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mDNS(1) BSD General Commands Manual mDNS(1)
NAME
mDNS -- Multicast DNS (mDNS) & DNS Service Discovery (DNS-SD) Test Tool
SYNOPSIS
mDNS -R name type domain port [key=value ...]
mDNS -B type domain
mDNS -L name type domain
DESCRIPTION
The mDNS command is a network diagnostic tool, much like ping(8) or traceroute(8). However, unlike those tools, most of its functionality is
not implemented in the mDNS executable itself, but in library code that is available to any application. The library API that mDNS uses is
documented in /usr/include/DNSServiceDiscovery/DNSServiceDiscovery.h. Note that this Mach-based API, first introduced in Mac OS X 10.2, is
now deprecated in favour of the newer /usr/include/dns_sd.h API, which is built on Unix Domain Sockets and is supported on multiple plat-
forms. The command-line tool to exercise the cross-platform dns_sd.h API is dns-sd(1).
The mDNS 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 con-
tinue 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 multi-threaded, 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 is not to execute the mDNS
command and then attempt to decipher the textual output, but instead to directly call the DNS-SD APIs using a binding for your chosen lan-
guage.
For example, if you are programming in Ruby, then you can directly call DNS-SD APIs using the dnssd package documented at
<http://rubyforge.org/projects/dnssd/>.
Similar bindings for other languages are also in development.
mDNS -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.
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. type must be of the form "_app-proto._tcp" or "_app-proto._udp", where "app-proto" is an appli-
cation protocol name registered at http://www.dns-sd.org/ServiceTypes.html.
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".
port is a number from 0 to 65535, and is the TCP or UDP port number upon 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.
mDNS -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."
mDNS -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 lookup (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 ser-
vice is resolved to its current IP address and port number every time the user presses Cmd-P to print.
EXAMPLES
To advertise the existence of LPR printing service on port 515 on this machine, such that it will be discovered by the Mac OS X printing
software and other DNS-SD compatible printing clients, use:
mDNS -R "My Test" _printer._tcp. . 515 pdl=application/postscript
For this registration to be useful, you need to actually have LPR service available on port 515. Advertising a service that does not exist is
not very useful, and will be confusing and annoying to other people on the network.
Similarly, to advertise a web page being served by an HTTP server on port 80 on this machine, such that it will show up in the Bonjour list
in Safari and other DNS-SD compatible Web clients, use:
mDNS -R "My Test" _http._tcp . 80 path=/path-to-page.html
To find the advertised web pages on the local network (the same list that Safari shows), use:
mDNS -B _http._tcp
While that command is running, in another window, try the mDNS -R example given above to advertise a web page, and you should see the "Add"
event reported to the mDNS -B window. Now press Ctrl-C in the mDNS -R window and you should see the "Remove" event reported to the mDNS -B
window.
FILES
/usr/bin/mDNS
SEE ALSO
dns-sd(1) mDNSResponder(8)
BUGS
mDNS bugs are tracked in Apple Radar component "mDNSResponder".
HISTORY
The mDNS command first appeared in Mac OS X 10.3 (Panther).
Darwin June 2, 2019 Darwin
