<s>
The	O
virtual	B-General_Concept
access	I-General_Concept
layer	I-General_Concept
(	O
VAL	O
)	O
refers	O
to	O
the	O
virtualization	B-General_Concept
of	O
the	O
access	O
layer	O
that	O
connects	O
servers	O
to	O
the	O
network	O
in	O
the	O
data	O
center	O
.	O
</s>
<s>
Server	B-General_Concept
virtualization	I-General_Concept
is	O
now	O
aggressively	O
deployed	O
in	O
data	O
centers	O
for	O
consolidation	O
of	O
applications	O
hosted	O
on	O
x86	O
servers	O
.	O
</s>
<s>
However	O
,	O
the	O
underlying	O
limitations	O
in	O
current	O
networks	O
prevent	O
organizations	O
from	O
meeting	O
the	O
performance	O
,	O
availability	O
,	O
security	O
,	O
and	O
mobility	O
requirements	O
of	O
server	B-General_Concept
virtualization	I-General_Concept
.	O
</s>
<s>
VAL	O
is	O
a	O
product	O
strategy	O
that	O
delivers	O
features	O
to	O
address	O
the	O
unintended	O
consequences	O
of	O
server	B-General_Concept
virtualization	I-General_Concept
.	O
</s>
<s>
A	O
commonly	O
deployed	O
three-tier	O
LAN	B-General_Concept
network	I-General_Concept
design	O
includes	O
the	O
access	O
layer	O
,	O
which	O
provides	O
initial	O
connectivity	O
for	O
devices	O
to	O
the	O
network	O
.	O
</s>
<s>
With	O
server	B-General_Concept
virtualization	I-General_Concept
,	O
the	O
access	O
layer	O
moved	O
into	O
the	O
server	O
via	O
embedded	O
Ethernet	O
switches	O
in	O
software	O
(	O
known	O
as	O
“	O
softswitches	O
”	O
)	O
inside	O
the	O
virtualization	B-General_Concept
hypervisor	O
.	O
</s>
<s>
Today	O
the	O
edge	O
of	O
the	O
network	O
extends	O
past	O
the	O
physical	O
access	O
layer	O
switch	O
and	O
now	O
includes	O
hypervisor-hosted	O
softswitches	O
,	O
virtualization-capable	O
adapters	O
,	O
the	O
physical	O
access	O
layer	O
switch	O
,	O
and	O
optionally	O
a	O
bladed	O
server	O
switch	O
.	O
</s>
<s>
The	O
requirements	O
for	O
the	O
virtual	B-General_Concept
access	I-General_Concept
layer	I-General_Concept
are	O
as	O
follows	O
:	O
</s>
<s>
This	O
requires	O
virtualization	B-General_Concept
of	O
the	O
network	O
access	O
layer	O
,	O
so	O
that	O
network	O
administrators	O
can	O
provide	O
consistent	O
enforcement	O
of	O
network	O
access	O
control	O
and	O
security	O
policies	O
—	O
and	O
integrate	O
them	O
with	O
configuration	O
templates	O
for	O
VMs	O
inside	O
the	O
physical	O
server	O
.	O
</s>
<s>
The	O
data	O
center	O
networking	O
challenge	O
today	O
is	O
how	O
to	O
simplify	O
,	O
optimize	O
,	O
and	O
manage	O
the	O
virtual	B-General_Concept
access	I-General_Concept
layer	I-General_Concept
.	O
</s>
