What is PTR and how does it work?

[Kevin Darcy]

cejet50 at aol.com wrote:

> What is PTR and how does it work?

  Technically, a PTR is just a way to associate one name with another,
without the aliasing functionality associated with CNAMEs.

By *convention*, however, PTRs are used primarily for reverse DNS, i.e.
mapping addresses to names. The convention is to take the address,
reverse the octets, and add ".in-addr.arpa" to the end. Any PTR records
owned by that name are supposed to point to a name which resolves to the
address.

E.g. the name of the reverse record for address 1.2.3.4 would be
4.3.2.1.in-addr.arpa. Any PTR records owned by 4.3.2.1.in-addr.arpa
would be expected to point to a name which resolves to 4.3.2.1.

Treating reverse records as regular names in the namespace hierarchy --
albeit a reserved part of the hierarchy -- means that the reverse
namespace can be delegated and maintained just like any other part of
the namespace.


- Kevin