<s>
The	O
Service	B-Protocol
Location	I-Protocol
Protocol	I-Protocol
(	O
SLP	O
,	O
srvloc	O
)	O
is	O
a	O
service	B-Protocol
discovery	I-Protocol
protocol	I-Protocol
that	O
allows	O
computers	O
and	O
other	O
devices	O
to	O
find	O
services	O
in	O
a	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
without	O
prior	O
configuration	O
.	O
</s>
<s>
SLP	O
is	O
used	O
by	O
devices	O
to	O
announce	O
services	O
on	O
a	O
local	B-General_Concept
network	I-General_Concept
.	O
</s>
<s>
The	O
protocol	O
used	O
by	O
the	O
printer	O
is	O
LPR	B-Protocol
.	O
</s>
<s>
The	O
first	O
three	O
components	O
of	O
the	O
"	O
service	O
:	O
"	O
URL	O
type	O
(	O
"	O
service:printer:lpr	O
"	O
)	O
are	O
also	O
called	O
service	O
type	O
.	O
</s>
<s>
The	O
query	O
can	O
be	O
combined	O
with	O
a	O
query	O
for	O
attributes	O
,	O
using	O
LDAP	B-Protocol
's	O
query	O
language	O
.	O
</s>
<s>
Today	O
most	O
implementations	O
are	O
daemons	B-Operating_System
that	O
can	O
act	O
both	O
as	O
UA	O
and	O
SA	O
.	O
</s>
<s>
Most	O
packets	O
are	O
transmitted	O
using	O
UDP	B-Protocol
,	O
but	O
TCP	B-Protocol
can	O
also	O
be	O
used	O
for	O
the	O
transmission	O
of	O
longer	O
packets	O
.	O
</s>
<s>
Because	O
of	O
the	O
potential	O
unreliability	O
of	O
UDP	B-Protocol
,	O
SLP	O
repeats	O
all	O
multicasts	O
several	O
times	O
in	O
increasing	O
intervals	O
until	O
an	O
answer	O
has	O
been	O
received	O
.	O
</s>
<s>
All	O
devices	O
are	O
required	O
to	O
listen	O
on	O
port	O
427	O
for	O
UDP	B-Protocol
packets	I-Protocol
,	O
SAs	O
and	O
DAs	O
should	O
also	O
listen	O
for	O
TCP	B-Protocol
on	O
the	O
same	O
port	O
.	O
</s>
<s>
In	O
order	O
to	O
send	O
a	O
query	O
in	O
a	O
network	O
without	O
a	O
DA	O
,	O
the	O
UA	O
sends	O
a	O
multicast	O
UDP	B-Protocol
packet	I-Protocol
that	O
contains	O
the	O
query	O
.	O
</s>
<s>
All	O
SAs	O
that	O
contain	O
matches	O
will	O
send	O
a	O
UDP	B-Protocol
answer	O
to	O
the	O
UA	O
.	O
</s>
<s>
If	O
the	O
answer	O
is	O
too	O
large	O
to	O
fit	O
into	O
a	O
single	O
UDP	B-Protocol
packet	I-Protocol
,	O
the	O
packet	O
will	O
be	O
marked	O
as	O
"	O
overflown	O
"	O
and	O
the	O
UA	O
is	O
free	O
to	O
send	O
the	O
query	O
directly	O
to	O
the	O
SA	O
using	O
TCP	B-Protocol
,	O
which	O
can	O
transmit	O
packets	O
of	O
any	O
size	O
.	O
</s>
<s>
In	O
order	O
to	O
send	O
a	O
query	O
in	O
a	O
network	O
with	O
a	O
DA	O
,	O
the	O
UA	O
will	O
send	O
the	O
query	O
packet	O
to	O
the	O
DA	O
using	O
either	O
UDP	B-Protocol
or	O
TCP	B-Protocol
.	O
</s>
<s>
SLP	O
contains	O
a	O
public-key	B-Application
cryptography	I-Application
based	O
security	O
mechanism	O
that	O
allows	O
signing	O
of	O
service	O
announcements	O
.	O
</s>
<s>
The	O
public	B-Application
keys	I-Application
of	O
every	O
service	O
provider	O
must	O
be	O
installed	O
on	O
every	O
UA	O
.	O
</s>
<s>
Service	O
URLs	O
contain	O
host	O
names	O
or	O
IP	O
addresses	O
,	O
and	O
in	O
a	O
local	B-General_Concept
network	I-General_Concept
it	O
is	O
almost	O
impossible	O
to	O
prevent	O
IP	O
or	O
DNS	O
spoofing	O
.	O
</s>
<s>
with	O
SSL	B-Protocol
)	O
or	O
in	O
the	O
packet	O
layer	O
(	O
IPsec	B-Protocol
)	O
.	O
</s>
<s>
SLP	O
is	O
often	O
found	O
in	O
LAN-enabled	O
printers	O
,	O
so	O
that	O
they	O
are	O
discoverable	O
out	O
of	O
the	O
box	O
.	O
</s>
<s>
The	O
classic	B-Application
Mac	I-Application
OS	I-Application
,	O
and	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
up	O
to	O
version	O
10.1	O
,	O
used	O
SLP	O
to	O
locate	O
file	O
shares	O
and	O
other	O
services	O
.	O
</s>
<s>
However	O
,	O
features	O
introduced	O
with	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
(	O
version	O
10.2	O
onwards	O
)	O
use	O
Zeroconf	B-Application
.	O
</s>
<s>
Netware	B-Protocol
Core	I-Protocol
Protocol	I-Protocol
(	O
NCP	O
)	O
clients	O
in	O
a	O
pure	O
IP	O
environment	O
use	O
SLP	O
to	O
locate	O
Novell	B-Operating_System
NetWare	I-Operating_System
and	O
Novell	B-Application
Open	I-Application
Enterprise	I-Application
Server	I-Application
(	O
OES	B-Application
)	O
servers	O
.	O
</s>
<s>
The	O
Storage	O
Networking	O
Industry	O
Association	O
has	O
mandated	O
the	O
use	O
of	O
SLP	O
for	O
services	O
discovery	O
in	O
the	O
Storage	B-General_Concept
Management	I-General_Concept
Initiative	I-General_Concept
-	I-General_Concept
Specification	I-General_Concept
.	O
</s>
