What Is DNS? How Does DNS Work?

  Category:  INFO | 15th February 2023 | Author:  CSI TEAM

DNS Stands For Domain Name System. It Is A System Used To Translate Human-readable Domain Names, Such As "google.com" Or "facebook.com", Into IP Addresses That Can Be Understood By Computers.

When You Enter A Domain Name Into A Web Browser, The Browser Sends A Request To A DNS Server, Which Looks Up The IP Address Associated With That Domain Name. The DNS Server Then Returns The IP Address To The Browser, Allowing It To Establish A Connection To The Web Server Hosting The Website.

DNS Is A Critical Component Of The Internet Infrastructure, And It Is Used Not Only For Web Browsing, But Also For Email, File Transfer, And Many Other Types Of Online Communication.

How Does DNS Work?

DNS, Or Domain Name System, Works By Translating Human-readable Domain Names, Such As "google.com" Or "facebook.com," Into IP Addresses That Computers Can Understand.

When A User Enters A Domain Name Into Their Web Browser Or Other Application, The Application Sends A Request To A DNS Resolver, Which Is A Program Or Service That Runs On The User's Device Or On A Network Server. The DNS Resolver Looks Up The IP Address Associated With The Domain Name By Querying A Series Of DNS Servers, Starting With A Root DNS Server And Working Its Way Down The DNS Hierarchy Until It Finds The IP Address.

The DNS Hierarchy Consists Of Multiple Types Of DNS Servers, Including Root Servers, Top-level Domain (TLD) Servers, And Authoritative DNS Servers. The Root Servers Are The Highest-level DNS Servers, And They Maintain A List Of TLD Servers For Each Top-level Domain, Such As .com, .org, And .net. The TLD Servers Maintain A List Of Authoritative DNS Servers For Each Domain Name Within Their TLD. The Authoritative DNS Servers Are Responsible For Maintaining The DNS Records, Or DNS Zone Files, For A Specific Domain Name.

When A DNS Resolver Queries A DNS Server, The Server Either Returns The IP Address Associated With The Domain Name Or Refers The Resolver To Another DNS Server That May Have The Information. The DNS Resolver Caches The Results Of Its Queries To Speed Up Future DNS Lookups.

Once The DNS Resolver Has Obtained The IP Address For The Domain Name, The Application Can Use The IP Address To Establish A Connection With The Server Hosting The Website Or Other Online Resource Associated With The Domain Name.

Overall, The DNS System Plays A Critical Role In The Functioning Of The Internet, Allowing Users To Access Online Resources Using Human-readable Domain Names Rather Than Having To Remember The IP Addresses Associated With Each Resource.

How Does DNS Server  Work?

DNS Servers Work By Maintaining A Database Of Domain Names And Their Corresponding IP Addresses. When A Client Device, Such As A Web Browser Or Email Client, Needs To Communicate With A Server Associated With A Particular Domain Name, It Sends A Request To A DNS Server Asking For The IP Address Associated With That Domain.

The DNS Server First Checks Its Own Local Cache To See If It Has A Record Of The Requested Domain Name And Its Corresponding IP Address. If The DNS Server Has A Cached Record, It Immediately Returns The IP Address To The Client.

If The DNS Server Does Not Have A Cached Record, It Starts To Search Through Its Own Database Of Domain Name And IP Address Mappings, Called A Zone File. If It Finds A Match, It Returns The IP Address To The Client.

If The DNS Server Cannot Find A Match In Its Own Database, It Will Forward The Request To One Or More Other DNS Servers In A Hierarchical Fashion. This Process Continues Until A DNS Server Is Found That Has A Record Of The Requested Domain Name And Its Corresponding IP Address.

Once The DNS Server Has Found The IP Address For The Requested Domain Name, It Returns The IP Address To The Client Device That Made The Request. The Client Device Can Then Use The IP Address To Establish A Connection With The Server Associated With The Requested Domain Name.

Difference Between DNS & DNS Server?

DNS Stands For Domain Name System, Which Is A System Used To Translate Human-readable Domain Names Into IP Addresses That Can Be Understood By Computers. The DNS System As A Whole Consists Of A Hierarchical Network Of Distributed DNS Servers, Each Of Which Maintains A Database Of Domain Name And IP Address Mappings.

A DNS Server, On The Other Hand, Is A Specific Type Of Computer Server That Is Responsible For Responding To DNS Queries From Client Devices. DNS Servers Maintain A Database Of DNS Records, Which Contain Information About Domain Names And Their Corresponding IP Addresses.

There Are Several Types Of DNS Servers, Including Authoritative DNS Servers, Which Are Responsible For Maintaining DNS Records For A Particular Domain Name Or Set Of Domain Names, And Recursive DNS Servers, Which Are Responsible For Resolving DNS Queries By Recursively Querying Other DNS Servers Until They Find The IP Address Associated With A Particular Domain Name.

In Summary, The DNS System Is The Overall System Used To Translate Domain Names Into IP Addresses, While A DNS Server Is A Specific Type Of Computer Server That Plays A Key Role In The Functioning Of The DNS System By Responding To DNS Queries From Client Devices.

How Many Types Of DNS Server?

There Are Several Types Of DNS Servers, Each With A Specific Role In The DNS System. Here Are Some Of The Main Types Of DNS Servers:

1. Recursive DNS Servers: These Servers Are Responsible For Resolving DNS Queries By Recursively Querying Other DNS Servers Until They Find The IP Address Associated With A Particular Domain Name. They Typically Cache The Results Of Their Queries To Speed Up Future Lookups.

2. Root DNS Servers: These Are The Highest-level DNS Servers In The DNS Hierarchy. There Are 13 Root DNS Servers Around The World, Which Maintain A List Of Top-level Domain (TLD) Servers For Each TLD, Such As .com, .org, And .net.

3. Top-Level Domain (TLD) DNS Servers: These Servers Maintain A List Of Authoritative DNS Servers For Each Domain Name Within Their TLD. For Example, The .com TLD Server Maintains A List Of Authoritative DNS Servers For All Domain Names Ending In .com.

4. Authoritative DNS Servers: These Servers Are Responsible For Maintaining DNS Records For A Particular Domain Name Or Set Of Domain Names. When A Recursive DNS Server Receives A DNS Query For A Particular Domain Name, It Sends A Query To The Authoritative DNS Server For That Domain Name To Obtain The IP Address Associated With The Domain Name.

5. Caching-only DNS Servers: These Servers Are Used To Cache DNS Records To Speed Up Future DNS Lookups. They Do Not Maintain Their Own Database Of DNS Records, But Instead Obtain The Records From Other DNS Servers And Cache Them Locally.

6. Forwarding DNS Servers: These Servers Are Used To Forward DNS Queries To Other DNS Servers If They Do Not Have The DNS Records In Their Local Cache. They Are Typically Used In Large Networks To Improve DNS Performance And Reduce Network Traffic.

Overall, These Different Types Of DNS Servers Work Together To Provide A Reliable And Efficient System For Translating Human-readable Domain Names Into IP Addresses That Can Be Understood By Computers.

What's The Difference Between An Authoritative DNS Server And A Recursive DNS Resolver?

An Authoritative DNS Server And A Recursive DNS Resolver Are Two Different Types Of DNS Servers That Play Distinct Roles In The Domain Name System (DNS). Here's How They Differ:

1. Authoritative DNS Server: An Authoritative DNS Server Is A DNS Server That Is Responsible For Storing And Providing The Official DNS Records For A Specific Domain. These Records Include The IP Addresses Of The Servers Associated With The Domain, Such As Web Servers Or Mail Servers. When A DNS Resolver Receives A DNS Query For A Domain Name, It Sends A Query To The Authoritative DNS Server For That Domain Name To Obtain The Correct IP Address. Authoritative DNS Servers Typically Respond Only To Queries For The Domains That They Are Responsible For And Are Not Involved In Recursive Lookups.

2. Recursive DNS Resolver: A Recursive DNS Resolver Is A DNS Server That Is Responsible For Resolving DNS Queries By Recursively Querying Other DNS Servers Until It Obtains The IP Address For A Specific Domain. When A User Enters A Domain Name Into Their Web Browser Or Other Application, The Application Sends A DNS Query To A Recursive DNS Resolver. If The Resolver Has The Requested DNS Records In Its Cache, It Returns The IP Address To The User's Application. If Not, The Resolver Initiates A Recursive Query By Sending A Query To One Of The Root Servers Or TLD Servers, Which Then Directs The Resolver To The Authoritative DNS Server For The Requested Domain.

In Summary, An Authoritative DNS Server Is Responsible For Providing The Official DNS Records For A Specific Domain, While A Recursive DNS Resolver Is Responsible For Recursively Querying DNS Servers To Obtain The Correct IP Address For A Given Domain Name. The Two Types Of DNS Servers Work Together To Provide A Reliable And Efficient DNS System That Translates Human-readable Domain Names Into IP Addresses That Can Be Understood By Computers.

What Are The Steps In A DNS Lookup?

Here Are The General Steps That A Typical DNS Lookup Takes:

1. The User Enters A Domain Name, Such As Www.example.com, Into Their Web Browser Or Other Application.

2. The Application Sends A DNS Query To The Local DNS Resolver, Which Is Usually Provided By The User's ISP.

3. If The Local DNS Resolver Has The Requested DNS Records In Its Cache, It Returns The IP Address To The User's Application. If Not, It Forwards The Request To One Of The Root Servers.

4. The Root Server Responds With A Referral To The Appropriate Top-Level Domain (TLD) DNS Server For The Requested Domain Name, Such As The .com TLD Server.

5. The Local DNS Resolver Then Sends A Query To The TLD DNS Server, Which Responds With A Referral To The Authoritative DNS Server For The Requested Domain Name.

6. The Local DNS Resolver Sends A Query To The Authoritative DNS Server, Which Responds With The IP Address For The Requested Domain Name.

7. The Local DNS Resolver Caches The DNS Records For The Requested Domain Name And Returns The IP Address To The User's Application.

8. The User's Application Uses The IP Address To Establish A Connection To The Web Server Associated With The Requested Domain Name.

In Summary, A DNS Lookup Involves A Series Of Queries And Responses Between Different Types Of DNS Servers, Starting With The Local DNS Resolver And Proceeding Through The Root Servers, TLD Servers, And Authoritative DNS Servers Until The Correct IP Address For The Requested Domain Name Is Obtained. The Process Is Designed To Be Fast, Efficient, And Reliable, And Relies On A Distributed Network Of DNS Servers Around The World To Ensure That DNS Lookups Are Resolved Quickly And Accurately.

What Is A DNS Resolver?

A DNS Resolver Is A Type Of DNS Server That Is Responsible For Resolving DNS Queries By Recursively Querying Other DNS Servers Until It Obtains The IP Address For A Specific Domain. When A User Enters A Domain Name Into Their Web Browser Or Other Application, The Application Sends A DNS Query To A DNS Resolver.

The DNS Resolver Receives The Query And Checks Its Cache To See If It Already Has The Requested DNS Records. If It Has The Records In Its Cache, It Returns The IP Address To The User's Application. If Not, The Resolver Initiates A Recursive Query By Sending A Query To One Of The Root Servers Or TLD Servers, Which Then Directs The Resolver To The Authoritative DNS Server For The Requested Domain.

Once The Authoritative DNS Server Responds With The Correct IP Address, The DNS Resolver Caches The Records For The Requested Domain And Returns The IP Address To The User's Application. The Resolver May Also Return Additional Information, Such As The Time To Live (TTL) For The DNS Records, Which Indicates How Long The Records Should Be Cached.

DNS Resolvers Are An Important Part Of The DNS System, As They Enable Users To Access Websites And Other Online Services Using Human-readable Domain Names Rather Than IP Addresses. They Are Typically Provided By Internet Service Providers (ISPs) Or Other Network Administrators And Are Used By Computers And Other Devices To Translate Domain Names Into IP Addresses.

What Are The Types Of DNS Queries?

There Are Several Types Of DNS Queries That Can Be Sent By A DNS Client To A DNS Server. Here Are Some Of The Most Common Types Of DNS Queries:

1. Recursive Query: This Is The Most Common Type Of DNS Query. In A Recursive Query, The DNS Client Asks The DNS Server To Find The IP Address For A Specific Domain Name, And The DNS Server Is Responsible For Recursively Querying Other DNS Servers Until It Obtains The IP Address. The DNS Server Then Returns The IP Address To The DNS Client.

2. Iterative Query: In An Iterative Query, The DNS Client Asks The DNS Server To Provide The IP Address For A Specific Domain Name, And The DNS Server Responds With The Best Information It Has Available, Even If It Is Not The Complete Answer. The DNS Client Then Uses This Information To Send Another Query To A Different DNS Server, And The Process Continues Until The IP Address Is Found.

3. Non-recursive Query: In A Non-recursive Query, The DNS Client Asks The DNS Server To Provide The IP Address For A Specific Domain Name, But The DNS Server Will Only Provide The Information If It Has The Answer In Its Cache. If The DNS Server Doesn't Have The Answer, It Will Respond With A Referral To Another DNS Server That Can Provide The Answer.

4. Reverse Lookup Query: In A Reverse Lookup Query, The DNS Client Asks The DNS Server To Provide The Domain Name Associated With A Specific IP Address. This Is The Opposite Of A Typical DNS Lookup, Where The DNS Client Asks For The IP Address Associated With A Domain Name.

5. Zone Transfer Query: A Zone Transfer Query Is Used To Transfer DNS Zone Data From One DNS Server To Another. This Is Typically Used For Backup Or Redundancy Purposes.

These Are Some Of The Most Common Types Of DNS Queries, But There Are Other Types Of DNS Queries As Well, Such As Dynamic DNS Updates And DNSSEC Queries.

What Is DNS Caching? Where Does DNS Caching Occur?

DNS Caching Is The Process Of Temporarily Storing DNS Records In Memory Or On Disk So That They Can Be Quickly Retrieved The Next Time They Are Needed. Caching Can Significantly Reduce The Time It Takes To Resolve DNS Queries, As It Allows Frequently Accessed DNS Records To Be Retrieved More Quickly Without The Need To Query A DNS Server Every Time.

DNS Caching Can Occur In Several Different Places:

1. DNS Client: When A DNS Client Receives A DNS Response From A DNS Server, It Caches The Response In Memory For A Specified Period Of Time, Which Is Typically Determined By The Time To Live (TTL) Value In The Response. The TTL Value Specifies How Long The DNS Record Should Be Cached Before It Expires.

2. DNS Resolver: A DNS Resolver Is A Type Of DNS Server That Is Responsible For Resolving DNS Queries. When A DNS Resolver Receives A DNS Response From Another DNS Server, It Caches The Response In Memory Or On Disk For A Specified Period Of Time, Which Is Also Determined By The TTL Value In The Response.

3. Intermediate DNS Server: Intermediate DNS Servers, Such As Root Servers And TLD Servers, Also Use Caching To Improve The Performance Of DNS Lookups. When An Intermediate DNS Server Receives A DNS Query, It First Checks Its Cache To See If It Has A Recent Response For The Query. If It Does, It Returns The Cached Response Without Having To Query Other DNS Servers.

DNS Caching Is An Important Feature Of The DNS System, As It Helps To Improve The Performance And Reliability Of DNS Lookups. However, It Can Also Create Problems If DNS Records Are Updated Or Changed, As Cached DNS Records May Be Out Of Date Or Incorrect. To Address This Issue, DNS Servers Use Various Mechanisms To Expire Cached Records After A Certain Amount Of Time, Which Helps To Ensure That DNS Lookups Always Return The Most Up-to-date Information.

What Is A DNS Zone?

A DNS Zone Is A Portion Of The Global Domain Name System (DNS) Namespace That Is Managed By A Specific Organization Or DNS Server. A DNS Zone Is Essentially A Database Of DNS Resource Records (RRs) That Define The Mapping Between Domain Names And IP Addresses Or Other Types Of Resource Records. Each Zone Is Responsible For A Specific Domain Name And Its Subdomains, And Contains All The Resource Records Associated With That Domain Name.

A DNS Zone Is Typically Managed By A DNS Server That Is Authoritative For The Domain Name Associated With The Zone. This DNS Server Is Responsible For Answering DNS Queries Related To The Domain Name And Its Subdomains, And For Updating The Zone's DNS Resource Records As Needed.

A DNS Zone Is Identified By A Zone Name, Which Is Usually The Domain Name Associated With The Zone. For Example, The Zone For The Domain Name "example.com" Would Be Identified By The Zone Name "example.com". DNS Zones Are Hierarchical In Nature, Meaning That They Can Be Subdivided Into Subdomains, Each Of Which Is Managed By Its Own Authoritative DNS Server.

There Are Different Types Of DNS Zones, Including Primary Zones, Secondary Zones, Stub Zones, And Conditional Forwarders. The Type Of Zone Determines How The Zone's DNS Resource Records Are Managed And Updated, And How The Zone Interacts With Other DNS Servers In The Global DNS Hierarchy.

Overall, A DNS Zone Is An Important Concept In The Domain Name System, As It Defines The Scope Of Authority For Managing A Specific Domain Name And Its Associated Resource Records.

What Is A DNS Zone File?

A DNS Zone File Is A Plain Text File That Contains The DNS Resource Records (RRs) For A Specific DNS Zone. The Zone File Is Used By A DNS Server To Map Domain Names To IP Addresses Or Other Types Of Resource Records.

The DNS Zone File Contains Information Such As The Domain Name For The Zone, The Time-to-live (TTL) Value For The Resource Records, And The Resource Records Themselves. The Resource Records May Include Information Such As The IP Addresses Of The DNS Servers For The Zone, The IP Addresses Of Web Servers And Other Network Resources, As Well As Other Types Of DNS Records, Such As MX Records For Email Servers And TXT Records For Storing Text-based Information.

A Typical DNS Zone File Consists Of Several Sections, Including A Header Section That Specifies The Domain Name And TTL Values For The Zone, As Well As Sections For Different Types Of Resource Records. The Most Common Types Of Resource Records In A DNS Zone File Include A Records, Which Map Domain Names To IP Addresses, And NS Records, Which Specify The Authoritative DNS Servers For The Zone.

DNS Zone Files Are Typically Edited By A System Administrator Or Other Person Responsible For Managing The DNS Server. The Changes Made To A Zone File Are Then Propagated To Other DNS Servers On The Internet Through A Process Called DNS Zone Transfer, Which Helps To Ensure That All DNS Servers Have The Most Up-to-date Information About The Zone's Resource Records.

Overall, The DNS Zone File Is An Important Component Of The Domain Name System, As It Defines The Resource Records For A Specific DNS Zone And Enables DNS Servers To Map Domain Names To IP Addresses And Other Network Resources.

What Is A Reverse Lookup Zone?

A Reverse Lookup Zone Is A DNS Zone That Is Used To Map IP Addresses To Domain Names, Instead Of Mapping Domain Names To IP Addresses Like A Standard Forward Lookup Zone. A Reverse Lookup Zone Is Also Known As A Reverse DNS (rDNS) Zone Or A Pointer (PTR) Zone.

A Reverse Lookup Zone Is Used By DNS Servers To Answer Reverse DNS Queries, Which Are Requests For The Domain Name Associated With A Particular IP Address. This Is The Opposite Of A Forward DNS Query, Which Requests The IP Address Associated With A Particular Domain Name.

A Reverse Lookup Zone Is Typically Associated With A Specific IP Address Range, And Contains A Set Of PTR Resource Records That Map IP Addresses To Domain Names. Each PTR Record In The Zone Corresponds To A Particular IP Address, And Provides The Domain Name Associated With That Address.

Reverse Lookup Zones Are Commonly Used For Network Management And Troubleshooting Purposes. For Example, They Can Be Used To Identify The Domain Name Associated With An IP Address That Is Causing Problems On A Network, Or To Verify The Identity Of An Email Server That Is Sending Messages To Your Network.

Overall, A Reverse Lookup Zone Is An Important Component Of The Domain Name System, As It Enables DNS Servers To Map IP Addresses To Domain Names And Provides Valuable Information For Network Management And Troubleshooting.