DNS SEMINAR ON ( Domain Name System )
WHAT IS Domain Name System (DNS) ?Domain Name System is a distributed database used by TCP/IP application to map between domain name to IP addressesThe process of resolving Domain name to IP address is called name resolution.The IP protocol used to differentiate each computer on the net work by assigning a unique IP address. IP addressEvery machine on the Internet has a unique identifying number, called an IP Address. A typical IP address looks like this -:192.168.100.1 IP addresses are normally expressed in decimal format as a "dotted decimal number" like the one above. But computers communicate in binary form. Look at the same IP address in binary: example-: 11000000. 10101000. 01100100. 00000001 The four numbers in an IP address are called octets, because they each have eight positions when viewed in binary form. If you add all the positions together, you get 32, which is why IP addresses are considered 32-bit numbers. Since each of the eightpositions can have two different states (1 or 0) .
A Domain Name is... · A way to identify computers · Hierarchical · Unique · A corresponding IP address Domain Name System (DNS) is a distributed database system for managing host names and their associated Internet Protocol (IP) addresses. Using DNS means that people can use simple names, such as "www.yahoo.com" to locate a host, rather than using the IP address (xxx.xxx.xxx.xxx). A single server may only be responsible for knowing the domain names and IP addresses for a small subset of a zone, but DNS servers can work together to map all domain names to their IP addresses. DNS servers working together is what allows computers to communicate across the Internet 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 is essentially the telephone directory of the Internet. Just as a phone number such as 0674-2392158 is mapped to a name like B.Nayak, every device that communicates over the Internet has a unique, machine-readable IP address that is mapped to a human readable domain name such as www.yahoo.com. If you need to contact that device, you can use its domain name.
History of DNS • In the early days of the Internet, all host names and their associated IP addresses were recorded in a single file called hosts.txt, maintained by the Network Information Centre in the USA. Not surprisingly, as the Internet grew so did this file, and by the mid-80's it had become impractically large to distribute to all systems over the network, and impossible to keep up to date. • The Internet Domain Name System (DNS) was developed as a distributed database to solve this problem. It's primary goal is to allow the allocation of host names to be distributed amongst multiple naming authorities, rather than centralized at a single point. Disadvantage of HOST.TXT file • Huge file (traffic and load) • Name collisions (name uniqueness) • Consistency • Always out of date • Single point of Administration
DNS Hierarchy DNS provides a hierarchical structure, called domain name space, for managing the DNS database. The hierarchical structure includes : Root domain: Situated at the top of the domain structure and it is represented by a period (.). Top-level domain: Situated below the root domain and used to represent the type of organization.. Every domain name has a suffix that indicates which Top Level Domain (TDL) it belongs to. There are only a limited number of such domains. For example: gov - Government agencies edu - Educational institutions org - Organizations (nonprofit) mil - Military com - commercial business net - Network organizations Second-level domain: Part of top-level domain and the name provided to the organization or to individual users. In the domain name the last part generally signifies the country name. for example, a domain name www.microsoft.com.us. In this case, the (us) mean that the domain is registered in the United States, Similarly, there are few other country name suffixes that are also common use. These include: India(in)Japan(jp)Australia(au)Canada(cn)
How DNS Works1)The host computer contacts the domain name and the DNS server looks in the database and maps the domain name to an IP address .2)It then returns the IP address to the host computer. 3)Imagine that the user want to access www,Microsoft.com in this case ,when the user enters the Web site name in the address bar of the Explorer window the request goes to the name server. 4)The request is forwarded to the DNS server using the lookup query .5)A lookup query resolves a domain name for the associated IP address.6) The server then accepts the request and sends the respective IP address to the user. 7)The detail of the name-to-IP address is stored in the zone file, which resides on the DNS server. 8)If the name server is unable to resolve the request, it may forward the request to the next name server that can resolve it or it will return a name resolution failure error to the.
Each domain namespace contains a zone file that stores the name-to-IP address data of that zone for example, the www.Microsoft.com domain namespace can be divided in to sub domains such as msn. Microsoft.com, shopping .Microsoft.com, or mrktg.Microsoft.com .To take this example further, the users on the Internet concern with: Shopping are directed to shopping.Microsoft.com Chatting are directed to msn.Microsoft.com Marketing are directed to mrktg.Microsoft.com DNS domain zones are database files that contain resource records for a domain, or a set of domains. DNS zones can be separated into two types: Forward lookup and Reverse lookup. What is a Zone file
Forward Lookup Zones • Forward lookup DNS zones allow a resolver (an application included in web browsers and most FTP software) to obtain an IP address when the domain name is known. Reverse Lookup Zones • A Reverse lookup DNS zone allows a resolver to obtain a domain name when an IP address is known.
DNS Query Types Queries are the request which is the translation of a hostname to an IP address There are two types of queries issued: • Recursive queries received by a server forces that server to find the information requested or post a message back to the querier that the information cannot be found. • Iterative queries allow the server to search for the information and pass back the best information it knows about. This is the type that is used between servers. Clients used the recursive query.
DNS Records-: The DNS record contains the data about a single activity of the translation of a domain name to an IP address. A record equates a domain name such as “www.google.com" to an IP address such as 192.168.90.10 and stores in to the DNS data base. Once the domain name has been converted or "resolved" to an IP address, then (and only then) can the user connect to your Web site.
Round Robin-: Round Robin is a technique that can be used to equally load several machines (Load Balancing). It is possible to use this technique for the majority of name servers (including Windows 2000/2003). This is a situation where we have more than one IP address for one name in DNS. For example, we may operate an exposed web server and because the performance of the machine is not sufficient, we buy another or two more. We start running the web server on all three of them (for example, www.company.com). The first one has an IP address 188.8.131.52, the second one 184.108.40.206, and the third one 220.127.116.11. There will be three records in DNS for www.company.com, and each of them will have a different IP address. Round Robin technique ensures that the answer to the: 1. First query (to the first user) will be that the web server return addresses 18.104.22.168, 22.214.171.124, and 126.96.36.199 2. The answer to the next query (to the second user) will be that the server return IP addresses 188.8.131.52, 184.108.40.206, and 220.127.116.11. 3. The answer to te next query (may be 3rd user) will return IP addresses 18.104.22.168, 22.214.171.124, and 126.96.36.199. 4. Procedure are repeating from 1st point again and again.
In Summary A domain name is a way to identify and locate computers connected to the Internet. A domain name must be unique; no two organizations on the Internet can have the same domain name. A typical domain name consists of a second-level domain and a top-level domain, such as “google.com". In addition, domain name and subdomain information can be added, for example: “cvraman.org.in". The top-level domain name describes the type of organization or the country with the domain name (EDU, COM, GOV, UK, etc.). Each domain name corresponds to numeric IP addresses which is used by the Internet to transmit data. The Domain Name System completes the task of matching domain names to IP addresses so that users of the Internet only have to remember domain names, not numbers .