<s>
OpenConnect	B-Application
is	O
an	O
open-source	B-Application
software	I-Application
application	O
for	O
connecting	O
to	O
virtual	B-Application
private	I-Application
networks	I-Application
(	O
VPN	B-Application
)	O
,	O
which	O
implement	O
secure	O
point-to-point	B-Architecture
connections	O
.	O
</s>
<s>
It	O
was	O
originally	O
written	O
as	O
an	O
open-source	B-Application
replacement	O
for	O
Cisco	O
's	O
proprietary	B-Application
AnyConnect	O
SSL	O
VPN	B-Application
client	I-Application
,	O
which	O
is	O
supported	O
by	O
several	O
Cisco	O
routers	B-Protocol
.	O
</s>
<s>
Pulse/Junos	B-Protocol
VPN	B-Application
in	O
version	O
8.04	O
,	O
and	O
for	O
Fortinet	O
FortiGate	O
,	O
F5	O
BiGIP	O
,	O
and	O
Array	O
Networks	O
in	O
version	O
8.20	O
.	O
</s>
<s>
Cisco	O
AnyConnect	O
VPNs	B-Application
utilize	O
TLS	B-Protocol
to	O
authenticate	O
and	O
configure	O
routing	O
,	O
then	O
DTLS	B-Protocol
to	O
efficiently	O
encrypt	O
and	O
transport	O
the	O
tunneled	O
VPN	B-Application
traffic	O
,	O
and	O
can	O
fall	O
back	O
to	O
TLS-based	O
transport	O
where	O
firewalls	B-Application
block	O
UDP-based	O
traffic	O
.	O
</s>
<s>
The	O
DTLS	B-Protocol
protocol	O
used	O
by	O
Cisco	O
AnyConnect	O
servers	O
was	O
based	O
on	O
a	O
non-standard	O
,	O
pre-release	O
draft	O
of	O
DTLS	B-Protocol
1.0	O
,	O
until	O
support	O
for	O
the	O
DTLS	B-Protocol
1.2	O
standard	O
was	O
added	O
in	O
2018	O
.	O
</s>
<s>
Cisco	O
's	O
proprietary	B-Application
AnyConnect	O
clients	O
and	O
servers	O
were	O
originally	O
built	O
against	O
a	O
patched	O
,	O
2007	O
release	O
of	O
OpenSSL	B-Language
0.9.8f	O
,	O
which	O
implemented	O
a	O
pre-release	O
version	O
of	O
DTLS	B-Protocol
that	O
was	O
not	O
compatible	O
with	O
DTLS	B-Protocol
1.0	O
as	O
standardized	O
in	O
.	O
</s>
<s>
Because	O
of	O
this	O
,	O
it	O
was	O
difficult	O
to	O
make	O
OpenConnect	B-Application
implement	O
a	O
Cisco-compatible	O
version	O
of	O
DTLS	B-Protocol
without	O
linking	O
against	O
OpenSSL	B-Language
.	O
</s>
<s>
Explicit	O
support	O
for	O
Cisco	O
's	O
non-standard	O
version	O
of	O
DTLS	B-Protocol
was	O
included	O
in	O
OpenSSL	B-Language
0.9.8m	O
(	O
where	O
it	O
is	O
known	O
as	O
)	O
and	O
then	O
GnuTLS	B-Application
3.2.1	O
(	O
where	O
it	O
is	O
known	O
as	O
)	O
.	O
</s>
<s>
Newer	O
versions	O
of	O
Cisco	O
's	O
AnyConnect	O
clients	O
and	O
servers	O
support	O
DTLS	B-Protocol
1.2	O
in	O
its	O
standardized	O
on-the-wire	O
form	O
(	O
)	O
,	O
though	O
they	O
continue	O
to	O
use	O
a	O
non-standard	O
mechanism	O
(	O
based	O
on	O
session	O
resumption	O
)	O
for	O
DTLS	B-Protocol
key	O
exchange	O
.	O
</s>
<s>
Modern	O
versions	O
of	O
OpenConnect	B-Application
can	O
be	O
built	O
to	O
use	O
either	O
the	O
GnuTLS	B-Application
or	O
OpenSSL	B-Language
for	O
TLS	B-Protocol
,	O
DTLS	B-Protocol
,	O
and	O
cryptographic	O
primitives	O
.	O
</s>
<s>
The	O
OpenConnect	B-Application
client	O
also	O
implements	O
Juniper	O
,	O
Junos	B-Protocol
Pulse	I-Protocol
,	O
and	O
GlobalProtect	O
VPN	B-Application
protocols	O
.	O
</s>
<s>
These	O
have	O
a	O
very	O
similar	O
structure	O
to	O
the	O
AnyConnect	O
protocol	O
:	O
they	O
authenticate	O
and	O
configure	O
routing	O
over	O
TLS	B-Protocol
,	O
except	O
that	O
they	O
use	O
ESP	O
for	O
efficient	O
,	O
encrypted	O
transport	O
of	O
tunneled	O
traffic	O
(	O
instead	O
of	O
DTLS	B-Protocol
)	O
,	O
but	O
they	O
too	O
can	O
fall	O
back	O
to	O
TLS-based	O
transport	O
.	O
</s>
<s>
As	O
of	O
version	O
8.20	O
,	O
it	O
also	O
implements	O
Fortinet	O
FortiGate	O
and	O
F5	O
BiGIP	O
,	O
which	O
use	O
TLS	B-Protocol
and	O
DTLS	B-Protocol
,	O
and	O
are	O
additionally	O
based	O
on	O
the	O
Point-to-point	B-Protocol
protocol	I-Protocol
(	O
PPP	B-Protocol
)	O
.	O
</s>
<s>
,	O
support	O
for	O
several	O
other	O
proprietary	B-Application
VPN	B-Application
protocols	O
is	O
in	O
development	O
:	O
</s>
<s>
The	O
OpenConnect	B-Application
client	O
is	O
written	O
primarily	O
in	O
C	B-Language
,	O
and	O
it	O
contains	O
much	O
of	O
the	O
infrastructure	O
necessary	O
to	O
add	O
additional	O
VPN	B-Application
protocols	O
operating	O
in	O
a	O
similar	O
flow	O
,	O
and	O
to	O
connect	O
to	O
them	O
via	O
a	O
common	O
user	O
interface	O
:	O
</s>
<s>
Authentication	O
phase	O
via	O
HTTPS	O
(	O
using	O
HTML	B-General_Concept
forms	I-General_Concept
,	O
client	O
certificates	O
,	O
XML	B-Protocol
,	O
etc	O
.	O
)	O
</s>
<s>
Built-in	O
event	O
loop	O
to	O
handle	O
Dead	B-Protocol
Peer	I-Protocol
Detection	I-Protocol
,	O
keepalive	B-Protocol
,	O
rekeying	B-General_Concept
,	O
etc	O
.	O
</s>
<s>
OpenConnect	B-Application
can	O
be	O
built	O
to	O
use	O
either	O
the	O
GnuTLS	B-Application
or	O
OpenSSL	B-Language
libraries	O
for	O
TLS	B-Protocol
,	O
DTLS	B-Protocol
and	O
cryptographic	O
primitives	O
.	O
</s>
<s>
OpenConnect	B-Application
is	O
available	O
on	O
Solaris	B-Application
,	O
Linux	B-Application
,	O
OpenBSD	B-Operating_System
,	O
FreeBSD	B-Operating_System
,	O
MacOS	B-Application
,	O
and	O
has	O
graphical	O
user	O
interface	O
clients	O
for	O
Windows	O
,	O
GNOME	B-Application
,	O
and	O
KDE	B-Application
.	O
</s>
<s>
A	O
graphical	O
client	O
for	O
OpenConnect	B-Application
is	O
also	O
available	O
for	O
Android	B-Application
devices	O
,	O
</s>
<s>
and	O
it	O
has	O
been	O
integrated	O
into	O
router	B-Protocol
firmware	O
packages	O
such	O
as	O
OpenWrt	B-Application
.	O
</s>
<s>
,	O
the	O
OpenConnect	B-Application
project	O
also	O
offers	O
an	O
AnyConnect-compatible	O
server	O
,	O
ocserv	B-Application
,	O
and	O
thus	O
offers	O
a	O
full	O
client-server	B-Operating_System
VPN	B-Application
solution	O
.	O
</s>
<s>
OpenConnect	B-Application
and	O
ocserv	B-Application
now	O
implement	O
an	O
extended	O
version	O
of	O
the	O
AnyConnect	O
VPN	B-Application
protocol	O
,	O
which	O
has	O
been	O
proposed	O
as	O
an	O
Internet	O
Standard	O
.	O
</s>
<s>
Both	O
OpenConnect	B-Application
and	O
ocserv	B-Application
strive	O
to	O
maintain	O
backwards-compatibility	B-General_Concept
with	O
Cisco	O
AnyConnect	O
servers	O
and	O
clients	O
.	O
</s>
<s>
OpenConnect	B-Application
's	O
implementation	O
of	O
the	O
AnyConnect	O
protocol	O
is	O
sufficiently	O
complete	O
,	O
such	O
that	O
some	O
of	O
Cisco	O
's	O
own	O
IP	B-Device
phone	I-Device
devices	O
embed	O
a	O
very	O
old	O
release	O
of	O
OpenConnect	B-Application
in	O
order	O
to	O
connect	O
to	O
Cisco	O
SSL	O
VPNs	B-Application
.	O
</s>
