<s>
A	O
network	B-Protocol
bridge	I-Protocol
is	O
a	O
computer	B-Device
networking	I-Device
device	I-Device
that	O
creates	O
a	O
single	O
,	O
aggregate	O
network	O
from	O
multiple	O
communication	O
networks	O
or	O
network	B-Protocol
segments	I-Protocol
.	O
</s>
<s>
This	O
function	O
is	O
called	O
network	B-Protocol
bridging	I-Protocol
.	O
</s>
<s>
Bridging	B-Protocol
is	O
distinct	O
from	O
routing	B-Protocol
.	O
</s>
<s>
Routing	B-Protocol
allows	O
multiple	O
networks	O
to	O
communicate	O
independently	O
and	O
yet	O
remain	O
separate	O
,	O
whereas	O
bridging	B-Protocol
connects	O
two	O
separate	O
networks	O
as	O
if	O
they	O
were	O
a	O
single	O
network	O
.	O
</s>
<s>
In	O
the	O
OSI	O
model	O
,	O
bridging	B-Protocol
is	O
performed	O
in	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
(	O
layer	B-Protocol
2	I-Protocol
)	O
.	O
</s>
<s>
If	O
one	O
or	O
more	O
segments	O
of	O
the	O
bridged	B-Protocol
network	I-Protocol
are	O
wireless	B-General_Concept
,	O
the	O
device	O
is	O
known	O
as	O
a	O
wireless	B-Protocol
bridge	I-Protocol
.	O
</s>
<s>
The	O
main	O
types	O
of	O
network	B-Protocol
bridging	I-Protocol
technologies	O
are	O
simple	O
bridging	B-Protocol
,	O
multiport	O
bridging	B-Protocol
,	O
and	O
learning	O
or	O
transparent	O
bridging	B-Protocol
.	O
</s>
<s>
Transparent	O
bridging	B-Protocol
uses	O
a	O
table	O
called	O
the	O
forwarding	B-Protocol
information	I-Protocol
base	I-Protocol
to	O
control	O
the	O
forwarding	O
of	O
frames	O
between	O
network	B-Protocol
segments	I-Protocol
.	O
</s>
<s>
If	O
a	O
destination	O
address	O
entry	O
is	O
not	O
found	O
in	O
the	O
table	O
,	O
the	O
frame	B-Protocol
is	O
flooded	O
to	O
all	O
other	O
ports	O
of	O
the	O
bridge	O
,	O
flooding	O
the	O
frame	B-Protocol
to	O
all	O
segments	O
except	O
the	O
one	O
from	O
which	O
it	O
was	O
received	O
.	O
</s>
<s>
By	O
means	O
of	O
these	O
flooded	O
frames	O
,	O
a	O
host	B-Device
on	O
the	O
destination	O
network	O
will	O
respond	O
and	O
a	O
forwarding	O
database	O
entry	O
will	O
be	O
created	O
.	O
</s>
<s>
Both	O
source	O
and	O
destination	O
addresses	O
are	O
used	O
in	O
this	O
process	O
:	O
source	O
addresses	O
are	O
recorded	O
in	O
entries	O
in	O
the	O
table	O
,	O
while	O
destination	O
addresses	O
are	O
looked	O
up	O
in	O
the	O
table	O
and	O
matched	O
to	O
the	O
proper	O
segment	O
to	O
send	O
the	O
frame	B-Protocol
to	O
.	O
</s>
<s>
In	O
the	O
context	O
of	O
a	O
two-port	O
bridge	O
,	O
the	O
forwarding	B-Protocol
information	I-Protocol
base	I-Protocol
can	O
be	O
seen	O
as	O
a	O
filtering	O
database	O
.	O
</s>
<s>
A	O
bridge	O
reads	O
a	O
frame	B-Protocol
's	O
destination	O
address	O
and	O
decides	O
to	O
either	O
forward	O
or	O
filter	O
.	O
</s>
<s>
If	O
the	O
bridge	O
determines	O
that	O
the	O
destination	O
host	B-Device
is	O
on	O
another	O
segment	O
on	O
the	O
network	O
,	O
it	O
forwards	O
the	O
frame	B-Protocol
to	O
that	O
segment	O
.	O
</s>
<s>
If	O
the	O
destination	O
address	O
belongs	O
to	O
the	O
same	O
segment	O
as	O
the	O
source	O
address	O
,	O
the	O
bridge	O
filters	O
the	O
frame	B-Protocol
,	O
preventing	O
it	O
from	O
reaching	O
the	O
other	O
network	O
where	O
it	O
is	O
not	O
needed	O
.	O
</s>
<s>
Transparent	O
bridging	B-Protocol
can	O
also	O
operate	O
over	O
devices	O
with	O
more	O
than	O
two	O
ports	O
.	O
</s>
<s>
A	O
sends	O
a	O
frame	B-Protocol
addressed	O
to	O
B	O
to	O
the	O
bridge	O
.	O
</s>
<s>
The	O
bridge	O
examines	O
the	O
source	O
address	O
of	O
the	O
frame	B-Protocol
and	O
creates	O
an	O
address	O
and	O
port	O
number	O
entry	O
for	O
host	B-Device
A	O
in	O
its	O
forwarding	B-Protocol
table	I-Protocol
.	O
</s>
<s>
The	O
bridge	O
examines	O
the	O
destination	O
address	O
of	O
the	O
frame	B-Protocol
and	O
does	O
not	O
find	O
it	O
in	O
its	O
forwarding	B-Protocol
table	I-Protocol
so	O
it	O
floods	O
(	O
broadcasts	O
)	O
it	O
to	O
all	O
other	O
ports	O
:	O
2	O
and	O
3	O
.	O
</s>
<s>
The	O
frame	B-Protocol
is	O
received	O
by	O
hosts	O
B	O
and	O
C	O
.	O
Host	B-Device
C	O
examines	O
the	O
destination	O
address	O
and	O
ignores	O
the	O
frame	B-Protocol
as	O
it	O
does	O
not	O
match	O
with	O
its	O
address	O
.	O
</s>
<s>
Host	B-Device
B	O
recognizes	O
a	O
destination	O
address	O
match	O
and	O
generates	O
a	O
response	O
to	O
A	O
.	O
</s>
<s>
On	O
the	O
return	O
path	O
,	O
the	O
bridge	O
adds	O
an	O
address	O
and	O
port	O
number	O
entry	O
for	O
B	O
to	O
its	O
forwarding	B-Protocol
table	I-Protocol
.	O
</s>
<s>
The	O
bridge	O
already	O
has	O
A	O
's	O
address	O
in	O
its	O
forwarding	B-Protocol
table	I-Protocol
so	O
it	O
forwards	O
the	O
response	O
only	O
to	O
port	O
1	O
.	O
</s>
<s>
Host	B-Device
C	O
or	O
any	O
other	O
hosts	O
on	O
port	O
3	O
are	O
not	O
burdened	O
with	O
the	O
response	O
.	O
</s>
<s>
Now	O
,	O
if	O
A	O
sends	O
a	O
frame	B-Protocol
addressed	O
to	O
C	O
,	O
the	O
same	O
procedure	O
will	O
be	O
used	O
,	O
but	O
this	O
time	O
the	O
bridge	O
will	O
not	O
create	O
a	O
new	O
forwarding-table	O
entry	O
for	O
A	O
's	O
address/port	O
because	O
it	O
has	O
already	O
done	O
so	O
.	O
</s>
<s>
Bridging	B-Protocol
is	O
called	O
transparent	O
when	O
the	O
frame	B-Protocol
format	O
and	O
its	O
addressing	O
are	O
n't	O
changed	O
substantially	O
.	O
</s>
<s>
Non-transparent	O
bridging	B-Protocol
is	O
required	O
especially	O
when	O
the	O
frame	B-Protocol
addressing	O
schemes	O
on	O
both	O
sides	O
of	O
a	O
bridge	O
are	O
not	O
compatible	O
with	O
each	O
other	O
,	O
e.g.	O
</s>
<s>
between	O
ARCNET	B-Protocol
with	O
local	O
addressing	O
and	O
Ethernet	O
using	O
IEEE	O
MAC	O
addresses	O
,	O
requiring	O
translation	O
.	O
</s>
<s>
However	O
,	O
most	O
often	O
such	O
incompatible	O
networks	O
are	O
routed	B-Protocol
in	O
between	O
,	O
not	O
bridged	O
.	O
</s>
<s>
A	O
simple	O
bridge	O
connects	O
two	O
network	B-Protocol
segments	I-Protocol
,	O
typically	O
by	O
operating	O
transparently	O
and	O
deciding	O
on	O
a	O
frame-by-frame	O
basis	O
whether	O
or	O
not	O
to	O
forward	O
from	O
one	O
network	O
to	O
the	O
other	O
.	O
</s>
<s>
A	O
store	B-Protocol
and	I-Protocol
forward	I-Protocol
technique	O
is	O
typically	O
used	O
so	O
,	O
as	O
part	O
of	O
forwarding	O
,	O
the	O
frame	B-Protocol
integrity	O
is	O
verified	O
on	O
the	O
source	O
network	O
and	O
CSMA/CD	O
delays	O
are	O
accommodated	O
on	O
the	O
destination	O
network	O
.	O
</s>
<s>
Additionally	O
,	O
bridges	O
reduce	O
collisions	O
by	O
creating	O
a	O
separate	O
collision	B-Protocol
domain	I-Protocol
on	O
either	O
side	O
of	O
the	O
bridge	O
.	O
</s>
<s>
A	O
multiport	O
bridge	O
connects	O
multiple	O
networks	O
and	O
operates	O
transparently	O
to	O
decide	O
on	O
a	O
frame-by-frame	O
basis	O
whether	O
to	O
forward	O
traffic	O
.	O
</s>
<s>
Like	O
the	O
simple	O
bridge	O
,	O
a	O
multiport	O
bridge	O
typically	O
uses	O
store	B-Protocol
and	I-Protocol
forward	I-Protocol
operation	O
.	O
</s>
<s>
The	O
multiport	O
bridge	O
function	O
serves	O
as	O
the	O
basis	O
for	O
network	B-Protocol
switches	I-Protocol
.	O
</s>
<s>
The	O
forwarding	B-Protocol
information	I-Protocol
base	I-Protocol
stored	O
in	O
content-addressable	B-Data_Structure
memory	I-Data_Structure
(	O
CAM	B-Data_Structure
)	O
is	O
initially	O
empty	O
.	O
</s>
<s>
For	O
each	O
received	O
Ethernet	B-Protocol
frame	I-Protocol
the	O
switch	O
learns	O
from	O
the	O
frame	B-Protocol
's	O
source	O
MAC	O
address	O
and	O
adds	O
this	O
together	O
with	O
an	O
interface	O
identifier	O
to	O
the	O
forwarding	B-Protocol
information	I-Protocol
base	I-Protocol
.	O
</s>
<s>
The	O
switch	O
then	O
forwards	O
the	O
frame	B-Protocol
to	O
the	O
interface	O
found	O
in	O
the	O
CAM	B-Data_Structure
based	O
on	O
the	O
frame	B-Protocol
's	O
destination	O
MAC	O
address	O
.	O
</s>
<s>
If	O
the	O
destination	O
address	O
is	O
unknown	O
the	O
switch	O
sends	O
the	O
frame	B-Protocol
out	O
on	O
all	O
interfaces	O
(	O
except	O
the	O
ingress	O
interface	O
)	O
.	O
</s>
<s>
Once	O
a	O
bridge	O
learns	O
the	O
addresses	O
of	O
its	O
connected	O
nodes	O
,	O
it	O
forwards	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
frames	O
using	O
a	O
layer-2	B-Protocol
forwarding	O
method	O
.	O
</s>
<s>
Store	B-Protocol
and	I-Protocol
forward	I-Protocol
:	O
the	O
switch	O
buffers	O
and	O
verifies	O
each	O
frame	B-Protocol
before	O
forwarding	O
it	O
;	O
a	O
frame	B-Protocol
is	O
received	O
in	O
its	O
entirety	O
before	O
it	O
is	O
forwarded	O
.	O
</s>
<s>
Cut	B-Protocol
through	I-Protocol
:	O
the	O
switch	O
starts	O
forwarding	O
after	O
the	O
frame	B-Protocol
's	O
destination	O
address	O
is	O
received	O
.	O
</s>
<s>
When	O
the	O
outgoing	O
port	O
is	O
busy	O
at	O
the	O
time	O
,	O
the	O
switch	O
falls	O
back	O
to	O
store-and-forward	B-Protocol
operation	O
.	O
</s>
<s>
Also	O
,	O
when	O
the	O
egress	O
port	O
is	O
running	O
at	O
a	O
faster	O
data	O
rate	O
than	O
the	O
ingress	O
port	O
,	O
store-and-forward	B-Protocol
is	O
usually	O
used	O
.	O
</s>
<s>
Fragment	O
free	O
:	O
a	O
method	O
that	O
attempts	O
to	O
retain	O
the	O
benefits	O
of	O
both	O
store	B-Protocol
and	I-Protocol
forward	I-Protocol
and	O
cut	B-Protocol
through	I-Protocol
.	O
</s>
<s>
Fragment	O
free	O
checks	O
the	O
first	O
64	O
bytes	B-Application
of	O
the	O
frame	B-Protocol
,	O
where	O
addressing	O
information	O
is	O
stored	O
.	O
</s>
<s>
According	O
to	O
Ethernet	O
specifications	O
,	O
collisions	O
should	O
be	O
detected	O
during	O
the	O
first	O
64	O
bytes	B-Application
of	O
the	O
frame	B-Protocol
,	O
so	O
frame	B-Protocol
transmissions	O
that	O
are	O
aborted	O
because	O
of	O
a	O
collision	O
will	O
not	O
be	O
forwarded	O
.	O
</s>
<s>
Adaptive	B-Device
switching	I-Device
:	O
a	O
method	O
of	O
automatically	O
selecting	O
between	O
the	O
other	O
three	O
modes	O
.	O
</s>
<s>
Shortest	B-Protocol
Path	I-Protocol
Bridging	I-Protocol
(	O
SPB	O
)	O
,	O
specified	O
in	O
the	O
IEEE	B-Protocol
802.1aq	I-Protocol
standard	O
and	O
based	O
on	O
Dijkstra	B-Algorithm
's	I-Algorithm
algorithm	I-Algorithm
,	O
is	O
a	O
computer	B-Architecture
networking	I-Architecture
technology	O
intended	O
to	O
simplify	O
the	O
creation	O
and	O
configuration	O
of	O
networks	O
,	O
while	O
enabling	O
multipath	B-Protocol
routing	I-Protocol
.	O
</s>
<s>
It	O
is	O
a	O
proposed	O
replacement	O
for	O
Spanning	B-Protocol
Tree	I-Protocol
Protocol	I-Protocol
which	O
blocks	O
any	O
redundant	O
paths	O
that	O
could	O
result	O
in	O
a	O
switching	B-Architecture
loop	I-Architecture
.	O
</s>
<s>
SPB	O
also	O
increases	O
the	O
number	O
of	O
VLANs	O
allowed	O
on	O
a	O
layer-2	B-Protocol
network	O
.	O
</s>
<s>
TRILL	B-Protocol
(	O
TRansparent	B-Protocol
Interconnection	I-Protocol
of	I-Protocol
Lots	I-Protocol
of	I-Protocol
Links	I-Protocol
)	O
is	O
the	O
successor	O
to	O
Spanning	B-Protocol
Tree	I-Protocol
Protocol	I-Protocol
,	O
both	O
having	O
been	O
created	O
by	O
the	O
same	O
person	O
,	O
Radia	O
Perlman	O
.	O
</s>
<s>
The	O
catalyst	O
for	O
TRILL	B-Protocol
was	O
an	O
event	O
at	O
Beth	O
Israel	O
Deaconess	O
Medical	O
Center	O
which	O
began	O
on	O
13	O
November	O
2002	O
.	O
</s>
<s>
The	O
concept	O
of	O
Rbridges	O
 [ sic ] 	O
was	O
first	O
proposed	O
to	O
the	O
Institute	O
of	O
Electrical	O
and	O
Electronics	O
Engineers	O
in	O
the	O
year	O
2004	O
,	O
whom	O
in	O
2005	O
rejected	O
what	O
came	O
to	O
be	O
known	O
as	O
TRILL	B-Protocol
,	O
and	O
in	O
the	O
years	O
2006	O
through	O
2012	O
devised	O
an	O
incompatible	O
variation	O
known	O
as	O
Shortest	B-Protocol
Path	I-Protocol
Bridging	I-Protocol
.	O
</s>
