Inside Macintosh: Networking With Open Transport / Part 1 - Open Transport Essentials

Chapter 11 - TCP/IP Services

About the Open Transport DNR

The functions described in "Resolving Internet Addresses" and "Getting Information About an Internet Host" are implemented by the Open Transport domain name resolver (DNR). The DNR also implements the OTLookupName function when you create a DNR mapper. The DNR can be invoked by a UDP endpoint's call to the OTSndUData function, a TCP endpoint's call to the OTConnect function, or a call to the OTResolveAddress function by either type of endpoint. This section describes how the Open Transport DNR operates.

The Open Transport DNR implements only the following specific DNS query types.

Type	Description
A	Resolve name to 32-bit IP host address.
HINFO	Return type of processor (CPU) and operating system of host.
MX	Return name of mail exchange for the domain.
PTR	Resolve address to a fully qualified domain name.

In addition, the Open Transport DNR provides a generic interface, allowing the user's application to send queries of any type. However, the application is then responsible for parsing the response.

The DNR caches name-to-address and canonical name-to-alias mappings, but not host information (CPU and operating-system types) or the results of mail exchange (MX) queries.