<s>
Software-defined	O
networking	O
(	O
SDN	O
)	O
is	O
a	O
marketing	O
term	O
which	O
refers	O
to	O
software	O
to	O
configure	O
and	O
operate	O
computer	O
networks	O
(	O
especially	O
data	B-Operating_System
center	I-Operating_System
networks	O
)	O
through	O
a	O
centralized	O
software	O
controller	O
that	O
dictates	O
how	O
the	O
network	O
behaves	O
.	O
</s>
<s>
SDN	O
controllers	O
for	O
the	O
network	B-Architecture
function	I-Architecture
virtualization	I-Architecture
(	O
NFV	O
)	O
of	O
a	O
datacenter	B-Operating_System
,	O
</s>
<s>
In	O
case	O
of	O
SDN	O
controllers	O
for	O
the	O
NFV	O
Infrastructure	O
of	O
a	O
datacenter	B-Operating_System
,	O
they	O
are	O
mostly	O
designed	O
to	O
provide	O
some	O
policy	O
and	O
centralized	O
managements	O
for	O
the	O
Openstack	O
Neutron	O
networking	O
layer	O
that	O
will	O
provide	O
inter-working	O
between	O
the	O
virtual	O
ports	O
created	O
by	O
Nova	O
.	O
</s>
<s>
The	O
technology	O
of	O
SDN	O
controllers	O
is	O
to	O
manage	O
the	O
Linux	O
kernel	O
features	O
made	O
of	O
L3	B-Protocol
IP	I-Protocol
routing	I-Protocol
,	O
Linux	B-Protocol
bridges	I-Protocol
,	O
iptables	B-Application
or	O
ebtables	O
,	O
network	O
namespaces	O
and	O
Open	B-Language
vSwitch	I-Language
.	O
</s>
