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Domain Name System (DNS)

Domain Name System (DNS). Network Information Center (NIC) : HOSTS.TXT. DNS -- Hierarchical Namespace. (Root). mil. edu. gov. com. Pentagon. emich. umich. Whitehouse. ibm. yahoo. cislab. Fully Qualified Domain Names & Domains. Ends with a “DOT” cispdc.cislab.emich.edu.

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Domain Name System (DNS)

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  1. Domain Name System (DNS) • Network Information Center (NIC) : HOSTS.TXT

  2. DNS -- Hierarchical Namespace (Root) mil edu gov com Pentagon emich umich Whitehouse ibm yahoo cislab

  3. Fully Qualified Domain Names& Domains • Ends with a “DOT” • cispdc.cislab.emich.edu. • www.yahoo.com • mail.emich.edu • Generic Domain • See right side >>

  4. Mapping Domain Names to IP Address • Name Server: Holds name-to-address database or point to other who does • Name Resolver: Answer requests from the client • Mapping IP Address to Domain Names • Pointer Query: A domain name query to find the host name associated with an IP addresss • Using reverse lookup • 129.34.139.30= 139.34.129.in-addr.arpa

  5. Distributed name space • Zones of Authority (Zones) • Group of Symbolic Domain Name • In each of these zones, on or more hosts maintains a database of names and IP mapping table • These local name servers are interconnected into a hierarchical tree of domain • Each zone contains a part or sub-tree of the hierarchical tree of the domain • Authority of a zone: Name server in the zone • Delegate authority: Superior domain name server

  6. Resolution Process • User issues gethostbyname() / gethostbyaddr() request • Resolver formulates a query to NS • NS check local authoritative DB or cache first and return. Otherwise, check one of 13 root Name Servers or as high as possible • Return to user program with corresponding IP address, host name, or error message

  7. Resolver Operation • Two types of queries • Recursive: find the answer all the way through all the name server • Non-Recursive: list name server references • Two types of responses • Authoritative: request for a domain in a zone over its authority • Non-authoritative:

  8. Domain Name Server Operation • Primary NS: • Loads a zone’s information from disk, and has authority over the zone • Secondary NS: • Has authority over the zone but obtains the zone information from primary NS using a process call ZONE TRANSFER • Caching-only: • No authority for any zone but obtain all info. and cache it in memory

  9. DNS Distributed database record format • DNS Resource Record (RR): it provides a mapping between domain names and host IP addresses • General Format • Name: Domain Name to be defined • TTL: Time-To-Live in second • Class: protocol family usually IN (internet) • Type: Type of resource (see next page) • Rdata: Depends on the type

  10. DNS Distributed database record format • Resource Record Type and Rdata • Start of Authority (SOA) = full NS name • Name Server (NS) = Host name • Domain Name Pointer (PTR) = Domain name • Canonical Name (CNAME) = Domain name • Mail Exchange (MX) = value and host name • Host Address (A) = 32 bit IP address

  11. BIND DNS Server named.conf file zone "0.0.127.in-addr.arpa" { ;loopback zone type master; file "pz/127.0.0"; }; zone "linux.net" {;forward Zone type master; file "pz/linux.net"; }; zone "196.168.192.in-addr.arpa" {;Reverse Zone type master; file "pz/192.168.196"; };

  12. pz/127.0.0 File $TTL 3D @ IN SOA ns.linux.net. ( 1 ; Serial 8H ; Refresh 2H ; Retry 4W ; Expire 1D) ; Minimum TTL NS ns.linux.net. 1 PTR localhost.

  13. pz/linux.net file $TTL 3D @ IN SOA ns.linux.net. ( 199802151 ; 8H ; 2H; 4W; 1D ) NS ns ; name server MX 10 mail ; Primary Mail localhost A 127.0.0.1 ns A 192.168.196.2 mail A 192.168.196.4 www A 192.168.196.5 web CNAME www

  14. pz/192.168.196 file $TTL 3D @ IN SOA ns.linux.net.( 199802151; 8H ;2H ;4W ;1D) ; NS ns.linux.net. 2 PTR ns.linux.net. 4 PTR mail.linux.net. 5 PTR www.linux.net.

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