7
IPsec VPN
119
Authentication
can
be
accomplished
through
using
pre
‐
shared
keys
(PSK)
or
certificates.
Using
pre
‐
shared
keys
is
the
most
common
authentication
method.
Both
PSK
and
certificates
‐
based
VPNs
are
supported
by
the
SEG.
IKE phase 2: IPsec security negotiation
In
phase
2,
another
negotiation
is
performed,
detailing
the
parameters
for
the
IPsec
connection.
During
phase
2
new
keying
material
from
the
Diffie
‐
Hellman
key
exchange
in
phase
1
in
extracted
in
order
to
provide
session
keys
to
use
in
protecting
the
VPN
data
flow.
If
perfect
forwarding
secrecy
(PFS)
is
used,
a
new
Diffie
‐
Hellman
exchange
is
performed
for
each
phase
2
negotiation.
While
this
method
is
slower,
it
ensures
that
no
keys
are
dependent
on
any
other
previously
used
keys,
and
that
no
keys
are
extracted
from
the
same
initial
keying
material.
This
prevents
subsequent
keys
from
being
derived
from
a
key
that
has
been
compromised
(an
unlikely
event).
Once
the
phase
2
negotiation
is
finished,
the
VPN
connection
is
established
and
ready
for
traffic
to
pass
through
it.
IKE parameters
There
are
a
number
of
parameters
used
in
the
IKE
negotiation
process.
These
are
summarized
next.
Local
endpoint
identification
This
is
a
piece
of
data
representing
the
identity
of
the
local
VPN
tunnel
endpoint.
Local
and
remote
networks/hosts
These
are
the
subnets
or
hosts
between
which
IP
traffic
will
be
protected
by
the
VPN.
In
a
LAN
‐
to
‐
LAN
connection,
these
will
be
the
network
addresses
of
the
respective
LANs.
Tunnel
and
transport
mode
IPsec
can
be
used
in
two
modes,
tunnel
or
transport.
Tunnel
mode
indicates
that
the
traffic
will
be
tunneled
to
a
remote
device,
which
will
decrypt/authenticate
the
data,
extract
it
from
its
tunnel,
and
pass
it
on
to
its
final
destination.
This
way,
an
eavesdropper
will
only
see
encrypted
traffic
going
from
one
of
VPN
endpoint
to
another.
In
transport
mode,
traffic
is
not
tunneled.
This
mode
can
be
used
to
secure
a
connection
from
a
VPN
client
directly
to
the
SEG,
for
example,
for
IPsec
‐
protected
remote
configuration.
Currently,
the
SEG
supports
tunnel
mode.