<s>
Graphical	B-Application
Network	I-Application
Simulator-3	I-Application
(	O
shortened	O
to	O
GNS3	B-Application
)	O
is	O
a	O
network	B-Architecture
software	I-Architecture
emulator	B-Application
first	O
released	O
in	O
2008	O
.	O
</s>
<s>
It	O
uses	O
Dynamips	O
emulation	B-Application
software	I-Application
to	O
simulate	O
Cisco	B-Protocol
IOS	I-Protocol
.	O
</s>
<s>
GNS3	B-Application
is	O
used	O
by	O
many	O
large	O
companies	O
including	O
Exxon	O
,	O
Walmart	O
,	O
AT&T	O
and	O
NASA	O
,	O
and	O
is	O
also	O
popular	O
for	O
preparation	O
of	O
network	B-Architecture
professional	O
certification	O
exams	O
.	O
</s>
