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  • 1. …… DNS…… 1
  • 2.  What is DNS ?  Resolving Why DNS ?  Message format Working of DNS.  ER diagram DNS Hierarchy  DNS DB Features  Summary… Intro to IP 2
  • 3.  The term DNS stands for “domain name system.” DNS created in 1983 by Paul Mockapetris . A globally distributed, scalable, reliable, dynamic database It translates human-friendly website addresses into computer-friendly IP addresses and viceversa. 3
  • 4.  the Internet is based on IP addresses, not domain names. IP Addresses are convinient for computers (IP address includes information used for routing.) IP addresses are tough for humans to remember. IP addresses are impossible to guess. Domain names comprise a hierarchy so that names are unique, easy to remember. 4
  • 5.  A domain is an arrangement of client and server computers that act together as one system. A domain name is key to doing just about anything on the Internet, from setting up a web site to sending and receiving email to building an online store. A domain name is the sequence of labels from a node to the root, separated by dots (“.”s), read left to right  The name space has a maximum depth of 127 levels  Domain names are limited to 255 characters in length 5
  • 6. Every interface on an internet must have a unique address called IP address. These addresses are 32 –bit numbers, normally written as four decimal numbers,one for each byte of the address. This is called dotted-decimal notation. 6
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  • 8.  Every machine has a unique identification in network. That will used to identify the specific system in the network. That unique identifier is called The IP address is basically the address that distinguishes where you want tosend information to, and from where the information comes. There simply has to be a way to distinguish with which of the millions of computers in the world you want to communicate. The IP address is represented by the dotted values. Eg 172.16.35.254. 8
  • 9.  The IP(internet Protocol) is available in two versions, There are,  IPv4(Internet Protocol version 4)  IPv6(Internet Protocol version 6) IPv4 is wisely using internet protocol. Ipv6 is upgraded version of IPv4. 9
  • 10.  The IPv4 addresses are 4 byte(32 bits) in length. The IPv4 addresses denoted with the dotted numbers The IP address is denoted as “n.n.n.n”. Here „n‟ is a decimal value. The n value range is 0 to 255. IPv4 is wisely using Internet Protocol. The IPv4 have the internet number as well as the host number. Eg:  172.16.35.254 10
  • 11.  IPv6(Internet Protocol version 6) is a upgraded version of the IPv4. IPv6 addressing is denoted with the 8 sets of 4 hexadecimal values, 16 bits in each sets. Each set is separated with the colon(:). IPv6 address is denoted as “xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx” ( ‟x‟ would be hexadecimal value). The hexadecimal values can be represented in the Upper-case or Lower case for the number „A-F‟. A leading zero in a set of numbers can be omitted  ABC:567:0:8888:0:9999:1111:0  abc:567:8888:0:9999:1111:0 The IPv6 is not using wisely. 11
  • 12.  The DNS(Domain Name Server) is a directory lookup service that provides a mapping between the name of the host on the internet and its numerical address. Four elements comprise  Domain Name Space  DNS database  Name servers  Resolvers 12
  • 13.  It is 32 bit address provides uniquely identifying device. It has two components  Network number  Host address Domain refers to a group of hosts that are administrative control. Domains are organizes hierarchically, so that the domain has sub routines. 13
  • 14.  DNS is a hierarchical system. DNS organizes all registered names in a tree structure. At the base or root of the tree are a group of top-level domains including familiar names like com, org, and edu. Below this level are the second-level registered domains such as about.com The tree can have 128 levels: level 0 (root) to level 127. 14
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  • 17.  The DNS database contains a list of registered domain names. The top level of the DNS hierarchy, also called the root level It is maintained by a set of 13 servers called root name servers. Those servers in turn knows all the TLDs which contain the same vital information They are coordinated by ICANN and are distributed around the world. 17
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  • 19. ICANNThe Internet Corporation for AssignedNames and NumbersThe headquarters is in Marina del Rey,California, United States, It was created on September 18, 1998,andincorporated on September 30, 1998. 19
  • 20.  To oversee administer Internet resources including  Addresses  Delegating blocks of addresses to the regional registries.  Protocol identifiers  Allocating port numbers, etc.  Names  Administration of the root zone file.  Oversight of the operation of the root name servers. 20
  • 21. 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 21
  • 22. 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. 22
  • 23. 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 23
  • 24. RESOLUTIONMapping a name to an address or an address to a name is called name-address resolution. Types of Resolution:-  Recursive Resolution  Iterative Resolution 24
  • 25. Recursive resolution 25
  • 26. Iterative resolution 26
  • 27. www.google.com 27
  • 28.  In the example a client somewhere on the Internet needs the IP address of www.google.com The following events take place: 1.The client contacts NameServer1 with a recursive query for www.google.com. The server must now return either the answer or an error message. 2.NameServer1 checks its cache and zones for the answer, but does not find it, so it contacts a server authoritative for the Internet (that is, a root server ) with an iterative query for www.google.com. 3.The server at the root of the Internet does not know the answer, so it responds with a referral to a server authoritative for the .com domain. 28
  • 29.  4.NameServer1 contacts a server authoritative for the .com domain with an iterative query for www.google.com. 5.The server authoritative for the .com domain does not know the exact answer, so it responds with a referral to a server authoritative for the google.com domain. 6.NameServer1 contacts the server authoritative for the google.com domain with an iterative query for www.google.com. 7.The server authoritative for the google.com domain does know the answer. It responds with the requested IP address. 8.NameServer1 responds to the client query with the IP address for www.google.com. 29
  • 30. DNS MESSAGES The DNS query message consists of a header and questionrecords; the DNS response message consists of a header, question records,answer records, authoritative records, and additional records. 30
  • 31. DNS messages 31
  • 32. Query and response messages 32
  • 33. Section Name Description Contains fields that describe the type of message and provide important information about it. Header Also contains fields that indicate the number of entries in the other sections of the message. Carries one or more “questions”, that is, queries for information Question being sent to a DNS name server. 33
  • 34. Section Name Description Carries one or more resource records that answer the Answer question(s) indicated in the Question section above. Contains one or more resource records that point to Authority authoritative name servers that can be used to continue the resolution process. Conveys one or more resource records that contain additional information related to the Additional query that is not strictly necessary to answer the queries (questions) in the message. 34
  • 35.  The system which is in network request a web page to it‟s local server. The local DNS of that server maintain the details of the local clients connected to it. From that server the page request forwarded to the DNS of the web content. The request or the query for the particular page is in the name of that local server. The query first processed by the resolver, it and then forward to the SLAVE NAME SERVER. If the domain name is found in that it will return the IP address to the requested resolver. 35
  • 36.  If the domain name is not found in the particular slave domain it and then forward the detail of the requested resolver and the domain name to the higher name server. The resolver details should be maintained in each level of name server if that regarding to it‟s own zone. The several zones are there under one primary name server. The primary name server of zones may be slave name server of another primary name server. Each and every zone has it‟s unique salve name server. 36
  • 37.  The IP address of the requested page can be directly forwarded from the current name server level., or the address should be returned through the backward direction in the path the request came. The details of the requested result stored in slave name server. If the IP address in found then the IP address and the domain name stored. Otherwise the negative result be stored. This is caching. The first thing the slave name server has to do is search the particular domain name in it‟s cached detail. If it is not found then it forward the request to the higher level NS. 37
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  • 39.  It is based on hierarchical database containing Resourses Records(RRs) that includes IP address and other information about hosts. Key features:  Variable-depth hierarchy for names  Distributed Database  Distribution controlled by the database. 39
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  • 41.  Name Servers:  These are server programs that hols information about a protion of the domain name tree structure and the associated RRs. Resolver.  These are programs that extract information from names servers in response to client request is for an IP address corresponding to a given domain name. 41
  • 42.  The need of DNS is demonstrated here. Without DNS we can not imagine the internet itself. The achievement done in the internet and web environment are the branch from the DNS invention. 42
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