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DNS



The DNS (or domain name system) is a system that stores information that is associated with domain names in a distributed database on the Internet. The DNS associates many types of information with domain names, but most importantly, it provides the IP address associated with the domain name. The DNS also lists mail exchange servers accepting e-mail for each domain.

The DNS is useful for a few different reasons. The most well known reason, the DNS makes it possible to attach hard-to-remember long IP addresses to easy-to-remember domain names. We take advantage of this when we recite URLs and e-mail addresses. Less recognized, the domain name system makes it possible for people to assign authoritative names, without needing to communicate with a central registrar each time.

The practice of using a domain name such as linfishing.com, rather than a numerical IP address goes back even farther than the use of TCP/IP, all the way back to the use of ARPAnet era. Originally, each computer on the network retrieved a file called HOSTS.TXT from SRI (now SRI International) which mapped an address of numbers to a domain name as was already explained.

What Is a DNS Server?

The Domain Name System or DNS is a fairly new technology for controlling the names of Web sites and other Internet domains. DNS technology allows you to type names into your Web browser like dnsserver.about.com and your computer to automatically find that address on the Internet. A key element of the DNS is a worldwide collection of DNS servers. What, then, is a DNS server?
A DNS server is any computer registered to join the Domain Name System. A DNS server runs special-purpose networking software, features a public IP address, and contains a database of network names and addresses for other Internet hosts.
About DNS Root Servers
DNS servers broadcast with each other using specific private network protocols. All DNS servers are organized in a hierarchy. At the top level of the hierarchy, so-called root servers store the complete database of Internet domain names and their corresponding IP addresses. The Internet employs 13 root servers that have become somewhat famous for their special role. Maintained by various independent agencies, the servers are appropriately named A, B, C and so on up to M. Ten of these servers are located in the United States, one in Japan, one in London, UK and one in Stockholm, Sweden.

How DNS work
If you've ever used the Internet, it's a good bet that you've used the Domain Name System, or DNS, even without realizing it. DNS is a protocol within the set of specifications for how computers interchange data on the Internet and on many private networks, known as the TCP/IP protocol suite. Its principal job is to turn a user-friendly domain name like "grhotels.com/travel/" into an Internet Protocol (IP) address like 70.42.251.42 that computers use to distinguish each other on the network. DNS is like a GPS on the Internet.
Computers and other network devices on the Internet use an IP address to direct or route your request to the site you're trying to get to. This is comparable to dialing a phone number to connect to the person you're trying to call. Thanks to the existence of DNS, you don't have to keep your own address book of IP addresses. Instead, you just connect through a domain name server, also called a DNS server or name server, which manipulates a massive database that maps domain names to IP addresses.
Whether you're accessing a Web site or sending e-mail, your computer uses a DNS server to look up the domain name you're trying to get to. The proper term for this task is DNS name resolution, and you would say that the DNS server resolves the domain name to the IP address. For example, when you enter "tesae.info" in your browser, part of the network connection includes resolving the domain name "tesae.info" into an IP address, like 70.42.251.42, for tesae.info' Web servers.
You can always bypass a DNS lookup by entering 70.42.251.42 directly in your browser (do it and see what happens). However, you're probably more likely to remember "tesae.info" when you want to return later. In addition, a Web site's IP address can change over time, and some sites affiliate multiple IP addresses with a single domain name.
Without DNS servers, the Internet would shut down very fast. But how does your computer know which DNS server to use? Typically, when you connect to your home network, Internet service provider (ISP) or WiFi network, the modem or router that distributes your computer's network address also sends some important network configuration information to your computer or mobile device. That configuration includes one or more DNS servers that the device should use when resolving DNS names to IP address.
So far, we have talked about some crucial DNS basics. The rest of this article springs deeper into domain name servers and name resolution. It even includes an introduction to managing your own DNS server. Let's start by looking at how IP addresses are structured and how that's important to the name resolution process.
Domain names are very attractive and highly advised as a service for people exploring for their place on the Internet, but rarely do we think what stays behind their availability online. Internet users feel obliged for this great privilege to name their websites the way they like, instead of using the websites' real numeric addresses (IP addresses), to the DNS service.


Host Name or Domain Name
There is often a lot of disorder when it comes to explaining the definition of a host name and a domain name.
A domain name is a specific and unique name that is acquired from a registrar. It will be something like dnshost.com or dnshost.co.uk. Observe that there is no www at the start of a domain name. A domain name can be divided into sub-domains - for example www.dnshost.com. Once you own a domain, there is no reasonable limit to the number (or names) of the sub-domains you can create. A sub-domain can be assigned to a host machine - for example a PC. In fact many sub-domains can be allocated to the same host machine. The way sub-domains are designated to a host machine is to create a record in the DNS (Domain Name Servers) that records the sub-domain name and the IP address of the host machine. Any requests for a sub-domain (e.g. www.dnshost.com) are converted to an IP address by DNS and the IP address is used to route the request through the network until it connects to the host machine.
Some time ago before the advancement of the Internet and the DNS, each sub-domain would have a unique IP address so it was pretty typical for a host machine to have only one sub domain name. Nowadays, the common practice is to have many sub-domains with the same IP address. It is also common for the domain name to be converted to the IP address of the host machine that runs the www sub domain.
A host name is the particular name of a machine. When the host operating system is set up it is given a name. This name may reflect the prime use of the machine. For example, a host machine that converts host names to IP addresses using DNS may be called dns.hostingdomain.com and a host machine that is a web server may be called www.hostingdomain.com. When we need to find the host name from an IP address we send a request to the host using its IP address. The host will respond with its host name.
IP addresses are assigned by provincial organisations.


What are public DNS servers ?
DNS servers are responsible for resolving user-friendly domain names (like tesae.info) into computer-friendly IP addresses (such as 45.55.211.132).
Public DNS servers are DNS servers that respond to almost domain-subdomain on the web.
Usually DNS servers will only answer to clients of a particular Internet Service Provider (ISP) network. Most DNS servers are private, and serve only those that own and advocate them. Some private DNS servers may appear to be public, but only because they haven’t been configured properly by the responsible system administrators. Usually, such problems are fixed and the DNS server becomes private.
MisuseWhat are Public DNS Servers 269x300 What are Public DNS Servers?
Incorrectly configured DNS servers may be vulnerable to denial of service attacks. Some of the types of attacks include sending a vast amount of queries to the server so that the DNS server can't handle it and it gets overloaded.
Other dangers to public DNS servers include:
pharming,
cache poisoning
DNS amplification attacks.
List of Public DNS Servers
Here is a list of some of the available public DNS servers and their location.
* 208.185.249.250 (San Jose, CA, US)
* 216.87.84.214 (Longmont, CO, US)
* 208.185.249.251 (San Jose, CA, US)
* 131.161.247.231 (Oakland, CA, US)
* 66.227.42.140 (Dallas, TX, US)
* 65.243.92.254 (US)
* 217.115.138.24 (Cologne, Germany)
* 219.127.89.37 (Tokyo, Japan)
* 219.127.89.34 (Tokyo, Japan)
* 202.89.131.4 (Auckland, New Zealand)
* 64.151.103.120 (San Francisco, CA, US)
* 67.102.133.222 (Los Angeles, CA, US)
* 199.166.29.3 (Amsterdam, Nederland)
Public DNS Cost
Public DNS servers’ services are provided free of charge by volunteer engineers. These services are usually run on UPS protected FreeBSD servers. The Internet Protocol (IP) addresses of these servers can be approached through querying either the DNS or WHOIS database using any of these tools, dig, whois, dnsquery and nslookup. The free aspect of the DNS server services was, according to some industry players, a reaction to the high fees introduced by ISPs for otherwise simple and uncomplicated services.
Support for Zone Files
A public DNS server allows the user to write his own zone file and distribute it to the internet through public DNS hosts. Public DNS provides the name service while the domain owner can select a primary server that they directly control thus allowing the owner to administer/edit the zone data directly on a private machine.
Some public DNS servers might constrain conditions for using them, especially in relation to zone file creation. Sending spam and other forms of spam mail may result in the zone file of the miscreant being excluded. Public name servers may also use third party programs such as nslint to obtain common zone file errors.

DNS Security
The Domain Name System (DNS) is indispensable to the Internet, implementing a mechanism for resolving host names into Internet Protocol (IP) addresses. Insecure underlying protocols and lack of authentication and integrity checking of the information within the DNS threaten the proper functionality of the DNS. The Internet Engineering Task Force (IETF) is working on DNS security extensions to increase security within the DNS, known as DNSSEC. These security issues and solutions are presented in this paper.
The DNS plays a crucial role in supporting the Internet support by providing a distributed and fairly vigorous structure that resolves Internet host names into IP addresses and IP addresses back into host names. The DNS also supports other Internet directory-like lookup facilities to obtain information related to DNS Name Servers, Canonical Names, Mail Exchangers, etc. Unfortunately many security weaknesses surround IP and the protocols transmitted by IP. The DNS is not unaffected by these security weaknesses. The accuracy of the information contained within the DNS is significant to many situations of IP based communications.
The possible threats that encompass the DNS are due in part to the lack of validity and simplicity of the data held within the DNS databases and partially to other protocols that use host names as an access control structure. In response to this, the IETF formed a working group to add DNS Security (DNSSEC) extensions to the existing DNS protocol.
This article gives an overview of the DNS, its security weaknesses, and the new security extensions being worked on by the IETF’s DNSSEC Working Group (WG).

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Article by Panos Vog
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