User's Manual

4 IP Network Planning
APCD-LM043-4.0 57
4.3 Network Address Translation
The following address translation alternatives are listed for reference purposes. Choose the
best alternative for your system. Your choice depends on the number of available registered
IP addresses. It also depends on the nature of your subscriber base; for example, static NAT
may be required to support some of your business users, but dynamic NAT may be adequate
for most of your home users.
Static NAT
Static NAT maps an unregistered IP address to a registered IP address on a one-to-one basis.
This method of translation is recommended if, for example, end users are using VPN facilities
to access remote applications.
Dynamic NAT
Dynamic NAT maps an unregistered IP address to a registered IP address, taken from a pool
of registered IP addresses. This method of translation is useful when you have a large number
of unregistered users who wish to access the Internet. Depending on the traffic pattern, 10
registered IP addresses may be able to serve 40 end users.
Overloading
Overloading, which is a form of dynamic NAT, maps multiple unregistered IP addresses to a
single registered IP address by using different ports. This technique is also known as port
address translation (PAT), single-address NAT, or port-level multiplexed NAT. PAT greatly
reduces the number of necessary registered IP addresses. When overloading is configured,
the router maintains enough information from higher-level protocols to translate the registered
address back to the unregistered address for traffic inbound from the Internet.