<s>
A	O
broadcast	B-Architecture
domain	I-Architecture
is	O
a	O
logical	O
division	O
of	O
a	O
computer	B-Architecture
network	I-Architecture
,	O
in	O
which	O
all	O
nodes	O
can	O
reach	O
each	O
other	O
by	O
broadcast	B-Operating_System
at	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
.	O
</s>
<s>
A	O
broadcast	B-Architecture
domain	I-Architecture
can	O
be	O
within	O
the	O
same	O
LAN	B-Protocol
segment	I-Protocol
or	O
it	O
can	O
be	O
bridged	O
to	O
other	O
LAN	B-Protocol
segments	I-Protocol
.	O
</s>
<s>
In	O
terms	O
of	O
current	O
popular	O
technologies	O
,	O
any	O
computer	O
connected	O
to	O
the	O
same	O
Ethernet	B-Protocol
repeater	I-Protocol
or	O
switch	B-Protocol
is	O
a	O
member	O
of	O
the	O
same	O
broadcast	B-Architecture
domain	I-Architecture
.	O
</s>
<s>
Further	O
,	O
any	O
computer	O
connected	O
to	O
the	O
same	O
set	O
of	O
interconnected	O
switches/repeaters	O
is	O
a	O
member	O
of	O
the	O
same	O
broadcast	B-Architecture
domain	I-Architecture
.	O
</s>
<s>
Routers	B-Protocol
and	O
other	O
higher-layer	B-Application
devices	O
form	O
boundaries	O
between	O
broadcast	B-Architecture
domains	I-Architecture
.	O
</s>
<s>
The	O
notion	O
of	O
broadcast	B-Architecture
domain	I-Architecture
should	O
be	O
contrasted	O
with	O
that	O
of	O
collision	B-Protocol
domain	I-Protocol
,	O
which	O
would	O
be	O
all	O
nodes	O
on	O
the	O
same	O
set	O
of	O
inter-connected	O
repeaters	O
,	O
divided	O
by	O
switches	O
and	O
learning	O
bridges	B-Protocol
.	O
</s>
<s>
Collision	B-Protocol
domains	I-Protocol
are	O
generally	O
smaller	O
than	O
,	O
and	O
contained	O
within	O
,	O
broadcast	B-Architecture
domains	I-Architecture
.	O
</s>
<s>
While	O
some	O
data-link-layer	B-Protocol
devices	O
are	O
able	O
to	O
divide	O
the	O
collision	B-Protocol
domains	I-Protocol
,	O
broadcast	B-Architecture
domains	I-Architecture
are	O
only	O
divided	O
by	O
layer	B-Application
3	I-Application
network	O
devices	O
such	O
as	O
routers	B-Protocol
or	O
layer	B-Application
3	I-Application
switches	O
.	O
</s>
<s>
Separating	O
VLANs	B-General_Concept
divides	O
broadcast	B-Architecture
domains	I-Architecture
as	O
well	O
.	O
</s>
<s>
The	O
distinction	O
between	O
broadcast	B-Operating_System
and	O
collision	B-Protocol
domains	I-Protocol
comes	O
about	O
because	O
simple	O
Ethernet	O
and	O
similar	O
systems	O
use	O
a	O
shared	O
transmission	O
system	O
.	O
</s>
<s>
In	O
simple	O
Ethernet	O
(	O
without	O
switches	O
or	O
bridges	B-Protocol
)	O
,	O
data	B-Protocol
frames	I-Protocol
are	O
transmitted	O
to	O
all	O
other	O
nodes	O
on	O
a	O
network	O
.	O
</s>
<s>
Each	O
receiving	O
node	B-Protocol
checks	O
the	O
destination	O
address	O
of	O
each	O
frame	O
,	O
and	O
simply	O
ignores	O
any	O
frame	O
not	O
addressed	O
to	O
its	O
own	O
MAC	O
address	O
or	O
the	O
broadcast	B-Protocol
address	I-Protocol
.	O
</s>
<s>
Switches	O
act	O
as	O
buffers	O
,	O
receiving	O
and	O
analyzing	O
the	O
frames	O
from	O
each	O
connected	O
network	B-Protocol
segment	I-Protocol
.	O
</s>
<s>
Frames	O
destined	O
for	O
nodes	O
connected	O
to	O
the	O
originating	O
segment	O
are	O
not	O
forwarded	O
by	O
the	O
switch	B-Protocol
.	O
</s>
<s>
Frames	O
destined	O
for	O
a	O
specific	O
node	B-Protocol
on	O
a	O
different	O
segment	O
are	O
sent	O
only	O
to	O
that	O
segment	O
.	O
</s>
<s>
Only	O
broadcast	B-Operating_System
frames	O
are	O
forwarded	O
to	O
all	O
other	O
segments	O
.	O
</s>
<s>
Nominally	O
,	O
only	O
broadcast	B-Operating_System
frames	O
will	O
be	O
received	O
by	O
all	O
other	O
nodes	O
.	O
</s>
<s>
Collisions	O
are	O
localized	O
to	O
the	O
physical-layer	O
network	B-Protocol
segment	I-Protocol
they	O
occur	O
on	O
.	O
</s>
<s>
Thus	O
,	O
the	O
broadcast	B-Architecture
domain	I-Architecture
is	O
the	O
entire	O
inter-connected	O
layer	B-Protocol
2	I-Protocol
network	O
,	O
and	O
the	O
segments	O
connected	O
to	O
each	O
switch/bridge	O
port	O
are	O
each	O
a	O
collision	B-Protocol
domain	I-Protocol
.	O
</s>
<s>
To	O
clarify	O
;	O
repeaters	O
do	O
not	O
divide	O
collision	B-Protocol
domains	I-Protocol
but	O
switches	O
do	O
.	O
</s>
<s>
This	O
means	O
that	O
since	O
switches	O
have	O
become	O
commonplace	O
,	O
collision	B-Protocol
domains	I-Protocol
are	O
isolated	O
to	O
the	O
specific	O
half-duplex	O
segment	O
between	O
the	O
switch	B-Protocol
port	I-Protocol
and	O
the	O
connected	O
node	B-Protocol
.	O
</s>
<s>
Full-duplex	O
segments	O
,	O
or	O
links	O
,	O
do	O
n't	O
form	O
a	O
collision	B-Protocol
domain	I-Protocol
as	O
there	O
is	O
a	O
dedicated	O
channel	O
between	O
each	O
transmitter	O
and	O
receiver	O
,	O
making	O
collisions	O
a	O
thing	O
of	O
the	O
past	O
in	O
modern	O
wired	O
networks	O
.	O
</s>
<s>
Such	O
frames	O
would	O
not	O
be	O
forwarded	O
by	O
the	O
switch	B-Protocol
to	O
any	O
ports	O
on	O
which	O
that	O
MAC	O
is	O
not	O
communicating	O
and	O
with	O
which	O
it	O
is	O
associated	O
in	O
the	O
MAC	O
address	O
table	O
.	O
</s>
<s>
Not	O
all	O
network	O
systems	O
or	O
media	O
feature	O
broadcast/collision	O
domains	O
.	O
</s>
<s>
For	O
example	O
,	O
PPP	B-Protocol
links	I-Protocol
.	O
</s>
<s>
With	O
a	O
sufficiently	O
sophisticated	O
switch	B-Protocol
,	O
it	O
is	O
possible	O
to	O
create	O
a	O
network	O
in	O
which	O
the	O
normal	O
notion	O
of	O
a	O
broadcast	B-Architecture
domain	I-Architecture
is	O
strictly	O
controlled	O
.	O
</s>
<s>
One	O
implementation	O
of	O
this	O
concept	O
is	O
termed	O
a	O
"	O
private	B-General_Concept
VLAN	I-General_Concept
"	O
.	O
</s>
<s>
Another	O
implementation	O
is	O
possible	O
with	O
Linux	B-Application
and	O
iptables	B-Application
.	O
</s>
<s>
One	O
analogy	O
is	O
that	O
by	O
creating	O
multiple	O
VLANs	B-General_Concept
,	O
the	O
number	O
of	O
broadcast	B-Architecture
domains	I-Architecture
increases	O
,	O
but	O
the	O
size	O
of	O
each	O
broadcast	B-Architecture
domain	I-Architecture
decreases	O
.	O
</s>
<s>
This	O
is	O
because	O
a	O
VLAN	B-General_Concept
(	O
or	O
virtual	B-General_Concept
LAN	I-General_Concept
)	O
is	O
technically	O
a	O
broadcast	B-Architecture
domain	I-Architecture
.	O
</s>
<s>
This	O
is	O
achieved	O
by	O
designating	O
one	O
or	O
more	O
"	O
server	B-Application
"	O
or	O
"	O
provider	O
"	O
nodes	O
,	O
either	O
by	O
MAC	O
address	O
or	O
switch	B-Protocol
port	I-Protocol
.	O
</s>
<s>
Broadcast	B-Operating_System
frames	O
are	O
allowed	O
to	O
originate	O
from	O
these	O
sources	O
and	O
are	O
sent	O
to	O
all	O
other	O
nodes	O
.	O
</s>
<s>
Broadcast	B-Operating_System
frames	O
from	O
all	O
other	O
sources	O
are	O
directed	O
only	O
to	O
the	O
server/provider	O
nodes	O
.	O
</s>
<s>
Traffic	O
from	O
other	O
sources	O
not	O
destined	O
to	O
the	O
server/provider	O
nodes	O
(	O
"	O
peer-to-peer	O
"	O
traffic	O
)	O
is	O
blocked	O
.	O
</s>
<s>
The	O
result	O
is	O
a	O
network	O
based	O
on	O
a	O
nominally	O
shared	O
transmission	O
system	O
;	O
like	O
Ethernet	O
,	O
but	O
in	O
which	O
"	O
client	B-Protocol
"	O
nodes	O
cannot	O
communicate	O
with	O
each	O
other	O
,	O
only	O
with	O
the	O
server/provider	O
.	O
</s>
<s>
Allowing	O
direct	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
communication	O
between	O
customer	O
nodes	O
exposes	O
the	O
network	O
to	O
various	O
security	O
attacks	O
,	O
such	O
as	O
ARP	O
spoofing	O
.	O
</s>
<s>
Controlling	O
the	O
broadcast	B-Architecture
domain	I-Architecture
in	O
this	O
fashion	O
provides	O
many	O
of	O
the	O
advantages	O
of	O
a	O
point-to-point	O
network	O
,	O
using	O
commodity	O
broadcast-based	O
hardware	O
.	O
</s>
