<s>
Hierarchical	B-Protocol
routing	I-Protocol
is	O
a	O
method	O
of	O
routing	B-Protocol
in	O
networks	O
that	O
is	O
based	O
on	O
hierarchical	O
addressing	B-Protocol
.	O
</s>
<s>
Most	O
Transmission	B-Protocol
Control	I-Protocol
Protocol/Internet	I-Protocol
Protocol	I-Protocol
(	O
TCP/IP	B-Protocol
)	O
routing	B-Protocol
is	O
based	O
on	O
a	O
two-level	O
hierarchical	B-Protocol
routing	I-Protocol
in	O
which	O
an	O
IP	O
address	B-Protocol
is	O
divided	O
into	O
a	O
network	B-Architecture
portion	O
and	O
a	O
host	B-Application
portion	O
.	O
</s>
<s>
Gateways	B-Application
use	O
only	O
the	O
network	B-Architecture
portion	O
until	O
an	O
IP	O
datagram	B-Protocol
reaches	O
a	O
gateway	B-Application
that	O
can	O
deliver	O
it	O
directly	O
.	O
</s>
<s>
Additional	O
levels	O
of	O
hierarchical	B-Protocol
routing	I-Protocol
are	O
introduced	O
by	O
the	O
addition	O
of	O
subnetworks	O
.	O
</s>
<s>
Hierarchical	B-Protocol
routing	I-Protocol
is	O
the	O
procedure	O
of	O
arranging	O
routers	B-Protocol
in	O
a	O
hierarchical	O
manner	O
.	O
</s>
<s>
A	O
good	O
example	O
would	O
be	O
to	O
consider	O
a	O
corporate	O
intranet	B-General_Concept
.	O
</s>
<s>
Most	O
corporate	O
intranets	B-General_Concept
consist	O
of	O
a	O
high	O
speed	O
backbone	B-General_Concept
network	I-General_Concept
.	O
</s>
<s>
Connected	O
to	O
this	O
backbone	O
are	O
routers	B-Protocol
which	O
are	O
in	O
turn	O
connected	O
to	O
a	O
particular	O
workgroup	O
.	O
</s>
<s>
These	O
workgroups	O
occupy	O
a	O
unique	O
LAN	B-General_Concept
.	O
</s>
<s>
The	O
reason	O
this	O
is	O
a	O
good	O
arrangement	O
is	O
because	O
even	O
though	O
there	O
might	O
be	O
dozens	O
of	O
different	O
workgroups	O
,	O
the	O
span	O
(	O
maximum	O
hop	B-Protocol
count	I-Protocol
to	O
get	O
from	O
one	O
host	B-Application
to	O
any	O
other	O
host	B-Application
on	O
the	O
network	B-Architecture
)	O
is	O
2	O
.	O
</s>
<s>
Even	O
if	O
the	O
workgroups	O
divided	O
their	O
LAN	B-General_Concept
network	I-General_Concept
into	O
smaller	O
partitions	O
,	O
the	O
span	O
could	O
only	O
increase	O
to	O
4	O
in	O
this	O
particular	O
example	O
.	O
</s>
<s>
Considering	O
alternative	O
solutions	O
with	O
every	O
router	B-Protocol
connected	O
to	O
every	O
other	O
router	B-Protocol
,	O
or	O
if	O
every	O
router	B-Protocol
was	O
connected	O
to	O
2	O
routers	B-Protocol
,	O
shows	O
the	O
convenience	O
of	O
hierarchical	B-Protocol
routing	I-Protocol
.	O
</s>
<s>
It	O
decreases	O
the	O
complexity	O
of	O
network	B-Architecture
topology	I-Architecture
,	O
increases	O
routing	B-Protocol
efficiency	O
,	O
and	O
causes	O
much	O
less	O
congestion	B-Protocol
because	O
of	O
fewer	O
routing	B-Protocol
advertisements	O
.	O
</s>
<s>
With	O
hierarchical	B-Protocol
routing	I-Protocol
,	O
only	O
core	O
routers	B-Protocol
connected	O
to	O
the	O
backbone	O
are	O
aware	O
of	O
all	O
routes	O
.	O
</s>
<s>
Routers	B-Protocol
that	O
lie	O
within	O
a	O
LAN	B-General_Concept
only	O
know	O
about	O
routes	O
in	O
the	O
LAN	B-General_Concept
.	O
</s>
