dns-sd

Runs on:

QNX OS

Options:

-B

Browse for instances of a service.

-L

Look up and display information about a service.

-R

Register (advertize) a service.

For more information, see below.

Description:

The dns-sd command is a network diagnostic tool, much like ping or traceroute. However, unlike those tools, most of its functionality isn't implemented in the dns-sd executable itself, but in library code that's available to any application. The library API that dns-sd uses is documented in <dns_sd.h>.

The dns-sd command is primarily intended for interactive use. Because its command-line arguments and output format are subject to change, invoking it from a shell script will generally be fragile. Additionally, the asynchronous nature of DNS Service Discovery does not lend itself easily to script-oriented programming. For example, calls like browse never complete; the action of performing a browse sets in motion machinery to notify the client whenever instances of that service type appear or disappear from the network. These notifications continue to be delivered indefinitely, for minutes, hours, or even days, as services come and go, until the client explicitly terminates the call.

This style of asynchronous interaction works best with applications that are either multithreaded, or use a main event-handling loop to receive keystrokes, network data, and other asynchronous event notifications as they happen. If you wish to perform DNS Service Discovery operations from a scripting language, then the best way to do this isn't to execute the dns-sd command and then attempt to decipher the textual output, but instead to directly call the DNS-SD APIs using a binding for your chosen language.

dns-sd -R name type domain port [key=value ...]

Register (advertise) a service in the specified domain with the given name and type as listening (on the current machine) on port.

The name can be arbitrary unicode text, containing any legal unicode characters (including dots, spaces, slashes, colons, etc. without restriction), up to 63 UTF-8 bytes long. The type must be of the form _app-proto._tcp or _app-proto._udp, where app-proto is an application protocol name registered at http://www.dns-sd.org/ServiceTypes.html.

The domain is the domain in which to register the service. In current implementations, only the local multicast domain local is supported. In the future, registering will be supported in any arbitrary domain that has a working DNS Update server [RFC 2136]. The domain "." is a synonym for pick a sensible default, which today means local.

The port is a number from 0 to 65535, and is the TCP or UDP port number on which the service is listening.

Additional attributes of the service may optionally be described by key/value pairs, which are stored in the advertised service's DNS TXT record. Allowable keys and values are listed with the service registration at http://www.dns-sd.org/ServiceTypes.html.

dns-sd -B type domain

Browse for instances of service type in domain.

For valid types see http://www.dns-sd.org/ServiceTypes.html as described above. Omitting the domain or using "." means pick a sensible default.

dns-sd -L name type domain

Look up and display the information necessary to contact and use the named service: the hostname of the machine where that service is available, the port number on which the service is listening, and (if present) TXT record attributes describing properties of the service.

Note that in a typical application, browsing happens rarely, while looking up (or resolving) happens every time the service is used. For example, a user browses the network to pick a default printer fairly rarely, but once a default printer has been picked, that named service is resolved to its current IP address and port number every time the user prints.