User Manual

VisionNet 202ER ADSL Ethernet Router User’s Guide
56
disguised source port number. The VisionNet 202ER changes the
IP address and source port number back to the original values
(having kept track of the changes it made earlier), and then routes
the packet to the originating computer.
NAT rules such as these provide several benefits:
 They eliminate the need for purchasing multiple public IP
addresses for computers on your LAN. You can make up
your own private IP addresses at no cost , and then have
them translated to the public IP address when your
computers access the Internet.
 They provide a measure of security for you LAN by
enabling you to assign private IP addresses. The VisionNet
202ER prevents external access your privately addressed
computers (except when using an rdr rule discussed on
page 65). In addition, the private addresses are replaced in
all outbound data packets, so external computers never
see the private addresses anyway.
The type of NAT function described above is called network
address port translation (napt). You can use other types, called
flavors, of NAT for other purposes; for example, providing outside
access to your LAN or translating multiple private addresses to
multiple public addresses.
Your Default NAT Setup
By default, NAT is enabled, with an napt rule configured to perform
the following translation:
These private IP addresses: ...are translated to:
10.0.0.3
10.0.0.4
.
.
.
10.0.0.15
Your ISP-assigned
public IP address
For a description of napt rules, see page 63. This default NAT setup
assumes that, on each LAN computer, you configured TCP/IP
properties as follows:
 You selected the check box that enables them to receive
their IP addresses automatically (that is, to use a DHCP
server);
or,
 You assigned static IP addresses to your PCs in the range
10.0.0.3 through 10.0.0.32.
If your computers are not configured in one of these ways, you
can either change the IP addresses on your computers to match the
NAT setup (see the Quick Start instructions, Part 2), or delete this
NAT rule and add a new one that matches the addresses you