<s>
Virtual	B-Protocol
Link	I-Protocol
Trunking	I-Protocol
(	O
VLT	O
)	O
is	O
a	O
name	O
that	O
has	O
been	O
used	O
for	O
at	O
least	O
two	O
proprietary	O
network	O
protocols	O
.	O
</s>
<s>
A	O
link	B-Architecture
aggregation	I-Architecture
protocol	O
developed	O
by	O
Force10	O
and	O
an	O
early	O
VLAN	O
tagging	O
capability	O
from	O
3Com	O
.	O
</s>
<s>
Virtual	B-Protocol
Link	I-Protocol
Trunking	I-Protocol
or	O
VLT	O
is	O
a	O
proprietary	O
aggregation	B-Architecture
protocol	O
developed	O
by	O
Force10	O
(	O
now	O
Dell	B-Application
Networking	I-Application
)	O
and	O
available	O
in	O
their	O
datacenter-class	O
or	O
enterprise-class	O
network	B-Protocol
switches	I-Protocol
.	O
</s>
<s>
VLT	O
is	O
implemented	O
in	O
the	O
latest	O
firmware	O
releases	O
of	O
legacy	O
(	O
FTOS	B-Protocol
)	O
OS9	O
for	O
their	O
high-end	O
switches	O
like	O
the	O
S-	O
,	O
Z	O
-	O
and	O
E-series	O
10/25	O
,	O
40	O
and	O
100	O
Gbit/s	O
datacenter	O
switches	O
.	O
</s>
<s>
Although	O
VLT	O
is	O
a	O
proprietary	O
protocol	O
from	O
Dell	B-Application
Networking	I-Application
(	O
formerly	O
Force10	O
)	O
other	O
vendors	O
offer	O
similar	O
features	O
to	O
allow	O
users	O
to	O
set	O
up	O
an	O
aggregated	O
link	O
towards	O
two	O
(	O
logical	O
)	O
different	O
switches	O
,	O
where	O
a	O
standard	O
aggregated	O
link	O
can	O
only	O
terminate	O
on	O
a	O
single	O
logical	O
switch	O
(	O
thus	O
either	O
a	O
single	O
physical	O
switch	O
or	O
on	O
different	O
members	O
in	O
a	O
stacked	O
switch	O
setup	O
)	O
like	O
Cisco	O
vpc	O
or	O
MLAG	B-Protocol
.	O
</s>
<s>
VLT	O
is	O
a	O
layer-2	O
link	B-Architecture
aggregation	I-Architecture
protocol	O
between	O
end-devices	O
(	O
servers	O
)	O
connected	O
to	O
(	O
different	O
)	O
access-switches	O
,	O
offering	O
these	O
servers	O
a	O
redundant	O
,	O
load-balancing	O
connection	O
to	O
the	O
core-network	O
in	O
a	O
loop-free	O
environment	O
,	O
eliminating	O
the	O
requirement	O
for	O
the	O
use	O
of	O
a	O
spanning-tree	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
Where	O
existing	O
link	B-Architecture
aggregation	I-Architecture
protocols	O
like	O
(	O
static	O
)	O
LAG	O
(	O
IEEE	O
802.3ad	O
)	O
or	O
LACP	O
(	O
IEEE	O
802.1ax	O
)	O
require	O
the	O
different	O
(	O
physical	O
)	O
links	O
to	O
be	O
connected	O
to	O
the	O
same	O
(	O
logical	O
)	O
switch	O
(	O
such	O
as	O
stacked	O
switches	O
)	O
,	O
the	O
VLT	O
,	O
for	O
example	O
,	O
allows	O
link	O
connectivity	O
between	O
a	O
server	O
and	O
the	O
network	O
via	O
two	O
different	O
switches	O
.	O
</s>
<s>
A	O
major	O
complication	O
of	O
existing	O
link	B-Architecture
aggregation	I-Architecture
or	O
bonding	B-Architecture
technologies	O
is	O
that	O
all	O
members	O
interfaces	O
of	O
such	O
a	O
team/group	O
need	O
to	O
terminate	O
on	O
one	O
single	O
logical	O
switch	O
.	O
</s>
<s>
Beside	O
increasing	O
bandwidth	O
another	O
reason	O
for	O
link	B-Architecture
aggregation	I-Architecture
is	O
redundancy	O
.	O
</s>
<s>
To	O
make	O
it	O
possible	O
to	O
connect	O
a	O
LAG	O
to	O
different	O
physical	O
switches	O
is	O
to	O
combine	O
more	O
than	O
one	O
physical	O
switch	O
into	O
one	O
logical	O
switch	O
using	O
switch	O
stacking	O
techniques	O
where	O
the	O
different	O
physical	O
boxes	O
are	O
seen	O
as	O
one	O
logical	O
switch	O
for	O
management	O
and	O
(	O
spanning-tree	B-Protocol
)	O
topology	O
.	O
</s>
<s>
The	O
alternative	O
is	O
to	O
have	O
different	O
logical	O
switches	O
,	O
but	O
then	O
one	O
of	O
the	O
used	O
links	O
will	O
have	O
to	O
be	O
blocked	O
to	O
ensure	O
a	O
loop-free	O
topology	O
(	O
which	O
can	O
partially	O
be	O
overcome	O
by	O
using	O
Multiple	B-Protocol
Spanning	I-Protocol
Tree	I-Protocol
or	O
Cisco	O
's	O
proprietary	O
per	O
VLAN	O
spanning	O
tree	O
.	O
</s>
<s>
Spanning	B-Protocol
Tree	I-Protocol
Protocol	I-Protocol
is	O
relatively	O
slow	O
in	O
convergence	O
,	O
which	O
can	O
result	O
in	O
periods	O
that	O
traffic	O
ca	O
n't	O
be	O
forwarded	O
over	O
the	O
network	O
-	O
and	O
thus	O
leads	O
to	O
outages	O
of	O
the	O
applications	O
.	O
</s>
<s>
VLT	O
should	O
address	O
all	O
these	O
issues	O
,	O
making	O
it	O
possible	O
to	O
create	O
a	O
loop	O
free	O
redundant	O
network	O
topology	O
without	O
using	O
the	O
Spanning	B-Protocol
Tree	I-Protocol
Protocol	I-Protocol
.	O
</s>
<s>
3Com	O
VLT	O
supported	O
VLAN	O
IDs	O
1	O
–	O
16	O
with	O
15	O
being	O
reserved	O
for	O
Autoselect	O
VLAN	O
Mode	O
(	O
where	O
a	O
VLAN	O
server	O
decides	O
port	O
membership	O
)	O
and	O
16	O
reserved	O
for	O
Spanning	B-Protocol
Tree	I-Protocol
Protocol	I-Protocol
.	O
</s>
