M2M
Cellular
Gateway
Index
skipping
is
used
to
reserve
slots
for
new
function
insertion,
when
required.
129
Virtual
Computer
Rule
Configuration
Item
Value
setting
Description
Global
IP
A
Must
filled
setting
This
field
is
to
specify
the
IP
address
of
the
WAN
IP.
Local
IP
A
Must
filled
setting
This
field
is
to
specify
the
IP
address
of
the
LAN
IP.
Enable
N/A
Then
check
Enable
box
to
enable
this
rule.
Save
N/A
Click
the
Save
button
to
save
the
settings.
3.9.5
Special
AP
&
ALG
As
a
pure
NAT
gateway,
it
doesn't
allow
an
active
connection
request
from
outside
world.
All
this
kind
of
requests
will
be
ignored
by
the
NAT
gateway.
But
at
the
client
hosts
in
the
Intranet,
users
may
use
applications
that
need
more
service
ports
to
be
allowed
for
passing
through
the
NAT
gateway.
The
"Special
AP"
feature
in
the
gateway
can
solve
this
problem.
That
is,
some
applications
require
multiple
connections,
like
Internet
games,
Video
conferencing,
Internet
telephony,
etc.
Because
of
the
firewall
function,
these
applications
cannot
work
with
a
pure
NAT
router.
The
Special
Applications
feature
allows
some
of
these
applications
to
work
with
this
product.
Besides,
application
‐
level
gateway
(ALG)
allows
customized
NAT
traversal
filters
to
be
plugged
into
the
gateway
to
support
address
and
port
translation
for
certain
application
layer
"control/data"
protocols
such
as
FTP,
BitTorrent,
SIP,
RTSP,
file
transfer
in
IM
applications,
etc.
In
order
for
these
protocols
to
work
through
NAT
or
a
firewall,
either
the
application
has
to
know
about
an
address/port
number
combination
that
allows
incoming
packets,
or
the
NAT
has
to
monitor
the
control
traffic
and
open
up
port
mappings
(firewall
pinhole)
dynamically
as
required.
Legitimate
application
data
can
thus
be
passed
through
the
security
checks
of
the
firewall
or
NAT
that
would
have
otherwise
restricted
the
traffic
for
not
meeting
its
limited
filter
criteria.
