M2M
Cellular
Gateway
Index
skipping
is
used
to
reserve
slots
for
new
function
insertion,
when
required.
281
5.5.9
GRE
Generic
Routing
Encapsulation
(GRE)
is
a
tunneling
protocol
developed
by
Cisco
Systems
that
encapsulate
a
wide
variety
of
network
layer
protocols
inside
virtual
point
‐
to
‐
point
links
over
an
Internet
Protocol
internetwork.
Deploy
a
security
gateway
for
local
office
and
establish
a
virtual
private
network
with
the
remote
gateway
of
another
office
by
using
GRE
tunneling.
So,
all
client
hosts
behind
local
security
gateway
can
make
data
communication
with
others
behind
remote
gateway.
The
most
popular
scenario
is
the
security
gateway
is
located
at
a
branch
office.
Employees
in
the
branch
office
want
to
use
their
client
hosts
or
devices
behind
the
security
gateway
to
access
the
resources
in
headquarters.
These
resources
are
located
in
the
Intranet
of
headquarters,
and
the
security
gateway
in
headquarters
supports
the
GRE
tunneling
function.
Then
local
security
gateway
can
establish
a
GRE
VPN
tunnel
with
remote
gateway
in
headquarters.
Client
hosts
in
these
both
Intranets
of
branch
office
and
headquarters
can
make
data
communication
each
other.
In
"GRE"
page,
there
is
a
"Configuration"
window
to
enable
the
GRE
VPN
function.
In
addition,
the
"GRE
Tunnel
List"
window
lists
all
your
defined
GRE
tunnels.
GRE
is
a
peer
to
peer
tunneling
between
two
gateways.
So,
one
set
of
parameters
can
be
used
for
these
both
gateways
to
establish
a
GRE
VPN
tunnel
by
matching
all
parameters
each
other.
Add
one
new
GRE
tunnel
by
using
the
"Add"
button,
and
edit
one
existed
tunnel
by
using
the
"Edit"
button.
At
last,
the
"GRE
Rule
Configuration"
window
lets
you
specify
all
required
parameters
for
a
GRE
tunnel.
A
security
gateway
can
be
the
client
and
server
for
a
GRE
tunnel
at
the
same
time.
That
is,
the
security
gateway,
configured
as
a
client,
can
initiate
the
establishing
of
one
GRE
tunnel
while
taking
a
request
for
tunnel
establishment
from
a
remote
GRE
client
security
gateway,
even
using
the
same
set
of
configuration
settings.
Configuration
