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					[DNS]
CONENTS
WHAT IS DNS ?
PURPOSE OF DNS .
DNS CONCEPTS.
DNS WORKS
MESSAGE FORMAT
DNS APPLICATION
ADVANTAGES OF DNS.
SUMMARY
      What is DNS ?
The Domain Name System (DNS) is
the method by which Internet
addresses in mnemonic form such as
sunc.scit.wlv.ac.uk. are converted into
the equivalent numeric IP address such
as 134.220.4.1.
DNS is a service that maps a local name
to an IP address and conversely an
address to a name.
   Purpose of DNS
Addresses are used to locate objects

Names are easier to remember than numbers

You would like to get to the address or other
objects using a name

 DNS provides a mapping from names to resources
of several types
           Concept of Domains
   Domains are “namespaces”
    Everything below .com is in the com
   domain.
   Everything below ripe.net
                                          •   com domain
                              net edu com
    is in the ripe.net                          •
  ripe.net domain               •         •   google
 domain and in             ripe isi sun tislabs
 the net
net domain
                           •         moon           •
 domain.               www  disi
                          ftp        •    www
                                    ws2   ws1
   TOP LEVEL DOMAINS
 TWO TYPES OF TOP LEVEL DOMAINS

1—Organizational :3 character code indicates the function
      Of organization
   used primarily within the us
       e.g--gov ,mil ,edu ,org ,com ,net

 2-geographical :2-character country or region code
      e.g- us, in ,jp ,de,uk
ORGANIZATIONAL TOP - LEVEL
     DOMAIN NAMES
  COM --- Typically       commercial organizations

  EDU --- Educational      institutions and universities

  GOV --- Government ,       Non- military

  MIL --- Military ,   Army , Navy

  ORG --- Miscellaneous       organizations

  NET --- Usually      service providers

  INT --- International   organizations
      CONCEPT OF NAME
People prefer to use easy –to-remember names
instead of IP addresses
Domain names are alphanumeric names for IP
addresses
E.G
 Neon .cs. Virginia.edu, www.google.com ,itef.org
The Domain name system (DNS) is an
internet – wide distributed database that
translates between domain names and IP
addresses
         DNS STRUCTURE

                 ROOT




ARPA
 ARPA
               EDU         MIL

        COM
         COM         GOV         ORG
             DNS CONCEPT :
              DNS Names 1

• The namespace needs to be made hierarchical
  to be able to scale.
• The idea is to name objects based on
   • location (within country, set of organizations, set
     of companies, etc)
   • unit within that location (company within set of
     company, etc)
   • object within unit (name of person in company)
              DNS Names 2
       How names appear in the DNS
Fully Qualified Domain Name (FQDN)
               WWW.RIPE.NET.
• labels separated by dots      Note the trailing dot


• DNS provides a mapping from FQDNs to
  resources of several types

• Names are used as a key when fetching data in
  the DNS
                DNS Names 3


   ftp
      ws1 ws2         • Domain names can be
        •               mapped to a tree.
www disi        www

   •         sun •
    ripe isi         •
               tislabs New   branches at the „dots‟
           •       moon
     •         •
                  google
      net educom
                      • No restriction to the
          •             amount of branches.
               DNS data Example
• Example Zone file
dacht.net 7200 IN         SOA            ns.ripe.net.   olaf.ripe.net.(
                                             2001061501     ; Serial
                                             43200 ; Refresh 12 hours
                                             14400 ; Retry 4 hours
                                             345600 ; Expire 4 days
                                             7200 ; Negative cache 2 hours
                                )
dacht.net 7200 IN    NS                   ns.ripe.net.
dacht.net 7200 IN    NS                   ns.high5.net.
pinkje.dacht.net  3600              IN       A     193.0.1.162
host25.dacht.net  2600              IN       A     193.0.3.25

Label               ttl         class      type            rdata
            Places where DNS data lives
            Changes in DNS do not propagate instantly!
                                              Slave
                   Might take up to refresh
                   to get data from master

                                                      Not going to net if TTL>0
                                                       Cache server
Upload of zone
data is local policy

                 Master

 Registry DB


                          Slave server
                    A DNS tree
                               .   root
                                                         domain

        top level       .net          .com


            .money.net .kids.net      .os.net                zone

corp.money.net   dop.kids.net                    nt.os.net
                       marnick.kids.net
                                           unix.os.net
                                          mac.os.net
         HOW DNS WORKS
                                        Root name server




               DNS CLIENT
                                 Local name server


BROWSER
                                                       Authoritative
 Browser passes host name to DNS client                Name server
 DNS client looks IP address from the distributed
 database located on the DNS name servers
 LOCAL
 ROOT
 AUTHORITATIVE
     DNS IN INTERNET
          ROOT




INVERSE   GENERIC   COUNTRY
DOMAINS   DOMAINS   DOMAINS
DNS MESSAGE FORMAT

  IDENTIFICATION          FLAGS
                                               12
NO. OF QUESTION        NO. OF ANSWER RRS       BYTES

NO. OF AUTHORITY RRS   NO. OF ADDITIONAL RRS


                   QUESTION

                   ANSWER
              AUTHORITY
        ADDITIONAL INFORMATION
 DNS MESSAGE FORMAT
                      (CONT..)



  QUERY DOMAIN NAME



QUERY TYPE   QUERY CLASS
   DNS MESSAGE FORMAT
                          (CONT..)


   RESOURCE DOMAIN NAME

   TYPE           CLASS
               RESOURCE
TIME TO LIVE
               DATA LENGTH


       RESOURCE DATA
Example of DNS Hierarchy

                   COM


                  FOOTBAR



         CANDY              SOAP


PEANUT   ALMOND   WALNUT
        DNS Name Space

• DNS names are managed by a
  hierarchy of DNS servers.
  – Hierarchy is related to DNS domain
    hierarchy
• Root server at top of tree knows about
  next level servers.
• Next level servers, in turn, know about
  lower level servers.
               Simple DNS example
                                                           root name server
host surf.eurecom.fr                        2               4
  wants IP address of                           5      3
  gaia.cs.umass.edu
1. Contacts its local DNS
   server, dns.eurecom.fr
                                  local name server   authorititive name server
2. dns.eurecom.fr                  dns.eurecom.fr         dns.umass.edu
   contacts root name server, if        1    6
   necessary
3. root name server contacts
   authoritative name server, requesting host          gaia.cs.umass.edu
   dns.umass.edu, if           surf.eurecom.fr

   necessary
 APPLICATION OF                        DNS

Used in Internet---primarily for computers with IP
addresses; any device with an IP address
Generic domains: edu, com, net, org, …
us, uk, in, au, …
To map host names to IP addresses
E-mail address mapping
DNS naming data divided into zones;
BIND: Berkeley implementation of DNS for Unix
ADVANTAGES OF DNS
Host Names are easy for humans to deal
with .
The layer of indirection allows
The IP addresses of a host name to change
transparently .
 Load balancing is possible .
Expand and add domains and sub domains as
soon as you want
         SUMMARY

DNS is simple .
DNS : Maps Names To Addresses
Names are Hierarchical: Administration
  is also hierarchical.

DNS administration is important .

No standard For Number of levels .
   REFERENCE

www.google.com/feeling lucky
www.yahoo.com/search
www.sims.berkeley.edu/group/vdb/diagram
.gib
http://www.ncn.com
http://www.fujits.com
http://www.digital dividend .org

				
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posted:9/27/2011
language:English
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