<s>
Interior	B-Protocol
Gateway	I-Protocol
Routing	I-Protocol
Protocol	I-Protocol
(	O
IGRP	B-Protocol
)	O
is	O
a	O
distance	B-Protocol
vector	I-Protocol
interior	B-Protocol
gateway	I-Protocol
protocol	I-Protocol
(	O
IGP	O
)	O
developed	O
by	O
Cisco	O
.	O
</s>
<s>
It	O
is	O
used	O
by	O
routers	B-Protocol
to	O
exchange	O
routing	B-Protocol
data	O
within	O
an	O
autonomous	B-Architecture
system	I-Architecture
.	O
</s>
<s>
IGRP	B-Protocol
is	O
a	O
proprietary	O
protocol	O
.	O
</s>
<s>
IGRP	B-Protocol
was	O
created	O
in	O
part	O
to	O
overcome	O
the	O
limitations	O
of	O
RIP	B-Protocol
(	O
maximum	O
hop	O
count	O
of	O
only	O
15	O
,	O
and	O
a	O
single	O
routing	B-Protocol
metric	O
)	O
when	O
used	O
within	O
large	O
networks	O
.	O
</s>
<s>
IGRP	B-Protocol
supports	O
multiple	O
metrics	O
for	O
each	O
route	O
,	O
including	O
bandwidth	O
,	O
delay	B-Protocol
,	O
load	B-Operating_System
,	O
and	O
reliability	B-Protocol
;	O
to	O
compare	O
two	O
routes	O
these	O
metrics	O
are	O
combined	O
into	O
a	O
single	O
metric	O
,	O
using	O
a	O
formula	O
which	O
can	O
be	O
adjusted	O
through	O
the	O
use	O
of	O
pre-set	O
constants	O
.	O
</s>
<s>
By	O
default	O
,	O
the	O
IGRP	B-Protocol
composite	O
metric	O
is	O
a	O
sum	O
of	O
the	O
segment	O
delays	O
and	O
the	O
lowest	O
segment	O
bandwidth	O
.	O
</s>
<s>
The	O
maximum	O
configurable	O
hop	O
count	O
of	O
IGRP-routed	O
packets	O
is	O
255	O
(	O
default	O
100	O
)	O
,	O
and	O
routing	B-Protocol
updates	O
are	O
broadcast	B-Operating_System
every	O
90	O
seconds	O
(	O
by	O
default	O
)	O
.	O
</s>
<s>
IGRP	B-Protocol
uses	O
protocol	B-Protocol
number	I-Protocol
9	O
for	O
communication	O
.	O
</s>
<s>
IGRP	B-Protocol
is	O
considered	O
a	O
classful	B-Protocol
routing	I-Protocol
protocol	O
.	O
</s>
<s>
Because	O
the	O
protocol	O
has	O
no	O
field	O
for	O
a	O
subnet	B-Protocol
mask	I-Protocol
,	O
the	O
router	B-Protocol
assumes	O
that	O
all	O
subnetwork	B-Protocol
addresses	O
within	O
the	O
same	O
Class	O
A	O
,	O
Class	O
B	O
,	O
or	O
Class	B-Protocol
C	I-Protocol
network	I-Protocol
have	O
the	O
same	O
subnet	B-Protocol
mask	I-Protocol
as	O
the	O
subnet	B-Protocol
mask	I-Protocol
configured	O
for	O
the	O
interfaces	O
in	O
question	O
.	O
</s>
<s>
This	O
contrasts	O
with	O
classless	B-Protocol
routing	I-Protocol
protocols	O
that	O
can	O
use	O
variable	B-Protocol
length	I-Protocol
subnet	I-Protocol
masks	I-Protocol
.	O
</s>
<s>
Classful	B-Protocol
protocols	O
have	O
become	O
less	O
popular	O
as	O
they	O
are	O
wasteful	O
of	O
IP	B-Protocol
address	I-Protocol
space	I-Protocol
.	O
</s>
<s>
In	O
order	O
to	O
address	O
the	O
issues	O
of	O
address	O
space	O
and	O
other	O
factors	O
,	O
Cisco	O
created	O
EIGRP	B-Protocol
(	O
Enhanced	B-Protocol
Interior	I-Protocol
Gateway	I-Protocol
Routing	I-Protocol
Protocol	I-Protocol
)	O
.	O
</s>
<s>
EIGRP	B-Protocol
adds	O
support	O
for	O
VLSM	O
(	O
variable	B-Protocol
length	I-Protocol
subnet	I-Protocol
mask	I-Protocol
)	O
and	O
adds	O
the	O
Diffusing	B-Protocol
Update	I-Protocol
Algorithm	I-Protocol
(	O
DUAL	O
)	O
in	O
order	O
to	O
improve	O
routing	B-Protocol
and	O
provide	O
a	O
loopless	O
environment	O
.	O
</s>
<s>
EIGRP	B-Protocol
has	O
completely	O
replaced	O
IGRP	B-Protocol
,	O
making	O
IGRP	B-Protocol
an	O
obsolete	O
routing	B-Protocol
protocol	O
.	O
</s>
<s>
In	O
Cisco	O
IOS	O
versions	O
12.3	O
and	O
greater	O
,	O
IGRP	B-Protocol
is	O
completely	O
unsupported	O
.	O
</s>
<s>
In	O
the	O
new	O
Cisco	O
CCNA	O
curriculum	O
(	O
version	O
4	O
)	O
,	O
IGRP	B-Protocol
is	O
mentioned	O
only	O
briefly	O
,	O
as	O
an	O
"	O
obsolete	O
protocol	O
"	O
.	O
</s>
