DOMAIN NAMING SYSTEM (AN OVERVIEW) By -DEEPAK

Topics --DNS What is DNS? Purpose of DNS DNS configuration files

DNS : 1) an Internet directory service which converts Host name to IP address and IP address to Host name. 2) Helps mail delivery agents, such as send mail and POP using mail exchange records (MX records).

History of DNS Internet TCP/IP protocol suite to communicate Protocol suite identifies by each machine a Media Access Control (MAC) address and an IP address. MAC Physical Address …burnt on the network card IP address..Operator defined 

(history cont..) IP address is used to identify what machine is to be contacted ( human interface level). OS then discovers the MAC address using the two identifiers to transmit packets. IP address-to-name relationship was developed Initially HOSTS.TXT recorded this information Large database -->decentralized management model

DNS  network of servers designed to route a requesting party to the information they seek. Two types of queries exist in this system 1) forward lookup 2) backward lookup host name genetic.siu.edu Ip address Noentry Genetics.siu.edu Siuc.edu Local Server Genetics.siu.edu Plantsoil.siu.edu

DNS Hierarchy

Zones and DNS yahoo mail groups photos games adds cities maps events

in.named and DNS Name Servers in.named is also called the Berkeley Internet Name Domain service, or BIND There are three types of DNS name servers. »Master server »Slave server »Stub server Each domain must have one master server and at least one slave server to provide backup.

DNS Files Configuration File  /etc/named.conf Data files  /var/named/named.ca /var/named/hosts /var/named/hosts.rev /var/named/named.local

/etc/named.conf contains a list of domain names and the file names that contain host information The /etc/named.conf file contains statements that implement the following.  Security through an Access Control List (ACL) that defines a collection of IP addresses that an host has read/write access  Logging specifications  Selectively applied options for a set of zones, rather than to all zones

The named.ca File Establishes the names of root servers and lists their addresses. If your network is connected to the Internet, it lists the Internet name servers; otherwise it lists the root domain name servers for your local network. The in.named daemon cycles through the list of servers until it contacts one of them. It then obtains from that server the current list of root servers, which it uses to update named.ca.

The hosts File The hosts file contains all the data about the machines in the local zone. The name of this file is specified in the configuration file. To avoid confusion with /etc/hosts, name the file something other than hosts, for example, you could name these files using the pattern db.domain.

The hosts.rev File The hosts.rev file specifies a zone in the in-addr.arpa. domain, the special domain that allows reverse (address-to-name) mapping The name of this file is specified in the configuration file.

The named.local File The named. local file specifies the address for the local loop back interface, or local host, with the network address The name of this file is specified in the configuration file.

DNS Clients and the Resolver To be a DNS client, a machine must run the resolver. is neither a daemon nor a single program. resolver's function is to resolve users' queries. resolver queries a name server, which then returns either the requested information

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