mDNSShared/mDNS.1

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.Dd April 2004              \" Date
.Dt mDNS 1                  \" Document Title
.Os Darwin                  \" Operating System
.\"
.Sh NAME
.Nm mDNS
.Nd Multicast DNS (mDNS) & DNS Service Discovery (DNS-SD) Test Tool \" For whatis
.\" 
.Sh SYNOPSIS
.Nm Fl R Ar name type domain port Op Ar key=value ...
.Pp
.Nm Fl B Ar      type domain
.Pp
.Nm Fl L Ar name type domain
.\"
.Sh DESCRIPTION
The
.Nm
command is a network diagnostic tool, much like
.Xr ping 8
or
.Xr traceroute 8 .
However, unlike those tools, most of its functionality is not implemented in the
.Nm
executable itself, but in library code that is available to any application.
The library API that
.Nm
uses is documented in
.Pa /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
.Pa /usr/include/dns_sd.h
API, which is built on Unix Domain Sockets and is supported on
multiple platforms.
The command-line tool to exercise the cross-platform
.Pa dns_sd.h
API is
.Xr dns-sd 1 .
.Pp
The
.Nm
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 multi-threaded, or use a
main event-handling loop to receive keystrokes, network data, and other
asynchronous event notifications as they happen.
.br
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
.Nm
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.
.br
For example, if you are programming in Ruby, then you can
directly call DNS-SD APIs using the dnssd package documented at
.Pa <http://rubyforge.org/projects/dnssd/> .
.br
Similar bindings for other languages are also in development.
.Pp
.Bl -tag -width R
.It Nm Fl R Ar name type domain port Op Ar key=value ...
register (advertise) a service in the specified
.Ar domain 
with the given
.Ar name
and
.Ar type
as listening (on the current machine) on
.Ar port.
.Pp
.Ar 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.
.Ar type
must be of the form "_app-proto._tcp" or "_app-proto._udp", where
"app-proto" is an application protocol name registered at
.Pa http://www.dns-sd.org/ServiceTypes.html .
.Pp
.Ar 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
.Ar domain
"." is a synonym for "pick a sensible default" which today
means "local".
.Pp
.Ar port
is a number from 0 to 65535, and is the TCP or UDP port number upon
which the service is listening.
.Pp 
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
.Pa http://www.dns-sd.org/ServiceTypes.html .
.It Nm Fl B Ar type domain
browse for instances of service
.Ar type
in
.Ar domain .
.Pp
For valid 
.Ar type Ns s
see
.Pa http://www.dns-sd.org/ServiceTypes.html
as described above. Omitting the
.Ar domain
or using "." means "pick a sensible default."
.It Nm Fl L Ar 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.
.Pp
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.
.El
.Sh EXAMPLES
.Pp
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:
.Pp
.Dl Nm Fl R Ns \ \&"My Test\&" _printer._tcp. \&. 515 pdl=application/postscript
.Pp
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.
.Pp
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:
.Pp
.Dl Nm Fl R Ns \ \&"My Test\&" _http._tcp \&. 80 path=/path-to-page.html
.Pp
To find the advertised web pages on the local network (the same list that
Safari shows), use:
.Pp
.Dl Nm Fl B Ns \ _http._tcp
.Pp
While that command is running, in another window, try the
.Nm Fl R
example given above to advertise a web page, and you should see the
"Add" event reported to the
.Nm Fl B
window. Now press Ctrl-C in the
.Nm Fl R
window and you should see the "Remove" event reported to the
.Nm Fl B
window.
.Pp
.Sh FILES
.Pa /usr/bin/mDNS \" Pathname
.\"
.Sh SEE ALSO
.Xr dns-sd 1
.Xr mDNSResponder 8
.\"
.Sh BUGS
.Nm
bugs are tracked in Apple Radar component "mDNSResponder".
.\"
.Sh HISTORY
The
.Nm
command first appeared in Mac OS X 10.3 (Panther).