<s>
The	O
link-state	B-Protocol
advertisement	I-Protocol
(	O
LSA	O
)	O
is	O
a	O
basic	O
communication	O
means	O
of	O
the	O
OSPF	B-Protocol
routing	O
protocol	O
for	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	O
)	O
.	O
</s>
<s>
It	O
communicates	O
the	O
router	O
's	O
local	O
routing	O
topology	O
to	O
all	O
other	O
local	O
routers	O
in	O
the	O
same	O
OSPF	B-Protocol
area	O
.	O
</s>
<s>
OSPF	B-Protocol
is	O
designed	O
for	O
scalability	O
,	O
so	O
some	O
LSAs	O
are	O
not	O
flooded	O
out	O
on	O
all	O
interfaces	O
,	O
but	O
only	O
on	O
those	O
that	O
belong	O
to	O
the	O
appropriate	O
area	O
.	O
</s>
<s>
The	O
original	O
IPv4-only	O
OSPFv2	B-Protocol
and	O
the	O
newer	O
IPv6-compatible	O
OSPFv3	B-Protocol
have	O
broadly	O
similar	O
LSA	B-Protocol
types	I-Protocol
.	O
</s>
<s>
The	O
LSA	B-Protocol
types	I-Protocol
defined	O
in	O
OSPF	B-Protocol
are	O
as	O
follows	O
:	O
</s>
<s>
+	O
OSPF	B-Protocol
link	O
state	O
advertisements	O
LS	O
type	O
LS	O
name	O
Generated	O
by	O
Distance	O
LSA	O
description	O
1	O
Router-LSAs	O
Each	O
internal	O
router	O
within	O
an	O
area	O
area-local	O
Originated	O
by	O
all	O
routers	O
.	O
</s>
<s>
This	O
LSA	O
contains	O
the	O
list	O
of	O
routers	O
connected	O
to	O
the	O
network.The	O
link-state	O
ID	O
of	O
the	O
type	O
2	O
LSA	O
is	O
the	O
IP	O
interface	O
address	O
of	O
the	O
DR.In	O
OSPFv3	B-Protocol
Network-LSAs	O
have	O
no	O
address	O
information	O
and	O
are	O
network	O
protocol	O
independent	O
.	O
</s>
<s>
Inter-Area-Prefix-LSAs	O
(	O
OSPFv3	B-Protocol
)	O
Area	O
Border	O
Router	O
(	O
ABR	O
)	O
routing	O
domain	O
an	O
Area	O
Border	O
Router	O
(	O
ABR	O
)	O
takes	O
information	O
it	O
has	O
learned	O
on	O
one	O
of	O
its	O
attached	O
areas	O
and	O
summarizes	O
it	O
before	O
sending	O
it	O
out	O
on	O
other	O
areas	O
it	O
is	O
connected	O
to	O
.	O
</s>
<s>
The	O
summarization	O
process	O
can	O
also	O
be	O
configured	O
to	O
remove	O
a	O
lot	O
of	O
detailed	O
address	O
prefixes	O
and	O
replace	O
them	O
with	O
a	O
single	O
summary	B-Protocol
prefix	I-Protocol
,	O
helping	O
scalability	O
.	O
</s>
<s>
In	O
OSPFv3	B-Protocol
Inter-Area-Prefix-LSAs	O
have	O
been	O
renamed	O
.	O
</s>
<s>
Inter-Area-Router-LSAs	O
(	O
OSPFv3	B-Protocol
)	O
Area	O
Border	O
Router	O
(	O
ABR	O
)	O
routing	O
domain	O
This	O
is	O
needed	O
because	O
Type	O
5	O
External	O
LSAs	O
are	O
flooded	O
to	O
all	O
areas	O
with	O
the	O
source	O
as	O
the	O
Autonomous	B-Architecture
System	I-Architecture
Boundary	O
Router	O
's	O
(	O
ASBR	O
)	O
router	O
ID	O
,	O
but	O
router	O
IDs	O
are	O
not	O
advertised	O
between	O
areas	O
.	O
</s>
<s>
The	O
link-state	O
ID	O
is	O
the	O
router	O
ID	O
of	O
the	O
described	O
ASBR	O
for	O
type	O
4	O
LSAs.In	O
OSPFv3	B-Protocol
Inter-Area-Router-LSAs	O
have	O
been	O
renamed	O
.	O
</s>
<s>
5	O
AS-external-LSAs	O
Autonomous	B-Architecture
System	I-Architecture
Boundary	O
Router	O
's	O
(	O
ASBR	O
)	O
routing	O
domain	O
these	O
LSAs	O
contain	O
information	O
imported	O
into	O
OSPF	B-Protocol
from	O
other	O
routing	O
processes	O
.	O
</s>
<s>
They	O
are	O
flooded	O
to	O
all	O
areas	O
unchanged	O
(	O
except	O
stub	B-Architecture
and	O
NSSA	O
areas	O
)	O
.	O
</s>
<s>
For	O
"	O
External	O
Metric	O
Type	O
1	O
"	O
LSAs	O
the	O
metric	O
sent	O
is	O
the	O
cost	O
from	O
the	O
ASBR	O
to	O
the	O
External	O
destination	O
network	O
and	O
must	O
be	O
added	O
to	O
the	O
OSPF	B-Protocol
cost	O
to	O
the	O
ASBR	O
advertising	O
the	O
Type	O
5	O
,	O
while	O
for	O
"	O
External	O
Type	O
2	O
"	O
LSAs	O
routing	O
decisions	O
are	O
made	O
using	O
the	O
Type	O
1	O
metric	O
cost	O
sent	O
as	O
the	O
total	O
cost	O
to	O
get	O
to	O
the	O
external	O
destination	O
including	O
the	O
cost	O
to	O
the	O
ASBR	O
.	O
</s>
<s>
6	O
This	O
was	O
defined	O
for	O
Multicast	O
extensions	O
to	O
OSPF	B-Protocol
(	O
MOSPF	B-Protocol
)	O
,	O
a	O
multicast	O
OSPF	B-Protocol
routing	O
protocol	O
which	O
was	O
not	O
in	O
general	O
use	O
.	O
</s>
<s>
MOSPF	B-Protocol
has	O
been	O
deprecated	O
since	O
OSPFv3	B-Protocol
and	O
is	O
not	O
currently	O
used	O
.	O
</s>
<s>
7	O
NSSA	O
External	O
Link-State	B-Protocol
Advertisements	I-Protocol
The	O
ASBR	O
,	O
within	O
a	O
Not-so-stubby	O
area	O
Intra-area	O
Type	O
7-LSAs	O
are	O
identical	O
to	O
type-5	O
LSAs.Type-7	O
LSAs	O
are	O
only	O
flooded	O
within	O
the	O
NSSA.This	O
are	O
allows	O
routers	O
in	O
NSSA	O
to	O
send	O
external	O
routing	O
information	O
for	O
redistribution	O
.	O
</s>
<s>
They	O
use	O
type	O
7	O
LSAs	O
to	O
tell	O
the	O
ABRs	O
about	O
these	O
external	O
routes	O
,	O
which	O
the	O
Area	O
Border	O
Router	O
then	O
translates	O
to	O
type	O
5	O
external	O
LSAs	O
and	O
floods	O
as	O
normal	O
to	O
the	O
rest	O
of	O
the	O
OSPF	B-Protocol
network	O
.	O
</s>
<s>
Link-local	O
LSAs	O
(	O
OSPFv3	B-Protocol
)	O
Each	O
internal	O
router	O
within	O
an	O
area	O
Link	O
A	O
Type	O
8	O
LSA	O
is	O
used	O
to	O
give	O
information	O
about	O
link-local	O
addresses	O
and	O
a	O
list	O
of	O
IPv6	B-Protocol
addresses	O
on	O
the	O
link	O
.	O
</s>
<s>
In	O
OSPFv2	B-Protocol
,	O
the	O
Type	O
8	O
was	O
originally	O
intended	O
to	O
be	O
used	O
as	O
a	O
so-called	O
External-Attributes-LSA	O
for	O
transit	O
autonomous	B-Architecture
systems	I-Architecture
where	O
OSPFv2	B-Protocol
could	O
replace	O
the	O
internal	B-Protocol
Border	I-Protocol
Gateway	I-Protocol
Protocol	I-Protocol
(	O
iBGP	B-Protocol
)	O
.	O
</s>
<s>
In	O
these	O
networks	O
,	O
the	O
BGP	B-Protocol
destinations	O
would	O
be	O
carried	O
in	O
LSA	O
Type	O
5	O
while	O
their	O
BGP	B-Protocol
attributes	O
would	O
be	O
inserted	O
into	O
LSA	O
Type	O
8	O
.	O
</s>
<s>
Most	O
OSPFv2	B-Protocol
implementations	O
never	O
supported	O
this	O
feature	O
,	O
and	O
it	O
was	O
never	O
standardised	O
for	O
OSPFv2	B-Protocol
.	O
</s>
<s>
Intra-Area-Prefix	O
(	O
OSPFv3	B-Protocol
)	O
link-local	O
It	O
is	O
the	O
OSPFv3	B-Protocol
LSA	O
that	O
contains	O
prefixes	O
for	O
stub	B-Architecture
and	O
transit	O
networks	O
in	O
the	O
link-state	O
ID	O
.	O
</s>
<s>
10	O
area-local	O
"	O
opaque	O
"	O
(	O
OSPFv2	B-Protocol
)	O
area-local	O
Opaque	O
LSAs	O
contain	O
information	O
which	O
should	O
be	O
flooded	O
by	O
other	O
routers	O
even	O
if	O
the	O
router	O
is	O
not	O
able	O
to	O
understand	O
the	O
extended	O
information	O
itself	O
.	O
</s>
<s>
Typically	O
type	O
10	O
LSAs	O
are	O
used	O
for	O
traffic	O
engineering	O
(	O
MPLS-TE	O
)	O
extensions	O
to	O
OSPF	B-Protocol
for	O
creating	O
the	O
Traffic	O
Engineering	O
Database	O
(	O
TED	O
)	O
,	O
by	O
flooding	O
extra	O
information	O
about	O
links	O
beyond	O
just	O
their	O
metric	O
,	O
such	O
as	O
link	O
bandwidth	O
and	O
color	O
.	O
</s>
<s>
11	O
Autonomous	B-Architecture
System	I-Architecture
(	O
AS	O
)	O
"	O
opaque	O
"	O
(	O
OSPFv2	B-Protocol
)	O
routing	O
domain	O
LSA	O
Type	O
11	O
packets	O
serve	O
the	O
same	O
purpose	O
as	O
LSA	O
Type	O
10	O
packets	O
but	O
are	O
not	O
flooded	O
into	O
special	O
area	O
types	O
(	O
Stub	B-Architecture
areas	O
)	O
.	O
</s>
<s>
The	O
opaque	O
LSAs	O
,	O
types	O
9	O
,	O
10	O
,	O
and	O
11	O
,	O
are	O
designated	O
for	O
upgrades	O
to	O
OSPF	B-Protocol
for	O
application-specific	O
purposes	O
.	O
</s>
<s>
For	O
example	O
,	O
OSPF-TE	B-Protocol
has	O
traffic	O
engineering	O
extensions	O
to	O
be	O
used	O
by	O
RSVP-TE	B-Protocol
in	O
Multiprotocol	B-Protocol
Label	I-Protocol
Switching	I-Protocol
(	O
MPLS	B-Protocol
)	O
.	O
</s>
<s>
As	O
per	O
of	O
RFC	O
2328	O
,	O
all	O
OSPF	B-Protocol
packets	O
start	O
with	O
a	O
common	O
LSA	O
"	O
24-byte	O
header	O
"	O
as	O
shown	O
below	O
.	O
</s>
<s>
Database	O
description	O
messages	O
contain	O
descriptions	O
of	O
the	O
topology	O
of	O
the	O
autonomous	B-Architecture
system	I-Architecture
or	O
area	O
.	O
</s>
<s>
Note	O
:	O
These	O
LSA	O
Packet	O
Headers	O
are	O
all	O
preceded	O
by	O
OSPFv2	B-Protocol
"	O
24-byte	O
"	O
OSPF	B-Protocol
Headers	O
.	O
</s>
<s>
+Common	O
OSPFv3	B-Protocol
packet	O
header	O
16-byteBit	O
0	O
1	O
2	O
3	O
4	O
5	O
6	O
7	O
8	O
9	O
10	O
11	O
12	O
13	O
14	O
15	O
16	O
17	O
18	O
19	O
20	O
21	O
22	O
23	O
24	O
25	O
26	O
27	O
28	O
29	O
30	O
31	O
0	O
Version	O
#	O
Type	O
Packet	O
length	O
32	O
Router	O
ID	O
64	O
Area	O
ID	O
96	O
Checksum	O
AuType	O
128	O
Depending	O
on	O
the	O
"	O
OSPF	B-Protocol
packet	O
types	O
"	O
details	O
of	O
the	O
contents	O
will	O
vary	O
.	O
</s>
<s>
Note	O
:	O
These	O
LSA	O
Packet	O
Headers	O
are	O
all	O
preceded	O
by	O
standard	O
"	O
16-byte	O
"	O
OSPF	B-Protocol
Headers	O
.	O
</s>
<s>
As	O
per	O
of	O
RFC	O
5340	O
(	O
OSPFv3	B-Protocol
for	O
IPv6	B-Protocol
)	O
depending	O
upon	O
the	O
LS	O
Type	O
,	O
there	O
are	O
nine	O
major	O
LSA	O
Packet	O
formats	O
as	O
follows	O
(	O
actually	O
eight	O
as	O
one	O
has	O
been	O
deprecated	O
)	O
:	O
</s>
<s>
Bit/Byte	O
0	O
1	O
2	O
3	O
4	O
5	O
6	O
7	O
8	O
9	O
10	O
11	O
12	O
13	O
14	O
15	O
16	O
17	O
18	O
19	O
20	O
21	O
22	O
23	O
24	O
25	O
26	O
27	O
28	O
29	O
30	O
31	O
N/A	O
This	O
LSA	O
Type	O
is	O
deprecated	O
in	O
OSPF	B-Protocol
v3	O
RFC	O
5340	O
and	O
thus	O
is	O
not	O
shown	O
here	O
.	O
</s>
