The Domain Name Service (DNS) protocol provides a distributed name resolution service. We need DNS because we humans have trouble remembering the numerical IP addresses of computers, so we let the computers running Domain Name Service perform the name lookup, changing a computer's name into the IP addressees computers need to communicate. Domain Name Service (DNS) is the mechanism used to translate the name of a computer into computer's IP address. DNS is provided by a special computer (a server) running DNS software such as Berkeley's Internet Name Daemon (BIND), Microsoft DNS or another DNS server application. Using DNS your web browser can translate an Internet domain name such as www.inetdaemon.com, into an IP address where the website is located. DNS servers provide this translation by performing a 'lookup'. When they lookup a name and return an address, it is referred to as forward DNS lookup. Domain Name Service can also translate IP addresses into domain names which is called reverse DNS lookup.
DOMAIN NAMES
A Domain includes all devices that fall under a particular part of the Domain Name System hierarchy. For instance, the domain name inetdaemon.com would be used for all computer names that belong to InetDaemon. Basically, a domain name is used as the identifier for a group of computers that as far as DNS are concerned are all part of the same group.
The IP address for eos.cs.berkeley.edu. would be stored at the eos node.
Domain Names as supported in the Domain Name System must be less than 63 characters in total length, begin and end with a printable character, and can contain only letters, numbers and the hyphen character (the hyphen '-' must be in the middle somewhere). Underscores are not valid.
FULLY QUALIFIED DOMAIN NAMES (FQDN)
Fully qualified domain names (FQDNs) are names that have been spelled out all the way to the root of the DNS hierarchy. Using the example DNS hierarchy diagram above, the true, fully qualified domain name for the host eos would be eos.cs.berkeley.edu. (note the trailing dot after the edu in the name). Most DNS resolvers are smart enough not to need the last dot and it is assumed to be there; however, when troubleshooting domain name service issues with applications such as nslookup, its a good idea to use the period at the end.
The domain can be divided into :
1. Top Level Domains
--Country Code Top Level Domains (ccTLD's)
2. Second Level
3. Sub-Domains
1.Top Level Domains
Top Level Domains are the very top level of the DNS hierarchy. Sub-domains are installed under each of these. There are servers responsible for the root level resolution of various domains. These top-level domains are the first step in resolution and can be divided up into categories:
COUNTRY CODE DOMAINS ( ccTLDs)
* .ca (Canada)
* .fr (France)
* .it (Italy)
* .gr (Germany)
* .us (United States)
* .tw (Taiwan)
Of course, these are not the only top level country code domains (cc-tld's). Also, in many countries, they use smimilar sub-domain patterns as follows:
* .net.tw
* .com.tw
US RESTRICTED TOP LEVEL DOMAINS
These domains are restricted to certain specific organizations and may not be used by any other entites. The .gov TLD is restricted to the United States Government. The .mil TLD is restricted to various branches of the United States Armed Forces. The last is the .edu organization, which, while not as restricted as .gov and .mil, still requires proof of accreditation as an educational organization to obtain a registration as part of the .edu TLD.
* .gov - US Government
* .mil - US Militiary
* .edu - United States educational organizations
US PUBLIC TOP LEVEL DOMAINS
These are the well-known and popular domain names everyone in the United States knows and loves. (gee... I own one myself -- InetD)
The following are the original domains:
* .com
* .edu
* .net
* .org
The following domains were added to the DNS system and are supported by the InterNIC as of November 2001:
* .aero
* .biz
* .coop
* .info
* .name
* .museum
* .ps
DOMAIN NAME DISPUTES
Well, if you want to register your company's trademarked name as a domain name and someone else already owns it, you can file a claim to get it even if someone wants 42 bajillion dollars for it. Good luck though. Getting your domain free from the sqatters is like pulling eyeteeth and a hell of a lot more painful.
* Domain Disputes
INTERNIC ROOT ZONE FILE
A copy of the root zone file for all top level domains can be downloaded from the InterNIC:
* ftp://rs.internic.net/domain/root.zone.gz
2. Second Level Domains
Speaking in a very general sense, second level domains belong to the organization who registered them, and are therefore their responsibility to resolve. Using IBM for an example, IBM is responsible for ibm.com. The IBM part of ibm.com is the 'second level'.
For country code domains, such as Taiwan's .tw, the top level is extended to include .com.tw, .net.tw, .org.tw, etc. Companies such as Abit (computer component manufacturers) would be abit.com.tw. Because the root registry in that region controls both the country code domain and the organization level domain, the owner is still the second level domain. Thus 'abit.com.tw' is still considered a second level domain.
In strictest resolution sense, abit.com.tw is actually a third level domain. Just exactly what you call such a domain is a bit esoteric and depends on the domain and who you are discussing it with. Generally, it is accepted that the term 'second level domains' are managed and owned by the organizations that purchased the right to register that particular domain name.
3. Sub-Domains
A sub-domain is a domain that an organization's DNS administrator created to make managing the DNS simpler or at least more logical.
Take a college campus for example. The DNS administrator for Berkeley might create a sub-domains for:
* Administration
* Faculty
* Computer Science Department
* Liberal Arts departments
* Science departments
* Research labs
...or for whatever else the administrator might set up. Note that sub-domains are totally at the discretion of the DNS administrator. Once the root has delegated to the DNS server managed by the organization who registered the domain, the organization can do whatever they please with resolution.
The DNS administrator would configure the berkeley.edu DNS server to delegate responsibility to another DNS machine located in the Computer Science department. The Computer Science department might delegate to their laboratory's DNS server for the Laboratory's DNS.
DNS ZONES
A zone contains all the names and IP addresses of a given group of hosts. Zones are a concept, not really a configurable object themselves, though most DNS administrators speak of zone files when configuring BND (named). Assuming a zone is the same as a zone file is not quite technically correct as a zone file contains additional information that just the host information. To configure a complete zone, you need one or more zone files, each containing resource records for all the hosts in the zone. The term zone is used to refer to a group of names that are part of a common unit and grouped together into a namespace. Namespace itself is another concept that refers to a group of names. The terms namespace, domain, and zone are frequently and incorrectly used interchangably, but for the purposes of most discussions, the differences aren't enough to worry about.
- The DNS namespace contains all domain names.
- My domain is inetdaemon.com.
- The DNS zone bored.bla-blather.org could contain the hosts silly, stiff and tears.
Let's use the example of a fictional global company called "Zap O Matic Inc." who has registered the domain name "zapomatic.com". Let's say the headquarters is in the United States and they have divisions in the Netherlands, Australia and Japan. If each division is self-supporting, with it's own management, human resources, accounting and sales departments, then they would probably set up something as follows:
zapomatic.com might contain:
- netherlands.zapomatic.com (which would itself contain..)
- management.netherlands.zapomatic.com
- hr.netherlherlands.zapomatic.com
- accounting.netherlands.zapomatic.com
- sales.netherlands.zapomatic.com
- australia.zapomatic.com (which would itself contain..)
- management.australia.zapomatic.com
- hr.australia.zapomatic.com
- accounting.australia.zapomatic.com
- sales.australia.zapomatic.com
- japan.zapomatic.com (which would itself contain..)
- management.japan.zapomatic.com
- hr.japan.zapomatic.com
- accounting.japan.zapomatic.com
- sales.japan.zapomatic.com
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