D.N.S

Nirbhay Narayan Upadhyay
I.T 3rdYear, 1010413902
Domain Name System

Content..
 Introduction
 History
 Classification
 How DNSWork
 Top level domains
 Domain Name Space
 Future
 Conclusion

Introduction
 Since internet addressing is done by IP
address, and
 Since people are not good at remembering
such things
 A translation service, DNS, is provided
 Servers are geographically distributed so
DNS provides a large scale example of the
client-server paradigm

Domain Name System
 A system which permits humans to use names and
machines to use addresses
 Scalable
 Over 90 million entries in the global DNS now
 Consistent
 You get the same answer where ever you ask
 Resilient
 Specifically designed to avoid single points of failure
 Without the DNS, the Internet would not be usable

Domain Name System..
 Properties of DNS
 Hierarchical name space divided into zones
 Distributed over a collection of DNS servers
 Hierarchy of DNS servers
 Root servers
 Top-level domain (TLD) servers
 Authoritative DNS servers
 Performing the translations
 Local DNS servers
 Resolver software

The domain
acmebw.com
Domains
 A domain is a node in the name space and all its
descendants
 That is, a sub tree of tname is the same as the name
of the node at the root
 A domain’s domain) of the sub tree
d a k o t a
w e s t
t o r n a d o
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a c m e b w m e t a in fo
c o m
b e r k e le y n w u
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it u
in t
a r m y
m il
u u
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" "
The node
acmebw.com

Host Names vs. IP addresses
 Host names
 Mnemonic name appreciated by humans
 Variable length, alpha-numeric characters
 Provide little (if any) information about location
 Examples: www.cnn.com and ftp.eurocom.fr
 IP addresses
 Numerical address appreciated by routers
 Fixed length, binary number
 Hierarchical, related to host location
 Examples: 64.236.16.20 and 193.30.227.161

TLD and Authoritative Servers
 Top-level domain (TLD) servers:
 responsible for com, org, net, edu, etc, and all top-level
country domains uk, fr, ca, jp.
 Network Solutions maintains servers for comTLD
 Educause for eduTLD
 Authoritative DNS servers:
 organization’s DNS servers, providing authoritative
hostname to IP mappings for organization’s servers (e.g.,
Web, mail).
 can be maintained by organization or service provider

How DNS work?
 To map a name onto an IP add, an application
program calls a library procedure called the
resolver
 The name is passed onto the resolver as a
parameter
 The resolver sends a UDP packet to a local DNS
server
 DNS server looks up the name and return the
corresponding IP address to the resolver
 The resolver then send this address to caller and
program can establish aTCP connection with the
destination

Domain Name Resolution
 When a domain name server receives a query,
it checks to see if the name lies in the sub
domain for which is an authority.
 If so, it appends the address and sends the
query back to the client. If not, it checks to
see what type of interaction the client
requested. It either contacts a server that can
resolve or sends the client the server the
client should contact next.

Domain Name Resolution (contd…)
 A client must know how to contact at least
one name server.
 Each server must know the address of at least
one root server and may know the address for
the domain immediately above it (its parent).
 How does a client know how to contact a
name server? Compiled into app, in a file on
secondary storage, or obtained at boot.

DNS as a Database
Keys to the database are “domain names”
www.foo.com, 18.in-addr.arpa, 6.4.e164.arpa
Over 100,000,000 domain names stored
Each domain name contains one or more attributes
Known as “resource records”
Each attribute individually retrievable

Futures (Technical)
 The DNS protocol suite continues to evolve
 Future improvements will include
 stronger DNS security
 DNS could be the basis for a PKI
 support for IPv6
 Should that be necessary
 Integration with directory service protocols
 LDAP, in particular
 DNS is being used for things far outside the original
scope

Conclusions
 Domain Name System
 Distributed, hierarchical database
 Distributed collection of servers
 Caching to improve performance
 The Domain Name System provides human-friendly identifiers for
Internet users to reference the sites they want to get to
 The DNS is a distributed, global name lookup system composed of
 A namespace in which all names reside
 Resolvers which are the clients in name lookups
 Servers which respond to queries from clients

D.N.S

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