TPTRRecord = class(TNAMERecord)

Domain Name Pointer resoure records are used to represent a pointer to another location in the domain name space. Domain Name Pointer resoure records contain simple data, and do not imply any special processing similar to that performed for Canonical Name resource records which identify an alias.

A Domain Name Pointer resource record uses the same DNS packet layout as other TResultRecord-based responses, but extends the use of RData to include the following definition and format:

  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
  .                                               .
  .                   PTRDNAME                    .
  .                                               .
  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

• PTRDNAME- Domain name which points to some location in the domain name space.

The IN-ADDR.ARPA domain on a name server often uses Domain Name Pointer resoure records to support gateway location and Internet address to host mapping. Other classes may employ a similar strategy in other domains. The intent of this domain is to provide a guaranteed method to perform host address to host name mapping, and to facilitate queries to locate all gateways on a particular network in the Internet.

Domain names in the IN-ADDR.ARPA domain are defined to have up to four labels in addition to the IN-ADDR.ARPA suffix. Each label represents one octet of an Internet address, and is expressed as a character string for a decimal value in the range 0-255 (with leading zeros omitted except in the case of a zero octet which is represented by a single zero).

Host addresses are represented by domain names that have all four labels specified. Thus data for Internet address 10.2.0.52 is located at domain name 52.0.2.10.IN-ADDR.ARPA. The reversal, though awkward to read, allows zones to be delegated which are exactly one network of address space. For example, 10.IN-ADDR.ARPA can be a zone containing data for the ARPANET, while 26.IN-ADDR.ARPA can be a separate zone for MILNET. Address nodes are used to hold Domain Name Pointer resource records to primary host names in the normal domain space.

Network numbers correspond to some non-terminal nodes at various depths in the IN-ADDR.ARPA domain, since Internet network numbers are either 1, 2, or 3 octets. Network nodes are used to hold Domain Name Pointer resource records to the primary host names of gateways attached to that network. Since a gateway is, by definition, on more than one network, it will typically have two or more network nodes which point at it. Gateways will also have host level Domain Name Pointer resource records at their fully qualified addresses.

Address resource records for Network or Host addresses at full address nodes use Domain Name Pointer resource records to point back to the primary domain names of the corresponding hosts.