Slides _PPT_ by jianghongl


             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
• 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
•    Initially HOSTS.TXT recorded this
•   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

                       Local Server
                                                    Ip address
DNS Hierarchy
           Zones and DNS



mail   groups   photos            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
         » Master server
         » Slave server
         » Stub server
• Each domain must have one master server
  and at least one slave server to provide
              DNS Files
• Configuration File  /etc/named.conf

• Data files  /var/named/
• 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 File
• Establishes the names of root servers and lists their
• If your network is connected to the Internet,
          it lists the Internet name servers;
         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
            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 domain, the special domain
  that allows reverse (address-to-name)
• 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
Thank you

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