<s>
SoftEther	B-Application
VPN	I-Application
is	O
free	O
open-source	B-Application
,	O
cross-platform	O
,	O
multi-protocol	O
VPN	B-Application
client	I-Application
and	O
VPN	B-Application
server	I-Application
software	O
,	O
developed	O
as	O
part	O
of	O
Daiyuu	O
Nobori	O
's	O
master	O
's	O
thesis	O
research	O
at	O
the	O
University	O
of	O
Tsukuba	O
.	O
</s>
<s>
VPN	B-Application
protocols	O
such	O
as	O
SSL	O
VPN	B-Application
,	O
L2TP/IPsec	O
,	O
OpenVPN	B-Language
,	O
and	O
Microsoft	O
Secure	B-Protocol
Socket	I-Protocol
Tunneling	I-Protocol
Protocol	I-Protocol
are	O
provided	O
in	O
a	O
single	O
VPN	B-Application
server	I-Application
.	O
</s>
<s>
The	O
license	O
was	O
switched	O
to	O
Apache	B-Application
License	I-Application
2.0	O
on	O
January	O
21	O
,	O
2019	O
.	O
</s>
<s>
SoftEther	B-Application
VPN	I-Application
supports	O
NAT	B-Protocol
traversal	I-Protocol
,	O
making	O
it	O
useful	O
to	O
run	O
VPN	B-Application
servers	I-Application
on	O
computers	O
that	O
are	O
behind	O
residential	B-Application
gateways	I-Application
,	O
facility	O
routers	B-Protocol
,	O
and	O
firewalls	B-Application
.	O
</s>
<s>
Firewalls	B-Application
performing	O
deep	B-Application
packet	I-Application
inspection	I-Application
are	O
unable	O
to	O
detect	O
SoftEther	B-Application
's	O
VPN	B-Application
transport	O
packets	O
as	O
a	O
VPN	B-Application
tunnel	O
because	O
HTTPS	O
is	O
used	O
to	O
camouflage	O
the	O
connection	O
.	O
</s>
<s>
SoftEther	B-Application
VPN	I-Application
optimizes	O
performance	O
by	O
using	O
full	O
Ethernet	O
frame	O
utilization	O
,	O
reducing	O
memory	O
copy	O
operations	O
,	O
parallel	O
transmission	O
,	O
and	O
clustering	O
.	O
</s>
<s>
Together	O
,	O
these	O
reduce	O
latency	O
normally	O
associated	O
with	O
VPN	B-Application
connections	O
while	O
increasing	O
throughput	O
.	O
</s>
<s>
SoftEther	B-Application
VPN	I-Application
Server	O
and	O
VPN	B-Application
Bridge	O
run	O
on	O
Windows	O
,	O
Linux	B-Application
,	O
OS	B-Operating_System
X	I-Operating_System
up	O
to	O
OS	B-Operating_System
X	I-Operating_System
10.8	I-Operating_System
,	O
FreeBSD	B-Operating_System
,	O
and	O
Solaris	B-Application
operating	I-Application
systems	I-Application
.	O
</s>
<s>
SoftEther	B-Application
VPN	I-Application
Client	O
runs	O
on	O
Windows	O
,	O
Linux	B-Application
,	O
and	O
macOS	B-Application
.	O
</s>
<s>
SoftEther	B-Application
VPN	I-Application
Server	O
serves	O
the	O
SoftEther	B-Application
VPN	I-Application
protocol	O
,	O
but	O
it	O
also	O
serves	O
OpenVPN	B-Language
,	O
Microsoft	O
Secure	B-Protocol
Socket	I-Protocol
Tunneling	I-Protocol
Protocol	I-Protocol
(	O
SSTP	O
)	O
,	O
SSL	O
VPN	B-Application
,	O
EtherIP	O
,	O
L2TPv3	B-Protocol
,	O
and	O
IPsec	B-Protocol
.	O
</s>
<s>
It	O
serves	O
mobile	O
devices	O
running	O
iOS	B-Application
,	O
Android	B-Application
,	O
and	O
Windows	O
Phone	O
via	O
L2TP/IPsec	O
.	O
</s>
<s>
VPN	B-Application
clients	I-Application
and	O
endpoints	O
supporting	O
other	O
VPN	B-Application
protocols	O
may	O
also	O
be	O
used	O
;	O
this	O
includes	O
many	O
routers	B-Protocol
from	O
Cisco	O
,	O
Juniper	O
,	O
Linksys	O
(	O
with	O
DD-WRT	B-Protocol
)	O
,	O
Asus	O
,	O
and	O
others	O
.	O
</s>
<s>
SoftEther	B-Application
VPN	I-Application
Server	I-Application
implements	O
the	O
VPN	B-Application
server	I-Application
function	O
.	O
</s>
<s>
It	O
listens	O
and	O
accepts	O
connections	O
from	O
VPN	B-Application
Client	I-Application
or	O
VPN	B-Application
Bridge	O
with	O
several	O
VPN	B-Application
protocols	O
.	O
</s>
<s>
A	O
VPN	B-Application
Server	I-Application
can	O
have	O
several	O
Virtual	O
Hubs	O
and	O
Virtual	O
Layer-3	O
Switches	O
.	O
</s>
<s>
A	O
Virtual	O
Layer-3	O
Switch	O
has	O
layer-3	O
IP	O
static	O
routing	O
functions	O
like	O
a	O
physical	O
router	B-Protocol
.	O
</s>
<s>
A	O
VPN	B-Application
Server	I-Application
can	O
have	O
local	O
bridges	O
.	O
</s>
<s>
The	O
administrator	O
defines	O
a	O
local	O
bridge	O
between	O
the	O
Virtual	O
Hub	O
and	O
the	O
existing	O
corporate	O
network	O
to	O
build	O
a	O
remote-access	O
VPN	B-Application
server	I-Application
or	O
a	O
site-to-site	O
VPN	B-Application
server	I-Application
.	O
</s>
<s>
SoftEther	B-Application
VPN	I-Application
Client	I-Application
is	O
a	O
VPN	B-Application
client	I-Application
program	O
which	O
has	O
the	O
virtualized	O
function	O
of	O
an	O
Ethernet	O
network	O
adapter	O
.	O
</s>
<s>
A	O
computer	O
with	O
installed	O
SoftEther	B-Application
VPN	I-Application
Client	O
can	O
establish	O
a	O
VPN	B-Application
connection	O
to	O
the	O
VPN	B-Application
Server	I-Application
.	O
</s>
<s>
Since	O
the	O
VPN	B-Application
Server	I-Application
has	O
the	O
support	O
for	O
multiple	O
VPN	B-Application
protocols	O
such	O
as	O
L2TP/IPsec	O
or	O
MS-SSTP	O
VPN	B-Application
,	O
VPN	B-Application
users	O
are	O
not	O
required	O
to	O
install	O
SoftEther	B-Application
VPN	I-Application
Client	O
on	O
client	O
computers	O
.	O
</s>
<s>
When	O
a	O
user	O
uses	O
L2TP/IPsec	O
or	O
MS-SSTP	O
VPN	B-Application
to	O
connect	O
to	O
the	O
VPN	B-Application
Server	I-Application
,	O
the	O
built-in	O
VPN	B-Application
client	I-Application
programs	O
on	O
the	O
operating	O
system	O
can	O
be	O
used	O
to	O
establish	O
a	O
VPN	B-Application
to	O
the	O
VPN	B-Application
Server	I-Application
.	O
</s>
<s>
However	O
,	O
SoftEther	B-Application
VPN	I-Application
Client	O
has	O
advanced	O
functions	O
(	O
e.g.	O
</s>
<s>
more	O
detailed	O
VPN	B-Application
communication	O
settings	O
)	O
than	O
OS	O
built-in	O
VPN	B-Application
clients	I-Application
.	O
</s>
<s>
To	O
exploit	O
the	O
full	O
performance	O
of	O
SoftEther	B-Application
VPN	I-Application
Server	O
,	O
it	O
is	O
recommended	O
to	O
install	O
SoftEther	B-Application
VPN	I-Application
Client	O
on	O
each	O
client	O
computer	O
.	O
</s>
<s>
SoftEther	B-Application
VPN	I-Application
Bridge	O
is	O
a	O
VPN	B-Application
program	O
for	O
building	O
a	O
site-to-site	O
VPN	B-Application
.	O
</s>
<s>
To	O
build	O
a	O
site-to-site	O
VPN	B-Application
network	O
,	O
the	O
system	O
administrator	O
has	O
to	O
install	O
SoftEther	B-Application
VPN	I-Application
Server	O
on	O
the	O
central	O
site	O
,	O
and	O
has	O
to	O
install	O
SoftEther	B-Application
VPN	I-Application
Bridge	O
on	O
one	O
or	O
more	O
remote	O
sites	O
.	O
</s>
<s>
A	O
VPN	B-Application
Bridge	O
connects	O
to	O
the	O
central	O
VPN	B-Application
Server	I-Application
by	O
cascade	O
connection	O
.	O
</s>
<s>
The	O
GUI	O
Tool	O
is	O
the	O
administrative	O
tool	O
for	O
SoftEther	B-Application
VPN	I-Application
Server	O
and	O
SoftEther	B-Application
VPN	I-Application
Bridge	O
.	O
</s>
<s>
It	O
is	O
a	O
program	O
that	O
runs	O
on	O
both	O
Windows	O
and	O
Linux	B-Application
with	O
WINE	O
.	O
</s>
<s>
A	O
system	O
administrator	O
installs	O
the	O
GUI	O
Tool	O
on	O
his	O
laptop	O
PC	O
,	O
and	O
makes	O
it	O
connect	O
to	O
the	O
remote	O
VPN	B-Application
Server	I-Application
or	O
VPN	B-Application
Bridge	O
for	O
administration	O
.	O
</s>
<s>
vpncmd	O
is	O
the	O
CUI	O
administrative	O
tool	O
for	O
SoftEther	B-Application
VPN	I-Application
Server	O
,	O
Client	O
and	O
Bridge	O
.	O
</s>
<s>
When	O
a	O
user	O
is	O
unable	O
to	O
use	O
Windows	O
or	O
Linux	B-Application
with	O
WINE	O
,	O
the	O
user	O
can	O
alternatively	O
use	O
vpncmd	O
to	O
manage	O
the	O
VPN	B-Application
programs	O
.	O
</s>
<s>
vpncmd	O
is	O
also	O
useful	O
to	O
execute	O
a	O
batch	O
operation	O
,	O
such	O
as	O
creating	O
many	O
users	O
on	O
the	O
Virtual	O
Hub	O
,	O
or	O
creating	O
many	O
Virtual	O
Hubs	O
on	O
the	O
VPN	B-Application
Server	I-Application
.	O
</s>
<s>
Some	O
parts	O
of	O
the	O
architecture	O
of	O
SoftEther	B-Application
VPN	I-Application
are	O
different	O
from	O
typical	O
traditional	O
IPsec-based	O
VPN	B-Application
systems	O
.	O
</s>
<s>
While	O
traditional	O
physical	O
Ethernet	O
switches	O
implement	O
this	O
function	O
by	O
hardware	O
,	O
SoftEther	B-Application
VPN	I-Application
implements	O
the	O
same	O
function	O
by	O
software	O
.	O
</s>
<s>
A	O
VPN	B-Application
Server	I-Application
can	O
have	O
several	O
Virtual	O
Hubs	O
.	O
</s>
<s>
A	O
Virtual	O
Hub	O
performs	O
the	O
packet-switching	O
between	O
concurrently	O
connected	O
VPN	B-Application
sessions	O
to	O
realize	O
the	O
communication	O
between	O
VPN	B-Application
Clients	I-Application
and	O
VPN	B-Application
Bridges	O
.	O
</s>
<s>
When	O
there	O
are	O
several	O
Virtual	O
Hubs	O
in	O
a	O
single	O
instance	O
of	O
VPN	B-Application
Server	I-Application
,	O
these	O
Virtual	O
Hubs	O
are	O
isolated	O
for	O
security	O
.	O
</s>
<s>
A	O
VPN	B-Application
Client	I-Application
can	O
create	O
several	O
Virtual	O
Network	O
Adapters	O
on	O
the	O
client	O
computer	O
.	O
</s>
<s>
A	O
VPN	B-Application
user	O
can	O
establish	O
a	O
VPN	B-Application
session	O
between	O
the	O
Virtual	O
Network	O
Adapter	O
and	O
the	O
destination	O
Virtual	O
Hub	O
of	O
the	O
remote	O
VPN	B-Application
Server	I-Application
.	O
</s>
<s>
While	O
the	O
VPN	B-Application
session	O
is	O
established	O
,	O
the	O
VPN	B-Application
user	O
can	O
communicate	O
to	O
the	O
remote	O
VPN	B-Application
network	O
through	O
the	O
Virtual	O
Network	O
Adapter	O
.	O
</s>
<s>
A	O
Virtual	O
Layer-3	O
Switch	O
is	O
the	O
software-emulated	O
virtual	O
IP	B-Protocol
router	I-Protocol
.	O
</s>
<s>
Several	O
Virtual	O
Layer-3	O
Switches	O
can	O
be	O
created	O
on	O
a	O
single	O
VPN	B-Application
Server	I-Application
instance	O
.	O
</s>
<s>
The	O
Virtual	O
Layer-3	O
Switch	O
is	O
useful	O
to	O
make	O
a	O
large-scale	O
site-to-site	O
VPN	B-Application
network	O
.	O
</s>
<s>
Although	O
the	O
easy	O
way	O
to	O
make	O
a	O
site-to-site	O
VPN	B-Application
network	O
is	O
to	O
build	O
the	O
layer-2	O
bridging	O
based	O
VPN	B-Application
,	O
if	O
the	O
number	O
of	O
computers	O
is	O
huge	O
the	O
number	O
of	O
broadcasting	O
packets	O
will	O
increase	O
to	O
load	O
the	O
inter-site	O
links	O
.	O
</s>
<s>
To	O
prevent	O
that	O
scaling	O
problem	O
,	O
the	O
VPN	B-Application
administrator	O
isolates	O
IP	O
networks	O
by	O
Virtual	O
Layer-3	O
switch	O
.	O
</s>
<s>
Therefore	O
,	O
a	O
bridge	O
between	O
the	O
virtual	O
and	O
the	O
physical	O
is	O
necessary	O
to	O
build	O
a	O
remote-access	O
VPN	B-Application
or	O
site-to-site	O
VPN	B-Application
.	O
</s>
<s>
After	O
defining	O
the	O
Local	O
Bridge	O
on	O
SoftEther	B-Application
VPN	I-Application
Server	I-Application
,	O
any	O
VPN	B-Application
Client	I-Application
can	O
connect	O
to	O
the	O
VPN	B-Application
Server	I-Application
and	O
communicate	O
to	O
all	O
existing	O
Ethernet	O
devices	O
(	O
e.g.	O
</s>
<s>
This	O
is	O
called	O
a	O
remote-access	O
VPN	B-Application
.	O
</s>
<s>
If	O
the	O
network	O
administrator	O
sets	O
up	O
the	O
remote-site	O
VPN	B-Application
Bridge	O
,	O
and	O
defines	O
two	O
Local	O
Bridges	O
on	O
both	O
VPN	B-Application
Server	I-Application
and	O
VPN	B-Application
Bridge	O
,	O
and	O
defines	O
a	O
cascade	O
connection	O
between	O
VPN	B-Application
Server	I-Application
and	O
VPN	B-Application
Bridge	O
,	O
then	O
the	O
remote	O
two	O
Ethernet	O
segments	O
are	O
connected	O
directly	O
in	O
layer-2	O
Ethernet	O
level	O
.	O
</s>
<s>
This	O
is	O
called	O
a	O
site-to-site	O
VPN	B-Application
.	O
</s>
<s>
One	O
of	O
the	O
key	O
features	O
of	O
SoftEther	B-Application
VPN	I-Application
is	O
the	O
transparency	O
for	O
firewalls	B-Application
,	O
proxy	O
servers	O
,	O
and	O
NATs	O
(	O
Network	O
Address	O
Translators	O
)	O
.	O
</s>
<s>
To	O
do	O
this	O
,	O
SoftEther	B-Application
VPN	I-Application
supports	O
SSL-VPN	O
and	O
NAT	B-Protocol
Traversal	I-Protocol
.	O
</s>
<s>
SoftEther	B-Application
VPN	I-Application
uses	O
HTTPS	O
protocol	O
in	O
order	O
to	O
establish	O
a	O
VPN	B-Application
tunnel	O
.	O
</s>
<s>
When	O
the	O
user	O
chooses	O
SSL-VPN	O
protocol	O
between	O
the	O
VPN	B-Application
Client	I-Application
and	O
VPN	B-Application
Server	I-Application
,	O
SoftEther	B-Application
VPN	I-Application
Server	I-Application
and	O
VPN	B-Application
Client	I-Application
use	O
a	O
parallel	O
transmission	O
mechanism	O
to	O
improve	O
the	O
throughput	O
of	O
the	O
SSL-VPN	O
tunnel	O
.	O
</s>
<s>
When	O
this	O
function	O
is	O
enabled	O
,	O
the	O
logical	O
VPN	B-Application
Session	O
will	O
consist	O
of	O
several	O
TCP	O
(	O
HTTPS	O
)	O
connections	O
.	O
</s>
<s>
If	O
some	O
packet	O
losses	O
have	O
been	O
detected	O
on	O
a	O
TCP	O
connection	O
of	O
the	O
logical	O
VPN	B-Application
Session	O
,	O
then	O
the	O
new	O
packet	O
will	O
use	O
another	O
healthy	O
VPN	B-Application
connection	O
.	O
</s>
<s>
Traditional	O
VPN	B-Application
systems	O
require	O
the	O
user	O
to	O
ask	O
the	O
firewall	B-Application
's	O
administrator	O
of	O
the	O
company	O
to	O
open	O
an	O
endpoint	O
(	O
TCP	O
or	O
UDP	O
port	O
)	O
on	O
the	O
firewall	B-Application
or	O
NAT	O
on	O
the	O
border	O
between	O
the	O
company	O
and	O
the	O
Internet	O
.	O
</s>
<s>
In	O
order	O
to	O
reduce	O
the	O
necessity	O
to	O
open	O
an	O
endpoint	O
on	O
the	O
firewall	B-Application
,	O
SoftEther	B-Application
VPN	I-Application
Server	O
has	O
the	O
NAT	B-Protocol
Traversal	I-Protocol
function	O
.	O
</s>
<s>
NAT	B-Protocol
Traversal	I-Protocol
is	O
enabled	O
by	O
default	O
.	O
</s>
<s>
As	O
long	O
as	O
it	O
is	O
enabled	O
,	O
SoftEther	B-Application
VPN	I-Application
Client	O
computers	O
can	O
connect	O
to	O
your	O
VPN	B-Application
Server	I-Application
behind	O
the	O
firewall	B-Application
or	O
NAT	O
.	O
</s>
<s>
No	O
special	O
settings	O
on	O
the	O
firewall	B-Application
or	O
NAT	O
are	O
necessary	O
.	O
</s>
<s>
A	O
few	O
very-restricted	O
networks	O
only	O
permit	O
to	O
pass	O
ICMP	B-Protocol
or	O
DNS	B-Application
packets	O
.	O
</s>
<s>
Only	O
ICMP	B-Protocol
and	O
DNS	B-Application
are	O
permitted	O
.	O
</s>
<s>
In	O
order	O
to	O
make	O
it	O
possible	O
to	O
establish	O
a	O
SoftEther	B-Application
VPN	I-Application
client-server	O
session	O
via	O
such	O
a	O
very-restricted	O
network	O
,	O
SoftEther	B-Application
VPN	I-Application
has	O
the	O
"	O
VPN	B-Application
over	I-Application
ICMP	I-Application
"	O
and	O
the	O
"	O
VPN	B-Application
over	O
DNS	B-Application
"	O
function	O
.	O
</s>
<s>
This	O
function	O
is	O
very	O
powerful	O
to	O
penetrate	O
such	O
a	O
restricted	O
firewall	B-Application
.	O
</s>
<s>
All	O
VPN	B-Application
packets	O
are	O
encapsulated	O
into	O
ICMP	B-Protocol
or	O
DNS	B-Application
packets	O
to	O
transmit	O
over	O
the	O
firewall	B-Application
.	O
</s>
<s>
Some	O
public	O
Wi-Fi	O
can	O
pass	O
only	O
ICMP	B-Protocol
or	O
DNS	B-Application
packets	O
.	O
</s>
<s>
If	O
you	O
have	O
a	O
VPN	B-Application
Server	I-Application
installed	O
on	O
your	O
home	O
or	O
office	O
in	O
advance	O
of	O
going	O
outdoors	O
,	O
you	O
can	O
enjoy	O
protocol-free	O
network	O
communication	O
by	O
using	O
such	O
a	O
restricted	O
network	O
.	O
</s>
<s>
VPN	B-Application
Gate	O
is	O
a	O
plugin	O
for	O
SoftEther	B-Application
VPN	I-Application
,	O
which	O
allows	O
users	O
to	O
connect	O
to	O
free	O
VPN	B-Application
servers	I-Application
,	O
run	O
by	O
volunteers	O
who	O
use	O
SoftEther	B-Application
to	O
host	O
their	O
VPN	B-Application
servers	I-Application
.	O
</s>
<s>
VPN	B-Application
Gate	O
is	O
sponsored	O
by	O
the	O
University	O
of	O
Tsukuba	O
.	O
</s>
