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14 DNS : The Domain Name System. 14 Introduction - Problem Computers are used to work with numbers Humans are used to work with names ==> IP addresses.

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Presentation on theme: "14 DNS : The Domain Name System. 14 Introduction - Problem Computers are used to work with numbers Humans are used to work with names ==> IP addresses."— Presentation transcript:

1 14 DNS : The Domain Name System

2 14 Introduction - Problem Computers are used to work with numbers Humans are used to work with names ==> IP addresses are NUMBERS :-/ ? 1011011011101110110110

3 14 Introduction Hosts.txt Distributed Database Mapping between IP-address and Hostnames Mail routing Client-Server Resolver - Name servers

4 14 Naming convention Hierarchical www.groept.be wwwsnmp.cs.utwente.nl [0..9,a..z,A..Z,-] Not case sensitive hostname domain wwwsnmp cs utwente nl. Geography IP Subnet No Relation ?

5 14 DNS Tree. arpacomdenlbeorgnetmilintgoveduin-addr1935891groeptmonsantoea country domainsgeneric domains TLD Root 1.9.58.193.in-addr.arpa.FQDN

6 14 Basics Delegation by zone Primary Name Server Root Name Server

7 14 1. Connection initiated from web-browser or other service to request the name. RESOLVER Internet DNS Server Forward Lookup www.groept.be

8 14 Internet DNS Server www.groept.be 1. Connection initiated from web-browser or other service to request the ip address. RESOLVER 2. DNS replies with ip address Forward Lookup

9 14 Internet DNS Server www.groept.be 1. Connection initiated from web-browser or other service to request the ip address. RESOLVER 2. DNS replies with ip address 3. Web browser requests page using the ip address Forward Lookup

10 14 Internet DNS Server www.groept.be 1. Connection initiated from web-browser or other service to request the ip address. RESOLVER 2. DNS replies with ip address 3. Web browser requests page using the ip address 4. Web server replies with webpage Forward Lookup

11 14 Lookup to www.cisco.com Internet groept.be. www.cisco.com 1. Resolver issues a recursive lookup 2. Local nameserver issues an itterative lookup to root name server for.com Root name server.com..cisco.com. recursive itterative

12 14 Lookup to www.cisco.com Internet groept.be. www.cisco.com 1. Resolver issues a recursive lookup 2. Local nameserver issues an itterative lookup to root name server for.com Root name server.com..cisco.com. recursive itterative

13 14 Lookup to www.cisco.com Internet groept.be. www.cisco.com 1. Resolver issues a recursive lookup 2. Local nameserver issues an itterative lookup to root name server for.com Root name server.com..cisco.com. recursive itterative

14 14 Lookup to www.cisco.com Internet groept.be. www.cisco.com 1. Resolver issues a recursive lookup 2. Local nameserver issues an itterative lookup to root name server for.com 3. Local nameserver answers with the IP address Root name server.com..cisco.com. recursive itterative

15 14 Lookup to www.cisco.com Internet groept.be. www.cisco.com 1. Resolver issues a recursive lookup 2. Local nameserver issues an itterative lookup to root name server for.com 3. Local nameserver answers with the IP address 4. Browser request the page using the IP address Root name server.com..cisco.com. recursive itterative

16 14 Sequential Lookup to www.cisco.com Internet groept.be. www.cisco.com 1. Second machine issues the same recursive lookup Root name server.com..cisco.com. recursive

17 14 Sequential Lookup to www.cisco.com Internet groept.be. www.cisco.com 1. Second machine issues the same recursive lookup 2. Local nameserver provides a cached answer Root name server.com..cisco.com. recursive

18 14 Sequential Lookup to www.cisco.com Internet groept.be. www.cisco.com 1. Second machine issues the same recursive lookup 2. Local nameserver provides a cached answer 3. Browser request the page using the IP address Root name server.com..cisco.com. recursive

19 14 Name server types Root name server Primary name server Secondary name server Caching-only name server Slave servers – forwarding server

20 14 NSLOOKUP – Your tool ! Forward Lookup nslookup gateway.pharmacia.com  Name: gateway.pharmacia.com  Address: 193.235.243.3 Reverse Lookup nslookup 193.235.243.3  Name: gateway.pharmacia.com  Address: 193.235.243.3

21 14 New developments DNS dynamic updates using Secure DNS Prompt notification of zone changes Incremental zone transfers

22 14 Resource records SOA-record NS-record A-record CNAME-record HINFO-record PTR-record MX-record

23 14 SOA-record # nslookup Default Server: bebrump001.bebru.eu.pnu.com Address: 10.240.72.65 > set type=SOA > monsanto.com Server: bebrump001.bebru.eu.pnu.com Address: 10.240.72.65 Non-authoritative answer: monsanto.com origin = srvsn0.monsanto.com mail addr = hostmaster.srvsn0.monsanto.com serial = 2001103098 refresh = 3600 (1H) retry = 1800 (30M) expire = 432000 (5D) minimum ttl = 86400 (1D) Authoritative answers can be found from: srvsn0.monsanto.com internet address = 164.144.230.67

24 14 NS-Record > set type=NS > groept.be Server: bebrump001.bebru.eu.pnu.com Address: 10.240.72.65 Non-authoritative answer: groept.be nameserver = mail.groept.be groept.be nameserver = ns.eu.net groept.be nameserver = dns.eunet.be Authoritative answers can be found from: mail.groept.be internet address = 193.75.206.83 ns.eu.net internet address = 192.16.202.11 dns.eunet.be internet address = 193.74.208.137 >

25 14 A-record > set type=A > www.groept.be Server: bebrump001.bebru.eu.pnu.com Address: 10.240.72.65 Name: www.groept.be Address: 193.75.206.93 > www.groept.beIN A 193.75.206.93

26 14 CNAME-record IN A chekov.Belgium.EU.net IN A193.74.208.163 relay.eunet.beIN CNAMEchekov.Belgium.EU.net > relay.eunet.be Server: bebrump001.bebru.eu.pnu.com Address: 10.240.72.65 Name: relay.eunet.be Addresses: 193.74.208.163, 193.74.22.138, 193.74.208.147

27 14 HINFO-record chekov.Belgium.EU.net IN HINFO“SUN E 450” “Solaris”

28 14 PTR-record > set type=PTR > 193.74.208.137 Server: bebrump001.bebru.eu.pnu.com Address: 10.240.72.65 137.208.74.193.in-addr.arpa name = jupiter.Belgium.EU.net 208.74.193.in-addr.arpa nameserver = dns.eunet.be 208.74.193.in-addr.arpa nameserver = ns.EU.net dns.eunet.be internet address = 193.74.208.137 > 137.208.74.193.in-addr.arpa IN PTR jupiter.Belgium.EU.net

29 14 MX-record > set type=MX > pharmacia.com Server: bebrump001.bebru.eu.pnu.com Address: 10.240.72.65 Non-authoritative answer: pharmacia.com preference = 100, mail exchanger = gateway.pharmacia.com pharmacia.com preference = 200, mail exchanger = gateway3.pharmacia.com pharmacia.com preference = 100, mail exchanger = ns3.pharmacia.com Authoritative answers can be found from: gateway.pharmacia.com internet address = 193.235.243.3 gateway3.pharmacia.com internet address = 193.235.243.8 > pharmacia.com IN MX100 gateway.pharmacia.com pharmacia.com IN MX100 ns3.pharmacia.com pharmacia.com IN MX200 gateway3.pharmacia.com

30 14 DNS Message Format identification flags QR opcode AA TC RD RA zero rcode number of questions questions answers (variable number of resource records) number of answer RRs number of authority RRsnumber of additional RRs authority (variable number of resource records) additional information (variable number of resource records) 12 bytes 0 151631

31 14 Question Portion of DNS Query Message query name query typequery class 0 151631

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