<s>
A	O
virtual	B-Application
private	I-Application
network	I-Application
(	O
VPN	B-Application
)	O
is	O
a	O
mechanism	O
for	O
creating	O
a	O
secure	O
connection	O
between	O
a	O
computing	O
device	O
and	O
a	O
computer	B-Architecture
network	I-Architecture
,	O
or	O
between	O
two	O
networks	O
,	O
using	O
an	O
insecure	O
communication	O
medium	O
such	O
as	O
the	O
public	O
Internet	O
.	O
</s>
<s>
A	O
VPN	B-Application
can	O
extend	O
a	O
private	B-Protocol
network	I-Protocol
(	O
one	O
that	O
disallows	O
or	O
restricts	O
public	O
access	O
)	O
,	O
in	O
such	O
a	O
way	O
that	O
it	O
enables	O
users	O
of	O
that	O
network	O
to	O
send	O
and	O
receive	O
data	O
across	O
public	O
networks	O
as	O
if	O
the	O
public	O
networks	O
 '	O
devices	O
were	O
directly	O
connected	O
to	O
the	O
private	B-Protocol
network	I-Protocol
.	O
</s>
<s>
The	O
benefits	O
of	O
a	O
VPN	B-Application
include	O
security	O
,	O
reduced	O
costs	O
for	O
dedicated	O
communication	O
lines	O
,	O
and	O
greater	O
flexibility	O
for	O
remote	O
workers	O
.	O
</s>
<s>
VPNs	B-Application
are	O
also	O
used	O
to	O
bypass	O
internet	B-Application
censorship	I-Application
.	O
</s>
<s>
Encryption	O
is	O
common	O
,	O
although	O
not	O
an	O
inherent	O
part	O
of	O
a	O
VPN	B-Application
connection	O
.	O
</s>
<s>
A	O
VPN	B-Application
is	O
created	O
by	O
establishing	O
a	O
virtual	O
point-to-point	B-Architecture
connection	I-Architecture
through	O
the	O
use	O
of	O
tunneling	B-Protocol
protocols	I-Protocol
over	O
existing	O
networks	O
.	O
</s>
<s>
A	O
VPN	B-Application
available	O
from	O
the	O
public	O
Internet	O
can	O
provide	O
some	O
of	O
the	O
benefits	O
of	O
a	O
wide	O
area	O
network	O
(	O
WAN	O
)	O
.	O
</s>
<s>
Virtual	B-Application
private	I-Application
networks	I-Application
may	O
be	O
classified	O
into	O
several	O
categories	O
:	O
</s>
<s>
Remote	O
access	O
A	O
host-to-network	O
configuration	O
is	O
analogous	O
to	O
connecting	O
a	O
computer	O
to	O
a	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
.	O
</s>
<s>
This	O
type	O
provides	O
access	O
to	O
an	O
enterprise	B-General_Concept
network	I-General_Concept
,	O
such	O
as	O
an	O
intranet	B-General_Concept
.	O
</s>
<s>
The	O
interconnecting	O
link	O
may	O
run	O
over	O
a	O
dissimilar	O
intermediate	O
network	O
,	O
such	O
as	O
two	O
IPv6	B-Protocol
networks	O
connected	O
over	O
an	O
IPv4	B-Protocol
network	I-Protocol
.	O
</s>
<s>
Extranet-based	O
site-to-site	O
In	O
the	O
context	O
of	O
site-to-site	O
configurations	O
,	O
the	O
terms	O
intranet	B-General_Concept
and	O
extranet	B-Architecture
are	O
used	O
to	O
describe	O
two	O
different	O
use	O
cases	O
.	O
</s>
<s>
An	O
intranet	B-General_Concept
site-to-site	O
VPN	B-Application
describes	O
a	O
configuration	O
where	O
the	O
sites	O
connected	O
by	O
the	O
VPN	B-Application
belong	O
to	O
the	O
same	O
organization	O
,	O
whereas	O
an	O
extranet	B-Architecture
site-to-site	O
VPN	B-Application
joins	O
sites	O
belonging	O
to	O
multiple	O
organizations	O
.	O
</s>
<s>
Typically	O
,	O
individuals	O
interact	O
with	O
remote	O
access	O
VPNs	B-Application
,	O
whereas	O
businesses	O
tend	O
to	O
make	O
use	O
of	O
site-to-site	O
connections	O
for	O
business-to-business	O
,	O
cloud	O
computing	O
,	O
and	O
branch	O
office	O
scenarios	O
.	O
</s>
<s>
VPN	B-Application
systems	O
also	O
may	O
be	O
classified	O
by	O
:	O
</s>
<s>
VPNs	B-Application
cannot	O
make	O
online	O
connections	O
completely	O
anonymous	O
,	O
but	O
they	O
can	O
increase	O
privacy	O
and	O
security	O
.	O
</s>
<s>
To	O
prevent	O
disclosure	O
of	O
private	O
information	O
or	O
data	B-Protocol
sniffing	I-Protocol
,	O
VPNs	B-Application
typically	O
allow	O
only	O
authenticated	O
remote	O
access	O
tunneling	B-Protocol
protocols	I-Protocol
and	O
secure	O
encryption	O
techniques	O
.	O
</s>
<s>
The	O
VPN	B-Application
security	O
model	O
provides	O
:	O
</s>
<s>
Secure	O
VPN	B-Application
protocols	O
include	O
the	O
following	O
:	O
</s>
<s>
Internet	B-Protocol
Protocol	I-Protocol
Security	I-Protocol
(	O
IPsec	B-Protocol
)	O
was	O
initially	O
developed	O
by	O
the	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
for	O
IPv6	B-Protocol
,	O
and	O
was	O
required	O
in	O
all	O
standards-compliant	O
implementations	O
of	O
IPv6	B-Protocol
before	O
made	O
it	O
only	O
a	O
recommendation	O
.	O
</s>
<s>
This	O
standards-based	O
security	O
protocol	O
is	O
also	O
widely	O
used	O
with	O
IPv4	B-Protocol
and	O
the	O
Layer	B-Application
2	I-Application
Tunneling	I-Application
Protocol	I-Application
.	O
</s>
<s>
IPsec	B-Protocol
uses	O
encryption	O
,	O
encapsulating	B-Protocol
an	O
IP	O
packet	B-Protocol
inside	O
an	O
IPsec	B-Protocol
packet	B-Protocol
.	O
</s>
<s>
De-encapsulation	O
happens	O
at	O
the	O
end	O
of	O
the	O
tunnel	B-Protocol
,	O
where	O
the	O
original	O
IP	O
packet	B-Protocol
is	O
decrypted	O
and	O
forwarded	O
to	O
its	O
intended	O
destination	O
.	O
</s>
<s>
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
SSL/TLS	B-Protocol
)	O
can	O
tunnel	B-Protocol
an	O
entire	O
network	O
's	O
traffic	O
(	O
as	O
it	O
does	O
in	O
the	O
OpenVPN	B-Language
project	O
and	O
SoftEther	B-Application
VPN	I-Application
project	O
)	O
or	O
secure	O
an	O
individual	O
connection	O
.	O
</s>
<s>
A	O
number	O
of	O
vendors	O
provide	O
remote-access	O
VPN	B-Application
capabilities	O
through	O
SSL	O
.	O
</s>
<s>
An	O
SSL	O
VPN	B-Application
can	O
connect	O
from	O
locations	O
where	O
IPsec	B-Protocol
with	O
Network	B-Protocol
Address	I-Protocol
Translation	I-Protocol
and	O
firewall	O
rules	O
.	O
</s>
<s>
Datagram	B-Protocol
Transport	I-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
DTLS	B-Protocol
)	O
–	O
used	O
in	O
Cisco	O
AnyConnect	O
VPN	B-Application
and	O
in	O
OpenConnect	B-Application
VPN	B-Application
to	O
solve	O
the	O
issues	O
TLS	B-Protocol
has	O
with	O
tunneling	O
over	O
TCP	B-Protocol
(	O
SSL/TLS	B-Protocol
are	O
TCP-based	O
,	O
and	O
tunneling	O
TCP	B-Protocol
over	O
TCP	B-Protocol
can	O
lead	O
to	O
big	O
delays	O
and	O
connection	O
aborts	O
)	O
.	O
</s>
<s>
Microsoft	B-Protocol
Point-to-Point	I-Protocol
Encryption	I-Protocol
(	O
MPPE	B-Protocol
)	O
works	O
with	O
the	O
Point-to-Point	B-Protocol
Tunneling	I-Protocol
Protocol	I-Protocol
and	O
in	O
several	O
compatible	O
implementations	O
on	O
other	O
platforms	O
.	O
</s>
<s>
Microsoft	O
Secure	B-Protocol
Socket	I-Protocol
Tunneling	I-Protocol
Protocol	I-Protocol
(	O
SSTP	B-Protocol
)	O
tunnels	O
Point-to-Point	B-Protocol
Protocol	I-Protocol
(	O
PPP	O
)	O
or	O
Layer	B-Application
2	I-Application
Tunneling	I-Application
Protocol	I-Application
traffic	O
through	O
an	O
SSL/TLS	B-Protocol
channel	O
(	O
SSTP	B-Protocol
was	O
introduced	O
in	O
Windows	B-Device
Server	I-Device
2008	I-Device
and	O
in	O
Windows	B-Application
Vista	I-Application
Service	O
Pack	O
1	O
)	O
.	O
</s>
<s>
Multi	O
Path	O
Virtual	B-Application
Private	I-Application
Network	I-Application
(	O
MPVPN	B-Application
)	O
.	O
</s>
<s>
Ragula	O
Systems	O
Development	O
Company	O
owns	O
the	O
registered	O
trademark	O
"	O
MPVPN	B-Application
"	O
.	O
</s>
<s>
Secure	O
Shell	O
(	O
SSH	O
)	O
VPN	B-Application
–	O
OpenSSH	B-Language
offers	O
VPN	B-Application
tunneling	O
(	O
distinct	O
from	O
port	B-Protocol
forwarding	I-Protocol
)	O
to	O
secure	O
remote	O
connections	O
to	O
a	O
network	O
,	O
inter-network	O
links	O
,	O
and	O
remote	O
systems	O
.	O
</s>
<s>
OpenSSH	B-Language
server	O
provides	O
a	O
limited	O
number	O
of	O
concurrent	O
tunnels	O
.	O
</s>
<s>
The	O
VPN	B-Application
feature	O
itself	O
does	O
not	O
support	O
personal	O
authentication	O
.	O
</s>
<s>
SSH	O
is	O
more	O
often	O
used	O
to	O
remotely	O
connect	O
to	O
machines	O
or	O
networks	O
instead	O
of	O
a	O
site	O
to	O
site	O
VPN	B-Application
connection	O
.	O
</s>
<s>
WireGuard	B-Application
is	O
a	O
protocol	O
.	O
</s>
<s>
In	O
2020	O
,	O
WireGuard	B-Application
support	O
was	O
added	O
to	O
both	O
the	O
Linux	B-Application
and	O
Android	O
kernels	O
,	O
opening	O
it	O
up	O
to	O
adoption	O
by	O
VPN	B-Application
providers	O
.	O
</s>
<s>
By	O
default	O
,	O
WireGuard	B-Application
utilizes	O
the	O
Curve25519	O
protocol	O
for	O
key	O
exchange	O
and	O
ChaCha20-Poly1305	B-Algorithm
for	O
encryption	O
and	O
message	O
authentication	O
,	O
but	O
also	O
includes	O
the	O
ability	O
to	O
pre-share	O
a	O
symmetric	O
key	O
between	O
the	O
client	O
and	O
server	O
.	O
</s>
<s>
Internet	B-Protocol
Key	I-Protocol
Exchange	I-Protocol
version	O
2	O
was	O
created	O
by	O
Microsoft	O
and	O
Cisco	O
and	O
is	O
used	O
in	O
conjunction	O
with	O
IPSec	B-Protocol
for	O
encryption	O
and	O
authentication	O
.	O
</s>
<s>
Its	O
primary	O
use	O
is	O
in	O
mobile	O
devices	O
,	O
whether	O
on	O
3G	B-Architecture
or	O
4G	B-Architecture
LTE	O
networks	O
,	O
since	O
it	O
automatically	O
reconnects	O
when	O
a	O
connection	O
is	O
lost	O
.	O
</s>
<s>
OpenVPN	B-Language
is	O
a	O
free	B-License
and	I-License
open-source	I-License
VPN	B-Application
protocol	O
based	O
on	O
the	O
TLS	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
It	O
supports	O
perfect	O
forward-secrecy	O
,	O
and	O
most	O
modern	O
secure	O
cipher	O
suites	O
,	O
like	O
AES	B-Algorithm
,	O
Serpent	B-Algorithm
,	O
TwoFish	B-Algorithm
,	O
etc	O
.	O
</s>
<s>
It	O
is	O
currently	O
being	O
developed	O
and	O
updated	O
by	O
OpenVPN	B-Language
Inc.	O
,	O
a	O
non-profit	O
providing	O
secure	O
VPN	B-Application
technologies	O
.	O
</s>
<s>
Crypto	O
IP	O
Encapsulation	B-Protocol
(	O
CIPE	O
)	O
is	O
a	O
free	B-License
and	I-License
open-source	I-License
VPN	B-Application
implementation	O
for	O
tunneling	O
IPv4	B-Protocol
packets	B-Protocol
over	O
UDP	B-Protocol
via	O
encapsulation	B-Protocol
.	O
</s>
<s>
CIPE	O
was	O
developed	O
for	O
Linux	B-Application
operating	I-Application
systems	I-Application
by	O
Olaf	O
Titz	O
,	O
with	O
a	O
Windows	B-Application
port	O
implemented	O
by	O
Damion	O
K	O
.	O
Wilson	O
.	O
</s>
<s>
Tunnel	B-Protocol
endpoints	O
must	O
be	O
authenticated	O
before	O
secure	O
VPN	B-Application
tunnels	O
can	O
be	O
established	O
.	O
</s>
<s>
User-created	O
remote-access	O
VPNs	B-Application
may	O
use	O
passwords	O
,	O
biometrics	O
,	O
two-factor	O
authentication	O
,	O
or	O
other	O
cryptographic	O
methods	O
.	O
</s>
<s>
Depending	O
on	O
the	O
VPN	B-Application
protocol	O
,	O
they	O
may	O
store	O
the	O
key	O
to	O
allow	O
the	O
VPN	B-Application
tunnel	B-Protocol
to	O
establish	O
automatically	O
,	O
without	O
intervention	O
from	O
the	O
administrator	O
.	O
</s>
<s>
Data	B-Protocol
packets	I-Protocol
are	O
secured	O
by	O
tamper	O
proofing	O
via	O
a	O
message	B-Algorithm
authentication	I-Algorithm
code	I-Algorithm
(	O
MAC	O
)	O
,	O
which	O
prevents	O
the	O
message	O
from	O
being	O
altered	O
or	O
tampered	O
without	O
being	O
rejected	O
due	O
to	O
the	O
MAC	O
not	O
matching	O
with	O
the	O
altered	O
data	B-Protocol
packet	I-Protocol
.	O
</s>
<s>
Tunneling	B-Protocol
protocols	I-Protocol
can	O
operate	O
in	O
a	O
point-to-point	B-Architecture
network	B-Architecture
topology	I-Architecture
though	O
this	O
would	O
theoretically	O
not	O
be	O
considered	O
a	O
VPN	B-Application
because	O
a	O
VPN	B-Application
by	O
definition	O
is	O
expected	O
to	O
support	O
arbitrary	O
and	O
changing	O
sets	O
of	O
network	O
nodes	O
.	O
</s>
<s>
But	O
since	O
most	O
router	B-Protocol
implementations	O
support	O
a	O
virtual	B-General_Concept
,	I-General_Concept
software-defined	I-General_Concept
tunnel	I-General_Concept
interface	I-General_Concept
,	O
customer-provisioned	O
VPNs	B-Application
often	O
are	O
simply	O
defined	O
tunnels	O
running	O
conventional	O
routing	O
protocols	O
.	O
</s>
<s>
Depending	O
on	O
whether	O
a	O
provider-provisioned	O
VPN	B-Application
(	O
PPVPN	O
)	O
operates	O
in	O
Layer	B-Protocol
2	I-Protocol
(	O
L2	O
)	O
or	O
Layer	B-Application
3	I-Application
(	O
L3	O
)	O
,	O
the	O
building	O
blocks	O
described	O
below	O
may	O
be	O
L2	O
only	O
,	O
L3	O
only	O
,	O
or	O
a	O
combination	O
of	O
both	O
.	O
</s>
<s>
Multi-protocol	B-Protocol
label	I-Protocol
switching	I-Protocol
(	O
MPLS	B-Protocol
)	O
functionality	O
blurs	O
the	O
L2-L3	O
identity	O
.	O
</s>
<s>
generalized	O
the	O
following	O
terms	O
to	O
cover	O
L2	O
MPLS	B-Application
VPNs	I-Application
and	O
L3	O
(	O
BGP	B-Protocol
)	O
VPNs	B-Application
,	O
but	O
they	O
were	O
introduced	O
in	O
.	O
</s>
<s>
C	O
devices	O
are	O
not	O
aware	O
of	O
the	O
VPN	B-Application
.	O
</s>
<s>
A	O
device	O
at	O
the	O
edge	B-Device
of	O
the	O
customer	O
's	O
network	O
which	O
provides	O
access	O
to	O
the	O
PPVPN	O
.	O
</s>
<s>
A	O
device	O
,	O
or	O
set	O
of	O
devices	O
,	O
at	O
the	O
edge	B-Device
of	O
the	O
provider	O
network	O
that	O
connects	O
to	O
customer	O
networks	O
through	O
CE	O
devices	O
and	O
presents	O
the	O
provider	O
's	O
view	O
of	O
the	O
customer	O
site	O
.	O
</s>
<s>
PEs	O
are	O
aware	O
of	O
the	O
VPNs	B-Application
that	O
connect	O
through	O
them	O
,	O
and	O
maintain	O
VPN	B-Application
state	O
.	O
</s>
<s>
While	O
the	O
P	O
device	O
is	O
a	O
key	O
part	O
of	O
implementing	O
PPVPNs	O
,	O
it	O
is	O
not	O
itself	O
VPN-aware	O
and	O
does	O
not	O
maintain	O
VPN	B-Application
state	O
.	O
</s>
<s>
VLAN	B-General_Concept
is	O
a	O
Layer	B-Protocol
2	I-Protocol
technique	O
that	O
allows	O
for	O
the	O
coexistence	O
of	O
multiple	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
(	O
LAN	B-General_Concept
)	O
broadcast	B-Architecture
domains	I-Architecture
interconnected	O
via	O
trunks	O
using	O
the	O
IEEE	O
802.1Q	O
trunking	O
protocol	O
.	O
</s>
<s>
Other	O
trunking	O
protocols	O
have	O
been	O
used	O
but	O
have	O
become	O
obsolete	O
,	O
including	O
Inter-Switch	O
Link	O
(	O
ISL	O
)	O
,	O
IEEE	O
802.10	O
(	O
originally	O
a	O
security	O
protocol	O
but	O
a	O
subset	O
was	O
introduced	O
for	O
trunking	O
)	O
,	O
and	O
ATM	O
LAN	B-General_Concept
Emulation	O
(	O
LANE	O
)	O
.	O
</s>
<s>
Developed	O
by	O
Institute	O
of	O
Electrical	O
and	O
Electronics	O
Engineers	O
,	O
VLANs	B-General_Concept
allow	O
multiple	O
tagged	O
LANs	B-General_Concept
to	O
share	O
common	O
trunking	O
.	O
</s>
<s>
VLANs	B-General_Concept
frequently	O
comprise	O
only	O
customer-owned	O
facilities	O
.	O
</s>
<s>
Whereas	O
VPLS	B-Application
as	O
described	O
in	O
the	O
above	O
section	O
(	O
OSI	O
Layer	O
1	O
services	O
)	O
supports	O
emulation	O
of	O
both	O
point-to-point	B-Architecture
and	O
point-to-multipoint	O
topologies	B-Architecture
,	O
the	O
method	O
discussed	O
here	O
extends	O
Layer	B-Protocol
2	I-Protocol
technologies	O
such	O
as	O
802.1d	O
and	O
802.1q	O
LAN	B-General_Concept
trunking	O
to	O
run	O
over	O
transports	O
such	O
as	O
Metro	B-Protocol
Ethernet	I-Protocol
.	O
</s>
<s>
As	O
used	O
in	O
this	O
context	O
,	O
a	O
VPLS	B-Application
is	O
a	O
Layer	B-Protocol
2	I-Protocol
PPVPN	O
,	O
emulating	O
the	O
full	O
functionality	O
of	O
a	O
traditional	O
LAN	B-General_Concept
.	O
</s>
<s>
From	O
a	O
user	O
standpoint	O
,	O
a	O
VPLS	B-Application
makes	O
it	O
possible	O
to	O
interconnect	O
several	O
LAN	B-General_Concept
segments	O
over	O
a	O
packet-switched	O
,	O
or	O
optical	O
,	O
provider	O
core	O
,	O
a	O
core	O
transparent	O
to	O
the	O
user	O
,	O
making	O
the	O
remote	O
LAN	B-General_Concept
segments	O
behave	O
as	O
one	O
single	O
LAN	B-General_Concept
.	O
</s>
<s>
In	O
a	O
VPLS	B-Application
,	O
the	O
provider	O
network	O
emulates	O
a	O
learning	O
bridge	O
,	O
which	O
optionally	O
may	O
include	O
VLAN	B-General_Concept
service	O
.	O
</s>
<s>
PW	O
is	O
similar	O
to	O
VPLS	B-Application
,	O
but	O
it	O
can	O
provide	O
different	O
L2	O
protocols	O
at	O
both	O
ends	O
.	O
</s>
<s>
Typically	O
,	O
its	O
interface	O
is	O
a	O
WAN	O
protocol	O
such	O
as	O
Asynchronous	O
Transfer	O
Mode	O
or	O
Frame	B-Protocol
Relay	I-Protocol
.	O
</s>
<s>
In	O
contrast	O
,	O
when	O
aiming	O
to	O
provide	O
the	O
appearance	O
of	O
a	O
LAN	B-General_Concept
contiguous	O
between	O
two	O
or	O
more	O
locations	O
,	O
the	O
Virtual	B-Application
Private	I-Application
LAN	I-Application
service	I-Application
or	O
IPLS	O
would	O
be	O
appropriate	O
.	O
</s>
<s>
EtherIP	O
(	O
)	O
is	O
an	O
Ethernet	O
over	O
IP	B-Protocol
tunneling	I-Protocol
protocol	O
specification	O
.	O
</s>
<s>
EtherIP	O
has	O
only	O
packet	B-Protocol
encapsulation	B-Protocol
mechanism	O
.	O
</s>
<s>
EtherIP	O
was	O
introduced	O
in	O
the	O
FreeBSD	B-Operating_System
network	O
stack	O
and	O
the	O
SoftEther	B-Application
VPN	I-Application
server	O
program	O
.	O
</s>
<s>
A	O
subset	O
of	O
VPLS	B-Application
,	O
the	O
CE	O
devices	O
must	O
have	O
Layer	B-Application
3	I-Application
capabilities	O
;	O
the	O
IPLS	O
presents	O
packets	B-Protocol
rather	O
than	O
frames	O
.	O
</s>
<s>
It	O
may	O
support	O
IPv4	B-Protocol
or	O
IPv6	B-Protocol
.	O
</s>
<s>
Ethernet	B-Protocol
VPN	I-Protocol
(	O
EVPN	B-Protocol
)	O
is	O
an	O
advanced	O
solution	O
for	O
providing	O
Ethernet	O
services	O
over	O
IP-MPLS	O
networks	O
.	O
</s>
<s>
In	O
contrast	O
to	O
the	O
VPLS	B-Application
architectures	O
,	O
EVPN	B-Protocol
enables	O
control-plane	O
based	O
MAC	O
(	O
and	O
MAC	O
,	O
IP	O
)	O
learning	O
in	O
the	O
network	O
.	O
</s>
<s>
PEs	O
participating	O
in	O
the	O
EVPN	B-Protocol
instances	O
learn	O
customer	O
's	O
MAC	O
(	O
MAC	O
,	O
IP	O
)	O
routes	O
in	O
control-plane	O
using	O
MP-BGP	O
protocol	O
.	O
</s>
<s>
Control-plane	O
MAC	O
learning	O
brings	O
a	O
number	O
of	O
benefits	O
that	O
allow	O
EVPN	B-Protocol
to	O
address	O
the	O
VPLS	B-Application
shortcomings	O
,	O
including	O
support	O
for	O
multi-homing	O
with	O
per-flow	O
load	O
balancing	O
and	O
avoidance	O
of	O
unnecessary	O
flooding	O
over	O
the	O
MPLS	B-Protocol
core	O
network	O
to	O
multiple	O
PEs	O
participating	O
in	O
the	O
P2MP/MP2MP	O
L2VPN	O
(	O
in	O
the	O
occurrence	O
,	O
for	O
instance	O
,	O
of	O
ARP	O
query	O
)	O
.	O
</s>
<s>
This	O
section	O
discusses	O
the	O
main	O
architectures	O
for	O
PPVPNs	O
,	O
one	O
where	O
the	O
PE	O
disambiguates	O
duplicate	O
addresses	O
in	O
a	O
single	O
routing	O
instance	O
,	O
and	O
the	O
other	O
,	O
virtual	O
router	B-Protocol
,	O
in	O
which	O
the	O
PE	O
contains	O
a	O
virtual	O
router	B-Protocol
instance	O
per	O
VPN	B-Application
.	O
</s>
<s>
One	O
of	O
the	O
challenges	O
of	O
PPVPNs	O
involves	O
different	O
customers	O
using	O
the	O
same	O
address	O
space	O
,	O
especially	O
the	O
IPv4	B-Protocol
private	B-Protocol
address	I-Protocol
space	O
.	O
</s>
<s>
In	O
the	O
method	O
defined	O
by	O
,	O
BGP	B-Protocol
extensions	O
advertise	O
routes	O
in	O
the	O
IPv4	B-Protocol
VPN	B-Application
address	O
family	O
,	O
which	O
are	O
of	O
the	O
form	O
of	O
12-byte	O
strings	O
,	O
beginning	O
with	O
an	O
8-byte	O
route	B-General_Concept
distinguisher	I-General_Concept
(	O
RD	O
)	O
and	O
ending	O
with	O
a	O
4-byte	O
IPv4	B-Protocol
address	O
.	O
</s>
<s>
PEs	O
understand	O
the	O
topology	B-Architecture
of	O
each	O
VPN	B-Application
,	O
which	O
are	O
interconnected	O
with	O
MPLS	B-Protocol
tunnels	O
either	O
directly	O
or	O
via	O
P	O
routers	B-Protocol
.	O
</s>
<s>
In	O
MPLS	B-Protocol
terminology	O
,	O
the	O
P	O
routers	B-Protocol
are	O
label	B-Protocol
switch	I-Protocol
routers	I-Protocol
without	O
awareness	O
of	O
VPNs	B-Application
.	O
</s>
<s>
The	O
virtual	O
router	B-Protocol
architecture	O
,	O
as	O
opposed	O
to	O
BGP/MPLS	O
techniques	O
,	O
requires	O
no	O
modification	O
to	O
existing	O
routing	O
protocols	O
such	O
as	O
BGP	B-Protocol
.	O
</s>
<s>
By	O
the	O
provisioning	O
of	O
logically	O
independent	O
routing	O
domains	O
,	O
the	O
customer	O
operating	O
a	O
VPN	B-Application
is	O
completely	O
responsible	O
for	O
the	O
address	O
space	O
.	O
</s>
<s>
In	O
the	O
various	O
MPLS	B-Protocol
tunnels	O
,	O
the	O
different	O
PPVPNs	O
are	O
disambiguated	O
by	O
their	O
label	O
but	O
do	O
not	O
need	O
routing	O
distinguishers	O
.	O
</s>
<s>
Some	O
virtual	O
networks	O
use	O
tunneling	B-Protocol
protocols	I-Protocol
without	O
encryption	O
for	O
protecting	O
the	O
privacy	O
of	O
data	O
.	O
</s>
<s>
While	O
VPNs	B-Application
often	O
do	O
provide	O
security	O
,	O
an	O
unencrypted	O
overlay	B-Architecture
network	I-Architecture
does	O
not	O
fit	O
within	O
the	O
secure	O
or	O
trusted	O
categorization	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
tunnel	B-Protocol
set	O
up	O
between	O
two	O
hosts	O
with	O
Generic	B-Protocol
Routing	I-Protocol
Encapsulation	I-Protocol
(	O
GRE	O
)	O
is	O
a	O
virtual	B-Application
private	I-Application
network	I-Application
but	O
is	O
neither	O
secure	O
nor	O
trusted	O
.	O
</s>
<s>
Native	O
plaintext	O
tunneling	B-Protocol
protocols	I-Protocol
include	O
Layer	B-Application
2	I-Application
Tunneling	I-Application
Protocol	I-Application
(	O
L2TP	B-Application
)	O
when	O
it	O
is	O
set	O
up	O
without	O
IPsec	B-Protocol
and	O
Point-to-Point	B-Protocol
Tunneling	I-Protocol
Protocol	I-Protocol
(	O
PPTP	B-Protocol
)	O
or	O
Microsoft	B-Protocol
Point-to-Point	I-Protocol
Encryption	I-Protocol
(	O
MPPE	B-Protocol
)	O
.	O
</s>
<s>
Trusted	O
VPNs	B-Application
do	O
not	O
use	O
cryptographic	O
tunneling	O
;	O
instead	O
they	O
rely	O
on	O
the	O
security	O
of	O
a	O
single	O
provider	O
's	O
network	O
to	O
protect	O
the	O
traffic	O
.	O
</s>
<s>
Multiprotocol	B-Protocol
Label	I-Protocol
Switching	I-Protocol
(	O
MPLS	B-Protocol
)	O
often	O
overlays	O
VPNs	B-Application
,	O
often	O
with	O
quality-of-service	O
control	O
over	O
a	O
trusted	O
delivery	O
network	O
.	O
</s>
<s>
L2TP	B-Application
which	O
is	O
a	O
standards-based	O
replacement	O
,	O
and	O
a	O
compromise	O
taking	O
the	O
good	O
features	O
from	O
each	O
,	O
for	O
two	O
proprietary	O
VPN	B-Application
protocols	O
:	O
Cisco	O
's	O
Layer	B-Protocol
2	I-Protocol
Forwarding	O
(	O
L2F	B-Protocol
)	O
(	O
obsolete	O
)	O
and	O
Microsoft	O
's	O
Point-to-Point	B-Protocol
Tunneling	I-Protocol
Protocol	I-Protocol
(	O
PPTP	B-Protocol
)	O
.	O
</s>
<s>
From	O
the	O
security	O
standpoint	O
,	O
VPNs	B-Application
either	O
trust	O
the	O
underlying	O
delivery	O
network	O
or	O
must	O
enforce	O
security	O
with	O
mechanisms	O
in	O
the	O
VPN	B-Application
itself	O
.	O
</s>
<s>
Unless	O
the	O
trusted	O
delivery	O
network	O
runs	O
among	O
physically	O
secure	O
sites	O
only	O
,	O
both	O
trusted	O
and	O
secure	O
models	O
need	O
an	O
authentication	O
mechanism	O
for	O
users	O
to	O
gain	O
access	O
to	O
the	O
VPN	B-Application
.	O
</s>
<s>
Mobile	B-Application
virtual	I-Application
private	I-Application
networks	I-Application
are	O
used	O
in	O
settings	O
where	O
an	O
endpoint	O
of	O
the	O
VPN	B-Application
is	O
not	O
fixed	O
to	O
a	O
single	O
IP	O
address	O
,	O
but	O
instead	O
roams	O
across	O
various	O
networks	O
such	O
as	O
data	B-Architecture
networks	I-Architecture
from	O
cellular	O
carriers	O
or	O
between	O
multiple	O
Wi-Fi	O
access	O
points	O
without	O
dropping	O
the	O
secure	O
VPN	B-Application
session	O
or	O
losing	O
application	O
sessions	O
.	O
</s>
<s>
Mobile	O
VPNs	B-Application
are	O
widely	O
used	O
in	O
public	O
safety	O
where	O
they	O
give	O
law-enforcement	O
officers	O
access	O
to	O
applications	O
such	O
as	O
computer-assisted	O
dispatch	O
and	O
criminal	O
databases	O
,	O
and	O
in	O
other	O
organizations	O
with	O
similar	O
requirements	O
such	O
as	O
field	B-Application
service	I-Application
management	I-Application
and	O
healthcare	O
..	O
</s>
<s>
A	O
limitation	O
of	O
traditional	O
VPNs	B-Application
is	O
that	O
they	O
are	O
point-to-point	B-Architecture
connections	O
and	O
do	O
not	O
tend	O
to	O
support	O
broadcast	B-Architecture
domains	I-Architecture
;	O
therefore	O
,	O
communication	O
,	O
software	O
,	O
and	O
networking	O
,	O
which	O
are	O
based	O
on	O
layer	B-Protocol
2	I-Protocol
and	O
broadcast	O
packets	B-Protocol
,	O
such	O
as	O
NetBIOS	B-Protocol
used	O
in	O
Windows	B-Protocol
networking	I-Protocol
,	O
may	O
not	O
be	O
fully	O
supported	O
as	O
on	O
a	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
.	O
</s>
<s>
Variants	O
on	O
VPN	B-Application
such	O
as	O
Virtual	B-Application
Private	I-Application
LAN	I-Application
Service	I-Application
(	O
VPLS	B-Application
)	O
and	O
layer	B-Application
2	I-Application
tunneling	I-Application
protocols	I-Application
are	O
designed	O
to	O
overcome	O
this	O
limitation	O
.	O
</s>
<s>
A	O
VPN	B-Application
does	O
not	O
make	O
your	O
Internet	O
"	O
private	O
"	O
.	O
</s>
<s>
You	O
can	O
still	O
be	O
tracked	O
through	O
tracking	O
cookies	O
and	O
device	B-Protocol
fingerprinting	I-Protocol
,	O
even	O
if	O
your	O
IP	O
address	O
is	O
hidden	O
.	O
</s>
<s>
A	O
VPN	B-Application
can	O
log	O
your	O
traffic	O
,	O
however	O
this	O
depends	O
on	O
the	O
VPN	B-Application
provider	O
.	O
</s>
<s>
A	O
VPN	B-Application
does	O
not	O
make	O
you	O
immune	O
to	O
hackers	O
.	O
</s>
<s>
A	O
VPN	B-Application
is	O
not	O
in	O
itself	O
a	O
means	O
for	O
good	O
Internet	O
privacy	O
.	O
</s>
<s>
The	O
burden	O
of	O
trust	O
is	O
simply	O
transferred	O
from	O
the	O
ISP	O
to	O
the	O
VPN	B-Application
service	I-Application
provider	I-Application
.	O
</s>
