DNS stands for Domain Name Service or Domain Name System. As it suggests is a simple system, which translates the meaningful Hostnames and Domain Names into valid IP Addresses. Without a DNS System, internet will not be what it is today. Imagine remembering IP Address for various resources on the Network or on the Internet than calling by names like bbc.co.uk or www.google.com, which is almost next to not possible. What is DNS?
What is DNS DNS stands for Domain Name Service or Domain Name System. As it suggests is a simple system, which translates the meaningful Hostnames and Domain Names into valid IP Addresses. Without a DNS System, internet will not be what it is today. Imagine remembering IP Address for various resources on the Network or on the Internet than calling by names like bbc.co.uk or www.google.com, which is almost next to not possible. Top How does it work? When you open a Internet Browser like Internet Explorer and type in www.google.com, the computer talks to a DNS server that it knows and queries for a valid IP address for www.google.com. The DNS server looks into its directory or rather into its database and provides you with the appropriate IP Address. In the event, it doesn’t have the information, it then queries other DNS servers on the internet, finds the information and returns the information to the browser which then talks to the server assigned with this IP Address and loads the website for you. This is how DNS works in simple terms. Although, it looks simple, there are a lot many things involved in the background that makes DNS special. Top What is a Name Space A collection of Networked computers that uses DNS for Name Services is called a Name Space. The DNS Namespace defines and identifies the domain structure that forms a Domain. For example, in London.itsyourip.com, the .com identifies the Top Level Domain, itsyourip is a secondary domain for .com and London is the Sub domain for the itsyourip.com Secondary domain. This whole structure can be called as a Name Space. Top What is a Domain? The DNS Name Space can be split into a hierarchy of small groups or otherwise called as Domains. These domains can further be split into Sub-domains and thereon. Every, Domain evolves out of a node (a higher level) above it forming a proper Domain Tree in the DNS Name Space. As explained above, in London.itsyourip.com, .com is the Top Level Domain itsyourip.com is the Secondary Domain for .com London.itsyourip.com is the Sub domain for its yourip.com. Top What is a Domain Name? The name used to identify the group of computers in a given domain is called a Domain Name. In other words, Domain Names are logical names that are given to a single or a group of computers. These names are then translated into appropriate IP Addresses by the DNS servers to find the location of the resource being looked for. For example, if you type www.itsyourip.com in the Internet Browser, it will first be translated into a valid IP Address of the form xxx.xxx.xxx.xxx and given back to the system/application (browser in this case) which then knows where to go and download the web page that you are looking for. Top Fully Qualified Domain Name (FQDN) A fully Qualified Domain Name is the one which comprises of the hostname attached to the Domain Name which inturn is attached to its Top Level Domain Name. In mail.itsyourip.com, mail is the hostname which is being identified by itsyourip.com Domain Name which in turn is identified by the .com Top Level Domain Name. Top Name Server A Name Server or a DNS server is the one, which can answer queries for a particular Domain. Top Authoritative Name Server An authoritative DNS server is the one which can answer from its own database or derived from another Authroritative Server without relying upon any other Name Server for information. In simple words, it is a DNS server which serves a particular Domain. There can be more than more than one Authoritative DNS Server for a particular Domain. Also, a DNS server can be Authoritative for one Domain and may not be Authoritative for another domain. Each Domain can have more than one Authoritative server wherein there will be one master server also called Primary servers and one or more Slave servers also called as Secondary Servers. Top Primary DNS or Master DNS Servers A Primary DNS server also called a Master DNS Server is an authoritative Name Server for a Domain answering queries for that domain from its configuration details and not relying on any other DNS servers. A DNS Server can be a Primary server for one Domain and may be a Slave server for another domain. Top Secondary DNS or Slave DNS Servers A Slave DNS server also called a Secondary DNS Server is an authoritative Name Server for a Domain answering queries for that domain from the information learnt from another server through Zone Transfers. These servers can act as a Load Balancer and or a backup DNS server in the event the Master Server fails. A DNS Server can be a Slave server for one Domain and may be a Primary server for another domain. Top Lame Server A Lame Server is an Authoritative Server for a particular domain, which cannot properly answer queries for the Domain and or has an incorrect configuration in its records pointing to Non-Authoritative servers or to incorrect desinations. Top Root Server The Root Servers are the Authoritative Name Servers for the root domain (.). There are 13 Root servers available. Every DNS server will have an entry for one or more or all of these servers.Top Forwarding Forwarding is a process in which a DNS server forwards queries for a particular domain for which it is not an Authoritative DNS Server or for which it cannot answer from its cache to another DNS server that it has in its Forward list. These servers in turn lookup for the query and respond if it knows else forwards to the DNS servers it knows, this happens until a DNS server has the NS records (the Root servers or the TLD Name servers) for the Domain which then is returned past down the chain the original server which then queries the Name Server for the host it looked up for. Top Zone A Zone is simply a DNS Domain. Top Forward Zone A forward Zone is the ones in which Hostnames are translated to Addresses. Top Reverse Zone As it suggests, it is the one in which the IP addresses are mapped to the Hostnames. These are important records to counter SPAM and other malicious DNS activities on the Internet. Top Zone Transfer Zone Transfer is a process of by which a Secondary server queries a Primary server for a complete copy of the Zone details. This is the general updating process in which the secondary or slave servers caches the entire copy of the zone data from the master server. Top Records Records in its simplet term means the Database like files which hold some information about a particular host or a domain. There are different Record types which has specific zone information for particular domains. Top CNAME A CNAME is a Canonical Name which is the true name of the host. A CNAME record is one which holds an alias name pointing to a particular host on the domain. Top NS record A NS record is the one, which declares the Authoritative Name Servers for a Particular domain. Top MX Record Mail Exchanger Record is the one, which points to the Mail host for a particular domain. A particular Domain can have more than one mail hosts each assigned with a priority number. The server with the lowest priority number is the default server mail exchanger for that domain, in the event this server goes unresponsive, the next immediate mail server does the duty. Top A Record An A Record is an Address Record. It maps an IP Address to a Domain Name. Top PTR Record or Reverse Record A PTR Record is a Pointer Record also known as a Reverse Record is the one, which associates an IP Address with a valid CNAME which should be able to resolve back to the IP Address. Top Glue Record A Glue Record is a record, which has the hostname and the IP Address for the DNS server which is authoritative for a particular domain. These are normally found on the Parent Servers. Top Query A query is a process of requesting certain information (request for records) for a particular Domain to a DNS Server. Top Recursive Query A Recursive Query is a process of requesting record data from different Name Servers when the DNS server does not have sufficient information to respond to a query. Top Root server The Root Servers are the Authoritative Name Servers for the root domain (.). There are 13 Root servers available. Every DNS server will have an entry for one or more or all of these servers. Top Root Zone Root(.) Zone is the top node of the Internet’s DNS Hierarchy from which all the Top Level Domains and then the Secondary Domains and the Sub Domains grow down the branch. Top Top Level Domains (TLD) Top Level Domains called as TLDs are the default domains that are the childs of the Root Domain (.). The .COM, ORG, .NET, .CO.UK. CO.IN are all top level domain names. The Top Level Domains are of 2 types, gTLDs and the ccTLDs. Top generic Top Level Domains (gTLD) A gTLD is a Generic TLD like .com, .org, .net etc., Top country coded Top Level Domains (ccTLD) A ccTLD is a Country Coded TLD like .co.uk, .co.in etc., Top Resolver A Resolve is a DNS Server which can perform a Recurrsive Query in the event it cannot find a record queried by a host. Top Boot file A boot file also called as a Config file is the one with which a DNS server loads at the startup. Top Start-of-Authority Record (SOA Record) The SOA record designates the start of a zone. Top name Field This field indicates the name of the zone. Note that the zone name must end with a trailing dot. Top class Field This field is the address class. For example, IN for Internet (the most commonly used class). Top SOA Field This field is the type of this resource record. Top origin Field This field is the name of the host where this data file resides. Note that this host name must end in a trailing dot. Top person-in-charge Field This field is the email address of the person responsible for the name server. Top serial Field This field is the version number of this data file. You must increment this number whenever you make a change to the data: slave servers use the serial field to detect whether the data file has been changed since the last time they copied the file from the master server. Top refresh Field This field indicates how often, in seconds, a slave name server should check with the master name server to see if an update is needed. For example, 3600 indicates an hour Top retry Field This field indicates how long, in seconds, a slave server is to retry after a failure to check for a refresh. Top expire Field This field is the upper limit, in seconds, that a slave name server is to use the data before it expires for lack of getting a refresh. Top ttl Field This field is the default number of seconds to be used for the time-to-live field on resource records that do not have a ttl specified elsewhere. There should only be one SOA record per zone. Top Caching The process of holding a local copy of responses to DNS queries to avoid network traffic when a different client requests for the same information. This will removed after a speciific period of redundancy from the server. Top Spoofing Spoofing is asecurity threat for those DNS servers which are identified vulnerable. It is a process by which a vulnerable DNS server is attacked and fed with incorrect record information. The DNS server accepts this information even though the source is not an Authoritative Zone for that domain and holds it in the cache. This can cause a serious security issue as confidential mails can then diverted to a different location or even a complete can be hijacked and redirected to a different website. Top