Sending Data to Your Network Application
Rev 1.4 Apr.08
67
The problem created by Network Address
Translation
Note: A similar problem may
occur if NAT is in use on your
network. The host application
may reside on a server that has
a private IP address. You must
configure the MP modem to
send data to a server on your
network with a public IP address,
and configure the server to
recognize the MTP data and
route it appropriately.
Many
service
providers
use
NAT
(Network
Address
Trans
‐
lation)
which
effectively
creates
a
firewall
in
front
of
the
network.
Inside
the
network,
the
service
providers
assign
private
IP
addresses
to
registered
devices,
since
public
IP
addresses
are
not
needed
to
route
data
within
the
network.
(This
saves
the
service
provider
the
expense
of
having
a
large
pool
of
public
IP
addresses.)
A
public
IP
address
is
substituted
for
the
private
IP
address
when
data
packets
pass
through
the
gateway
between
the
network
and
the
Internet.
This
public
IP
address
might
be
used
on
data
transmissions
from
many
different
devices.
Therefore,
the
network
server
is
only
aware
of
the
substituted
public
IP
address.
If
the
server
replies
to
this
address,
the
network
cannot
identify
the
device
for
which
the
data
was
intended.
Assume,
for
example,
an
MP
modem
is
registered
on
a
network.
The
MP
modem
is
assigned
a
private
IP
address
of
10.95.236.1.
When
the
MP
modem
sends
MTP
data
to
the
network
server,
a
public
IP
address
of
24.7.6.30
is
substituted
at
the
gateway
to
the
Internet.
When
the
network
server
receives
the
data,
the
host
application
is
only
aware
of
the
public
IP
address,
24.7.6.30.
However,
if
the
network
server
sends
data
back
to
the
IP
address
24.7.6.30,
the
network
has
no
way
of
identifying
the
MP
modem
for
which
it
is
intended
and
is
unable
to
route
the
data
appropriately.
Figure 8-1: An MP modem connected to a network server. In this scenario, the
IP address is “NAT’d” from 10.95.236.1 to 24.7.6.30. The network server is
only aware of the address 24.7.6.30, but if it sends data to that address the
network cannot route the data to the MP modem.
Network
Internet
Firewall
Summary of Contents for MP 881W
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