<s>
Link	B-Protocol
State	I-Protocol
Packet	I-Protocol
(	O
LSP	O
)	O
is	O
a	O
packet	B-Protocol
of	O
information	O
generated	O
by	O
a	O
network	B-Protocol
router	I-Protocol
in	O
a	O
link	B-Protocol
state	I-Protocol
routing	I-Protocol
protocol	I-Protocol
that	O
lists	O
the	O
router	B-Protocol
's	O
neighbors	O
.	O
</s>
<s>
Link	B-Protocol
state	I-Protocol
packets	I-Protocol
can	O
be	O
further	O
defined	O
as	O
special	O
datagrams	O
that	O
determine	O
the	O
names	O
of	O
and	O
the	O
cost	O
or	O
distance	O
to	O
any	O
neighboring	O
routers	B-Protocol
and	O
associated	O
networks	B-Architecture
.	O
</s>
<s>
When	O
Information	O
needed	O
for	O
exchange	O
is	O
collected	O
,	O
a	O
router	B-Protocol
then	O
builds	O
a	O
packet	B-Protocol
containing	O
all	O
the	O
data	O
.	O
</s>
<s>
The	O
packet	B-Protocol
starts	O
with	O
the	O
identity	O
of	O
the	O
sender	O
,	O
followed	O
by	O
a	O
sequence	B-Protocol
number	I-Protocol
and	O
age	O
,	O
and	O
a	O
list	O
of	O
neighbors	O
.	O
</s>
<s>
Building	O
a	O
link	B-Protocol
state	I-Protocol
packet	I-Protocol
is	O
usually	O
easy	O
,	O
the	O
complex	O
part	O
is	O
determining	O
when	O
to	O
build	O
them	O
.	O
</s>
<s>
A	O
major	O
procedure	O
called	O
flooding	B-Protocol
which	O
is	O
used	O
for	O
distributing	O
link	B-Protocol
state	I-Protocol
algorithms	O
throughout	O
the	O
routing	O
domain	O
can	O
be	O
implemented	O
with	O
link	B-Protocol
state	I-Protocol
packets	I-Protocol
.	O
</s>
<s>
However	O
,	O
ordinary	O
flooding	B-Protocol
may	O
result	O
in	O
problems	O
,	O
because	O
it	O
generates	O
exponential	O
behavior	O
.	O
</s>
<s>
Smart	O
flooding	B-Protocol
,	O
on	O
the	O
other	O
hand	O
,	O
recognizes	O
link	B-Protocol
state	I-Protocol
packets	I-Protocol
appropriately	O
.	O
</s>
<s>
Link	B-Protocol
state	I-Protocol
packets	I-Protocol
are	O
usually	O
implemented	O
with	O
Open	B-Protocol
Shortest	I-Protocol
Path	I-Protocol
First	I-Protocol
(	O
OSPF	B-Protocol
)	O
protocol	O
.	O
</s>
<s>
OSPF	B-Protocol
's	O
reliable	O
flooding	B-Protocol
mechanism	O
is	O
implemented	O
by	O
Link	B-Protocol
State	I-Protocol
Update	O
and	O
Link	B-Protocol
State	I-Protocol
Acknowledgment	O
packets	B-Protocol
.	O
</s>
<s>
Link	B-Protocol
State	I-Protocol
Update	O
packets	B-Protocol
are	O
OSPF	B-Protocol
packet	B-Protocol
type	O
4	O
.	O
</s>
<s>
These	O
packets	B-Protocol
implement	O
the	O
flooding	B-Protocol
of	O
link	B-Protocol
state	I-Protocol
advertisements	O
.	O
</s>
<s>
Each	O
Link	B-Protocol
State	I-Protocol
Update	O
packet	B-Protocol
carries	O
a	O
collection	O
of	O
link	B-Protocol
state	I-Protocol
advertisements	O
one	O
hop	O
further	O
from	O
its	O
origin	O
.	O
</s>
<s>
Several	O
link-state	B-Protocol
advertisement	I-Protocol
may	O
be	O
included	O
in	O
a	O
single	O
packet	B-Protocol
.	O
</s>
<s>
Link	B-Protocol
State	I-Protocol
Update	O
packets	B-Protocol
are	O
multicast	O
on	O
those	O
physical	O
networks	B-Architecture
that	O
support	O
multicast/broadcast	O
.	O
</s>
<s>
In	O
order	O
to	O
make	O
the	O
flooding	B-Protocol
procedure	O
reliable	O
,	O
flooded	O
advertisements	O
are	O
acknowledged	O
in	O
Link	B-Protocol
State	I-Protocol
Acknowledgment	O
packets	B-Protocol
.	O
</s>
<s>
If	O
retransmission	O
of	O
certain	O
advertisements	O
is	O
necessary	O
,	O
the	O
retransmitted	O
advertisements	O
are	O
always	O
carried	O
by	O
unicast	B-Protocol
Link	B-Protocol
State	I-Protocol
Update	O
packets	B-Protocol
.	O
</s>
<s>
Link	B-Protocol
State	I-Protocol
Acknowledgment	O
Packets	B-Protocol
are	O
OSPF	B-Protocol
packet	B-Protocol
type	O
5	O
.	O
</s>
<s>
To	O
make	O
the	O
flooding	B-Protocol
of	O
link	B-Protocol
state	I-Protocol
advertisements	O
reliable	O
,	O
flooded	O
advertisements	O
are	O
explicitly	O
acknowledged	O
.	O
</s>
<s>
This	O
acknowledgment	O
is	O
accomplished	O
through	O
the	O
sending	O
and	O
receiving	O
of	O
Link	B-Protocol
State	I-Protocol
Acknowledgment	O
packets	B-Protocol
.	O
</s>
<s>
Multiple	O
link	B-Protocol
state	I-Protocol
advertisements	O
can	O
be	O
acknowledged	O
in	O
a	O
single	O
Link	B-Protocol
State	I-Protocol
Acknowledgment	O
packet	B-Protocol
.	O
</s>
<s>
Depending	O
on	O
the	O
state	O
of	O
the	O
sending	O
interface	O
and	O
the	O
source	O
of	O
the	O
advertisements	O
being	O
acknowledged	O
,	O
a	O
Link	B-Protocol
State	I-Protocol
Acknowledgment	O
packet	B-Protocol
is	O
sent	O
either	O
to	O
the	O
multicast	O
address	O
AllSPFRouters	O
,	O
to	O
the	O
multicast	O
address	O
AllDRouters	O
,	O
or	O
as	O
a	O
unicast	B-Protocol
.	O
</s>
