<s>
Internet	B-Protocol
Protocol	I-Protocol
networks	O
to	O
automatically	O
assign	O
an	O
IP	B-Protocol
address	I-Protocol
to	O
network	O
devices	O
from	O
a	O
configuration	O
server	O
.	O
</s>
<s>
The	O
BOOTP	B-Device
was	O
originally	O
defined	O
in	O
RFC	O
951	O
.	O
</s>
<s>
While	O
some	O
parts	O
of	O
BOOTP	B-Device
have	O
been	O
effectively	O
superseded	O
by	O
the	O
Dynamic	B-Protocol
Host	I-Protocol
Configuration	I-Protocol
Protocol	I-Protocol
(	O
DHCP	B-Protocol
)	O
,	O
which	O
adds	O
the	O
feature	O
of	O
leases	O
,	O
parts	O
of	O
BOOTP	B-Device
are	O
used	O
to	O
provide	O
service	O
to	O
the	O
DHCP	B-Protocol
protocol	O
.	O
</s>
<s>
DHCP	B-Protocol
servers	I-Protocol
also	O
provide	O
the	O
legacy	O
BOOTP	B-Device
functionality	O
.	O
</s>
<s>
When	O
a	O
network-connected	O
computer	O
boots	B-Operating_System
up	O
,	O
its	O
IP	O
stack	O
broadcasts	O
BOOTP	B-Device
network	O
messages	O
requesting	O
an	O
IP-address	B-Protocol
assignment	O
.	O
</s>
<s>
A	O
BOOTP	B-Device
configuration-server	O
replies	O
to	O
the	O
request	O
by	O
assigning	O
an	O
IP	B-Protocol
address	I-Protocol
from	O
a	O
pool	O
of	O
addresses	O
,	O
which	O
is	O
preconfigured	O
by	O
an	O
administrator	O
.	O
</s>
<s>
BOOTP	B-Device
is	O
implemented	O
using	O
the	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
for	O
transport	O
protocol	O
,	O
port	O
number	O
67	O
is	O
used	O
by	O
the	O
(	O
DHCP	B-Protocol
)	O
server	O
for	O
receiving	O
client-requests	O
and	O
port	O
number	O
68	O
is	O
used	O
by	O
the	O
client	O
for	O
receiving	O
(	O
DHCP	B-Protocol
)	O
server	O
responses	O
.	O
</s>
<s>
BOOTP	B-Device
operates	O
only	O
on	O
IPv4	B-Protocol
networks	I-Protocol
.	O
</s>
<s>
Historically	O
,	O
BOOTP	B-Device
has	O
also	O
been	O
used	O
for	O
Unix-like	B-Operating_System
diskless	B-Device
workstations	I-Device
to	O
obtain	O
the	O
network	O
location	O
of	O
their	O
boot	B-Operating_System
image	I-Operating_System
,	O
in	O
addition	O
to	O
the	O
IP	B-Protocol
address	I-Protocol
assignment	O
.	O
</s>
<s>
Enterprises	O
used	O
it	O
to	O
roll	O
out	O
a	O
pre-configured	O
client	O
(	O
e.g.	O
,	O
Windows	B-Application
)	O
installation	O
to	O
newly	O
installed	O
PCs	O
.	O
</s>
<s>
Initially	O
requiring	O
the	O
use	O
of	O
a	O
boot	B-Operating_System
floppy	B-Device
disk	I-Device
to	O
establish	O
the	O
initial	O
network	O
connection	O
,	O
manufacturers	O
of	O
network	O
cards	O
later	O
embedded	O
the	O
protocol	O
in	O
the	O
BIOS	B-Operating_System
of	O
the	O
interface	O
cards	O
as	O
well	O
as	O
system	O
boards	O
with	O
on-board	O
network	O
adapters	O
,	O
thus	O
allowing	O
direct	O
network	O
booting	B-Operating_System
.	O
</s>
<s>
The	O
BOOTP	B-Device
was	O
first	O
defined	O
in	O
September	O
1985	O
in	O
RFC	O
951	O
as	O
a	O
replacement	O
for	O
the	O
Reverse	B-Protocol
Address	I-Protocol
Resolution	I-Protocol
Protocol	I-Protocol
RARP	B-Protocol
,	O
published	O
in	O
RFC	O
903	O
in	O
June	O
1984	O
.	O
</s>
<s>
The	O
primary	O
motivation	O
for	O
replacing	O
RARP	B-Protocol
with	O
BOOTP	B-Device
is	O
that	O
RARP	B-Protocol
was	O
a	O
link	B-Protocol
layer	I-Protocol
protocol	O
.	O
</s>
<s>
This	O
made	O
implementation	O
difficult	O
on	O
many	O
server	O
platforms	O
,	O
and	O
required	O
that	O
a	O
server	O
be	O
present	O
on	O
each	O
individual	O
IP	B-Protocol
subnet	I-Protocol
.	O
</s>
<s>
BOOTP	B-Device
introduced	O
the	O
innovation	O
of	O
relay	O
agents	O
,	O
which	O
forwarded	O
BOOTP	B-Device
packets	O
from	O
the	O
local	O
network	O
using	O
standard	O
IP	O
routing	O
,	O
so	O
that	O
one	O
central	O
BOOTP	B-Device
server	O
could	O
serve	O
hosts	O
on	O
many	O
subnets	B-Protocol
.	O
</s>
<s>
When	O
a	O
BOOTP	B-Device
client	O
is	O
started	O
,	O
it	O
has	O
no	O
IP	B-Protocol
address	I-Protocol
,	O
so	O
it	O
broadcasts	O
a	O
message	O
containing	O
its	O
MAC	O
address	O
onto	O
the	O
network	O
.	O
</s>
<s>
This	O
message	O
is	O
called	O
a	O
“	O
BOOTP	B-Device
request	O
”	O
,	O
and	O
it	O
is	O
picked	O
up	O
by	O
the	O
BOOTP	B-Device
server	O
,	O
which	O
replies	O
to	O
the	O
client	O
with	O
the	O
following	O
information	O
that	O
the	O
client	O
needs	O
:	O
</s>
<s>
The	O
client	O
’s	O
IP	B-Protocol
address	I-Protocol
,	O
subnet	B-Protocol
mask	I-Protocol
,	O
and	O
default	O
gateway	O
address	O
.	O
</s>
<s>
The	O
IP	B-Protocol
address	I-Protocol
and	O
host	O
name	O
of	O
the	O
BOOTP	B-Device
server	O
.	O
</s>
<s>
The	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
server	O
that	O
has	O
the	O
boot	B-Operating_System
image	I-Operating_System
,	O
which	O
the	O
client	O
needs	O
to	O
load	O
its	O
operating	O
system	O
.	O
</s>
<s>
When	O
the	O
client	O
receives	O
this	O
information	O
from	O
the	O
BOOTP	B-Device
server	O
,	O
it	O
configures	O
and	O
initializes	O
its	O
TCP/IP	O
protocol	O
stack	O
,	O
and	O
then	O
connects	O
to	O
the	O
server	O
on	O
which	O
the	O
boot	B-Operating_System
image	I-Operating_System
is	O
shared	O
.	O
</s>
<s>
The	O
client	O
loads	O
the	O
boot	B-Operating_System
image	I-Operating_System
and	O
uses	O
this	O
information	O
to	O
load	O
and	O
start	O
its	O
operating	O
system	O
.	O
</s>
<s>
The	O
Dynamic	B-Protocol
Host	I-Protocol
Configuration	I-Protocol
Protocol	I-Protocol
(	O
DHCP	B-Protocol
)	O
was	O
developed	O
as	O
an	O
extension	O
of	O
BOOTP	B-Device
.	O
</s>
<s>
BOOTP	B-Device
is	O
defined	O
in	O
Request	O
for	O
Comments	O
(	O
RFC	O
)	O
951	O
and	O
1084	O
.	O
</s>
<s>
Problem	O
with	O
the	O
bootp	B-Device
request	O
is	O
that	O
the	O
request	O
is	O
broadcast	O
.	O
</s>
<s>
The	O
relay	O
agent	O
knows	O
the	O
uni-cast	O
address	O
of	O
bootp	B-Device
server	O
and	O
listens	O
for	O
broadcast	O
message	O
on	O
port	O
67	O
.	O
</s>
<s>
When	O
it	O
receives	O
this	O
broadcast	O
packet	O
,	O
it	O
encapsulates	O
the	O
message	O
in	O
unicast	B-Protocol
datagram	O
and	O
sends	O
request	O
to	O
bootp	B-Device
server	O
.	O
</s>
<s>
The	O
packet	O
carrying	O
a	O
unicast	B-Protocol
destination	O
address	O
is	O
routed	O
by	O
any	O
router	O
and	O
reaches	O
the	O
bootp	B-Device
server	O
.	O
</s>
<s>
The	O
relay	O
agent	O
,	O
after	O
receiving	O
the	O
reply	O
,	O
sends	O
it	O
to	O
bootp	B-Device
client	O
.	O
</s>
