Domain Name System DNS Basics

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Domains are managed by using a worldwide system of domain registrars and databases. The Domain Name System DNS are the Internet’s equivalent of a phone book. They maintain a directory of domain names and translate them to Internet Protocol (IP) addresses.
For example, is a domain name with the following three levels:
  • .com is the top-level domain
  • contoso is the second-level domain
  • mail is the third-level domain
DNS Record Types and Function

MX Record
Mail Exchange (MX) records direct a domain’s email to the servers hosting the domain’s user accounts. 
TXT Record
A TXT record is a DNS record that provides text information to sources outside your domain, that can be used for a number of arbitrary purposes like domain ownwership etc. The record’s value can be either human- or machine-readable text.
CNAME Record
A Canonical Name or CNAME record is a type of DNS record that maps an alias name to a true or canonicaldomain name. CNAME records are typically used to map a subdomain such as www or mail to the domain hosting that subdomain’s content. For example, a CNAME record can map the web address to the actual web site for the domain
A Record
An A record maps a domain to the physical IP address of the computer hosting that domain. Internet traffic uses the A record to find the computer hosting your domain’s DNS settings. The value of an A record is always an IP address, and multiple A records can be configured for one domain name.
NS Record
Name server (NS) records determine which servers will communicate DNS information for a domain. Generally, you have primary and secondary name server records for your domain. When using Google for Work services, you may configure NS records that point to Google servers for DNS queries.
 The TTL is a value in a DNS record that determines the number of seconds before subsequent changes to the record go into effect. Each of your domain’s DNS records, such as an MX record, CNAME record, and so on, has a TTL value. A record’s current TTL determines how long it will take any change you make now to go into effect.
A URL is the web address of a resource on the Internet. This is the address you type in a browser to visit a particular web site. For example, the URL of the google
SPF (sender policy framework)
An email validation system designed to help prevent email spoofing and phishing.
SRV (service record)
Specifies information about available services. SRV records are used by some Microsoft cloud services such as Lync Online and Exchange Online to coordinate the flow of information between services.
Credit: Google, Microsoft,Technet

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