Netopia R2020 - Manual (Page 128)

10-2 User’s Reference Guide
The terms public and external refer to the Internet side of the Netopia Router's connection. A machine on the
public network cannot necessarily access a machine behind a Netopia Router's NAT remapping, unless you
specify that it can.
Multiple Network Address Translation (MultiNAT) introduces several new NAT-related features. These features
can be divided into three categories that can be used simultaneously in different combinations on a
per-Connection Profile basis.
A brief description follows:
■ PAT stands for Por t Address Translation (also known as NAPT for Network Address Por t Translation). It
allows an entire network or par t of a network to be represented to the outside world as a single IP address.
A limitation of PAT is that communication must be initiated from the internal network. A user on the external
side can not access a machine behind a PAT connection. Now, with the Netopia R2020 Router, you can
define multiple PAT remappings. Each of these can optionally alias a section or
range of IP addresses of
the internal network. PAT remapping allows only internal users to initiate traffic flow between the internal
and external networks.
■ Static remappings are a way to represent an internal single address or sequence of addresses as an
external address or sequence of addresses on a one-to-one basis. As with PAT remappings, you can
simultaneously use several static rules. Machines on the external network can initiate conversations with
statically remapped internal computers by accessing the aliased values. It is impor tant to note that in most
uses of static remappings a static route on the external router must be created to tell the external network
to go through the NAT Netopia Router to get to the remapped external addresses. Static remapping allows
an entire machine to be available to the external net. Either the internal NATed machine or the external
network can initiate traffic flow to or from the remapped machine.
■ Ser ver Lists are also known as expor ted ser vices. By creating a ser ver list, you can tell the outside world
that specific
ser vices such as Web, ftp, e-mail, etc. can be accessed at specific external addresses. Ser ver
lists differ from static remappings in that the specified ser vice is only available to external users at the
stated alias address. In most uses of ser ver lists you must create a static route on the external router to
tell the external network to go through the NAT Netopia Router to get to the remapped address of the
ser ver lists. Expor ted ser vers and Ser ver Lists allow only specific IP ser vices (IP por ts) to be available to
the outside world. Ser vices from different internal machines can be presented as a single external IP
address.
Map Lists and Ser ver Lists are completely independent of each other. A Connection Profile can use one or the
other or both.
MultiNAT allows complex mapping and requires some complex configuration. Multiple mapped interior subnets
are suppor ted, and the rules for mapping each of the subnets may be different. The figure below illustrates a
possible multiNAT configuration.