DNS AND DDNS

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 Nam e S ystem 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: Flat 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. Lab el : 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. Z o n e 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. Z o n e

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: Generic domains Country domains 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 avai label 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. Re s ol u ti o n 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.Recursive name-address resolution 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 

39. 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.

40. 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.