Article ID: 4140, created on Mar 24, 2008, last review on May 10, 2014

  • Applies to:
  • Sphera

Symptoms

Follows an explanation about the different types of DNS records and its structure.

Resolution

A Record (Address Record)

Each of these records map a name to an IP address.

Example:

Name TTL Type IP
www.domain.com. 10800 A 172.16.1.2
  • Name - The www.domain.com is the host.
  • TTL (time to live) - The 10800 indicates how often (in seconds) that this record will exist (will be cached) in other systems. The lower the number the more frequent systems will go to the DNS server for queries.
  • IP - 172.16.1.2 indicates the IP which this host will go to.

CNAME Record (Canonical Name Record)

These are usually referred to as alias records since they usually map an alias to its canonical name. The name server does handle these queries differently from an A record. When a name server looks up a name and finds a CNAME record, it replaces the name with the canonical name and looks up the new name. This allows you to point multiple systems to one IP without specifically assigning an A record to each host name. This was is you IP ever has to change you only have to change your A record once.

Example:

Name TTL Type Data
www.domain.com. 10800 A 172.16.1.2
ftp.domain.com. 10800 CNAME www.domain.com.

 

  • The A record is similar to the example above. Please read the section on A Records if this does not make sense to you.
  • Name - ftp.domain.com is the host which are we are making an alias for.
  • TTL (time to live) - The 10800 indicates how often (in seconds) that this record will exist (will be cached) in other systems. The lower the number the more frequent systems will go to the DNS server for queries.
  • Data - www.domain.com is the host which ftp.domain.com is an alias to. It is important to realize that this value is never a CNAME value. This value should primarily be A record but could use an IP.

When the DNS server is queried for the ftp.domain.com. system it realizes that it is an alias for www.dnsmadeeasy.com.. The system then returns the value of www.domain.com.. which is 192.168.1.2. Whatever www.dnsmadeeasy.com. points to then so does ftp.domain.com..

NOTE: It is important to know that only an A record can be made for your root host record. If you have a domain called example.com. and if you want an IP for example.com. then A record is the only valid solution for this. CNAME records are invalid.

 

NS Record (Name Server Record)

These records indicate which name servers are authoritative for the zone.

Example:

Name TTL Type Data
ns.domain.com. 10800 A 192.168.10.12
domain.com. 10800 NS ns.domain.com
  • The A record is similar to the example above. Please read the section on A Records if this does not make sense to you.
  • Name - domain.com. is the domain which is being assigned an authoritative name server.
  • TTL (time to live) - The 10800 indicates the how often (in seconds) that this record will exist (will be cached) in other systems. The lower the number the more frequent systems will go to the DNS server for queries.
  • Data - ns.domain.com. is the host which name servers will query for records in the domain.com.. domain. It is important to realize that this value is never a CNAME value. This value should primarily be A record but could use an IP.

 

MX Record (Mail Exchange Record)

These records tell mail servers where to deliver mail. The name field of an MX record contains the host name which appears in the e-mail address, and the data field contains the hostname of the server to which the mail should be delivered. Two MX records that define the mail servers for the dnsmadeeasy.com domain might contain the following:

Name Expire Time Type MX level Data (A Record)
domain.com. 10800 MX 10 mail.domain.com.
domain.com. 10800 MX 20 secondmail.domain.com.

 

  • Name - Contains the domain domain.com., meaning that these records are used for the entire domain. If the mail was addressed to username@domain.com, the mail is directed to the mail exchangers defined by these records.
  • TTL (time to live) - The 10800 indicates the how often (in seconds) that this record will exist (will be cached) in other systems.
  • MX level - Sets the preference for the MX record. The mailserver will first try mail.domain.com.. The lower the number the higher the preference. If the mail server with highest precedence is inaccessible the mail will be delivered to the mail server next in precedence. So if the server mail.domain.com. is unavailable then secondmail.domain.com. will get mail to be queued until mail.domain.com. is ready to accept mail again. At that time secondmail.domain.com will send it's queued mail to mail.domain.com. Note: The email server must also be configured properly to queue mail for another system
  • Data - The host names which will have mail delivered to them for the domain. It is important to realize that this value is never a CNAME value. This value should primarily be A record but could use an IP.

 

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