<s>
Private	B-General_Concept
VLAN	I-General_Concept
,	O
also	O
known	O
as	O
port	B-General_Concept
isolation	I-General_Concept
,	O
is	O
a	O
technique	O
in	O
computer	B-Architecture
networking	I-Architecture
where	O
a	O
VLAN	B-General_Concept
contains	O
switch	B-Protocol
ports	I-Protocol
that	O
are	O
restricted	O
such	O
that	O
they	O
can	O
only	O
communicate	O
with	O
a	O
given	O
uplink	B-Application
.	O
</s>
<s>
Each	O
private	B-General_Concept
VLAN	I-General_Concept
typically	O
contains	O
many	O
private	O
ports	O
,	O
and	O
a	O
single	O
uplink	B-Application
.	O
</s>
<s>
The	O
uplink	B-Application
will	O
typically	O
be	O
a	O
port	O
(	O
or	O
link	B-Architecture
aggregation	I-Architecture
group	I-Architecture
)	O
connected	O
to	O
a	O
router	B-Protocol
,	O
firewall	B-Application
,	O
server	B-Application
,	O
provider	O
network	O
,	O
or	O
similar	O
central	O
resource	O
.	O
</s>
<s>
The	O
concept	O
was	O
primarily	O
introduced	O
as	O
a	O
result	O
of	O
the	O
limitation	O
on	O
the	O
number	O
of	O
VLANs	B-General_Concept
in	O
network	B-Protocol
switches	I-Protocol
,	O
a	O
limit	O
quickly	O
exhausted	O
in	O
highly	O
scaled	O
scenarios	O
.	O
</s>
<s>
Hence	O
,	O
there	O
was	O
a	O
requirement	O
to	O
create	O
multiple	O
network	O
segregations	O
with	O
a	O
minimum	O
number	O
of	O
VLANs	B-General_Concept
.	O
</s>
<s>
The	O
switch	B-Protocol
forwards	O
all	O
frames	B-Protocol
received	O
from	O
a	O
private	O
port	O
to	O
the	O
uplink	B-Application
port	O
,	O
regardless	O
of	O
VLAN	B-General_Concept
ID	O
or	O
destination	O
MAC	O
address	O
.	O
</s>
<s>
Frames	B-Protocol
received	O
from	O
an	O
uplink	B-Application
port	O
are	O
forwarded	O
in	O
the	O
normal	O
way	O
(	O
i.e.	O
</s>
<s>
to	O
the	O
port	O
hosting	O
the	O
destination	O
MAC	O
address	O
,	O
or	O
to	O
all	O
ports	O
of	O
the	O
VLAN	B-General_Concept
for	O
broadcast	B-Operating_System
frames	I-Operating_System
or	O
for	O
unknown	O
destination	O
MAC	O
addresses	O
)	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
direct	O
peer-to-peer	O
traffic	O
between	O
peers	O
through	O
the	O
switch	B-Protocol
is	O
blocked	O
,	O
and	O
any	O
such	O
communication	O
must	O
go	O
through	O
the	O
uplink	B-Application
.	O
</s>
<s>
While	O
private	B-General_Concept
VLANs	I-General_Concept
provide	O
isolation	O
between	O
peers	O
at	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
,	O
communication	O
at	O
higher	O
layers	O
may	O
still	O
be	O
possible	O
depending	O
on	O
further	O
network	O
configuration	O
.	O
</s>
<s>
A	O
typical	O
application	O
for	O
a	O
private	B-General_Concept
VLAN	I-General_Concept
is	O
a	O
hotel	O
or	O
Ethernet	O
to	O
the	O
home	O
network	O
where	O
each	O
room	O
or	O
apartment	O
has	O
a	O
port	O
for	O
Internet	O
access	O
.	O
</s>
<s>
Similar	O
port	B-General_Concept
isolation	I-General_Concept
is	O
used	O
in	O
Ethernet-based	O
ADSL	O
DSLAMs	B-Protocol
.	O
</s>
<s>
Allowing	O
direct	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
communication	O
between	O
customer	O
nodes	O
would	O
expose	O
the	O
local	O
network	O
to	O
various	O
security	O
attacks	O
,	O
such	O
as	O
ARP	O
spoofing	O
,	O
as	O
well	O
as	O
increase	O
the	O
potential	O
for	O
damage	O
due	O
to	O
misconfiguration	O
.	O
</s>
<s>
Another	O
application	O
of	O
private	B-General_Concept
VLANs	I-General_Concept
is	O
to	O
simplify	O
IP	B-Protocol
address	O
assignment	O
.	O
</s>
<s>
Ports	O
can	O
be	O
isolated	O
from	O
each	O
other	O
at	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
(	O
for	O
security	O
,	O
performance	O
,	O
or	O
other	O
reasons	O
)	O
,	O
while	O
belonging	O
to	O
the	O
same	O
IP	B-Protocol
subnet	I-Protocol
.	O
</s>
<s>
In	O
such	O
a	O
case	O
,	O
direct	O
communication	O
between	O
the	O
IP	B-Protocol
hosts	O
on	O
the	O
protected	O
ports	O
is	O
only	O
possible	O
through	O
the	O
uplink	B-Application
connection	O
by	O
using	O
MAC-Forced	B-Protocol
Forwarding	I-Protocol
or	O
a	O
similar	O
Proxy	B-Protocol
ARP	I-Protocol
based	O
solution	O
.	O
</s>
<s>
Cisco	O
Systems	O
 '	O
Private	B-General_Concept
VLANs	I-General_Concept
are	O
defined	O
in	O
RFC	O
5517	O
.	O
</s>
<s>
A	O
Private	B-General_Concept
VLAN	I-General_Concept
divides	O
a	O
VLAN	B-General_Concept
(	O
Primary	O
)	O
into	O
sub-VLANs	O
(	O
Secondary	O
)	O
while	O
keeping	O
existing	O
IP	B-Protocol
subnet	I-Protocol
and	O
layer	B-Application
3	I-Application
configuration	O
.	O
</s>
<s>
A	O
regular	O
VLAN	B-General_Concept
is	O
a	O
single	O
broadcast	B-Architecture
domain	I-Architecture
,	O
while	O
private	B-General_Concept
VLAN	I-General_Concept
partitions	O
one	O
broadcast	B-Architecture
domain	I-Architecture
into	O
multiple	O
smaller	O
broadcast	B-Operating_System
subdomains	O
.	O
</s>
<s>
Primary	O
VLAN	B-General_Concept
:	O
Simply	O
the	O
original	O
VLAN	B-General_Concept
.	O
</s>
<s>
This	O
type	O
of	O
VLAN	B-General_Concept
is	O
used	O
to	O
forward	O
frames	B-Protocol
downstream	O
to	O
all	O
Secondary	O
VLANs	B-General_Concept
.	O
</s>
<s>
Secondary	O
VLAN	B-General_Concept
:	O
Secondary	O
VLAN	B-General_Concept
is	O
configured	O
with	O
one	O
of	O
the	O
following	O
types	O
:	O
</s>
<s>
Isolated	O
:	O
Any	O
switch	B-Protocol
ports	I-Protocol
associated	O
with	O
an	O
Isolated	O
VLAN	B-General_Concept
can	O
reach	O
the	O
primary	O
VLAN	B-General_Concept
,	O
but	O
not	O
any	O
other	O
Secondary	O
VLAN	B-General_Concept
.	O
</s>
<s>
In	O
addition	O
,	O
hosts	O
associated	O
with	O
the	O
same	O
Isolated	O
VLAN	B-General_Concept
cannot	O
reach	O
each	O
other	O
.	O
</s>
<s>
There	O
can	O
be	O
multiple	O
Isolated	O
VLANs	B-General_Concept
in	O
one	O
Private	B-General_Concept
VLAN	I-General_Concept
domain	O
(	O
which	O
may	O
be	O
useful	O
if	O
the	O
VLANs	B-General_Concept
need	O
to	O
use	O
distinct	O
paths	O
for	O
security	O
reasons	O
)	O
;	O
the	O
ports	O
remain	O
isolated	O
from	O
each	O
other	O
within	O
each	O
VLAN	B-General_Concept
.	O
</s>
<s>
Community	O
:	O
Any	O
switch	B-Protocol
ports	I-Protocol
associated	O
with	O
a	O
common	O
community	O
VLAN	B-General_Concept
can	O
communicate	O
with	O
each	O
other	O
and	O
with	O
the	O
primary	O
VLAN	B-General_Concept
but	O
not	O
with	O
any	O
other	O
secondary	O
VLAN	B-General_Concept
.	O
</s>
<s>
There	O
can	O
be	O
multiple	O
distinct	O
community	O
VLANs	B-General_Concept
within	O
one	O
Private	B-General_Concept
VLAN	I-General_Concept
domain	O
.	O
</s>
<s>
There	O
are	O
mainly	O
two	O
types	O
of	O
ports	O
in	O
a	O
Private	B-General_Concept
VLAN	I-General_Concept
:	O
Promiscuous	O
port	O
(	O
P-Port	O
)	O
and	O
Host	O
port	O
.	O
</s>
<s>
Promiscuous	O
port	O
(	O
P-Port	O
)	O
:	O
The	O
switch	B-Protocol
port	I-Protocol
connects	O
to	O
a	O
router	B-Protocol
,	O
firewall	B-Application
or	O
other	O
common	O
gateway	O
device	O
.	O
</s>
<s>
This	O
port	O
can	O
communicate	O
with	O
anything	O
else	O
connected	O
to	O
the	O
primary	O
or	O
any	O
secondary	O
VLAN	B-General_Concept
.	O
</s>
<s>
In	O
other	O
words	O
,	O
it	O
is	O
a	O
type	O
of	O
a	O
port	O
that	O
is	O
allowed	O
to	O
send	O
and	O
receive	O
frames	B-Protocol
from	O
any	O
other	O
port	O
on	O
the	O
VLAN	B-General_Concept
.	O
</s>
<s>
Isolated	O
Port	O
(	O
I-Port	O
)	O
:	O
Connects	O
to	O
the	O
regular	O
host	O
that	O
resides	O
on	O
isolated	O
VLAN	B-General_Concept
.	O
</s>
<s>
Community	O
Port	O
(	O
C-Port	O
)	O
:	O
Connects	O
to	O
the	O
regular	O
host	O
that	O
resides	O
on	O
community	O
VLAN	B-General_Concept
.	O
</s>
<s>
This	O
port	O
communicates	O
with	O
P-Ports	O
and	O
ports	O
on	O
the	O
same	O
community	O
VLAN	B-General_Concept
.	O
</s>
<s>
Example	O
scenario	O
:	O
a	O
switch	B-Protocol
with	O
VLAN	B-General_Concept
100	O
,	O
converted	O
into	O
a	O
Private	B-General_Concept
VLAN	I-General_Concept
with	O
one	O
P-Port	O
,	O
two	O
I-Ports	O
in	O
Isolated	O
VLAN	B-General_Concept
101	O
(	O
Secondary	O
)	O
and	O
two	O
community	O
VLANs	B-General_Concept
102	O
and	O
103	O
(	O
Secondary	O
)	O
,	O
with	O
2	O
ports	O
in	O
each	O
.	O
</s>
<s>
The	O
switch	B-Protocol
has	O
one	O
uplink	B-Application
port	O
(	O
trunk	O
)	O
,	O
connected	O
to	O
another	O
switch	B-Protocol
.	O
</s>
<s>
Traffic	O
from	O
an	O
Uplink	B-Application
port	O
to	O
an	O
Isolated	O
port	O
will	O
be	O
denied	O
if	O
it	O
is	O
in	O
the	O
Isolated	O
VLAN	B-General_Concept
.	O
</s>
<s>
Traffic	O
from	O
an	O
Uplink	B-Application
port	O
to	O
an	O
isolated	O
port	O
will	O
be	O
permitted	O
if	O
it	O
is	O
in	O
the	O
primary	O
VLAN	B-General_Concept
.	O
</s>
<s>
Private	B-General_Concept
VLANs	I-General_Concept
are	O
used	O
for	O
network	O
segregation	O
when	O
:	O
</s>
<s>
Moving	O
from	O
a	O
flat	O
network	O
to	O
a	O
segregated	O
network	O
without	O
changing	O
the	O
IP	B-Protocol
addressing	O
of	O
the	O
hosts	O
.	O
</s>
<s>
A	O
firewall	B-Application
can	O
replace	O
a	O
router	B-Protocol
,	O
and	O
then	O
hosts	O
can	O
be	O
slowly	O
moved	O
to	O
their	O
secondary	O
VLAN	B-General_Concept
assignment	O
without	O
changing	O
their	O
IP	B-Protocol
addresses	O
.	O
</s>
<s>
There	O
is	O
a	O
need	O
for	O
a	O
firewall	B-Application
with	O
many	O
tens	O
,	O
hundreds	O
or	O
even	O
thousands	O
interfaces	O
.	O
</s>
<s>
Using	O
Private	B-General_Concept
VLANs	I-General_Concept
the	O
firewall	B-Application
can	O
have	O
only	O
one	O
interface	O
for	O
all	O
the	O
segregated	O
networks	O
.	O
</s>
<s>
There	O
is	O
a	O
need	O
to	O
preserve	O
IP	B-Protocol
addressing	O
.	O
</s>
<s>
With	O
Private	B-General_Concept
VLANs	I-General_Concept
,	O
all	O
Secondary	O
VLANs	B-General_Concept
can	O
share	O
the	O
same	O
IP	B-Protocol
subnet	I-Protocol
.	O
</s>
<s>
Overcome	O
license	O
fees	O
for	O
number	O
of	O
supported	O
VLANs	B-General_Concept
per	O
firewall	B-Application
.	O
</s>
<s>
With	O
Isolated	O
VLAN	B-General_Concept
,	O
there	O
can	O
be	O
endless	O
number	O
of	O
segregated	O
networks	O
.	O
</s>
<s>
Private	B-General_Concept
VLANs	I-General_Concept
in	O
hosting	O
operation	O
allows	O
segregation	O
between	O
customers	O
with	O
the	O
following	O
benefits	O
:	O
</s>
<s>
No	O
need	O
for	O
separate	O
IP	B-Protocol
subnet	I-Protocol
for	O
each	O
customer	O
.	O
</s>
<s>
Using	O
Isolated	O
VLAN	B-General_Concept
,	O
there	O
is	O
no	O
limit	O
on	O
the	O
number	O
of	O
customers	O
.	O
</s>
<s>
No	O
need	O
to	O
change	O
firewall	B-Application
's	O
interface	O
configuration	O
to	O
extend	O
the	O
number	O
of	O
configured	O
VLANs	B-General_Concept
.	O
</s>
<s>
An	O
Isolated	O
VLAN	B-General_Concept
can	O
be	O
used	O
to	O
segregate	O
VDI	B-Protocol
desktops	I-Protocol
from	O
each	O
other	O
,	O
allowing	O
filtering	O
and	O
inspection	O
of	O
desktop	O
to	O
desktop	O
communication	O
.	O
</s>
<s>
Using	O
non-isolated	O
VLANs	B-General_Concept
would	O
require	O
a	O
different	O
VLAN	B-General_Concept
and	O
subnet	B-Protocol
for	O
each	O
VDI	O
desktop	O
.	O
</s>
<s>
Backup	O
clients	O
can	O
be	O
placed	O
in	O
one	O
Isolated	O
VLAN	B-General_Concept
and	O
the	O
backup	O
servers	O
can	O
be	O
placed	O
as	O
promiscuous	O
on	O
the	O
Primary	O
VLAN	B-General_Concept
,	O
this	O
will	O
allow	O
hosts	O
to	O
communicate	O
only	O
with	O
the	O
backup	O
servers	O
.	O
</s>
<s>
Because	O
broadcast	B-Operating_System
traffic	I-Operating_System
on	O
a	O
network	O
must	O
be	O
sent	O
to	O
each	O
wireless	O
host	O
serially	O
,	O
it	O
can	O
consume	O
large	O
shares	O
of	O
air	O
time	O
,	O
making	O
the	O
wireless	O
network	O
unresponsive	O
.	O
</s>
<s>
Where	O
there	O
is	O
more	O
than	O
one	O
wireless	O
access	O
point	O
connected	O
to	O
a	O
switch	B-Protocol
,	O
private	B-General_Concept
VLANs	I-General_Concept
can	O
prevent	O
broadcast	B-Operating_System
frames	I-Operating_System
from	O
propagating	O
from	O
one	O
AP	O
to	O
another	O
,	O
preserving	O
network	O
performance	O
for	O
connected	O
hosts	O
.	O
</s>
