DNS records

(redirected from A record)

DNS records

A DNS server is configured with a "zone file" for each domain that contains "resource records." There are several types of records, and the most common are described below. See DNS.

Forward DNS and Reverse DNS (A and PTR)
The Address (A) record associates a domain name with an IP address, which is the primary purpose of the DNS system. The Pointer (PTR) record provides data for reverse DNS, which is used for logging the domain name and verification purposes. Also called "inverse DNS," the PTR record is an option. See reverse DNS.

Aliasing Names (CNAME)
The Canonical Name (CNAME) record is used to create aliases that point to other names. It is commonly used to map WWW, FTP and MAIL subdomains to a domain name; for example, a CNAME record can associate the subdomain FTP.COMPUTERLANGUAGE.COM with COMPUTERLANGUAGE.COM.

DNS Name Servers (NS)
The Name Server (NS) record identifies the authoritative DNS servers for a domain. A second name server is required for redundancy, and two NS records must be in the zone file (one for the primary; one for the secondary). The secondary server queries the primary server for changes.

Mail Servers (MX)
The Mail Exchange (MX) record identifies the server to which e-mail is directed. It also contains a priority field so that mail can be directed to multiple servers in a prescribed order.

Text Record (TXT)
A TXT record can be used for any kind of documentation. It is also used to provide information to the SPF e-mail authentication system. See SPF.

First Record in File (SOA)
Start of Authority (SOA) is the first record in the zone file. It contains the name of the primary DNS server, which must correspond to an NS record in the file, the administrator's e-mail address and the length of time records can be cached before going back to the authoritative DNS server.

The SOA also includes data for the secondary DNS server such as the date of last update (the "Serial Number") and time intervals for checking the domain.
SUMMARY OF COMMON ZONE FILE RECORDSRecord Name (purpose) Associate This to ThatSOA record (1st record)

 TXT record (documentation)

 CNAME record (aliases)
  associate an alias to a domain

 DNAME record (aliases)
  associate an alias to a subdomain

 MX record (mail server)
  associate mail to a mail server

 NS record (authoritative server)
  associate a domain to a DNS server

 A record (forward DNS - IPv4)
  associate subdomain to 32-bit IP

 AAAA record (forward DNS - IPv6)
  (1st IPv6 record)
  associate subdomain to 128-bit IP

 A6 record (forward DNS - IPv6)
  (future IPv6 record)
  associate subdomain to 128-bit IP

 PTR record (reverse DNS)
  associate IP address to a subdomain
References in classic literature ?
Under this row of faint grease prints he would write a record on the strip of white paper--thus:
Wilson knew Roxy by sight, and when the duel of wits begun to play out, he stepped outside to gather in a record or two.
The memories of innocent people may suffer, hereafter, for want of a record of the facts to which those who come after us can appeal.
Is some one trying to make a record round the world?
In a book was a record of all the ascents which have ever been made, beginning with Nos.
Such a one, a big steamship, too, whose working life had been a record of faithful keeping time from land to land, in disregard of wind and sea, once lost her propeller down south, on her passage out to New Zealand.
Noted sports collector Gary Cypres of Los Angeles paid a record $395,240 for the 1941 Heisman Trophy given to Minnesota tailback Bruce Smith at an auction Friday in New York.
Businesses are concerned that at some point in the future a Revenue Canada auditor may deny input tax credits because a record otherwise unnecessary for managing the taxpayer's business either is not retained for tax purposes or, more likely, is retained in a format that the auditor is unfamiliar with or uncomfortable accepting for audit purposes.
In 1993, Chick-fil-A opened a record 58 locations and introduced its double drive-thru-only concept.
Having just closed the books on its 20th year in operation, BD&A has made company history once again, posting a record $137 million in sales.
The 1906 Chicago Cubs and the 2001 Seattle Mariners each won a record 116 games - the Cubs played 10 fewer games - but didn't win when it mattered.
3 million of Damion Easley's salary, a record for a player who has been cut.