<s>
Zero-configuration	B-Application
networking	I-Application
(	O
zeroconf	B-Application
)	O
is	O
a	O
set	O
of	O
technologies	O
that	O
automatically	O
creates	O
a	O
usable	O
computer	B-Architecture
network	I-Architecture
based	O
on	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
Suite	I-Protocol
(	O
TCP/IP	B-Protocol
)	O
when	O
computers	O
or	O
network	O
peripherals	O
are	O
interconnected	O
.	O
</s>
<s>
Without	O
zeroconf	B-Application
,	O
a	O
network	O
administrator	O
must	O
set	O
up	O
network	B-General_Concept
services	I-General_Concept
,	O
such	O
as	O
Dynamic	B-Protocol
Host	I-Protocol
Configuration	I-Protocol
Protocol	I-Protocol
(	O
DHCP	B-Protocol
)	O
and	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
(	O
DNS	B-Protocol
)	O
,	O
or	O
configure	O
each	O
computer	O
's	O
network	O
settings	O
manually	O
.	O
</s>
<s>
Zeroconf	B-Application
is	O
built	O
on	O
three	O
core	O
technologies	O
:	O
automatic	O
assignment	O
of	O
numeric	O
network	O
addresses	O
for	O
networked	O
devices	O
,	O
automatic	O
distribution	O
and	O
resolution	O
of	O
computer	O
hostnames	B-Protocol
,	O
and	O
automatic	O
location	B-Protocol
of	I-Protocol
network	I-Protocol
services	I-Protocol
,	O
such	O
as	O
printing	O
devices	O
.	O
</s>
<s>
Computer	B-Architecture
networks	I-Architecture
use	O
numeric	O
network	O
addresses	O
to	O
identify	O
communications	O
endpoints	O
in	O
a	O
network	O
of	O
participating	O
devices	O
.	O
</s>
<s>
In	O
modern	O
networking	O
protocols	O
,	O
information	O
to	O
be	O
transmitted	O
is	O
divided	O
into	O
a	O
series	O
of	O
network	B-Protocol
packets	I-Protocol
.	O
</s>
<s>
Every	O
packet	B-Protocol
contains	O
the	O
source	O
and	O
destination	O
addresses	O
for	O
the	O
transmission	O
.	O
</s>
<s>
Network	B-Protocol
routers	I-Protocol
examine	O
these	O
addresses	O
to	O
determine	O
the	O
best	O
network	O
path	O
in	O
forwarding	B-Protocol
the	I-Protocol
data	I-Protocol
packet	I-Protocol
at	O
each	O
step	O
toward	O
its	O
destination	O
.	O
</s>
<s>
Early	O
computer	B-Architecture
networking	I-Architecture
was	O
built	O
upon	O
technologies	O
of	O
the	O
telecommunications	O
networks	O
and	O
thus	O
protocols	O
tended	O
to	O
fall	O
into	O
two	O
groups	O
:	O
those	O
intended	O
to	O
connect	O
local	B-Protocol
devices	O
into	O
a	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
(	O
LAN	B-General_Concept
)	O
,	O
and	O
those	O
intended	O
primarily	O
for	O
long-distance	O
communications	O
.	O
</s>
<s>
LAN	B-General_Concept
systems	O
tended	O
to	O
provide	O
more	O
automation	O
of	O
these	O
tasks	O
so	O
that	O
new	O
equipment	O
could	O
be	O
added	O
to	O
a	O
LAN	B-General_Concept
with	O
a	O
minimum	O
of	O
operator	O
and	O
administrator	O
intervention	O
.	O
</s>
<s>
An	O
early	O
example	O
of	O
a	O
zero-configuration	B-Application
LAN	B-General_Concept
system	O
is	O
AppleTalk	B-Application
,	O
a	O
protocol	O
introduced	O
by	O
Apple	O
Inc	O
.	O
for	O
the	O
early	O
Macintosh	B-Device
computers	I-Device
in	O
the	O
1980s	O
.	O
</s>
<s>
Macs	B-Device
,	O
as	O
well	O
as	O
other	O
devices	O
supporting	O
the	O
protocol	O
,	O
could	O
be	O
added	O
to	O
the	O
network	O
by	O
simply	O
plugging	O
them	O
in	O
;	O
all	O
further	O
configuration	O
was	O
automated	O
.	O
</s>
<s>
Network	O
addresses	O
were	O
automatically	O
selected	O
by	O
each	O
device	O
using	O
a	O
protocol	O
known	O
as	O
AppleTalk	B-Application
Address	I-Application
Resolution	I-Application
Protocol	I-Application
(	O
AARP	O
)	O
,	O
while	O
each	O
machine	O
built	O
its	O
own	O
local	B-Protocol
directory	O
service	O
using	O
a	O
protocol	O
known	O
as	O
Name	O
Binding	O
Protocol	O
(	O
NBP	O
)	O
.	O
</s>
<s>
Users	O
could	O
look	O
up	O
any	O
device	O
on	O
the	O
network	O
with	O
the	O
application	O
Chooser	B-Operating_System
,	O
which	O
filtered	O
names	O
based	O
on	O
the	O
device	O
type	O
.	O
</s>
<s>
On	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	O
)	O
networks	O
,	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
database	O
for	O
a	O
network	O
was	O
initially	O
maintained	O
manually	O
by	O
a	O
network	O
administrator	O
.	O
</s>
<s>
Efforts	O
to	O
automate	O
maintenance	O
of	O
this	O
database	O
,	O
led	O
to	O
the	O
introduction	O
of	O
a	O
number	O
of	O
new	O
protocols	O
providing	O
automated	O
services	O
,	O
such	O
as	O
the	O
Dynamic	B-Protocol
Host	I-Protocol
Configuration	I-Protocol
Protocol	I-Protocol
(	O
DHCP	B-Protocol
)	O
.	O
</s>
<s>
Hosts	O
on	O
a	O
network	O
must	O
be	O
assigned	O
IP	B-Protocol
addresses	I-Protocol
that	O
uniquely	O
identify	O
them	O
to	O
other	O
devices	O
on	O
the	O
same	O
network	O
.	O
</s>
<s>
Mechanisms	O
were	O
introduced	O
to	O
handle	O
this	O
task	O
automatically	O
,	O
and	O
both	O
IPv4	O
and	O
IPv6	O
now	O
include	O
systems	O
for	O
address	B-Protocol
autoconfiguration	I-Protocol
,	O
which	O
allows	O
a	O
device	O
to	O
determine	O
a	O
safe	O
address	O
to	O
use	O
through	O
simple	O
mechanisms	O
.	O
</s>
<s>
For	O
link-local	B-Protocol
addressing	I-Protocol
,	O
IPv4	O
uses	O
the	O
special	O
block	O
,	O
while	O
IPv6	O
hosts	O
use	O
the	O
prefix	O
.	O
</s>
<s>
More	O
commonly	O
addresses	O
are	O
assigned	O
by	O
a	O
DHCP	B-Protocol
server	I-Protocol
,	O
often	O
built	O
into	O
common	O
networking	O
hardware	O
like	O
computer	O
hosts	O
or	O
routers	B-Protocol
.	O
</s>
<s>
Most	O
IPv4	O
hosts	O
use	O
link-local	B-Protocol
addressing	I-Protocol
only	O
as	O
a	O
last	O
resort	O
when	O
a	O
DHCP	B-Protocol
server	I-Protocol
is	O
unavailable	O
.	O
</s>
<s>
An	O
IPv4	O
host	O
otherwise	O
uses	O
its	O
DHCP-assigned	O
address	O
for	O
all	O
communications	O
,	O
global	O
or	O
link-local	O
.	O
</s>
<s>
Another	O
is	O
that	O
not	O
every	O
IPv4	O
host	O
implements	O
distributed	O
name	O
resolution	O
(	O
e.g.	O
,	O
multicast	B-Protocol
DNS	I-Protocol
)	O
,	O
so	O
discovering	O
the	O
autoconfigured	O
link-local	B-Protocol
address	I-Protocol
of	O
another	O
host	O
on	O
the	O
network	O
can	O
be	O
difficult	O
.	O
</s>
<s>
Discovering	O
the	O
DHCP-assigned	O
address	O
of	O
another	O
host	O
requires	O
either	O
distributed	O
name	O
resolution	O
or	O
a	O
unicast	O
DNS	B-Protocol
server	O
with	O
this	O
information	O
;	O
Some	O
networks	O
feature	O
DNS	B-Protocol
servers	O
that	O
are	O
automatically	O
updated	O
with	O
DHCP-assigned	O
host	O
and	O
address	O
information	O
.	O
</s>
<s>
IPv6	O
hosts	O
are	O
required	O
to	O
support	O
multiple	O
addresses	O
per	O
interface	O
;	O
moreover	O
,	O
every	O
IPv6	O
host	O
is	O
required	O
to	O
configure	O
a	O
link-local	B-Protocol
address	I-Protocol
even	O
when	O
global	O
addresses	O
are	O
available	O
.	O
</s>
<s>
IPv6	O
hosts	O
may	O
additionally	O
self-configure	O
additional	O
addresses	O
on	O
receipt	O
of	O
router	B-Protocol
advertisement	O
messages	B-Protocol
,	O
thus	O
eliminating	O
the	O
need	O
for	O
a	O
DHCP	B-Protocol
server	I-Protocol
.	O
</s>
<s>
IPv6	O
hosts	O
generally	O
combine	O
a	O
prefix	O
of	O
up	O
to	O
64	O
bits	O
with	O
a	O
64-bit	O
EUI-64	O
derived	O
from	O
the	O
factory-assigned	O
48-bit	O
IEEE	O
MAC	B-Device
address	O
.	O
</s>
<s>
The	O
MAC	B-Device
address	O
has	O
the	O
advantage	O
of	O
being	O
globally	O
unique	O
,	O
a	O
basic	O
property	O
of	O
the	O
EUI-64	O
.	O
</s>
<s>
The	O
IPv6	O
protocol	B-Protocol
stack	I-Protocol
also	O
includes	O
duplicate	O
address	O
detection	O
to	O
avoid	O
conflicts	O
with	O
other	O
hosts	O
.	O
</s>
<s>
In	O
IPv4	O
,	O
the	O
method	O
is	O
called	O
link-local	B-Protocol
address	I-Protocol
autoconfiguration	I-Protocol
.	O
</s>
<s>
However	O
,	O
Microsoft	O
refers	O
to	O
this	O
as	O
Automatic	O
Private	O
IP	B-Protocol
Addressing	I-Protocol
(	O
APIPA	B-Protocol
)	O
or	O
Internet	B-Protocol
Protocol	I-Protocol
Automatic	O
Configuration	O
(	O
IPAC	O
)	O
.	O
</s>
<s>
The	O
feature	O
is	O
supported	O
in	O
Windows	O
since	O
at	O
least	O
Windows	B-Device
98	I-Device
.	O
</s>
<s>
Internet	B-Protocol
protocols	I-Protocol
use	O
IP	B-Protocol
addresses	I-Protocol
for	O
communications	O
,	O
but	O
these	O
are	O
not	O
easy	O
for	O
humans	O
to	O
use	O
;	O
IPv6	O
in	O
particular	O
uses	O
very	O
long	O
strings	O
of	O
digits	O
that	O
are	O
not	O
easily	O
entered	O
manually	O
.	O
</s>
<s>
To	O
address	O
this	O
issue	O
,	O
the	O
internet	O
has	O
long	O
used	O
DNS	B-Protocol
,	O
which	O
allows	O
human-readable	O
names	O
to	O
be	O
associated	O
with	O
IP	B-Protocol
addresses	I-Protocol
,	O
and	O
includes	O
code	O
for	O
looking	O
up	O
these	O
names	O
from	O
a	O
hierarchical	O
database	O
system	O
.	O
</s>
<s>
Users	O
type	O
in	O
domain	O
names	O
,	O
such	O
as	O
example.org,	O
which	O
the	O
computer	O
's	O
DNS	B-Protocol
software	O
looks	O
up	O
in	O
the	O
DNS	B-Protocol
databases	O
to	O
retrieve	O
an	O
IP	B-Protocol
address	I-Protocol
,	O
and	O
then	O
hands	O
off	O
that	O
address	O
to	O
the	O
protocol	B-Protocol
stack	I-Protocol
for	O
further	O
communications	O
.	O
</s>
<s>
Looking	O
up	O
an	O
address	O
using	O
DNS	B-Protocol
requires	O
the	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
DNS	B-Protocol
server	O
to	O
be	O
known	O
.	O
</s>
<s>
In	O
early	O
systems	O
,	O
this	O
was	O
normally	O
required	O
on	O
every	O
device	O
,	O
but	O
this	O
has	O
been	O
pushed	O
up	O
one	O
layer	O
in	O
the	O
hierarchy	O
to	O
the	O
DHCP	B-Protocol
servers	I-Protocol
or	O
broadband	B-General_Concept
devices	O
like	O
cable	B-Device
modems	I-Device
that	O
receive	O
this	O
information	O
from	O
their	O
internet	O
service	O
provider	O
.	O
</s>
<s>
This	O
has	O
reduced	O
the	O
user-side	O
administration	O
requirements	O
and	O
provides	O
a	O
key	O
element	O
of	O
zero-configuration	B-Application
access	O
.	O
</s>
<s>
DNS	B-Protocol
was	O
intended	O
to	O
provide	O
uniform	O
names	O
to	O
groups	O
of	O
devices	O
within	O
the	O
same	O
administration	O
realm	O
,	O
such	O
as	O
example.org,	O
provided	O
by	O
a	O
name	O
service	O
.	O
</s>
<s>
Assigning	O
an	O
address	O
to	O
a	O
local	B-Protocol
device	O
,	O
e.g.	O
,	O
thirdfloorprinter.example.org,	O
normally	O
requires	O
administrator	O
access	O
to	O
the	O
DNS	B-Protocol
server	O
and	O
is	O
often	O
accomplished	O
manually	O
.	O
</s>
<s>
Additionally	O
,	O
traditional	O
DNS	B-Protocol
servers	O
are	O
not	O
expected	O
to	O
automatically	O
correct	O
for	O
changes	O
in	O
configuration	O
.	O
</s>
<s>
For	O
instance	O
,	O
if	O
a	O
printer	O
is	O
moved	O
from	O
one	O
floor	O
to	O
another	O
it	O
might	O
be	O
assigned	O
a	O
new	O
IP	B-Protocol
address	I-Protocol
by	O
the	O
local	B-Protocol
DHCP	B-Protocol
server	I-Protocol
.	O
</s>
<s>
To	O
address	O
the	O
need	O
for	O
automatic	O
configuration	O
,	O
Microsoft	O
implemented	O
NetBIOS	B-Protocol
Name	O
Service	O
,	O
part	O
of	O
which	O
is	O
the	O
Computer	B-General_Concept
Browser	I-General_Concept
Service	I-General_Concept
already	O
in	O
Microsoft	O
Windows	O
for	O
Workgroups	O
3.11	O
as	O
early	O
as	O
1992	O
.	O
</s>
<s>
NetBIOS	B-Protocol
Name	O
Service	O
is	O
zero-configuration	B-Application
on	O
networks	O
with	O
a	O
single	O
subnet	O
and	O
may	O
be	O
used	O
in	O
conjunction	O
with	O
a	O
WINS	B-Device
server	I-Device
or	O
a	O
Microsoft	O
DNS	B-Protocol
server	O
that	O
supports	O
secure	O
automatic	O
registration	O
of	O
addresses	O
.	O
</s>
<s>
The	O
protocols	O
NetBIOS	B-Protocol
can	O
use	O
are	O
part	O
of	O
the	O
Server	B-Operating_System
Message	I-Operating_System
Block	I-Operating_System
(	O
SMB	O
)	O
suite	O
of	O
open	O
protocols	O
which	O
are	O
also	O
available	O
on	O
Linux	B-Application
and	O
iOS	O
,	O
although	O
Windows	O
typically	O
supports	O
a	O
wider	O
range	O
of	O
so-called	O
dialects	O
which	O
can	O
be	O
negotiated	O
between	O
Windows	O
clients	O
that	O
support	O
it	O
.	O
</s>
<s>
For	O
example	O
,	O
Computer	B-General_Concept
Browser	I-General_Concept
Services	I-General_Concept
running	O
on	O
server	O
operating	O
systems	O
or	O
later	O
versions	O
of	O
Windows	O
are	O
elected	O
as	O
so-called	O
master	O
browser	O
over	O
those	O
that	O
are	O
not	O
running	O
a	O
server	O
operating	O
system	O
or	O
running	O
older	O
versions	O
of	O
Windows	O
.	O
</s>
<s>
In	O
2000	O
,	O
Bill	O
Manning	O
and	O
Bill	O
Woodcock	O
described	O
the	O
Multicast	O
Domain	B-Protocol
Name	I-Protocol
Service	I-Protocol
which	O
spawned	O
the	O
implementations	O
by	O
Apple	O
and	O
Microsoft	O
.	O
</s>
<s>
Apple	O
's	O
Multicast	B-Protocol
DNS	I-Protocol
(	O
mDNS	B-Protocol
)	O
is	O
published	O
as	O
a	O
standards	O
track	O
proposal	O
,	O
while	O
Microsoft	O
's	O
Link-local	B-Protocol
Multicast	I-Protocol
Name	I-Protocol
Resolution	I-Protocol
(	O
LLMNR	B-Protocol
)	O
is	O
published	O
as	O
informational	O
.	O
</s>
<s>
LLMNR	B-Protocol
is	O
included	O
in	O
every	O
Windows	O
version	O
from	O
Windows	O
Vista	O
onwards	O
and	O
acts	O
as	O
a	O
side-by-side	O
alternative	O
for	O
Microsoft	O
's	O
NetBIOS	B-Protocol
Name	O
Service	O
over	O
IPv4	O
and	O
as	O
a	O
replacement	O
over	O
IPv6	O
,	O
since	O
NetBIOS	B-Protocol
is	O
not	O
available	O
over	O
IPv6	O
.	O
</s>
<s>
Apple	O
's	O
implementation	O
is	O
available	O
as	O
the	O
Bonjour	B-Application
service	I-Application
since	O
2002	O
in	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
v10.2	I-Operating_System
.	O
</s>
<s>
The	O
Bonjour	B-Application
implementation	O
(	O
mDNSResponder	O
)	O
is	O
available	O
under	O
the	O
Apache	B-Application
2	I-Application
Open	I-Application
Source	I-Application
License	I-Application
and	O
is	O
included	O
in	O
Android	B-Application
Jelly	I-Application
Bean	I-Application
and	O
later	O
under	O
the	O
same	O
license	O
.	O
</s>
<s>
Use	O
of	O
either	O
NetBIOS	B-Protocol
or	O
LLMNR	B-Protocol
services	O
on	O
Windows	O
is	O
essentially	O
automatic	O
,	O
since	O
using	O
standard	O
DNS	B-Protocol
client	O
APIs	O
will	O
result	O
in	O
the	O
use	O
of	O
either	O
NetBIOS	B-Protocol
or	O
LLMNR	B-Protocol
depending	O
on	O
what	O
name	O
is	O
being	O
resolved	O
(	O
whether	O
the	O
name	O
is	O
a	O
local	B-Protocol
name	O
or	O
not	O
)	O
,	O
the	O
network	O
configuration	O
in	O
effect	O
(	O
e.g.	O
</s>
<s>
DNS	B-Protocol
suffixes	O
in	O
effect	O
)	O
and	O
(	O
in	O
corporate	O
networks	O
)	O
the	O
policies	O
in	O
effect	O
(	O
whether	O
LLMNR	B-Protocol
or	O
NetBIOS	B-Protocol
are	O
disabled	O
)	O
,	O
although	O
developers	O
may	O
opt	O
into	O
bypassing	O
these	O
services	O
for	O
individual	O
address	O
lookups	O
.	O
</s>
<s>
The	O
mDNS	B-Protocol
and	O
LLMNR	B-Protocol
protocols	O
have	O
minor	O
differences	O
in	O
their	O
approach	O
to	O
name	O
resolution	O
.	O
</s>
<s>
mDNS	B-Protocol
allows	O
a	O
network	O
device	O
to	O
choose	O
a	O
domain	O
name	O
in	O
the	O
local	B-Protocol
DNS	B-Protocol
namespace	O
and	O
announce	O
it	O
using	O
a	O
special	O
multicast	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
This	O
introduces	O
special	O
semantics	O
for	O
the	O
domain	O
local	B-Protocol
,	O
which	O
is	O
considered	O
a	O
problem	O
by	O
some	O
members	O
of	O
the	O
IETF	O
.	O
</s>
<s>
The	O
current	O
LLMNR	B-Protocol
draft	O
allows	O
a	O
network	O
device	O
to	O
choose	O
any	O
domain	O
name	O
,	O
which	O
is	O
considered	O
a	O
security	O
risk	O
by	O
some	O
members	O
of	O
the	O
IETF	O
.	O
</s>
<s>
mDNS	B-Protocol
is	O
compatible	O
with	O
DNS-SD	O
as	O
described	O
in	O
the	O
next	O
section	O
,	O
while	O
LLMNR	B-Protocol
is	O
not	O
.	O
</s>
<s>
Name	O
services	O
such	O
as	O
mDNS	B-Protocol
,	O
LLMNR	B-Protocol
and	O
others	O
do	O
not	O
provide	O
information	O
about	O
the	O
type	O
of	O
device	O
or	O
its	O
status	O
.	O
</s>
<s>
Service	B-Protocol
discovery	I-Protocol
provides	O
additional	O
information	O
about	O
devices	O
.	O
</s>
<s>
Service	B-Protocol
discovery	I-Protocol
is	O
sometimes	O
combined	O
with	O
a	O
name	O
service	O
,	O
as	O
in	O
Apple	O
's	O
Name	O
Binding	O
Protocol	O
and	O
Microsoft	O
's	O
NetBIOS	B-Protocol
.	O
</s>
<s>
NetBIOS	B-Protocol
on	O
Windows	O
supports	O
individual	O
hosts	O
on	O
the	O
network	O
to	O
advertise	O
services	O
,	O
such	O
as	O
file	O
shares	O
and	O
printers	O
.	O
</s>
<s>
However	O
,	O
Windows	O
clients	O
connecting	O
to	O
it	O
may	O
prefer	O
to	O
use	O
SSDP	B-Protocol
or	O
WSD	B-Protocol
using	O
NetBIOS	B-Protocol
.	O
</s>
<s>
NetBIOS	B-Protocol
is	O
one	O
of	O
the	O
providers	O
on	O
Windows	O
implementing	O
the	O
more	O
general	O
discovery	O
process	O
dubbed	O
function	O
discovery	O
which	O
includes	O
built-in	O
providers	O
for	O
PnP	O
,	O
Registry	O
,	O
NetBIOS	B-Protocol
,	O
SSDP	B-Protocol
and	O
WSD	B-Protocol
of	O
which	O
the	O
former	O
two	O
are	O
local-only	O
and	O
the	O
latter	O
three	O
support	O
discovery	O
of	O
networked	O
devices	O
.	O
</s>
<s>
None	O
of	O
these	O
need	O
any	O
configuration	O
for	O
use	O
on	O
the	O
local	B-Protocol
subnet	O
.	O
</s>
<s>
NetBIOS	B-Protocol
has	O
traditionally	O
been	O
supported	O
only	O
in	O
expensive	O
printers	O
for	O
corporate	O
use	O
though	O
some	O
entry-level	O
printers	O
with	O
Wi-Fi	O
or	O
Ethernet	O
support	O
it	O
natively	O
,	O
allowing	O
the	O
printer	O
to	O
be	O
used	O
without	O
configuration	O
even	O
on	O
very	O
old	O
operating	O
systems	O
.	O
</s>
<s>
Web	O
Services	O
Dynamic	O
Discovery	O
(	O
WS-Discovery	O
)	O
is	O
a	O
technical	O
specification	O
that	O
defines	O
a	O
multicast	O
discovery	O
protocol	O
to	O
locate	O
services	O
on	O
a	O
local	B-General_Concept
network	I-General_Concept
.	O
</s>
<s>
Windows	O
supports	O
it	O
in	O
the	O
form	O
of	O
Web	B-Protocol
Services	I-Protocol
for	I-Protocol
Devices	I-Protocol
and	O
Devices	B-Protocol
Profile	I-Protocol
for	I-Protocol
Web	I-Protocol
Services	I-Protocol
.	O
</s>
<s>
allows	O
clients	O
to	O
discover	O
a	O
named	O
list	O
of	O
service	O
instances	O
and	O
to	O
resolve	O
those	O
services	O
to	O
hostnames	B-Protocol
using	O
standard	O
DNS	B-Protocol
queries	I-Protocol
.	O
</s>
<s>
The	O
specification	O
is	O
compatible	O
with	O
existing	O
unicast	O
DNS	B-Protocol
server	O
and	O
client	O
software	O
,	O
but	O
works	O
equally	O
well	O
with	O
mDNS	B-Protocol
in	O
a	O
zero-configuration	B-Application
environment	O
.	O
</s>
<s>
Each	O
service	O
instance	O
is	O
described	O
using	O
a	O
DNS	B-Protocol
SRV	I-Protocol
and	O
DNS	B-Protocol
TXT	I-Protocol
record	O
.	O
</s>
<s>
A	O
client	O
discovers	O
the	O
list	O
of	O
available	O
instances	O
for	O
a	O
given	O
service	O
type	O
by	O
querying	O
the	O
DNS	B-Protocol
PTR	O
record	O
of	O
that	O
service	O
type	O
's	O
name	O
;	O
the	O
server	O
returns	O
zero	O
or	O
more	O
names	O
of	O
the	O
form	O
Service.Domain	O
,	O
each	O
corresponding	O
to	O
a	O
SRV/TXT	O
record	O
pair	O
.	O
</s>
<s>
The	O
SRV	B-Protocol
record	I-Protocol
resolves	O
to	O
the	O
domain	O
name	O
providing	O
the	O
instance	O
,	O
while	O
the	O
TXT	B-Protocol
can	O
contain	O
service-specific	O
configuration	O
parameters	O
.	O
</s>
<s>
A	O
service	O
type	O
registry	O
was	O
originally	O
maintained	O
by	O
DNS-SD.org,	O
but	O
has	O
since	O
been	O
merged	O
into	O
IANA	O
's	O
registry	O
for	O
DNS	B-Protocol
SRV	I-Protocol
records	O
.	O
</s>
<s>
In	O
1997	O
Stuart	O
Cheshire	O
proposed	O
adapting	O
Apple	O
's	O
mature	O
Name	O
Binding	O
Protocol	O
to	O
IP	B-Protocol
networks	I-Protocol
to	O
address	O
the	O
lack	O
of	O
service	B-Protocol
discovery	I-Protocol
capability	O
.	O
</s>
<s>
Cheshire	O
subsequently	O
joined	O
Apple	O
and	O
authored	O
IETF	O
draft	O
proposals	O
for	O
mDNS	B-Protocol
and	O
DNS-based	O
Service	B-Protocol
Discovery	I-Protocol
,	O
supporting	O
the	O
transition	O
from	O
AppleTalk	B-Application
to	O
IP	O
networking	O
.	O
</s>
<s>
In	O
2002	O
,	O
Apple	O
announced	O
an	O
implementation	O
of	O
both	O
protocols	O
under	O
the	O
name	O
Rendezvous	O
(	O
later	O
renamed	O
Bonjour	B-Application
)	O
.	O
</s>
<s>
It	O
was	O
first	O
included	O
in	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
10.2	I-Operating_System
,	O
replacing	O
the	O
Service	B-Protocol
Location	I-Protocol
Protocol	I-Protocol
(	O
SLP	O
)	O
used	O
in	O
10.1	B-Operating_System
.	O
</s>
<s>
mDNS	B-Protocol
uses	O
packets	B-Protocol
similar	O
to	O
unicast	O
DNS	B-Protocol
to	O
resolve	O
hostnames	B-Protocol
except	O
they	O
are	O
sent	O
over	O
a	O
multicast	O
link	O
.	O
</s>
<s>
Each	O
host	O
listens	O
on	O
the	O
mDNS	B-Protocol
port	O
,	O
5353	O
,	O
transmitted	O
to	O
a	O
well-known	O
multicast	O
address	O
and	O
resolves	O
requests	O
for	O
the	O
DNS	B-Protocol
record	O
of	O
its	O
.local	B-Protocol
hostname	B-Protocol
(	O
e.g.	O
</s>
<s>
the	O
A	O
,	O
AAAA	O
,	O
CNAME	B-Protocol
)	O
to	O
its	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
When	O
an	O
mDNS	B-Protocol
client	O
needs	O
to	O
resolve	O
a	O
local	B-Protocol
hostname	B-Protocol
to	O
an	O
IP	B-Protocol
address	I-Protocol
,	O
it	O
sends	O
a	O
DNS	B-Protocol
request	O
for	O
that	O
name	O
to	O
the	O
well-known	O
multicast	O
address	O
;	O
the	O
computer	O
with	O
the	O
corresponding	O
A/AAAA	O
record	O
replies	O
with	O
its	O
IP	B-Protocol
address	I-Protocol
.	O
</s>
<s>
The	O
mDNS	B-Protocol
multicast	O
address	O
is	O
for	O
IPv4	O
and	O
for	O
IPv6	O
link-local	B-Protocol
addressing	I-Protocol
.	O
</s>
<s>
DNS	B-Protocol
Service	B-Protocol
Discovery	I-Protocol
(	O
DNS-SD	O
)	O
requests	O
can	O
also	O
be	O
sent	O
using	O
mDNS	B-Protocol
to	O
yield	O
zero-configuration	B-Application
DNS-SD	O
.	O
</s>
<s>
This	O
uses	O
DNS	B-Protocol
PTR	O
,	O
SRV	O
,	O
TXT	B-Protocol
records	I-Protocol
to	O
advertise	O
instances	O
of	O
service	O
types	O
,	O
domain	O
names	O
for	O
those	O
instances	O
,	O
and	O
optional	O
configuration	O
parameters	O
for	O
connecting	O
to	O
those	O
instances	O
.	O
</s>
<s>
But	O
SRV	B-Protocol
records	I-Protocol
can	O
now	O
resolve	O
to	O
.local	B-Protocol
domain	O
names	O
,	O
which	O
mDNS	B-Protocol
can	O
resolve	O
to	O
local	B-Protocol
IP	B-Protocol
addresses	I-Protocol
.	O
</s>
<s>
DNS-SD	O
is	O
used	O
by	O
Apple	O
products	O
,	O
most	O
network	O
printers	O
,	O
many	O
Linux	B-Application
distributions	O
including	O
Debian	O
and	O
Ubuntu	B-Operating_System
,	O
and	O
a	O
number	O
of	O
third-party	O
products	O
for	O
various	O
operating	O
systems	O
.	O
</s>
<s>
For	O
example	O
,	O
many	O
OS	B-Operating_System
X	I-Operating_System
network	O
applications	O
written	O
by	O
Apple	O
,	O
including	O
Safari	B-Application
,	O
iChat	B-Protocol
,	O
and	O
Messages	B-Protocol
,	O
can	O
use	O
DNS-SD	O
to	O
locate	O
nearby	O
servers	O
and	O
peer-to-peer	O
clients	O
.	O
</s>
<s>
Windows	O
10	O
includes	O
support	O
for	O
DNS-SD	O
for	O
applications	O
written	O
using	O
JavaScript	O
.	O
</s>
<s>
Individual	O
applications	O
may	O
include	O
their	O
own	O
support	O
in	O
older	O
versions	O
of	O
the	O
operating	O
system	O
,	O
such	O
that	O
most	O
instant	O
messaging	O
and	O
VoIP	B-Application
clients	O
on	O
Windows	O
support	O
DNS-SD	O
.	O
</s>
<s>
Some	O
Unix	B-Application
,	O
BSD	B-Operating_System
,	O
and	O
Linux	B-Application
distributions	O
also	O
include	O
DNS-SD	O
.	O
</s>
<s>
For	O
example	O
,	O
Ubuntu	B-Operating_System
ships	O
Avahi	B-Language
,	O
an	O
mDNS/DNS	B-Protocol
-SD	I-Protocol
implementation	O
,	O
in	O
its	O
base	O
distribution	O
.	O
</s>
<s>
UPnP	B-Application
has	O
some	O
protocol	O
components	O
with	O
the	O
purpose	O
of	O
service	B-Protocol
discovery	I-Protocol
.	O
</s>
<s>
Simple	B-Protocol
Service	I-Protocol
Discovery	I-Protocol
Protocol	I-Protocol
(	O
SSDP	B-Protocol
)	O
is	O
a	O
UPnP	B-Application
protocol	O
,	O
used	O
in	O
Windows	B-Application
XP	I-Application
and	O
later	O
.	O
</s>
<s>
SSDP	B-Protocol
uses	O
HTTP	O
notification	O
announcements	O
that	O
give	O
a	O
service-type	O
URI	B-Protocol
and	O
a	O
Unique	O
Service	O
Name	O
(	O
USN	O
)	O
.	O
</s>
<s>
Service	O
types	O
are	O
regulated	O
by	O
the	O
Universal	B-Application
Plug	I-Application
and	I-Application
Play	I-Application
Steering	O
Committee	O
.	O
</s>
<s>
SSDP	B-Protocol
is	O
supported	O
by	O
many	O
printer	O
,	O
NAS	O
and	O
appliance	O
manufacturers	O
such	O
as	O
Brother	O
.	O
</s>
<s>
Digital	O
Living	O
Network	O
Alliance	O
(	O
DLNA	O
)	O
is	O
another	O
suite	O
of	O
standards	O
that	O
uses	O
UPnP	B-Application
for	O
the	O
discovery	O
of	O
networked	O
devices	O
.	O
</s>
<s>
DLNA	O
service	B-Protocol
discovery	I-Protocol
is	O
layered	O
on	O
top	O
of	O
SSDP	B-Protocol
.	O
</s>
<s>
SLP	O
is	O
described	O
in	O
and	O
and	O
implementations	O
are	O
available	O
for	O
both	O
Solaris	B-Application
and	O
Linux	B-Application
.	O
</s>
<s>
AllJoyn	B-Device
is	O
an	O
open-source	B-Application
software	I-Application
stack	O
for	O
a	O
myriad	O
of	O
devices	O
,	O
ranging	O
from	O
IoT	O
devices	O
to	O
full-size	O
computers	O
,	O
for	O
discovery	O
and	O
control	O
of	O
devices	O
on	O
networks	O
(	O
Wifi	O
,	O
Ethernet	O
)	O
and	O
other	O
links	O
(	O
Bluetooth	O
,	O
ZigBee	O
,	O
etc	O
.	O
)	O
.	O
</s>
<s>
It	O
uses	O
mDNS	B-Protocol
and	O
HTTP	O
over	O
UDP	O
and	O
other	O
protocols	O
.	O
</s>
<s>
,	O
the	O
SLP	O
standard	O
for	O
figuring	O
out	O
where	O
to	O
get	O
services	O
,	O
was	O
published	O
in	O
June	O
1999	O
by	O
the	O
SVRLOC	B-Protocol
IETF	O
working	O
group	O
.	O
</s>
<s>
,	O
a	O
standard	O
for	O
choosing	O
addresses	O
for	O
networked	O
items	O
,	O
was	O
published	O
in	O
March	O
2005	O
by	O
the	O
IETF	O
Zeroconf	B-Application
working	O
group	O
.	O
</s>
<s>
LLMNR	B-Protocol
was	O
submitted	O
for	O
official	O
adoption	O
in	O
the	O
IETF	O
DNSEXT	O
working	O
group	O
,	O
however	O
,	O
failed	O
to	O
gain	O
consensus	O
and	O
thus	O
was	O
published	O
as	O
informational	O
in	O
January	O
2007	O
.	O
</s>
<s>
Following	O
the	O
failure	O
of	O
LLMNR	B-Protocol
to	O
become	O
an	O
Internet	O
standard	O
and	O
given	O
that	O
mDNS/DNS	B-Protocol
-SD	I-Protocol
is	O
used	O
much	O
more	O
widely	O
than	O
LLMNR	B-Protocol
,	O
Apple	O
was	O
asked	O
by	O
the	O
IETF	O
to	O
submit	O
the	O
mDNS/DNS	B-Protocol
-SD	I-Protocol
specs	O
for	O
publication	O
as	O
Informational	O
RFC	O
as	O
well	O
.	O
</s>
<s>
In	O
February	O
2013	O
mDNS	B-Protocol
and	O
DNS-SD	O
were	O
published	O
as	O
Standards	O
Track	O
Proposals	O
and	O
.	O
</s>
<s>
Because	O
mDNS	B-Protocol
operates	O
under	O
a	O
different	O
trust	O
model	O
than	O
unicast	O
DNS	B-Protocol
—	O
trusting	O
the	O
entire	O
network	O
rather	O
than	O
a	O
designated	O
DNS	B-Protocol
server	O
,	O
it	O
is	O
vulnerable	O
to	O
spoofing	O
attacks	O
by	O
any	O
system	O
within	O
the	O
same	O
broadcast	B-Architecture
domain	I-Architecture
.	O
</s>
<s>
Like	O
SNMP	B-Protocol
and	O
many	O
other	O
network	O
management	O
protocols	O
,	O
it	O
can	O
also	O
be	O
used	O
by	O
attackers	O
to	O
quickly	O
gain	O
detailed	O
knowledge	O
of	O
the	O
network	O
and	O
its	O
machines	O
.	O
</s>
<s>
via	O
RSA	B-Architecture
,	O
SSH	B-Protocol
,	O
etc	O
.	O
)	O
</s>
<s>
after	O
discovering	O
and	O
resolving	O
them	O
through	O
DNS-SD/mDNS	O
.	O
</s>
<s>
LLMNR	B-Protocol
suffers	O
from	O
similar	O
vulnerabilities	O
.	O
</s>
<s>
Bonjour	B-Application
from	O
Apple	O
,	O
uses	O
mDNS	B-Protocol
and	O
DNS	B-Protocol
Service	B-Protocol
Discovery	I-Protocol
.	O
</s>
<s>
Apple	O
changed	O
its	O
preferred	O
zeroconf	B-Application
technology	O
from	O
SLP	O
to	O
mDNS	B-Protocol
and	O
DNS-SD	O
between	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
10.1	I-Operating_System
and	O
10.2	B-Operating_System
,	O
though	O
SLP	O
continues	O
to	O
be	O
supported	O
by	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
.	O
</s>
<s>
Apple	O
's	O
mDNSResponder	O
has	O
interfaces	O
for	O
C	B-Language
and	O
Java	B-Language
and	O
is	O
available	O
on	O
BSD	B-Operating_System
,	O
Apple	B-Operating_System
Mac	I-Operating_System
OS	I-Operating_System
X	I-Operating_System
,	O
Linux	B-Application
,	O
other	O
POSIX	O
based	O
operating	O
systems	O
and	O
MS	O
Windows	O
.	O
</s>
<s>
Avahi	B-Language
is	O
a	O
Zeroconf	B-Application
implementation	O
for	O
Linux	B-Application
and	O
BSDs	B-Operating_System
.	O
</s>
<s>
It	O
implements	O
IPv4LL	B-Protocol
,	O
mDNS	B-Protocol
and	O
DNS-SD	O
.	O
</s>
<s>
It	O
is	O
part	O
of	O
most	O
Linux	B-Application
distributions	O
,	O
and	O
is	O
installed	O
by	O
default	O
on	O
some	O
.	O
</s>
<s>
If	O
run	O
in	O
conjunction	O
with	O
nss-mdns	O
,	O
it	O
also	O
offers	O
host	B-Protocol
name	I-Protocol
resolution	O
.	O
</s>
<s>
Avahi	B-Language
also	O
implements	O
binary	O
compatibility	O
libraries	O
that	O
emulate	O
Bonjour	B-Application
and	O
the	O
historical	O
mDNS	B-Protocol
implementation	O
Howl	B-Application
,	O
so	O
software	O
made	O
to	O
use	O
those	O
implementations	O
can	O
also	O
utilize	O
Avahi	B-Language
through	O
the	O
emulation	O
interfaces	O
.	O
</s>
<s>
Microsoft	B-Operating_System
Windows	I-Operating_System
CE	I-Operating_System
5.0	O
includes	O
Microsoft	O
's	O
own	O
implementation	O
of	O
LLMNR	B-Protocol
.	O
</s>
<s>
Systemd	B-Application
implements	O
both	O
mDNS	B-Protocol
and	O
LLMNR	B-Protocol
in	O
systemd-resolved	B-Application
.	O
</s>
<s>
Where	O
no	O
DHCP	B-Protocol
server	I-Protocol
is	O
available	O
to	O
assign	O
a	O
host	O
an	O
IP	B-Protocol
address	I-Protocol
,	O
the	O
host	O
can	O
select	O
its	O
own	O
link-local	B-Protocol
address	I-Protocol
.	O
</s>
<s>
Using	O
a	O
link-local	B-Protocol
address	I-Protocol
,	O
hosts	O
can	O
communicate	O
over	O
this	O
link	O
but	O
only	O
locally	O
;	O
Access	O
to	O
other	O
networks	O
and	O
the	O
Internet	O
is	O
not	O
possible	O
.	O
</s>
<s>
There	O
are	O
some	O
link-local	O
IPv4	O
address	O
implementations	O
available	O
:	O
</s>
<s>
Apple	B-Device
Mac	I-Device
OS	O
and	O
MS	O
Windows	O
have	O
supported	O
link-local	O
addresses	O
since	O
Windows	B-Device
98	I-Device
and	O
Mac	B-Device
OS	O
8.5	O
(	O
both	O
released	O
in	O
1998	O
)	O
.	O
</s>
<s>
Apple	O
released	O
its	O
open-source	B-Application
implementation	O
in	O
the	O
Darwin	B-Operating_System
bootp	O
package	O
.	O
</s>
<s>
Avahi	B-Language
contains	O
an	O
implementation	O
of	O
IPv4LL	B-Protocol
in	O
the	O
avahi-autoipd	O
tool	O
.	O
</s>
<s>
BusyBox	B-Application
can	O
embed	O
a	O
simple	O
IPv4LL	B-Protocol
implementation	O
.	O
</s>
<s>
Stablebox	O
,	O
a	O
fork	O
from	O
Busybox	B-Application
,	O
offers	O
a	O
slightly	O
modified	O
IPv4LL	B-Protocol
implementation	O
named	O
llad	O
.	O
</s>
<s>
Zeroconf	B-Application
is	O
a	O
package	O
based	O
on	O
Simple	O
IPv4LL	B-Protocol
,	O
a	O
shorter	O
implementation	O
by	O
Arthur	O
van	O
Hoff	O
.	O
</s>
<s>
The	O
above	O
implementations	O
are	O
all	O
stand-alone	O
daemons	O
or	O
plugins	O
for	O
DHCP	B-Protocol
clients	O
that	O
only	O
deal	O
with	O
link-local	O
IP	B-Protocol
addresses	I-Protocol
.	O
</s>
<s>
Another	O
approach	O
is	O
to	O
include	O
support	O
in	O
new	O
or	O
existing	O
DHCP	B-Protocol
clients	O
:	O
</s>
<s>
dhcpcd	O
is	O
an	O
open	B-Application
source	I-Application
DHCP	B-Protocol
client	O
for	O
Linux	B-Application
and	O
BSD	B-Operating_System
that	O
includes	O
IPv4LL	B-Protocol
support	O
.	O
</s>
<s>
It	O
is	O
included	O
as	O
standard	O
in	O
NetBSD	B-Device
.	O
</s>
