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Understanding Netopia NAT Behavior C-7
the Internet.
If the address range of 192.168.X.X is not used and another range of addresses such as 100.1.1.X is
used instead, this address space can potentially overlap an address space that is owned by a user
attached to the Internet. Thus if a user on the Netopia R5000 Series Router’s LAN interface has an IP
address of 100.1.1.2 while the Netopia R5000 Series Router’s LAN interface is 100.1.1.2 and the local
host wants to access a host on the Internet with the address of 100.1.1.8, the Netopia R5000 Series
Router has no way of knowing that the 200.1.1.8 address is actually on the Internet and not on its local
LAN interface, since the local LAN interface is assigned the IP address range of 200.1.1.1 to 200.1.1.14.
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NAT is enabled by default with the SmartStart configuration utility. You can toggle Enable Address Translation to
No or Yes in the Connection Profile screen in System Configuration under the IP Profile Parameters section. NAT
is enabled on a per-profile basis, so it is possible to have any combination of NAT and non-NAT profiles. An
example of enabling NAT is as follows:
Toggling Address Translation Enabled to Yes enables the Netopia R5000 Series Router to send out an all-zeros
IPCP address that requests an IP to be assigned to the Netopia R5000 Series Router’s WAN interface. Note
that the remote IP address is 127.0.0.2, which should also be the default gateway under IP Setup in System
Configuration. This is done for profile matching purposes and because the IP address of the router the Netopia
R5000 Series Router is dialing is not always known.
As mentioned earlier in this appendix, NAT works well for IP sessions originated on the Netopia R5000 Series
Router’s LAN interface destined for the Internet without any additional configuration. For incoming IP
connections from the Internet to a host on the Netopia R5000 Series Router’s LAN interface, exported services
need to be used.
Exported services are configured under IP Setup in System Configuration. This is where a particular type of TCP
or UDP service originating from the Internet is redirected to a host on the Netopia R5000 Series Router’s LAN
interface. An example of this screen follows:
IP Profile Parameters
Remote IP Address: 127.0.0.2
Remote IP Mask: 255.255.255.0
Address Translation Enabled: Yes
Filter Set...
Remove Filter Set
Receive RIP: No
Enter the remote IP network's IP address (form xxx.xxx.xxx.xxx decimal).
Configure IP requirements for a remote network connection here.