Transcript DNS

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
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(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
Noentry Genetics.siu.edu
Siuc.edu
host name genetic .siu.edu
Local Server
Ip address
Genetics.siu.edu
Plantsoil.siu.edu
DNS Hierarchy
Zones and DNS
yahoo
cities
adds
mail
groups
photos
maps
games
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 127.0.0.1.
• 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
Thank you