Seminar

On
DNS

Submitted To: Submitted By:

Dr. Kaneez Zainab Abhijeet Kumar Pandey
 Content

 INTRODUCTION
 DNS HISTORY
 WHAT IS DNS?
 DNS COMPONENTS
o Name Space:
o Resolvers:
o Name Servers:
 WHY WE NEED OF DNS?
 CONCLUSION
 REFERENCES
 Introduction

 The Domain Name System (DNS) is basically a large

database which resides on various computers and it
contains the names and IP addresses of various hosts on
the internet and various domains.
 The Domain Name System is used to provide
information to the Domain Name Service to use when
queries are made.
 DNS History

 ARPANET utilized a central file HOSTS.TXT

 Contains names to addresses mapping
 Maintained by SRI’s NIC (Stanford-Research-Institute: Network-
Information-Center)

 Administrators email changes to NIC

 NIC updates HOSTS.TXT periodically
 Administrators FTP (download) HOSTS.TXT
 DNS History Cont…

 As the system grew, HOSTS.TXT had problems with:

 Scalability (traffic and load)
 Name collisions
 Consistency

 In 1984, Paul Mockapetris released the first version

(RFCs 882 and 883, superseded by 1034 and 1035 …)
 What is DNS ?

 The “Domain Name System”

 What Internet users use to reference anything by name on
the Internet
 The mechanism by which Internet software translates
names to attributes such as addresses
 What is DNS ?

 A globally distributed, scalable, reliable database

 Comprised of three components
 A “name space”
 Servers making that name space available
 Resolvers (clients) which query the servers about the name space
 Why we need DNS?

 DNS as a Database
 Global Distribution
 Loose Coherency
 Scalability
 Reliability
 Dynamicity
 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

 Global Distribution

 Data is maintained locally, but retrievable globally

 No single computer has all DNS data

 DNS lookups can be performed by any device

 Remote DNS data is locally cachable to improve
performance
 Loose Coherency

 The database is always internally consistent

 Each version of a subset of the database (a zone) has a serial
number
 The serial number is incremented on each database change
 Changes to the master copy of the database are
replicated according to timing set by the zone
administrator
 Cached data expires according to timeout set by zone
administrator
 Scalability

 No limit to the size of the database

 One server has over 20,000,000 names
 Not a particularly good idea
 No limit to the number of queries
 24,000 queries per second handled easily

 Queries distributed among masters, slaves, and caches

 Reliability

 Data is replicated
 Data from master is copied to multiple slaves

 Clients can query

 Master server
 Any of the copies at slave servers

 Clients will typically query local caches

 DNS protocols can use either UDP or TCP
 If UDP, DNS protocol handles retransmission,
sequencing, etc.
 Dynamicity

 Database can be updated dynamically

 Add/delete/modify of any record

 Modification of the master database triggers replication

 Only master can be dynamically updated
 Creates a single point of failure
 DNS Components

There are 3 components:

 Name Space:
Specifications for a structured name space and data
associated with the names
 Resolvers:
Client programs that extract information from Name
Servers.
 Name Servers:
Server programs which hold information about the
structure and the names.
 Name Space
16

 Flat Name Space

In a flat name space, a name is assigned to an address. A name in
this space is a sequence of characters without structure.

 Hierarchical Name Space

In a hierarchical name space, each name is made of several parts.
The first part can define the organization, the second part can
define the name, the third part can define departments, and so on.
 Resolvers
17

A Resolver maps a name to an address and vice

versa.

Query

Response

Resolver Name Server

 Iterative Resolution
a.root
18
server

a3.nstl a.gtld-
d.com server
5
udel ns1.goo
server gle.com
3 iterative response (referral)7
“I don't know. Try a.root-servers.net.”
iterative response (referral) 9
“I don't know. Try a.gtld-servers.net.”
1 iterative response (referral)
“I don't know. Try a3.nstld.com.”
iterative response (referral)
2 4 “I don't know. Try ns1.google.com.”
6 iterative response
8 “The IP address of www.google.com
client 10 is 216.239.37.99.”
iterative request
“What is the IP address of
www.google.com?”
 Recursive Resolution
root19
server
edu 3 com
server server
7 4
udel 2 8 google
serve server
6 5
r
9

1
10 recursive request
“What is the IP address of
www.google.com?”
client recursive response
“The IP address of www.google.com is
216.239.37.99.”
 Name Server
20
Architecture: Zone
From data
Name Server Process
disk file
Authoritative Data Master
Zone transfer server
(primary master and
slave zones)
Cache Data
(responses from
other name servers)
Agent
(looks up queries
on behalf of resolvers)
 Name Server (cont’d)
21
Authoritative Data:
Name Server Process
Authoritative Data
(primary master and
slave zones) Response

Cache Data
(responses from
other name servers)
Agent
(looks up queries Resolver
Query
on behalf of resolvers)
 Name Server (cont’d)
22
Using Other Name Servers:
Name Server Process
Authoritative Data
(primary master and
slave zones)
Response
Cache Data
Response
(responses from
Arbitrary
other name servers)
name
Agent Query server
(looks up queries Resolver
Query
on behalf of resolvers)
 Name Server (cont’d)
23
Cached Data :
Name Server Process
Authoritative Data
(primary master and
slave zones) Response

Cache Data
(responses from
other name servers)
Agent
(looks up queries Query Resolver

on behalf of resolvers)
 Reference

www.csschool.com
 www.wikipedia.com