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A significant advantage of NAT is that you can configure it without changing 
hosts or routers, other than those few routers on which NAT is configured. 
NAT multiplexes internal network traffic and presents it to the Internet as if it 
is from a single source with one IP address.
Enable/Disable NAT Translation by Port
Each IAD is configured with NAT disabled. To enable NAT translation, 
follow the steps below.
1
Type “P” on the NAT Configuration menu. If at least one virtual circuit on 
the WAN exists and the LAN port is also configured with an IP address, or 
more than one PVC exists, the IAD displays the interfaces (sample 
following) on this IAD as shown in Figure 4.9. Otherwise, the IAD displays 
the WAN port table and prompts you to select a port.
2
Type the port number on which to enable NAT and press Enter. The IAD 
prompts you to enable or disable NAT.
3
Type “E” to enable NAT, or “D” to disable. The IAD saves the setting and 
displays the NAT Configuration menu.
4
Continue with other NAT configuration tasks, or press Escape to return to 
the Main menu.
Configure NAT TCP and UDP Timeouts
Under normal circumstances, the timeout default setting is adequate. 
However, if users interact with products including multiple-player IP games 
or video conferencing, you may need to configure the timeout.
The local server protocol you select determines which timeout to configure. 
TDP and UDP are similar, except that TCP tracks TCP clients on a per-
connection basis and removes them from the table as soon as the connection 
closes.
To configure a NAT timeout, follow the steps below.
1
On the NAT Configuration menu, type “T” to select TCP connections, or 
type “U” to select UDP connections. The IAD displays a TCP or UPD 
prompt.
2
Type the timeout value and press Enter. The IAD displays the NAT 
Configuration menu.
3
Continue with other NAT configuration tasks, or press Escape to return to 
the Main menu (Figure 2.2).
4
Reset the IAD.
Configure NAT Port Range
The size of the NAT port range defines the number of simultaneous 
connections permitted. A small port range limits the number of connections. 
Since the range that you assign must be outside the range of assigned ports, 
do not set port ranges below 5,000.