DOMAIN NAME SYSTEM AND DYNAMIC DOMAIN NAME SYSTEM Machines on the internet are identified by a unique IP address. But it is difficult for people to remember these addresses. Humans are more comfortable with names rather than numbers. Hence it would be easier to identify a machine using a name instead of an address. DDNS (Dynamic Domain Name System) allows us to overcome the issues related to Dynamic IP Addresses, in attempting to connect to a DVR somewhere on the Internet whose IP Address may change at any time.

1. DOMAIN NAME SYSTEM AND
DYNAMIC DOMAIN NAME SYSTEM
NAME-VIRENDRA THAKUR
ROLL NO-A005
SAP NO-40507190005

2. Domain Name System
 Machines on the internet are identified by
a unique IP address.
 But it is difficult for people to remember these
addresses.
 Humans are more comfortable with
names rather than numbers.
 Hence it would be easier to identify a
machine using a name instead of an address.

3. Namespace
 The names must be unique as the
IP addresses are unique.
 A namespace that maps each address to
a unique name.
 It can be organized in two ways:
I. Flat
II. Hierarchical

4. 1 Flat NameSpace: A flat name space is a sequence of
characters without structure.
 The main drawback of flat name space is that it
cannot used in large system.
2 Hierarchical NameSpace: In hierarchical name
space , each name is made of several parts.
 The first part can define nature of the organization,
 second part can define the name of the organization,
 the third part can define departments in the
organization and so on.
 E.g. unipune.ac.in indicates university of pune is
an academic institution and located in India.

5. Domain Name Space
 The mechanism that implements
hierarchical name space is called
Domain Name Space.
 In this design the names are defined in
an inverted tree structure with the root at
the top.
 The tree can have only 128 levels 0(root)
to level (127).

6. Domain name space

7.  Label: Each node in the tree has a
label, which is a string with a
maximum of 63 characters. The root
label is a null string (empty string)
 Domain Name: Each node in a tree has
a domain name.
 A full domain name is a sequence of
labels separated by dots(.)
 The domain name is always read from
the node upto the root.

8. Domain names and labels

9. Fully Qualified Domain Name(FQDN)
 If a label is terminated by null string(dot), it is
called a Fully Qualified Domain
Name(FQDN).
 FQDN is a domain name that contains the
full name of the host.
 FQDN can reach to the root.
 E.g. pg.compsc.mycollege.edu.
 is the FQDN of server named “pg”
installed at the “compsc” department in
college “mycollege”.
 The label “edu” represents a top level domain.

10. Partially Qualified Domain Name(PQDN)
 If a label is not terminated by null string(dot),
it is called a Partially Qualified Domain
Name(PQDN).
 A PQDN starts from a node, but it does not
reach to the root.
 It does not give the full path to the domain.

11. FQDN and PQDN

12. Domain
 A domain is a sub tree of the Domain
name space.
 The name of the domain is the domain
name of the node at the top of the
subtree.

13. Domains

14. Distribution of Name Space
 The information of domain name space
must be stored on domain name server .
 But this huge amount of information cannot
be stored at a central place in a single
server.
 Because responding to requests from all
over the world places a heavy load on the
system.
 Sometimes failure makes the
data inaccessible.

15.  DNS Server: The solution is to the
above problem is to distribute this
information among several computers
across world.
 These computer are called DNS
Server.
 Each server is responsible for storing
a domain or a subdomain.

16. Hierarchy of name servers

17. Zone
 A server is responsible for or has
authority over called a zone.
 Zone is a contiguous part of the tree.
 The server makes a database called a zone
file and keeps all the information for
every node under that domain.

18. Zone

19. Types of Server
1.Root Server: A root server is a server whose
zone consists of the whole tree.
 A root server does not store any information
about domains but delegates(hand overs) its
authority to other servers.
 There are many root servers around the world,
each covering a whole top level domain
hierarchy.

20. 2. Primary Server: A primary server is a
server that stores a file about the zone.
 It is responsible for updating and
maintaining all information about that
zone.
 It sends this information to other secondary
servers when requested.

21. 3. Secondary Server: A secondary server
retrieves information from another primary
or secondary server and stores this
information (Zone transfer).
 It does not create or update the file.

22. DNS in the Internet
 DNS is a protocol that can be used
in different platforms..
 In Internet, the domain name space (tree)
is divided into three different sections:
1. Generic domains
2. Country domains
3. Inverse domain

23. DNS IN THE INTERNET

24. 1.Generic domains
 The generic domains define registered
hosts according to their generic behaviour.
 It allows organizations to be grouped
by organizational types.
 Each node in the tree defines a domain.
 There are around 14 generic domains
availabel under organizational schemes
as listed below

25. Generic domains

26. Generic domain labels

27. 2.Country domains
 This divides the servers by country.
 It uses two character country
abbreviations. E.g.
 India - in
 United Kingdom – uk
 United states – us

28. Country domains

29. 3.Inverse domain
 It is used to map an address to name.
 E.g. If a server receives a request from a
client and the server has only the IP
addresses of the clients in its list then
the server asks its resolver(DNS Client)
to query to the DNS server to map the
IP address to name to verify if the
client is authorized.
 This type of query is also called
inverse query or pointer query.

30. Inverse domain

31. Resolution
 The process of mapping name to an
address or an address to a name is called
address resolution.
 Resolver : DNS is designed as
a client/server application.
 A host that needs to map an address to a
name or a name to an address calls a
DNS client called a resolver.
 It accesses closest DNS server with
a mapping request.

32. Types of resolution
1) 1.Recursive name-address resolution
2) Iterative resolution

33. 1.Recursive name-address
resolution

34.  The resolver expects the server to supply
the final answer.
 If the server is the authority for the domain
name, it checks its database and responds.
 If the server is not the authority for the
domain name it sends the request to another
server and waits for the response.
 When the query is finally resolved the
response travels back until finally reaches
the requesting client.
 This is called Recursive resolution.

35. 2.Iterative resolution

36.  If the server is an authority for the name,
it sends the answer.
 If it is not , it returns IP address of the
server that it thinks can resolve the query.
 The client is responsible for repeating
the query to this second server.
 This process is called Iterative Resolution
because the client repeats the same query
to multiple servers.

37. Caching
 Each time a server receives a query for a
name that is not in its domain, it needs to
search its database for a server IP
address.
 Reduction of this search time
would increase efficiency.
 DNS handles this with a mechanism
called caching.
 When a server asks for a mapping from
another server and receives the response,
it stores this information in its cache
memory before sending it to the client.

38. DNS Messages
 DNS has two types of messages: query and
response. Both types have the same format.
 The query message consists of a header and
question records; the response message
consists of a header, question records,
answer records, authoritative records, and
additional records

40. TYPES OF RECORDS
 Two types of records are used in DNS. The
question records are used in the question
section of the query and response messages.
 The resource records are used in the answer,
authoritative, and additional information
sections of the response message.

41. DYNAMIC DOMAIN NAME
SYSTEM (DDNS)
DDNS (Dynamic Domain Name System)
allows us to overcome the issues related to
Dynamic IP Addresses, in attempting to
connect to a DVR somewhere on the
Internet whose IP Address may change at
any time.