agency Net </li></ul></ul><ul><li>Beginn der 80er: </li></ul><ul><ul><li>Entwicklung von TCP/IP </li></ul></ul><ul><ul><li>SRI-NIC am Stanford Research Institute verwaltet hosts.txt </li></ul></ul><ul><li>Mitte der 80er: </li></ul><ul><ul><li>DNS wird ins ARPAnet implementiert und wird zum Standard </li></ul></ul><ul><li>Beginn der 90er: </li></ul><ul><ul><li>Das WWW entsteht (Tim Berners-Lee am CERN (Genf)) </li></ul></ul>
  13. 13. Wie funktioniert DNS? <ul><li>Zuerst /etc/hosts </li></ul><ul><li>Dann den Nameserver (/etc/resolv.conf) </li></ul><ul><li>Was abgefragt wird und die Reihenfolge regelt die /etc/nsswitch.conf </li></ul><ul><li>Nameserver weiss Antwort falls Cache ist oder Zone verwaltet </li></ul><ul><li>Sonst normale Namensauflösung </li></ul>
  14. 14. Die Datei /etc/resolv.conf <ul><li>Beinhaltet die DNS Konfiguration des Clients </li></ul><ul><li>Wird bei DHCP automatisch konfiguriert </li></ul><ul><li>Beispiel: </li></ul><ul><li>search saxsys.de galaxis.de </li></ul><ul><li>nameserver 134.109.192.18 </li></ul><ul><li>nameserver 192.168.85.1 </li></ul>
  15. 15. Die Datei /etc/nsswitch.conf <ul><li>Regelt die Reihenfolge der Namensauflösung </li></ul><ul><li>Beispiel: </li></ul><ul><li>hosts: files dns </li></ul><ul><li>Damit werden zuerst die Dateien (files) und dann der Namensdienst (DNS) befragt. </li></ul>
  16. 16. Die Namensauflösung per DNS <ul><li>Grundsätzlich werden zwei Arten der Namensauflösung unterschieden: </li></ul><ul><ul><li>rekursive Namensauflösung </li></ul></ul><ul><ul><li>iterative Namensauflösung </li></ul></ul><ul><li>Der Client übermittelt in beiden Fällen den Hostnamen und legt den Abfragetyp fest </li></ul>
  17. 17. Die rekursive Namensauflösung
  18. 18. Die iterative Namensauflösung <ul><li>Der DNS-Server des Clients teilt dem Client nur mit, welches der nächste Nameserver ist </li></ul><ul><li>Die Abfrage der auf der letzten Folie gezeigten Server muss der Client selbst vornehmen </li></ul>
  19. 19. Eigener Cache-only DNS-Server <ul><li>Download der Software von ftp://ftp.isc.org/isc/bind9/ </li></ul><ul><li>Eventuell auch Installation über ein Package-Management </li></ul><ul><li>Aktuell bei Bind9 ist zur Zeit die Version 9.2.5. Die unstable Version ist 9.3.1 </li></ul><ul><li>Anlegen von </li></ul><ul><ul><li>named.conf </li></ul></ul><ul><ul><li>named.root </li></ul></ul><ul><li>Nameserver starten und beim Client eintragen </li></ul>
  20. 20. /etc/named.conf <ul><li>options { </li></ul><ul><li>directory &quot;/etc/named&quot;; </li></ul><ul><li>}; </li></ul><ul><li>zone &quot;.&quot; IN { </li></ul><ul><li>type hint; </li></ul><ul><li>file &quot;named.root&quot;; </li></ul><ul><li>}; </li></ul>
  21. 21. /etc/named/named.root <ul><li>Download per FTP von ftp://ftp.internic.net/domain/named.root (ftp://192.0.34.27/domain/named.root) </li></ul><ul><li>named.root enthält die IP-Adressen der Root-Server. (Auszug): </li></ul><ul><li>. 3600000 NS B.ROOT-SERVERS.NET. </li></ul><ul><li>B.ROOT-SERVERS.NET. 3600000 A 192.228.79.201 </li></ul><ul><li>. 3600000 NS C.ROOT-SERVERS.NET. </li></ul><ul><li>C.ROOT-SERVERS.NET. 3600000 A 192.33.4.12 </li></ul>
  22. 22. Die eigene Domain <ul><li>Registrieren einfach </li></ul><ul><li>Kein Luxus mehr </li></ul><ul><li>Man braucht zwei DNS-Server </li></ul>
  23. 23. /etc/named/named.domain.ch <ul><li>@ IN SOA dns1.domain.ch. root.dns1.domain.ch. ( </li></ul><ul><li>2002012401 ; Serial </li></ul><ul><li>10800 ; Refresh 3 hours </li></ul><ul><li>3600 ; Retry 1 hour </li></ul><ul><li>604800 ; Expire 1000 hours </li></ul><ul><li>86400) ; Minimum 24 hours </li></ul><ul><li>IN NS dns1.domain.ch. </li></ul><ul><li>IN NS dns2.zweiterserver.ch. </li></ul><ul><li>; </li></ul><ul><li>dns1 IN A 195.162.162.160 </li></ul><ul><li>; </li></ul><ul><li>domain.ch. IN MX 0 mail.domain.ch. </li></ul><ul><li>; </li></ul><ul><li>www IN A 195.162.162.160 </li></ul><ul><li>ftp IN CNAME www </li></ul><ul><li>mail IN A 195.162.162.160 </li></ul><ul><li>smtp IN CNAME mail </li></ul><ul><li>pop IN CNAME mail </li></ul>
  24. 24. Änderungen an der named.conf <ul><li>allow-transfer { </li></ul><ul><li>130.59.1.80; </li></ul><ul><li>130.59.211.10; </li></ul><ul><li>192.16.202.11; </li></ul><ul><li>128.112.129.15; </li></ul><ul><li>147.28.0.39; </li></ul><ul><li>200.16.97.77; </li></ul><ul><li>194.42.48.120; </li></ul><ul><li>203.37.255.97; </li></ul><ul><li>164.128.36.32/27; </li></ul><ul><li>195.162.161.182; Unser Secondary Nameserver </li></ul><ul><li>}; </li></ul><ul><li>zone &quot;.domain.ch&quot; in { </li></ul><ul><li>type master; </li></ul><ul><li>file &quot;named.domain.ch&quot;; </li></ul><ul><li>}; </li></ul>
  25. 25. Die named.conf des Slave Servers <ul><li>zone &quot;domain.ch&quot; { </li></ul><ul><li>type slave; </li></ul><ul><li>file &quot;secondary-domain.ch&quot;; </li></ul><ul><li>masters { </li></ul><ul><li>195.162.162.160; </li></ul><ul><li>}; </li></ul><ul><li>}; </li></ul>
  26. 26. Uebersicht der gebräuchlichen Record-Typen <ul><li>A <IP> Authoritativ Record IPv4 </li></ul><ul><li>AAAA <IPv6> Authoritativ Record IPv6 </li></ul><ul><li>A6 <IPv6> Authoritativ Record IPv6 </li></ul><ul><li>NS <hostname> Nameserver Record </li></ul><ul><li>MX <prio> <hostname> Mail Exchanger </li></ul><ul><li>CNAME <hostname> Canonical Name </li></ul><ul><li>SOA <Domain> Start Of Authority </li></ul><ul><li>PTR <hostname> Pointer für Reverse-DNS </li></ul>
  27. 27. Andere Record-Typen <ul><li>Seltener benutzte Record-Typen </li></ul><ul><ul><li>HINFO <Text> Host-Info, Angaben zur Hardware, OS, Standort etc </li></ul></ul><ul><ul><li>TXT <Text> Freier Text </li></ul></ul><ul><ul><li>RP <Text> Responsible Person, Name der zuständigen Person </li></ul></ul><ul><li>Experimentelle oder nicht mehr gebräuchliche Record-Typen </li></ul><ul><ul><li>ISDN <Telnummer> ISDN Nummer </li></ul></ul><ul><ul><li>MINFO <resp-mbox> Mailbox oder Mailinglisten Information </li></ul></ul><ul><ul><li>NULL <irgendwas> Tut nichts </li></ul></ul>
  28. 28. Weitere Infos <ul><li>http://de.wikipedia.org/wiki/Anycast </li></ul><ul><li>http://www.linuxfibel.de/dns_cli.htm </li></ul><ul><li>http://www.linuxfibel.de/dns_srv.htm </li></ul><ul><li>http://european.ch.orsn.net/ </li></ul><ul><li>http://de.wikipedia.org/wiki/Internet </li></ul><ul><li>http://www.isc.org/index.pl </li></ul><ul><li>http://www.oreilly.de/german/freebooks/linag2/netz1307.htm </li></ul><ul><li>http://de.wikipedia.org/wiki/Top_Level_Domain </li></ul><ul><li>http://www.tecchannel.de/netzwerk/grundlagen/401207/ </li></ul><ul><li>http://de.wikipedia.org/wiki/Domain_Name_System </li></ul><ul><li>http://www.denic.de/de/domains/technik/nameserverdienst/ </li></ul>

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