Wednesday, August 23, 2017
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Domain Name Server (DNS)

The Domain Name System (DNS) is a distributed database, arranged hierarchically, containing records for domain names. The DNS system’s main aim is to match a domain name to an IP Address. In order to fulfill this role, the DNS Server contains Resource Records (Records) in a Zone File, which contains the domain name and IP address mappings for computers contained within that Zone.

All Resource Records have a Time To Live TTL (TTL), specifying the number of seconds other DNS servers and applications are allowed to cache the Record.

Types of Resource Records (RRs) manageable through DNS Service

Address (IPv4 A) Record

These are used to translate domain names into IP addresses.

AAAA (IPv6) Record

The IPv6 Address Record is a much larger address space than that of a IPv4 Address Record. Addresses in IPv6 Address Records are 128 bits long while those in IPv4 Address Records are 32 bits long.

Mail Exchanger (MX) Record

An MX Record identifies the email server(s) responsible for a domain name. When sending an email to user@xyz.com, your email server must first looks up the MX Record for xyz.com to see which email server actually handles email for xyz.com (this could be mail.xyz.com or someone else’s email server like mail.isp.com). Then it looks up the A Record for the email server to connect to its IP address.

Canonical Name (CNAME) Record

CNAME Records are domain name aliases. Often computers on the Internet have multiple functions such as Web Server, FTP Server, Chat Server, etc.. To mask this, CNAME Records can be used, to give a single computer multiple names (aliases).

Sometimes companies register multiple domain names for their brand-names but still wish to maintain a single website. In such cases, a CNAME Record maybe used to forward traffic to their actual website.

Example:

www.abc.in could be CNAME to www.abc.com.

Name Server (NS) Record

NS Records identify the DNS servers responsible (authoritative) for a Zone. A Zone should contain one NS Record for each of its own DNS servers (primary and secondary). This mostly is used for Zone Transfer purposes (notify). These NS Records have the same name as the Zone in which they are located.

Text (TXT) Records

TXT Records provide the ability to associate some text with a domain or a sub-domain. This text is meant to strictly provide information and has no functionality as such. A TXT Record can store upto 255 characters of free form text. This Record is generally used to convey information about the zone. Multiple TXT Records are permitted but their order is not necessarily retained.

Service (SRV) Record

An SRV or Service Record is a category of data in the DNS specifying information on available services. When looking up for a service, you must first lookup the SRV Record for the service to see which server actually handles it. Then it looks up the Address Record for the server to connect to its IP Address.

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