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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 docu-
     mented in /usr/include/DNSServiceDiscovery/DNSServiceDiscovery.h.  Note
     that this Mach-based API, first introduced in Mac OS X 10.2, is now dep-
     recated in favour of the newer /usr/include/dns_sd.h API, which is built
     on Unix Domain Sockets and is supported on multiple platforms.  The com-
     mand-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 asyn-
     chronous nature of DNS Service Discovery does not lend itself easily to
     script-oriented programming. For example, calls like "browse" never com-
     plete; the action of performing a "browse" sets in motion machinery to
     notify the client whenever instances of that service type appear or dis-
     appear 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 asynchro-
     nous interaction works best with applications that are either multi-
     threaded, or use a main event-handling loop to receive keystrokes, net-
     work 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 language.
     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 char-
        acters (including dots, spaces, slashes, colons, etc. without restric-
        tion), 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 application
        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 regis-
        tration 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 sensi-
        ble 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 service
        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 soft-
     ware 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                        September 17, 2009                        Darwin

Mac OS X 10.6 - Generated Thu Sep 17 20:08:04 CDT 2009
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