<s>
A	O
Layer	B-General_Concept
2	I-General_Concept
MPLS	I-General_Concept
VPN	I-General_Concept
is	O
a	O
term	O
in	O
computer	B-Architecture
networking	I-Architecture
.	O
</s>
<s>
It	O
is	O
a	O
method	O
that	O
Internet	O
service	O
providers	O
use	O
to	O
segregate	O
their	O
network	O
for	O
their	O
customers	O
,	O
to	O
allow	O
them	O
to	O
transmit	O
data	O
over	O
an	O
IP	B-Protocol
network	I-Protocol
.	O
</s>
<s>
Layer	B-Protocol
2	I-Protocol
VPNs	B-Application
are	O
a	O
type	O
of	O
Virtual	B-Application
Private	I-Application
Network	I-Application
(	O
VPN	B-Application
)	O
that	O
uses	O
MPLS	B-Protocol
labels	O
to	O
transport	O
data	O
.	O
</s>
<s>
The	O
communication	O
occurs	O
between	O
routers	B-Protocol
that	O
are	O
known	O
as	O
Provider	O
Edge	B-Protocol
routers	I-Protocol
(	O
PEs	O
)	O
,	O
as	O
they	O
sit	O
on	O
the	O
edge	O
of	O
the	O
provider	O
's	O
network	O
,	O
next	O
to	O
the	O
customer	O
's	O
network	O
.	O
</s>
<s>
Internet	O
providers	O
who	O
have	O
an	O
existing	O
Layer	B-Protocol
2	I-Protocol
network	O
(	O
such	O
as	O
ATM	O
or	O
Frame	B-Protocol
Relay	I-Protocol
)	O
may	O
choose	O
to	O
use	O
these	O
VPNs	B-Application
instead	O
of	O
the	O
other	O
common	O
MPLS	B-Protocol
VPN	B-Application
,	O
Layer	B-Application
3	I-Application
.	O
</s>
<s>
There	O
is	O
no	O
one	O
IETF	O
standard	O
for	O
Layer	B-General_Concept
2	I-General_Concept
MPLS	I-General_Concept
VPNs	I-General_Concept
.	O
</s>
<s>
Both	O
methods	O
use	O
a	O
standard	O
MPLS	B-Protocol
header	O
to	O
encapsulate	B-Protocol
data	O
.	O
</s>
<s>
The	O
BGP-based	O
type	O
is	O
based	O
on	O
a	O
draft	O
specification	O
by	O
Kireeti	O
Kompella	O
,	O
from	O
Juniper	O
Networks	O
.	O
</s>
<s>
It	O
uses	O
the	O
Border	B-Protocol
Gateway	I-Protocol
Protocol	I-Protocol
(	O
BGP	B-Protocol
)	O
as	O
the	O
mechanism	O
for	O
PE	O
routers	B-Protocol
to	O
communicate	O
with	O
each	O
other	O
about	O
their	O
customer	O
connections	O
.	O
</s>
<s>
Each	O
router	B-Protocol
connects	O
to	O
a	O
central	O
cloud	O
,	O
using	O
BGP	B-Protocol
.	O
</s>
<s>
This	O
means	O
that	O
when	O
new	O
customers	O
are	O
added	O
(	O
usually	O
to	O
new	O
routers	B-Protocol
)	O
,	O
the	O
existing	O
routers	B-Protocol
will	O
communicate	O
with	O
each	O
other	O
,	O
via	O
BGP	B-Protocol
,	O
and	O
automatically	O
add	O
the	O
new	O
customers	O
to	O
the	O
service	O
.	O
</s>
<s>
This	O
method	O
is	O
also	O
known	O
as	O
a	O
Layer	B-Protocol
2	I-Protocol
circuit	O
.	O
</s>
<s>
It	O
uses	O
the	O
Label	B-Protocol
Distribution	I-Protocol
Protocol	I-Protocol
(	O
LDP	O
)	O
to	O
communicate	O
between	O
PE	O
routers	B-Protocol
.	O
</s>
<s>
In	O
this	O
case	O
,	O
every	O
LDP-speaking	O
router	B-Protocol
will	O
exchange	O
FECs	O
(	O
forwarding	O
equivalence	O
classes	O
)	O
and	O
establish	O
LSPs	O
with	O
every	O
other	O
LDP-speaking	O
router	B-Protocol
on	O
the	O
network	O
(	O
or	O
just	O
the	O
other	O
PE	O
router	B-Protocol
,	O
in	O
the	O
case	O
when	O
LDP	O
is	O
tunnelled	O
over	O
RSVP-TE	B-Protocol
)	O
,	O
which	O
differs	O
from	O
the	O
BGP-based	O
methodology	O
.	O
</s>
<s>
The	O
LDP-based	O
style	O
of	O
layer	B-Protocol
2	I-Protocol
VPN	B-Application
defines	O
new	O
TLVs	O
and	O
parameters	O
for	O
LDP	O
to	O
aid	O
in	O
the	O
signaling	O
of	O
the	O
VPNs	B-Application
.	O
</s>
