DNS Records

DNS Records Types

Entries for hostnames, IP addresses, and other information in the zone database are stored in records. Each host has at least one record in the DNS database that maps the hostname to the IP address.

The following table lists common resource records.

Record Type

Use

SOA (Start of

Authority)

The first record in any DNS database file is the SOA. It defines the general parameters for the DNS zone, and it is assigned to the DNS server hosting the primary copy of a zone. There is only one SOA record, and it is the first record in the zone database file. The SOA record includes parameters such as the authoritative server and the zone file serial number.

NS (name server)

The NS resource record identifies all name servers that can perform name resolution for the zone. Typically, there is an entry for the primary server and all secondary servers for the zone (all authoritative DNS servers).

A (host address)

The A record maps an IPv4 (32-bit) DNS host name to an IP address. This is the most common resource record type.

AAAA (quad-A)

The AAAA record maps an IPv6 (128-bit) DNS host name to an IP address.

MX (Mail

Exchanger)

The MX record identifies servers that can be used to deliver e-mail.

CNAME (canonical name)

The CNAME record provides alternate names (or aliases) to hosts that already have a host record. Using a single A record with multiple CNAME records means that when the IP address changes, only the one A record needs to be modified.

Common uses of a CNAME record include:

  • Adding the alias of www for Web servers. Users typically contact the Web server using a name like http://www.habib.com instead of using the actual server name.
  • Associating a server with the domain name itself. For example, create a CNAME record with a blank name to allow a specific host to be identified with the domain name (such as habib.com).
DNAME (Domain Alias)

The DNAME record provides alternate names (or aliases) to domains that already have a host record.

SRV (service locator)

The SRV record is used by Windows Server 2008 to register network services. This allows clients to find services (such as domain controllers) through DNS. Windows 2008 automatically creates these records as needed and during domain controller installation.

PTR (pointer)

In a reverse lookup zone, the PTR record maps an IP address to a host name (i.e. “points” to an A record). Where IPv4 PTR records are created in the in-addr.arpa namespace, reverse lookup zones for IPv6 addresses should be created in the ip6.arpa namespace.

(Note: When you manually create an A record, you can choose to create the corresponding PTR record at the same time. Creating the PTR record will fail if the reverse lookup zone does not exist.)

WINS and WINS-R resource records

Add these records to a zone when you want to allow DNS to use WINS resolution. The WINS resource record allows DNS queries that fail to resolve to be forwarded to the WINS servers in the WINS resource record. The WINS-R resource record allows the resolution of a reverse query that is not resolvable through DNS.

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