<s>
The	O
Internetworking	O
Operating	O
System	O
(	O
IOS	B-Protocol
)	O
is	O
a	O
family	O
of	O
proprietary	B-Application
network	B-Protocol
operating	I-Protocol
systems	I-Protocol
used	O
on	O
several	O
router	B-Protocol
and	O
network	B-Protocol
switch	I-Protocol
models	O
manufactured	O
by	O
Cisco	O
Systems	O
.	O
</s>
<s>
The	O
system	O
is	O
a	O
package	O
of	O
routing	B-Protocol
,	O
switching	B-Protocol
,	O
internetworking	O
,	O
and	O
telecommunications	O
functions	O
integrated	O
into	O
a	O
multitasking	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
.	O
</s>
<s>
Although	O
the	O
IOS	B-Protocol
code	O
base	O
includes	O
a	O
cooperative	B-Operating_System
multitasking	I-Operating_System
kernel	O
,	O
most	O
IOS	B-Protocol
features	O
have	O
been	O
ported	O
to	O
other	O
kernels	O
,	O
such	O
as	O
Linux	B-Application
and	O
QNX	B-Operating_System
,	O
for	O
use	O
in	O
Cisco	O
products	O
.	O
</s>
<s>
Not	O
all	O
Cisco	O
networking	O
products	O
run	O
IOS	B-Protocol
.	O
</s>
<s>
Exceptions	O
include	O
some	O
Cisco	B-Device
Catalyst	I-Device
switches	O
,	O
which	O
run	O
IOS	B-Device
XE	I-Device
,	O
and	O
Cisco	B-Protocol
ASR	I-Protocol
routers	B-Protocol
,	O
which	O
run	O
either	O
IOS	B-Device
XE	I-Device
or	O
IOS	B-Device
XR	I-Device
;	O
both	O
are	O
Linux-based	O
operating	O
systems	O
.	O
</s>
<s>
For	O
data	O
center	O
environments	O
,	O
Cisco	B-Protocol
Nexus	I-Protocol
switches	I-Protocol
(	O
Ethernet	O
)	O
and	O
Cisco	O
MDS	O
switches	O
(	O
Fibre	B-Architecture
Channel	I-Architecture
)	O
both	O
run	O
Cisco	B-Operating_System
NX-OS	I-Operating_System
,	O
also	O
a	O
Linux-based	O
operating	O
system	O
.	O
</s>
<s>
The	O
IOS	B-Protocol
network	B-Protocol
operating	I-Protocol
system	I-Protocol
was	O
created	O
from	O
code	O
written	O
by	O
William	O
Yeager	O
at	O
Stanford	O
University	O
,	O
which	O
was	O
developed	O
in	O
the	O
1980s	O
for	O
routers	B-Protocol
with	O
256	O
kB	O
of	O
memory	O
and	O
low	O
CPU	B-Device
processing	O
power	O
.	O
</s>
<s>
Through	O
modular	O
extensions	O
,	O
IOS	B-Protocol
has	O
been	O
adapted	O
to	O
increasing	O
hardware	O
capabilities	O
and	O
new	O
networking	O
protocols	O
.	O
</s>
<s>
When	O
IOS	B-Protocol
was	O
developed	O
,	O
Cisco	O
Systems	O
 '	O
main	O
product	O
line	O
were	O
routers	B-Protocol
.	O
</s>
<s>
The	O
company	O
acquired	O
a	O
number	O
of	O
young	O
companies	O
that	O
focused	O
on	O
network	B-Protocol
switches	I-Protocol
,	O
such	O
as	O
the	O
inventor	O
of	O
the	O
first	O
Ethernet	B-Protocol
switch	I-Protocol
Kalpana	O
,	O
and	O
as	O
a	O
result	O
Cisco	B-Device
switches	I-Device
did	O
not	O
initially	O
run	O
IOS	B-Protocol
.	O
</s>
<s>
Prior	O
to	O
IOS	B-Protocol
,	O
the	O
Cisco	B-Device
Catalyst	I-Device
series	O
ran	O
CatOS	B-Device
.	O
</s>
<s>
The	O
IOS	B-Protocol
command-line	B-Application
interface	I-Application
(	O
CLI	O
)	O
provides	O
a	O
fixed	O
set	O
of	O
multiple-word	O
commands	B-Application
.	O
</s>
<s>
"	O
Global	B-Protocol
configuration	I-Protocol
mode	I-Protocol
"	O
provides	O
commands	B-Application
to	O
change	O
the	O
system	O
's	O
configuration	O
,	O
and	O
"	O
interface	O
configuration	O
mode	O
"	O
provides	O
commands	B-Application
to	O
change	O
the	O
configuration	O
of	O
a	O
specific	O
interface	O
.	O
</s>
<s>
All	O
commands	B-Application
are	O
assigned	O
a	O
privilege	O
level	O
,	O
from	O
0	O
to	O
15	O
,	O
and	O
can	O
only	O
be	O
accessed	O
by	O
users	O
with	O
the	O
necessary	O
privilege	O
.	O
</s>
<s>
Through	O
the	O
CLI	O
,	O
the	O
commands	B-Application
available	O
to	O
each	O
privilege	O
level	O
can	O
be	O
defined	O
.	O
</s>
<s>
Most	O
builds	O
of	O
IOS	B-Protocol
include	O
a	O
Tcl	B-Operating_System
interpreter	O
.	O
</s>
<s>
Cisco	B-Protocol
IOS	I-Protocol
has	O
a	O
monolithic	B-Operating_System
architecture	O
,	O
owing	O
to	O
the	O
limited	O
hardware	O
resources	O
of	O
routers	B-Protocol
and	O
switches	O
in	O
the	O
1980s	O
.	O
</s>
<s>
This	O
means	O
that	O
all	O
processes	O
have	O
direct	O
hardware	O
access	O
to	O
conserve	O
CPU	B-Device
processing	O
time	O
.	O
</s>
<s>
There	O
is	O
no	O
memory	B-General_Concept
protection	I-General_Concept
between	O
processes	O
and	O
IOS	B-Protocol
has	O
a	O
run	B-Algorithm
to	I-Algorithm
completion	I-Algorithm
scheduler	I-Algorithm
,	O
which	O
means	O
that	O
the	O
kernel	O
does	O
not	O
pre-empt	O
a	O
running	O
process	B-Operating_System
.	O
</s>
<s>
Instead	O
the	O
process	B-Operating_System
must	O
make	O
a	O
kernel	O
call	O
before	O
other	O
processes	O
get	O
a	O
chance	O
to	O
run	O
.	O
</s>
<s>
IOS	B-Protocol
considers	O
each	O
process	B-Operating_System
a	O
single	B-Operating_System
thread	I-Operating_System
and	O
assigns	O
it	O
a	O
priority	O
value	O
,	O
so	O
that	O
high	O
priority	O
processes	O
are	O
executed	O
on	O
the	O
CPU	B-Device
before	O
queued	O
low	O
priority	O
processes	O
,	O
but	O
high	O
priority	O
processes	O
cannot	O
interrupt	O
running	O
low	O
priority	O
processes	O
.	O
</s>
<s>
The	O
Cisco	B-Protocol
IOS	I-Protocol
monolithic	B-Operating_System
kernel	I-Operating_System
does	O
not	O
implement	O
memory	B-General_Concept
protection	I-General_Concept
for	O
the	O
data	O
of	O
different	O
processes	O
.	O
</s>
<s>
The	O
Cisco	B-Protocol
IOS	I-Protocol
kernel	O
does	O
not	O
perform	O
any	O
memory	B-Architecture
paging	I-Architecture
or	O
swapping	O
.	O
</s>
<s>
IOS	B-Protocol
does	O
however	O
support	O
aliasing	O
of	O
duplicated	O
virtual	O
memory	O
contents	O
to	O
the	O
same	O
physical	O
memory	O
.	O
</s>
<s>
The	O
disadvantage	O
of	O
the	O
IOS	B-Protocol
architecture	O
is	O
that	O
it	O
increases	O
the	O
complexity	O
of	O
the	O
operating	O
system	O
,	O
data	O
corruption	O
is	O
possible	O
as	O
one	O
process	B-Operating_System
can	O
write	O
over	O
the	O
data	O
of	O
another	O
,	O
and	O
one	O
process	B-Operating_System
can	O
destabilize	O
the	O
entire	O
operating	O
system	O
or	O
even	O
cause	O
a	O
software-forced	O
crash	B-General_Concept
.	O
</s>
<s>
In	O
the	O
event	O
of	O
an	O
IOS	B-Protocol
crash	B-General_Concept
,	O
the	O
operating	O
system	O
automatically	O
reboots	O
and	O
reloads	O
the	O
saved	O
configuration	O
.	O
</s>
<s>
In	O
all	O
versions	O
of	O
Cisco	B-Protocol
IOS	I-Protocol
,	O
packet	B-Protocol
routing	I-Protocol
and	O
forwarding	B-Protocol
(	O
switching	B-Protocol
)	O
are	O
distinct	O
functions	O
.	O
</s>
<s>
Routing	B-Protocol
and	O
other	O
protocols	O
run	O
as	O
Cisco	B-Protocol
IOS	I-Protocol
processes	O
and	O
contribute	O
to	O
the	O
Routing	B-Protocol
Information	I-Protocol
Base	O
(	O
RIB	O
)	O
.	O
</s>
<s>
This	O
is	O
processed	O
to	O
generate	O
the	O
final	O
IP	O
forwarding	B-Protocol
table	O
(	O
FIB	O
,	O
Forwarding	B-Protocol
Information	O
Base	O
)	O
,	O
which	O
is	O
used	O
by	O
the	O
forwarding	B-Protocol
function	O
of	O
the	O
router	B-Protocol
.	O
</s>
<s>
On	O
router	B-Protocol
platforms	O
with	O
software-only	O
forwarding	B-Protocol
(	O
e.g.	O
,	O
Cisco	O
7200	O
)	O
,	O
most	O
traffic	O
handling	O
,	O
including	O
access	O
control	O
list	O
filtering	O
and	O
forwarding	B-Protocol
,	O
is	O
done	O
at	O
interrupt	O
level	O
using	O
Cisco	B-Protocol
Express	I-Protocol
Forwarding	I-Protocol
(	O
CEF	O
)	O
or	O
dCEF	O
(	O
Distributed	O
CEF	O
)	O
.	O
</s>
<s>
This	O
means	O
IOS	B-Protocol
does	O
not	O
have	O
to	O
do	O
a	O
process	B-Operating_System
context	B-Operating_System
switch	I-Operating_System
to	O
forward	O
a	O
packet	O
.	O
</s>
<s>
Routing	B-Protocol
functions	O
such	O
as	O
OSPF	B-Protocol
or	O
BGP	B-Protocol
run	O
at	O
the	O
process	B-Operating_System
level	O
.	O
</s>
<s>
In	O
routers	B-Protocol
with	O
hardware-based	O
forwarding	B-Protocol
,	O
such	O
as	O
the	O
Cisco	B-Device
12000	I-Device
series	O
,	O
IOS	B-Protocol
computes	O
the	O
FIB	O
in	O
software	O
and	O
loads	O
it	O
into	O
the	O
forwarding	B-Protocol
hardware	O
(	O
such	O
as	O
an	O
ASIC	O
or	O
network	O
processor	O
)	O
,	O
which	O
performs	O
the	O
actual	O
packet	B-Protocol
forwarding	I-Protocol
function	O
.	O
</s>
<s>
An	O
Interface	B-Protocol
Descriptor	I-Protocol
Block	I-Protocol
,	O
or	O
simply	O
IDB	O
,	O
is	O
a	O
portion	O
of	O
memory	O
or	O
Cisco	B-Protocol
IOS	I-Protocol
internal	O
data	O
structure	O
that	O
contains	O
information	O
such	O
as	O
the	O
IP	O
address	O
,	O
interface	O
state	O
,	O
and	O
packet	O
statistics	O
for	O
networking	O
data	O
.	O
</s>
<s>
Cisco	O
's	O
IOS	B-Protocol
software	O
maintains	O
one	O
IDB	O
for	O
each	O
hardware	O
interface	O
in	O
a	O
particular	O
Cisco	O
switch	O
or	O
router	B-Protocol
and	O
one	O
IDB	O
for	O
each	O
subinterface	O
.	O
</s>
<s>
IOS	B-Protocol
is	O
shipped	O
as	O
a	O
unique	O
file	O
that	O
has	O
been	O
compiled	O
for	O
specific	O
Cisco	O
network	O
devices	O
.	O
</s>
<s>
Each	O
IOS	B-Protocol
Image	O
therefore	O
include	O
a	O
feature	O
set	O
,	O
which	O
determine	O
the	O
command-line	B-Application
interface	I-Application
(	O
CLI	O
)	O
commands	B-Application
and	O
features	O
that	O
are	O
available	O
on	O
different	O
Cisco	O
devices	O
.	O
</s>
<s>
Upgrading	O
to	O
another	O
feature	O
set	O
therefore	O
entails	O
the	O
installation	O
of	O
a	O
new	O
IOS	B-Protocol
image	O
on	O
the	O
networking	O
device	O
and	O
reloading	O
the	O
IOS	B-Protocol
operating	O
system	O
.	O
</s>
<s>
Information	O
about	O
the	O
IOS	B-Protocol
version	O
and	O
feature-set	O
running	O
on	O
a	O
Cisco	O
device	O
can	O
be	O
obtained	O
with	O
the	O
show	O
version	O
command	O
.	O
</s>
<s>
Most	O
Cisco	O
products	O
that	O
run	O
IOS	B-Protocol
also	O
have	O
one	O
or	O
more	O
"	O
feature	O
sets	O
"	O
or	O
"	O
packages	O
"	O
,	O
typically	O
eight	O
packages	O
for	O
Cisco	O
routers	B-Protocol
and	O
five	O
packages	O
for	O
Cisco	O
network	B-Protocol
switches	I-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
Cisco	B-Protocol
IOS	I-Protocol
releases	O
meant	O
for	O
use	O
on	O
Catalyst	B-Device
switches	I-Device
are	O
available	O
as	O
"	O
standard	O
"	O
versions	O
(	O
providing	O
only	O
basic	O
IP	O
routing	B-Protocol
)	O
,	O
"	O
enhanced	O
"	O
versions	O
,	O
which	O
provide	O
full	O
IPv4	B-Protocol
routing	B-Protocol
support	O
,	O
and	O
"	O
advanced	O
IP	O
services	O
"	O
versions	O
,	O
which	O
provide	O
the	O
enhanced	O
features	O
as	O
well	O
as	O
IPv6	B-Protocol
support	O
.	O
</s>
<s>
Beginning	O
with	O
the	O
1900	O
,	O
2900	O
and	O
3900	O
series	O
of	O
ISR	O
Routers	B-Protocol
,	O
Cisco	O
revised	O
the	O
licensing	O
model	O
of	O
IOS	B-Protocol
.	O
</s>
<s>
To	O
simplify	O
the	O
process	B-Operating_System
of	O
enlarging	O
the	O
feature-set	O
and	O
reduce	O
the	O
need	O
for	O
network	B-Protocol
operating	I-Protocol
system	I-Protocol
reloads	O
,	O
Cisco	O
introduced	O
universal	O
IOS	B-Protocol
images	O
,	O
that	O
include	O
all	O
features	O
available	O
for	O
a	O
device	O
and	O
customers	O
may	O
unlock	O
certain	O
features	O
by	O
purchasing	O
an	O
additional	O
software	B-License
license	I-License
.	O
</s>
<s>
Routers	B-Protocol
come	O
with	O
IP	O
Base	O
installed	O
,	O
and	O
additional	O
feature	O
pack	O
licenses	O
can	O
be	O
installed	O
as	O
bolt-on	O
additions	O
to	O
expand	O
the	O
feature	O
set	O
of	O
the	O
device	O
.	O
</s>
<s>
Data	O
adds	O
features	O
like	O
BFD	O
,	O
IP	O
SLAs	O
,	O
IPX	O
,	O
L2TPv3	O
,	O
Mobile	O
IP	O
,	O
MPLS	O
,	O
SCTP	B-Protocol
.	O
</s>
<s>
IOS	B-Protocol
images	O
can	O
not	O
be	O
updated	O
with	O
software	B-Error_Name
bug	I-Error_Name
fixes	O
.	O
</s>
<s>
To	O
patch	O
a	O
vulnerability	O
in	O
IOS	B-Protocol
,	O
a	O
binary	O
file	O
with	O
the	O
entire	O
operating	O
system	O
needs	O
to	O
be	O
loaded	O
.	O
</s>
<s>
Cisco	B-Protocol
IOS	I-Protocol
is	O
versioned	O
using	O
three	O
numbers	O
and	O
some	O
letters	O
,	O
in	O
the	O
general	O
form	O
a.b(c.d )	O
e	O
,	O
where	O
:	O
</s>
<s>
Rebuilds	O
–	O
Often	O
a	O
rebuild	O
is	O
compiled	O
to	O
fix	O
a	O
single	O
specific	O
problem	O
or	O
vulnerability	O
for	O
a	O
given	O
IOS	B-Protocol
version	O
.	O
</s>
<s>
Maintenance	O
releases	O
–	O
Rigorously	O
tested	O
releases	O
that	O
are	O
made	O
available	O
and	O
include	O
enhancements	O
and	O
bug	B-Error_Name
fixes	O
.	O
</s>
<s>
Before	O
Cisco	B-Protocol
IOS	I-Protocol
release	O
15	O
,	O
releases	O
were	O
split	O
into	O
several	O
trains	O
,	O
each	O
containing	O
a	O
different	O
set	O
of	O
features	O
.	O
</s>
<s>
Updates	O
are	O
released	O
only	O
to	O
address	O
bugs	B-Error_Name
in	O
the	O
product	O
.	O
</s>
<s>
The	O
T	O
–	O
Technology	O
train	O
,	O
gets	O
new	O
features	O
and	O
bug	B-Error_Name
fixes	O
throughout	O
its	O
life	O
,	O
and	O
is	O
therefore	O
potentially	O
less	O
stable	O
than	O
the	O
mainline	O
.	O
</s>
<s>
(	O
In	O
releases	O
prior	O
to	O
Cisco	B-Protocol
IOS	I-Protocol
Release	O
12.0	O
,	O
the	O
P	O
train	O
served	O
as	O
the	O
Technology	O
train	O
.	O
)	O
</s>
<s>
Cisco	O
does	O
n't	O
recommend	O
usage	O
of	O
T	O
train	O
in	O
production	O
environments	O
unless	O
there	O
is	O
urgency	O
to	O
implement	O
a	O
certain	O
T	O
train	O
's	O
new	O
IOS	B-Protocol
feature	O
.	O
</s>
<s>
The	O
S	O
–	O
Service	O
Provider	O
train	O
,	O
runs	O
only	O
on	O
the	O
company	O
's	O
core	B-Protocol
router	I-Protocol
products	O
and	O
is	O
heavily	O
customized	O
for	O
Service	O
Provider	O
customers	O
.	O
</s>
<s>
–	O
Special	O
Release	O
train	O
,	O
contains	O
one-off	O
releases	O
designed	O
to	O
fix	O
a	O
certain	O
bug	B-Error_Name
or	O
provide	O
a	O
new	O
feature	O
.	O
</s>
<s>
Starting	O
with	O
Cisco	B-Protocol
IOS	I-Protocol
release	O
15	O
,	O
there	O
is	O
just	O
a	O
single	O
train	O
,	O
the	O
M/T	O
train	O
.	O
</s>
<s>
The	O
M	O
releases	O
are	O
extended	O
maintenance	O
releases	O
,	O
and	O
Cisco	O
will	O
provide	O
bug	B-Error_Name
fixes	O
for	O
44	O
months	O
.	O
</s>
<s>
The	O
T	O
releases	O
are	O
standard	O
maintenance	O
releases	O
,	O
and	O
Cisco	O
will	O
only	O
provide	O
bug	B-Error_Name
fixes	O
for	O
18	O
months	O
.	O
</s>
<s>
Because	O
IOS	B-Protocol
needs	O
to	O
know	O
the	O
cleartext	O
password	O
for	O
certain	O
uses	O
,	O
(	O
e.g.	O
,	O
CHAP	B-Protocol
authentication	O
)	O
passwords	O
entered	O
into	O
the	O
CLI	O
by	O
default	O
are	O
weakly	O
encrypted	O
as	O
'	O
Type	O
7	O
 '	O
ciphertext	O
,	O
such	O
as	O
"	O
Router(config )	O
#username	O
jdoe	O
password	O
7	O
0832585B1910010713181F	O
"	O
.	O
</s>
<s>
This	O
is	O
designed	O
to	O
prevent	O
"	O
shoulder-surfing	O
"	O
attacks	O
when	O
viewing	O
router	B-Protocol
configurations	O
and	O
is	O
not	O
secure	O
–	O
they	O
are	O
easily	O
decrypted	O
using	O
software	O
called	O
"	O
getpass	O
"	O
available	O
since	O
1995	O
,	O
or	O
"	O
ios7crypt	O
"	O
,	O
a	O
modern	O
variant	O
,	O
although	O
the	O
passwords	O
can	O
be	O
decoded	O
by	O
the	O
router	B-Protocol
using	O
the	O
"	O
key	O
chain	O
"	O
command	O
and	O
entering	O
the	O
type	O
7	O
password	O
as	O
the	O
key	O
,	O
and	O
then	O
issuing	O
a	O
"	O
show	O
key	O
"	O
command	O
;	O
the	O
above	O
example	O
decrypts	O
to	O
"	O
stupidpass	O
"	O
.	O
</s>
<s>
Cisco	O
recommends	O
that	O
all	O
Cisco	B-Protocol
IOS	I-Protocol
devices	O
implement	O
the	O
authentication	O
,	O
authorization	O
,	O
and	O
accounting	O
(	O
AAA	O
)	O
security	O
model	O
.	O
</s>
<s>
AAA	O
can	O
use	O
local	O
,	O
RADIUS	B-Protocol
,	O
and	O
TACACS+	B-Protocol
databases	O
.	O
</s>
<s>
At	O
the	O
Black	O
Hat	O
Briefings	O
conference	O
in	O
July	O
2005	O
,	O
Michael	O
Lynn	O
,	O
working	O
for	O
Internet	O
Security	O
Systems	O
at	O
the	O
time	O
,	O
presented	O
information	O
about	O
a	O
vulnerability	O
in	O
IOS	B-Protocol
.	O
</s>
<s>
For	O
Cisco	O
products	O
that	O
required	O
very	O
high	O
availability	O
,	O
such	O
as	O
the	O
Cisco	B-Protocol
CRS-1	I-Protocol
,	O
the	O
limitations	O
of	O
a	O
monolithic	B-Operating_System
kernel	I-Operating_System
were	O
not	O
acceptable	O
.	O
</s>
<s>
In	O
addition	O
,	O
competitive	O
router	B-Protocol
operating	O
systems	O
that	O
emerged	O
10	O
–	O
20	O
years	O
after	O
IOS	B-Protocol
,	O
such	O
as	O
Juniper	O
's	O
Junos	B-Application
OS	I-Application
,	O
were	O
designed	O
to	O
not	O
have	O
these	O
limitations	O
.	O
</s>
<s>
Cisco	O
's	O
response	O
was	O
to	O
develop	O
a	O
tree	O
of	O
Cisco	B-Protocol
IOS	I-Protocol
that	O
offered	O
modularity	O
and	O
memory	B-General_Concept
protection	I-General_Concept
between	O
processes	O
,	O
lightweight	O
threads	B-Operating_System
,	O
pre-emptive	B-Operating_System
scheduling	I-Operating_System
and	O
the	O
ability	O
to	O
independently	O
restart	O
failed	O
processes	O
.	O
</s>
<s>
The	O
IOS	B-Device
XR	I-Device
development	O
train	O
initially	O
used	O
the	O
real-time	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
microkernel	B-Operating_System
(	O
QNX	B-Operating_System
)	O
and	O
a	O
large	O
part	O
of	O
the	O
IOS	B-Protocol
source	O
code	O
was	O
re-written	O
to	O
take	O
advantage	O
of	O
the	O
features	O
offered	O
by	O
the	O
kernel	O
.	O
</s>
<s>
In	O
2005	O
Cisco	O
introduced	O
the	O
Cisco	B-Device
IOS	I-Device
XR	I-Device
network	B-Protocol
operating	I-Protocol
system	I-Protocol
on	O
the	O
12000	B-Device
series	I-Device
of	O
network	B-Protocol
routers	I-Protocol
,	O
extending	O
the	O
microkernel	B-Operating_System
architecture	O
from	O
the	O
CRS-1	O
routers	B-Protocol
to	O
Cisco	O
's	O
widely	O
deployed	O
core	B-Protocol
routers	I-Protocol
.	O
</s>
<s>
In	O
2006	O
Cisco	O
introduced	O
IOS	B-Protocol
Software	O
Modularity	O
,	O
which	O
extends	O
the	O
microkernel	B-Operating_System
architecture	O
into	O
the	O
IOS	B-Protocol
environment	O
,	O
while	O
still	O
providing	O
the	O
software	O
upgrade	O
capabilities	O
.	O
</s>
