<s>
A	O
virtual	B-General_Concept
local	I-General_Concept
area	I-General_Concept
network	I-General_Concept
(	O
VLAN	B-General_Concept
)	O
is	O
any	O
broadcast	B-Architecture
domain	I-Architecture
that	O
is	O
partitioned	B-Architecture
and	O
isolated	O
in	O
a	O
computer	B-Architecture
network	I-Architecture
at	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
(	O
OSI	B-Protocol
layer	I-Protocol
2	I-Protocol
)	O
.	O
</s>
<s>
In	O
this	O
context	O
,	O
virtual	B-General_Concept
,	O
refers	O
to	O
a	O
physical	O
object	O
recreated	O
and	O
altered	O
by	O
additional	O
logic	O
,	O
within	O
the	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
.	O
</s>
<s>
VLANs	B-General_Concept
work	O
by	O
applying	O
tags	O
to	O
network	B-Protocol
frames	I-Protocol
and	O
handling	O
these	O
tags	O
in	O
networking	O
systems	O
–	O
creating	O
the	O
appearance	O
and	O
functionality	O
of	O
network	O
traffic	O
that	O
is	O
physically	O
on	O
a	O
single	O
network	O
but	O
acts	O
as	O
if	O
it	O
is	O
split	O
between	O
separate	O
networks	O
.	O
</s>
<s>
In	O
this	O
way	O
,	O
VLANs	B-General_Concept
can	O
keep	O
network	O
applications	O
separate	O
despite	O
being	O
connected	O
to	O
the	O
same	O
physical	O
network	O
,	O
and	O
without	O
requiring	O
multiple	O
sets	O
of	O
cabling	O
and	O
networking	B-Device
devices	I-Device
to	O
be	O
deployed	O
.	O
</s>
<s>
VLANs	B-General_Concept
allow	O
network	O
administrators	O
to	O
group	O
hosts	O
together	O
even	O
if	O
the	O
hosts	O
are	O
not	O
directly	O
connected	O
to	O
the	O
same	O
network	B-Protocol
switch	I-Protocol
.	O
</s>
<s>
Because	O
VLAN	B-General_Concept
membership	O
can	O
be	O
configured	O
through	O
software	O
,	O
this	O
can	O
greatly	O
simplify	O
network	B-Architecture
design	I-Architecture
and	O
deployment	O
.	O
</s>
<s>
Without	O
VLANs	B-General_Concept
,	O
grouping	O
hosts	O
according	O
to	O
their	O
resource	O
needs	O
the	O
labor	O
of	O
relocating	O
nodes	B-Protocol
or	O
rewiring	O
data	O
links	O
.	O
</s>
<s>
VLANs	B-General_Concept
allow	O
devices	O
that	O
must	O
be	O
kept	O
separate	O
to	O
share	O
the	O
cabling	O
of	O
a	O
physical	O
network	O
and	O
yet	O
be	O
prevented	O
from	O
directly	O
interacting	O
with	O
one	O
another	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
VLAN	B-General_Concept
can	O
be	O
used	O
to	O
separate	O
traffic	O
within	O
a	O
business	O
based	O
on	O
individual	O
users	O
or	O
groups	O
of	O
users	O
or	O
their	O
roles	O
(	O
e.g.	O
</s>
<s>
Many	O
Internet	O
hosting	O
services	O
use	O
VLANs	B-General_Concept
to	O
separate	O
customers	O
 '	O
private	O
zones	O
from	O
one	O
other	O
,	O
allowing	O
each	O
customer	O
's	O
servers	O
to	O
be	O
grouped	O
in	O
a	O
single	O
network	O
segment	O
no	O
matter	O
where	O
the	O
individual	O
servers	O
are	O
located	O
in	O
the	O
data	B-Operating_System
center	I-Operating_System
.	O
</s>
<s>
Some	O
precautions	O
are	O
needed	O
to	O
prevent	O
traffic	O
"	O
escaping	O
"	O
from	O
a	O
given	O
VLAN	B-General_Concept
,	O
an	O
exploit	O
known	O
as	O
VLAN	B-Protocol
hopping	I-Protocol
.	O
</s>
<s>
To	O
subdivide	O
a	O
network	O
into	O
VLANs	B-General_Concept
,	O
one	O
configures	O
network	B-Device
equipment	I-Device
.	O
</s>
<s>
Simpler	O
equipment	O
might	O
partition	O
only	O
each	O
physical	O
port	O
(	O
if	O
even	O
that	O
)	O
,	O
in	O
which	O
case	O
each	O
VLAN	B-General_Concept
runs	O
over	O
a	O
dedicated	O
network	B-Protocol
cable	I-Protocol
.	O
</s>
<s>
More	O
sophisticated	O
devices	O
can	O
mark	O
frames	B-Protocol
through	O
VLAN	B-General_Concept
tagging	O
,	O
so	O
that	O
a	O
single	O
interconnect	O
(	O
trunk	O
)	O
may	O
be	O
used	O
to	O
transport	O
data	O
for	O
multiple	O
VLANs	B-General_Concept
.	O
</s>
<s>
Since	O
VLANs	B-General_Concept
share	O
bandwidth	O
,	O
a	O
VLAN	B-General_Concept
trunk	O
can	O
use	O
link	B-Architecture
aggregation	I-Architecture
,	O
quality-of-service	O
prioritization	O
,	O
or	O
both	O
to	O
route	B-Protocol
data	O
efficiently	O
.	O
</s>
<s>
VLANs	B-General_Concept
address	O
issues	O
such	O
as	O
scalability	B-Architecture
,	O
security	O
,	O
and	O
network	O
management	O
.	O
</s>
<s>
Network	O
architects	O
set	O
up	O
VLANs	B-General_Concept
to	O
provide	O
network	B-Architecture
segmentation	I-Architecture
.	O
</s>
<s>
Routers	B-Protocol
between	O
VLANs	B-General_Concept
filter	O
broadcast	B-Operating_System
traffic	I-Operating_System
,	O
enhance	O
network	O
security	O
,	O
perform	O
address	B-Protocol
summarization	I-Protocol
,	O
and	O
mitigate	O
network	B-Protocol
congestion	I-Protocol
.	O
</s>
<s>
In	O
a	O
network	O
utilizing	O
broadcasts	B-Operating_System
for	O
service	B-Protocol
discovery	I-Protocol
,	O
address	O
assignment	B-Protocol
and	O
resolution	O
and	O
other	O
services	O
,	O
as	O
the	O
number	O
of	O
peers	O
on	O
a	O
network	O
grows	O
,	O
the	O
frequency	O
of	O
broadcasts	B-Operating_System
also	O
increases	O
.	O
</s>
<s>
VLANs	B-General_Concept
can	O
help	O
manage	O
broadcast	B-Operating_System
traffic	I-Operating_System
by	O
forming	O
multiple	O
broadcast	B-Architecture
domains	I-Architecture
.	O
</s>
<s>
Breaking	O
up	O
a	O
large	O
network	O
into	O
smaller	O
independent	O
segments	O
reduces	O
the	O
amount	O
of	O
broadcast	B-Operating_System
traffic	I-Operating_System
each	O
network	B-Device
device	I-Device
and	O
network	O
segment	O
has	O
to	O
bear	O
.	O
</s>
<s>
Switches	O
may	O
not	O
bridge	O
network	O
traffic	O
between	O
VLANs	B-General_Concept
,	O
as	O
doing	O
so	O
would	O
violate	O
the	O
integrity	O
of	O
the	O
VLAN	B-General_Concept
broadcast	B-Architecture
domain	I-Architecture
.	O
</s>
<s>
VLANs	B-General_Concept
can	O
also	O
help	O
create	O
multiple	O
layer	B-Application
3	I-Application
networks	O
on	O
a	O
single	O
physical	O
infrastructure	O
.	O
</s>
<s>
VLANs	B-General_Concept
are	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
(	O
OSI	B-Protocol
layer	I-Protocol
2	I-Protocol
)	O
constructs	O
,	O
analogous	O
to	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	O
)	O
subnets	B-Protocol
,	O
which	O
are	O
network	B-Application
layer	I-Application
(	O
OSI	B-Application
layer	I-Application
3	I-Application
)	O
constructs	O
.	O
</s>
<s>
In	O
an	O
environment	O
employing	O
VLANs	B-General_Concept
,	O
a	O
one-to-one	O
relationship	O
often	O
exists	O
between	O
VLANs	B-General_Concept
and	O
IP	B-Protocol
subnets	I-Protocol
,	O
although	O
it	O
is	O
possible	O
to	O
have	O
multiple	O
subnets	B-Protocol
on	O
one	O
VLAN	B-General_Concept
.	O
</s>
<s>
Without	O
VLAN	B-General_Concept
capability	O
,	O
users	O
are	O
assigned	O
to	O
networks	O
based	O
on	O
geography	O
and	O
are	O
limited	O
by	O
physical	O
topologies	O
and	O
distances	O
.	O
</s>
<s>
VLANs	B-General_Concept
can	O
logically	O
group	O
networks	O
to	O
decouple	O
the	O
users	O
 '	O
network	O
location	O
from	O
their	O
physical	O
location	O
.	O
</s>
<s>
By	O
using	O
VLANs	B-General_Concept
,	O
one	O
can	O
control	O
traffic	O
patterns	O
and	O
react	O
quickly	O
to	O
employee	O
or	O
equipment	O
relocations	O
.	O
</s>
<s>
VLANs	B-General_Concept
provide	O
the	O
flexibility	O
to	O
adapt	O
to	O
changes	O
in	O
network	O
requirements	O
and	O
allow	O
for	O
simplified	O
administration	O
.	O
</s>
<s>
VLANs	B-General_Concept
can	O
be	O
used	O
to	O
partition	O
a	O
local	B-General_Concept
network	I-General_Concept
into	O
several	O
distinctive	O
segments	O
,	O
for	O
instance	O
:	O
</s>
<s>
A	O
common	O
infrastructure	O
shared	O
across	O
VLAN	B-General_Concept
trunks	O
can	O
provide	O
a	O
measure	O
of	O
security	O
with	O
great	O
flexibility	O
for	O
a	O
comparatively	O
low	O
cost	O
.	O
</s>
<s>
VoIP	B-Application
)	O
or	O
low-latency	O
requirements	O
(	O
e.g.	O
</s>
<s>
However	O
,	O
VLANs	B-General_Concept
as	O
a	O
security	O
solution	O
should	O
be	O
implemented	O
with	O
great	O
care	O
as	O
they	O
can	O
be	O
defeated	O
unless	O
implemented	O
carefully	O
.	O
</s>
<s>
In	O
cloud	B-Architecture
computing	I-Architecture
VLANs	B-General_Concept
,	O
IP	O
addresses	O
,	O
and	O
MAC	O
addresses	O
in	B-Architecture
the	I-Architecture
cloud	I-Architecture
are	O
resources	O
that	O
end	O
users	O
can	O
manage	O
.	O
</s>
<s>
To	O
help	O
mitigate	O
security	O
issues	O
,	O
placing	O
cloud-based	B-Architecture
virtual	B-General_Concept
machines	O
on	O
VLANs	B-General_Concept
may	O
be	O
preferable	O
to	O
placing	O
them	O
directly	O
on	O
the	O
Internet	O
.	O
</s>
<s>
Network	O
technologies	O
with	O
VLAN	B-General_Concept
capabilities	O
include	O
:	O
</s>
<s>
After	O
successful	O
experiments	O
with	O
voice	O
over	O
Ethernet	O
from	O
1981	O
to	O
1984	O
,	O
W	O
.	O
David	O
Sincoskie	O
joined	O
Bellcore	O
and	O
began	O
addressing	O
the	O
problem	O
of	O
scaling	B-Architecture
up	O
Ethernet	O
networks	O
.	O
</s>
<s>
However	O
,	O
Ethernet	O
was	O
a	O
broadcast	B-Operating_System
network	O
and	O
there	O
was	O
no	O
good	O
way	O
of	O
connecting	O
multiple	O
Ethernet	O
networks	O
together	O
.	O
</s>
<s>
This	O
limited	O
the	O
total	O
bandwidth	O
of	O
an	O
Ethernet	O
network	O
to	O
10Mbit/s	O
and	O
the	O
maximum	O
distance	O
between	O
nodes	B-Protocol
to	O
a	O
few	O
hundred	O
feet	O
.	O
</s>
<s>
Although	O
it	O
was	O
possible	O
to	O
use	O
IP	B-Protocol
routing	I-Protocol
to	O
connect	O
multiple	O
Ethernet	O
networks	O
together	O
,	O
it	O
was	O
expensive	O
and	O
relatively	O
slow	O
.	O
</s>
<s>
In	O
the	O
process	O
,	O
he	O
independently	O
reinvented	O
transparent	O
bridging	O
,	O
the	O
technique	O
used	O
in	O
modern	O
Ethernet	B-Protocol
switches	I-Protocol
.	O
</s>
<s>
However	O
,	O
using	O
switches	O
to	O
connect	O
multiple	O
Ethernet	O
networks	O
in	O
a	O
fault-tolerant	O
fashion	O
requires	O
redundant	O
paths	O
through	O
that	O
network	O
,	O
which	O
in	O
turn	O
requires	O
a	O
spanning	B-Protocol
tree	I-Protocol
configuration	O
.	O
</s>
<s>
This	O
causes	O
centrally	O
located	O
switches	O
to	O
become	O
bottlenecks	O
,	O
limiting	O
scalability	B-Architecture
as	O
more	O
networks	O
are	O
interconnected	O
.	O
</s>
<s>
To	O
help	O
alleviate	O
this	O
problem	O
,	O
Sincoskie	O
invented	O
VLANs	B-General_Concept
by	O
adding	O
a	O
tag	O
to	O
each	O
Ethernet	O
frame	O
.	O
</s>
<s>
In	O
this	O
scheme	O
,	O
each	O
switch	O
could	O
be	O
assigned	O
to	O
handle	O
frames	B-Protocol
of	O
a	O
single	O
color	O
,	O
and	O
ignore	O
the	O
rest	O
.	O
</s>
<s>
This	O
color	O
is	O
what	O
is	O
now	O
known	O
in	O
the	O
Ethernet	O
frame	O
as	O
the	O
IEEE	O
802.1Q	O
header	O
,	O
or	O
the	O
VLAN	B-General_Concept
tag	O
.	O
</s>
<s>
While	O
VLANs	B-General_Concept
are	O
commonly	O
used	O
in	O
modern	O
Ethernet	O
networks	O
,	O
they	O
are	O
not	O
used	O
in	O
the	O
manner	O
first	O
envisioned	O
here	O
.	O
</s>
<s>
In	O
1998	O
,	O
Ethernet	O
VLANs	B-General_Concept
were	O
described	O
in	O
the	O
first	O
edition	O
of	O
the	O
IEEE	O
802.1Q-1998	O
standard	O
.	O
</s>
<s>
This	O
was	O
extended	O
with	O
IEEE	O
802.1ad	O
to	O
allow	O
nested	O
VLAN	B-General_Concept
tags	O
in	O
service	O
of	O
provider	O
bridging	O
.	O
</s>
<s>
Early	O
network	O
designers	O
often	O
segmented	O
physical	O
LANs	B-General_Concept
with	O
the	O
aim	O
of	O
reducing	O
the	O
size	O
of	O
the	O
Ethernet	O
collision	O
domainthus	O
improving	O
performance	O
.	O
</s>
<s>
When	O
Ethernet	B-Protocol
switches	I-Protocol
made	O
this	O
a	O
non-issue	O
(	O
because	O
each	O
switch	B-Protocol
port	I-Protocol
is	O
a	O
collision	B-Protocol
domain	I-Protocol
)	O
,	O
attention	O
turned	O
to	O
reducing	O
the	O
size	O
of	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
broadcast	B-Architecture
domain	I-Architecture
.	O
</s>
<s>
VLANs	B-General_Concept
were	O
first	O
employed	O
to	O
separate	O
several	O
broadcast	B-Architecture
domains	I-Architecture
across	O
one	O
physical	O
medium	O
.	O
</s>
<s>
A	O
VLAN	B-General_Concept
can	O
also	O
serve	O
to	O
restrict	O
access	O
to	O
network	O
resources	O
without	O
regard	O
to	O
physical	O
topology	O
of	O
the	O
network	O
.	O
</s>
<s>
VLANs	B-General_Concept
operate	O
at	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
of	O
the	O
OSI	O
model	O
.	O
</s>
<s>
Administrators	O
often	O
configure	O
a	O
VLAN	B-General_Concept
to	O
map	O
directly	O
to	O
an	O
IP	O
network	O
,	O
or	O
subnet	B-Protocol
,	O
which	O
gives	O
the	O
appearance	O
of	O
involving	O
the	O
network	B-Application
layer	I-Application
.	O
</s>
<s>
Generally	O
,	O
VLANs	B-General_Concept
within	O
the	O
same	O
organization	O
will	O
be	O
assigned	O
different	O
non-overlapping	O
network	B-Protocol
address	I-Protocol
ranges	O
.	O
</s>
<s>
This	O
is	O
not	O
a	O
requirement	O
of	O
VLANs	B-General_Concept
.	O
</s>
<s>
There	O
is	O
no	O
issue	O
with	O
separate	O
VLANs	B-General_Concept
using	O
identical	O
overlapping	O
address	O
ranges	O
(	O
e.g.	O
</s>
<s>
two	O
VLANs	B-General_Concept
each	O
use	O
the	O
private	B-Protocol
network	I-Protocol
)	O
.	O
</s>
<s>
However	O
,	O
it	O
is	O
not	O
possible	O
to	O
route	B-Protocol
data	O
between	O
two	O
networks	O
with	O
overlapping	O
addresses	O
without	O
delicate	O
IP	B-Protocol
remapping	I-Protocol
,	O
so	O
if	O
the	O
goal	O
of	O
VLANs	B-General_Concept
is	O
segmentation	O
of	O
a	O
larger	O
overall	O
organizational	O
network	O
,	O
non-overlapping	O
addresses	O
must	O
be	O
used	O
in	O
each	O
separate	O
VLAN	B-General_Concept
.	O
</s>
<s>
A	O
basic	O
switch	O
that	O
is	O
not	O
configured	O
for	O
VLANs	B-General_Concept
has	O
VLAN	B-General_Concept
functionality	O
disabled	O
or	O
permanently	O
enabled	O
with	O
a	O
default	O
VLAN	B-General_Concept
that	O
contains	O
all	O
ports	O
on	O
the	O
device	O
as	O
members	O
.	O
</s>
<s>
The	O
default	O
VLAN	B-General_Concept
typically	O
uses	O
VLAN	B-General_Concept
identifier	O
1	O
.	O
</s>
<s>
Separating	O
ports	O
by	O
VLAN	B-General_Concept
groups	O
separates	O
their	O
traffic	O
very	O
much	O
like	O
connecting	O
each	O
group	O
using	O
a	O
distinct	O
switch	O
for	O
each	O
group	O
.	O
</s>
<s>
Remote	O
management	O
of	O
the	O
switch	O
requires	O
that	O
the	O
administrative	O
functions	O
be	O
associated	O
with	O
one	O
or	O
more	O
of	O
the	O
configured	O
VLANs	B-General_Concept
.	O
</s>
<s>
In	O
the	O
context	O
of	O
VLANs	B-General_Concept
,	O
the	O
term	O
trunk	O
denotes	O
a	O
network	O
link	O
carrying	O
multiple	O
VLANs	B-General_Concept
,	O
which	O
are	O
identified	O
by	O
labels	O
(	O
or	O
tags	O
)	O
inserted	O
into	O
their	O
packets	O
.	O
</s>
<s>
Such	O
trunks	O
must	O
run	O
between	O
tagged	O
ports	O
of	O
VLAN-aware	O
devices	O
,	O
so	O
they	O
are	O
often	O
switch-to-switch	O
or	O
switch-to-router	O
links	O
rather	O
than	O
links	O
to	O
hosts	O
.	O
</s>
<s>
(	O
Note	O
that	O
the	O
term	O
'	O
trunk	O
 '	O
is	O
also	O
used	O
for	O
what	O
Cisco	O
calls	O
"	O
channels	O
"	O
:	O
Link	B-Architecture
Aggregation	I-Architecture
or	I-Architecture
Port	I-Architecture
Trunking	I-Architecture
)	O
.	O
</s>
<s>
A	O
router	B-Protocol
(	O
Layer	B-Application
3	I-Application
device	O
)	O
serves	O
as	O
the	O
backbone	B-General_Concept
for	O
network	O
traffic	O
going	O
across	O
different	O
VLANs	B-General_Concept
.	O
</s>
<s>
It	O
is	O
only	O
when	O
the	O
VLAN	B-General_Concept
port	O
group	O
is	O
to	O
extend	O
to	O
another	O
device	O
that	O
tagging	O
is	O
used	O
.	O
</s>
<s>
Since	O
communications	O
between	O
ports	O
on	O
two	O
different	O
switches	O
travel	O
via	O
the	O
uplink	O
ports	O
of	O
each	O
switch	O
involved	O
,	O
every	O
VLAN	B-General_Concept
containing	O
such	O
ports	O
must	O
also	O
contain	O
the	O
uplink	O
port	O
of	O
each	O
switch	O
involved	O
,	O
and	O
traffic	O
through	O
these	O
ports	O
must	O
be	O
tagged	O
.	O
</s>
<s>
Switches	O
typically	O
have	O
no	O
built-in	O
method	O
to	O
indicate	O
VLAN	B-General_Concept
to	O
port	O
associations	O
to	O
someone	O
working	O
in	O
a	O
wiring	O
closet	O
.	O
</s>
<s>
It	O
is	O
necessary	O
for	O
a	O
technician	O
to	O
either	O
have	O
administrative	O
access	O
to	O
the	O
device	O
to	O
view	O
its	O
configuration	O
,	O
or	O
for	O
VLAN	B-General_Concept
port	O
assignment	B-Protocol
charts	O
or	O
diagrams	O
to	O
be	O
kept	O
next	O
to	O
the	O
switches	O
in	O
each	O
wiring	O
closet	O
.	O
</s>
<s>
The	O
protocol	O
most	O
commonly	O
used	O
today	O
to	O
support	O
VLANs	B-General_Concept
is	O
IEEE	O
802.1Q	O
.	O
</s>
<s>
The	O
IEEE	O
802.1	O
working	O
group	O
defined	O
this	O
method	O
of	O
multiplexing	O
VLANs	B-General_Concept
in	O
an	O
effort	O
to	O
provide	O
multivendor	O
VLAN	B-General_Concept
support	O
.	O
</s>
<s>
Prior	O
to	O
the	O
introduction	O
of	O
the	O
802.1Q	O
standard	O
,	O
several	O
proprietary	O
protocols	O
existed	O
,	O
such	O
as	O
Cisco	B-Protocol
Inter-Switch	I-Protocol
Link	I-Protocol
(	O
ISL	O
)	O
and	O
3Com	O
's	O
Virtual	B-General_Concept
LAN	I-General_Concept
Trunk	O
(	O
VLT	O
)	O
.	O
</s>
<s>
Cisco	O
also	O
implemented	O
VLANs	B-General_Concept
over	O
FDDI	B-Protocol
by	O
carrying	O
VLAN	B-General_Concept
information	O
in	O
an	O
IEEE	O
802.10	O
frame	O
header	O
,	O
contrary	O
to	O
the	O
purpose	O
of	O
the	O
IEEE	O
802.10	O
standard	O
.	O
</s>
<s>
Both	O
ISL	O
and	O
IEEE	O
802.1Q	O
perform	O
explicit	O
tagging	O
–	O
the	O
frame	O
itself	O
is	O
tagged	O
with	O
VLAN	B-General_Concept
identifiers	O
.	O
</s>
<s>
Under	O
IEEE	O
802.1Q	O
,	O
the	O
maximum	O
number	O
of	O
VLANs	B-General_Concept
on	O
a	O
given	O
Ethernet	O
network	O
is	O
4,094	O
(	O
4,096	O
values	O
provided	O
by	O
the	O
12-bit	O
field	O
minus	O
reserved	O
values	O
at	O
each	O
end	O
of	O
the	O
range	O
,	O
0	O
and	O
4,095	O
)	O
.	O
</s>
<s>
This	O
does	O
not	O
impose	O
the	O
same	O
limit	O
on	O
the	O
number	O
of	O
IP	B-Protocol
subnets	I-Protocol
in	O
such	O
a	O
network	O
since	O
a	O
single	O
VLAN	B-General_Concept
can	O
contain	O
multiple	O
IP	B-Protocol
subnets	I-Protocol
.	O
</s>
<s>
IEEE	O
802.1ad	O
extends	O
the	O
number	O
of	O
VLANs	B-General_Concept
supported	O
by	O
adding	O
support	O
for	O
multiple	O
,	O
nested	O
VLAN	B-General_Concept
tags	O
.	O
</s>
<s>
IEEE	B-Protocol
802.1aq	I-Protocol
(	O
Shortest	B-Protocol
Path	I-Protocol
Bridging	I-Protocol
)	O
expands	O
the	O
VLAN	B-General_Concept
limit	O
to	O
16	O
million	O
.	O
</s>
<s>
Inter-Switch	O
Link	O
(	O
ISL	O
)	O
is	O
a	O
Cisco	O
proprietary	O
protocol	O
used	O
to	O
interconnect	O
switches	O
and	O
maintain	O
VLAN	B-General_Concept
information	O
as	O
traffic	O
travels	O
between	O
switches	O
on	O
trunk	O
links	O
.	O
</s>
<s>
VLAN	B-General_Concept
Trunking	O
Protocol	O
(	O
VTP	O
)	O
is	O
a	O
Cisco	O
proprietary	O
protocol	O
that	O
propagates	O
the	O
definition	O
of	O
VLANs	B-General_Concept
on	O
the	O
whole	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
.	O
</s>
<s>
VTP	O
is	O
available	O
on	O
most	O
of	O
the	O
Cisco	B-Device
Catalyst	I-Device
Family	O
products	O
.	O
</s>
<s>
The	O
comparable	O
IEEE	O
standard	O
in	O
use	O
by	O
other	O
manufacturers	O
is	O
GARP	O
VLAN	B-General_Concept
Registration	O
Protocol	O
(	O
GVRP	O
)	O
or	O
the	O
more	O
recent	O
Multiple	O
VLAN	B-General_Concept
Registration	O
Protocol	O
(	O
MVRP	O
)	O
.	O
</s>
<s>
Multiple	O
VLAN	B-General_Concept
Registration	O
Protocol	O
is	O
an	O
application	O
of	O
Multiple	O
Registration	O
Protocol	O
that	O
allows	O
automatic	O
configuration	O
of	O
VLAN	B-General_Concept
information	O
on	O
network	B-Protocol
switches	I-Protocol
.	O
</s>
<s>
Specifically	O
,	O
it	O
provides	O
a	O
method	O
to	O
dynamically	O
share	O
VLAN	B-General_Concept
information	O
and	O
configure	O
the	O
needed	O
VLANs	B-General_Concept
.	O
</s>
<s>
VLAN	B-General_Concept
membership	O
can	O
be	O
established	O
either	O
statically	O
or	O
dynamically	O
.	O
</s>
<s>
Static	O
VLANs	B-General_Concept
are	O
also	O
referred	O
to	O
as	O
port-based	O
VLANs	B-General_Concept
.	O
</s>
<s>
Static	O
VLAN	B-General_Concept
assignments	O
are	O
created	O
by	O
assigning	O
ports	O
to	O
a	O
VLAN	B-General_Concept
.	O
</s>
<s>
As	O
a	O
device	O
enters	O
the	O
network	O
,	O
the	O
device	O
automatically	O
assumes	O
the	O
VLAN	B-General_Concept
of	O
the	O
port	O
.	O
</s>
<s>
If	O
the	O
user	O
changes	O
ports	O
and	O
needs	O
access	O
to	O
the	O
same	O
VLAN	B-General_Concept
,	O
the	O
network	O
administrator	O
must	O
manually	O
make	O
a	O
port-to-VLAN	O
assignment	B-Protocol
for	O
the	O
new	O
connection	O
.	O
</s>
<s>
Dynamic	O
VLANs	B-General_Concept
are	O
created	O
using	O
software	O
or	O
by	O
protocol	O
.	O
</s>
<s>
With	O
a	O
VLAN	B-Protocol
Management	I-Protocol
Policy	I-Protocol
Server	I-Protocol
(	O
VMPS	O
)	O
,	O
an	O
administrator	O
can	O
assign	O
switch	B-Protocol
ports	I-Protocol
to	O
VLANs	B-General_Concept
dynamically	O
based	O
on	O
information	O
such	O
as	O
the	O
source	O
MAC	O
address	O
of	O
the	O
device	O
connected	O
to	O
the	O
port	O
or	O
the	O
username	O
used	O
to	O
log	O
onto	O
that	O
device	O
.	O
</s>
<s>
As	O
a	O
device	O
enters	O
the	O
network	O
,	O
the	O
switch	O
queries	O
a	O
database	O
for	O
the	O
VLAN	B-General_Concept
membership	O
of	O
the	O
port	O
that	O
device	O
is	O
connected	O
to	O
.	O
</s>
<s>
Protocol	O
methods	O
include	O
Multiple	O
VLAN	B-General_Concept
Registration	O
Protocol	O
(	O
MVRP	O
)	O
and	O
the	O
somewhat	O
obsolete	O
GARP	O
VLAN	B-General_Concept
Registration	O
Protocol	O
(	O
GVRP	O
)	O
.	O
</s>
<s>
In	O
a	O
switch	O
that	O
supports	O
protocol-based	O
VLANs	B-General_Concept
,	O
traffic	O
may	O
be	O
handled	O
on	O
the	O
basis	O
of	O
its	O
protocol	O
.	O
</s>
<s>
VLAN	B-General_Concept
cross	O
connect	O
(	O
CC	O
or	O
VLAN-XC	O
)	O
is	O
a	O
mechanism	O
used	O
to	O
create	O
Switched	O
VLANs	B-General_Concept
,	O
VLAN	B-General_Concept
CC	O
uses	O
IEEE	O
802.1ad	O
frames	B-Protocol
where	O
the	O
S	O
Tag	O
is	O
used	O
as	O
a	O
Label	O
as	O
in	O
MPLS	B-Protocol
.	O
</s>
