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Page 136 / 324 Scroll up to view Page 131 - 135
Chapter 9 Network Address Translation (NAT)
P-660HN-TxA User’s Guide
136
NAT
In the simplest form, NAT changes the source IP address in a packet received from
a subscriber (the inside local address) to another (the inside global address)
before forwarding the packet to the WAN side. When the response comes back,
NAT translates the destination address (the inside global address) back to the
inside local address before forwarding it to the original inside host.
Port Forwarding
A port forwarding set is a list of inside (behind NAT on the LAN) servers, for
example, web or FTP, that you can make visible to the outside world even though
NAT makes your whole inside network appear as a single computer to the outside
world.
SUA (Single User Account) Versus NAT
SUA (Single User Account) is a ZyNOS implementation of a subset of NAT that
supports two types of mapping,
Many-to-One
and
Server
. The ZyXEL Device also
supports
Full Feature
NAT to map multiple global IP addresses to multiple private
LAN IP addresses of clients or servers using mapping types as outlined in
Table 48
on page 149
.
• Choose
SUA Only
if you have just one public WAN IP address for your ZyXEL
Device.
• Choose
Full Feature
if you have multiple public WAN IP addresses for your
ZyXEL Device.
Finding Out More
See
Section 9.6 on page 146
for advanced technical information on NAT.
Page 137 / 324
Chapter 9 Network Address Translation (NAT)
P-660HN-TxA User’s Guide
137
9.2
The NAT General Setup Screen
Use this screen to activate NAT. Click
Network > NAT
to open the following
screen.
Note: You must create a firewall rule in addition to setting up SUA/NAT, to allow traffic
from the WAN to be forwarded through the ZyXEL Device.
Figure 64
Network > NAT > General
The following table describes the labels in this screen.
Table 41
Network > NAT > General
LABEL
DESCRIPTION
Active Network
Address
Translation
Select this check box to enable NAT.
SUA Only
Select this radio button if you have just one public WAN IP address for
your ZyXEL Device.
Full Feature
Select this radio button if you have multiple public WAN IP addresses for
your ZyXEL Device.
Max NAT/
Firewall Session
Per User
When computers use peer to peer applications, such as file sharing
applications, they need to establish NAT sessions. If you do not limit the
number of NAT sessions a single client can establish, this can result in
all of the available NAT sessions being used. In this case, no additional
NAT sessions can be established, and users may not be able to access
the Internet.
Each NAT session establishes a corresponding firewall session. Use this
field to limit the number of NAT/Firewall sessions client computers can
establish through the ZyXEL Device.
If your network has a small number of clients using peer to peer
applications, you can raise this number to ensure that their
performance is not degraded by the number of NAT sessions they can
establish. If your network has a large number of users using peer to
peer applications, you can lower this number to ensure no single client
is exhausting all of the available NAT sessions.
Page 138 / 324
Chapter 9 Network Address Translation (NAT)
P-660HN-TxA User’s Guide
138
9.3
The Port Forwarding Screen
Note: This screen is available only when you select
SUA only
in the
NAT > General
screen.
Use this screen to forward incoming service requests to the server(s) on your local
network.
You may enter a single port number or a range of port numbers to be forwarded,
and the local IP address of the desired server. The port number identifies a
service; for example, web service is on port 80 and FTP on port 21. In some
cases, such as for unknown services or where one server can support more than
one service (for example both FTP and web service), it might be better to specify
a range of port numbers. You can allocate a server IP address that corresponds to
a port or a range of ports.
The most often used port numbers and services are shown in
Appendix E on page
307
. Please refer to RFC 1700 for further information about port numbers.
Note: Many residential broadband ISP accounts do not allow you to run any server
processes (such as a Web or FTP server) from your location. Your ISP may
periodically check for servers and may suspend your account if it discovers any
active services at your location. If you are unsure, refer to your ISP.
Default Server IP Address
In addition to the servers for specified services, NAT supports a default server IP
address. A default server receives packets from ports that are not specified in this
screen.
Note: If you do not assign a
Default Server
IP address, the ZyXEL Device discards
all packets received for ports that are not specified here or in the remote
management setup.
Apply
Click this to save your changes.
Cancel
Click this to restore your previously saved settings.
Table 41
Network > NAT > General (continued)
LABEL
DESCRIPTION
Page 139 / 324
Chapter 9 Network Address Translation (NAT)
P-660HN-TxA User’s Guide
139
Configuring Servers Behind Port Forwarding (Example)
Let's say you want to assign ports 21-25 to one FTP, Telnet and SMTP server (
A
in
the example), port 80 to another (
B
in the example) and assign a default server IP
address of 192.168.1.35 to a third (
C
in the example). You assign the LAN IP
addresses and the ISP assigns the WAN IP address. The NAT network appears as a
single host on the Internet.
Figure 65
Multiple Servers Behind NAT Example
9.3.1
Configuring the Port Forwarding Screen
Click
Network > NAT > Port Forwarding
to open the following screen.
See
Appendix E on page 307
for port numbers commonly used for particular
services.
Figure 66
Network > NAT > Port Forwarding
A=192.168.1.33
D=192.168.1.36
C=192.168.1.35
B=192.168.1.34
WAN
LAN
192.168.1.1
IP Address assigned by ISP
Page 140 / 324
Chapter 9 Network Address Translation (NAT)
P-660HN-TxA User’s Guide
140
The following table describes the fields in this screen.
Table 42
Network > NAT > Port Forwarding
LABEL
DESCRIPTION
Default Server Setup
Default Server
In addition to the servers for specified services, NAT supports a default
server. A default server receives packets from ports that are not
specified in this screen. If you do not assign a
Default Server
IP
address, the ZyXEL Device discards all packets received for ports that
are not specified here or in the remote management setup.
Port Forwarding
Service Name
Select a service from the drop-down list box.
Server IP
Address
Enter the IP address of the server for the specified service.
Add
Click this button to add a rule to the table below.
#
This is the rule index number (read-only).
Active
This field indicates whether the rule is active or not.
Clear the check box to disable the rule. Select the check box to enable
it.
Service Name
This is a service’s name.
Start Port
This is the first port number that identifies a service.
End Port
This is the last port number that identifies a service.
Port Translation
Start/End Port
This is the start/end port number that the device translates.
Server IP
Address
This is the server’s IP address.
Modify
Click the edit icon to go to the screen where you can edit the port
forwarding rule.
Click the delete icon to delete an existing port forwarding rule. Note that
subsequent address mapping rules move up by one when you take this
action.
Apply
Click this to save your changes.
Cancel
Click this to restore your previously saved settings.

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