mDNSShared/mDNS.1

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  17 .Dd April 2004              \" Date
  18 .Dt mDNS 1                  \" Document Title
  19 .Os Darwin                  \" Operating System
  20 .\"
  21 .Sh NAME
  22 .Nm mDNS
  23 .Nd Multicast DNS (mDNS) & DNS Service Discovery (DNS-SD) Test Tool \" For whatis
  24 .\"
  25 .Sh SYNOPSIS
  26 .Nm Fl R Ar name type domain port Op Ar key=value ...
  27 .Pp
  28 .Nm Fl B Ar      type domain
  29 .Pp
  30 .Nm Fl L Ar name type domain
  31 .\"
  32 .Sh DESCRIPTION
  33 The
  34 .Nm
  35 command is a network diagnostic tool, much like
  36 .Xr ping 8
  37 or
  38 .Xr traceroute 8 .
  39 However, unlike those tools, most of its functionality is not implemented in the
  40 .Nm
  41 executable itself, but in library code that is available to any application.
  42 The library API that
  43 .Nm
  44 uses is documented in
  45 .Pa /usr/include/DNSServiceDiscovery/DNSServiceDiscovery.h .
  46 Note that this Mach-based API, first introduced in Mac OS X 10.2,
  47 is now deprecated in favour of the newer
  48 .Pa /usr/include/dns_sd.h
  49 API, which is built on Unix Domain Sockets and is supported on
  50 multiple platforms.
  51 The command-line tool to exercise the cross-platform
  52 .Pa dns_sd.h
  53 API is
  54 .Xr dns-sd 1 .
  55 .Pp
  56 The
  57 .Nm
  58 command is primarily intended for interactive use.
  59 Because its command-line arguments and output format are subject to change,
  60 invoking it from a shell script will generally be fragile. Additionally,
  61 the asynchronous nature of DNS Service Discovery does
  62 not lend itself easily to script-oriented programming. For example,
  63 calls like "browse" never complete; the action of performing a "browse"
  64 sets in motion machinery to notify the client whenever instances of
  65 that service type appear or disappear from the network. These
  66 notifications continue to be delivered indefinitely, for minutes,
  67 hours, or even days, as services come and go, until the client
  68 explicitly terminates the call. This style of asynchronous interaction
  69 works best with applications that are either multi-threaded, or use a
  70 main event-handling loop to receive keystrokes, network data, and other
  71 asynchronous event notifications as they happen.
  72 .br
  73 If you wish to perform DNS Service Discovery operations from a
  74 scripting language, then the best way to do this is not to execute the
  75 .Nm
  76 command and then attempt to decipher the textual output, but instead to
  77 directly call the DNS-SD APIs using a binding for your chosen language.
  78 .br
  79 For example, if you are programming in Ruby, then you can
  80 directly call DNS-SD APIs using the dnssd package documented at
  81 .Pa <http://rubyforge.org/projects/dnssd/> .
  82 .br
  83 Similar bindings for other languages are also in development.
  84 .Pp
  85 .Bl -tag -width R
  86 .It Nm Fl R Ar name type domain port Op Ar key=value ...
  87 register (advertise) a service in the specified
  88 .Ar domain
  89 with the given
  90 .Ar name
  91 and
  92 .Ar type
  93 as listening (on the current machine) on
  94 .Ar port.
  95 .Pp
  96 .Ar name
  97 can be arbitrary unicode text, containing any legal unicode characters
  98 (including dots, spaces, slashes, colons, etc. without restriction),
  99 up to 63 UTF-8 bytes long.
 100 .Ar type
 101 must be of the form "_app-proto._tcp" or "_app-proto._udp", where
 102 "app-proto" is an application protocol name registered at
 103 .Pa http://www.dns-sd.org/ServiceTypes.html .
 104 .Pp
 105 .Ar domain
 106 is the domain in which to register the service.
 107 In current implementations, only the local multicast domain "local" is
 108 supported. In the future, registering will be supported in any arbitrary
 109 domain that has a working DNS Update server [RFC 2136]. The
 110 .Ar domain
 111 "." is a synonym for "pick a sensible default" which today
 112 means "local".
 113 .Pp
 114 .Ar port
 115 is a number from 0 to 65535, and is the TCP or UDP port number upon
 116 which the service is listening.
 117 .Pp
 118 Additional attributes of the service may optionally be described by
 119 key/value pairs, which are stored in the advertised service's DNS TXT
 120 record. Allowable keys and values are listed with the service
 121 registration at
 122 .Pa http://www.dns-sd.org/ServiceTypes.html .
 123 .It Nm Fl B Ar type domain
 124 browse for instances of service
 125 .Ar type
 126 in
 127 .Ar domain .
 128 .Pp
 129 For valid
 130 .Ar type Ns s
 131 see
 132 .Pa http://www.dns-sd.org/ServiceTypes.html
 133 as described above. Omitting the
 134 .Ar domain
 135 or using "." means "pick a sensible default."
 136 .It Nm Fl L Ar name type domain
 137 look up and display the information necessary to contact and use the
 138 named service: the hostname of the machine where that service is
 139 available, the port number on which the service is listening, and (if
 140 present) TXT record attributes describing properties of the service.
 141 .Pp
 142 Note that in a typical application, browsing happens rarely, while lookup
 143 (or "resolving") happens every time the service is used. For example, a
 144 user browses the network to pick a default printer fairly rarely, but once
 145 a default printer has been picked, that named service is resolved to its
 146 current IP address and port number every time the user presses Cmd-P to
 147 print.
 148 .El
 149 .Sh EXAMPLES
 150 .Pp
 151 To advertise the existence of LPR printing service on port 515 on this
 152 machine, such that it will be discovered by the Mac OS X printing software
 153 and other DNS-SD compatible printing clients, use:
 154 .Pp
 155 .Dl Nm Fl R Ns \ \&"My Test\&" _printer._tcp. \&. 515 pdl=application/postscript
 156 .Pp
 157 For this registration to be useful, you need to actually have LPR service
 158 available on port 515. Advertising a service that does not exist is not
 159 very useful, and will be confusing and annoying to other people on the
 160 network.
 161 .Pp
 162 Similarly, to advertise a web page being served by an HTTP
 163 server on port 80 on this machine, such that it will show up in the
 164 Bonjour list in Safari and other DNS-SD compatible Web clients, use:
 165 .Pp
 166 .Dl Nm Fl R Ns \ \&"My Test\&" _http._tcp \&. 80 path=/path-to-page.html
 167 .Pp
 168 To find the advertised web pages on the local network (the same list that
 169 Safari shows), use:
 170 .Pp
 171 .Dl Nm Fl B Ns \ _http._tcp
 172 .Pp
 173 While that command is running, in another window, try the
 174 .Nm Fl R
 175 example given above to advertise a web page, and you should see the
 176 "Add" event reported to the
 177 .Nm Fl B
 178 window. Now press Ctrl-C in the
 179 .Nm Fl R
 180 window and you should see the "Remove" event reported to the
 181 .Nm Fl B
 182 window.
 183 .Pp
 184 .Sh FILES
 185 .Pa /usr/bin/mDNS \" Pathname
 186 .\"
 187 .Sh SEE ALSO
 188 .Xr dns-sd 1
 189 .Xr mDNSResponder 8
 190 .\"
 191 .Sh BUGS
 192 .Nm
 193 bugs are tracked in Apple Radar component "mDNSResponder".
 194 .\"
 195 .Sh HISTORY
 196 The
 197 .Nm
 198 command first appeared in Mac OS X 10.3 (Panther).