TW-H6W1IR ISDN Remote Router
82 Configuration and
Management
The difference between static and dynamic NAT is that once the five
global addresses are manually assigned when using static NAT, they
will never change. The only way to change them is by using the console
program to manually reassign them. When using dynamic NAT, the
router will map a local IP address to a global IP address whenever a
request is made. Since there are only 5 global IP addresses in the
example above, there can only be 5 mappings at any one time. In other
words, much like static NAT, only 5 local machines can access the
Internet at any one time. However, contrary to static NAT, the router
will discard the mapping between the global and local IP addresses
after a certain length of time (which is quite long so rarely happens), or
after the session is finished (an example of a session is when requesting
a web page, the entire page has completed downloading). The most
common implementation of NAT is to define a range of dynamic
addresses to be used by hosts, but assign static addresses to your
servers if you wish for them to be accessible from outside your
network.
NAPT
NAPT is an advanced version of NAT that uses IP port numbers in the
network address translation process. It is much more widely
implemented on networks today due to the fact that it uses only a single
global IP address (as opposed to NAT which uses a range of global
addresses), thus providing greater cost savings. For Internet access for
everyone on the network through a single IP address (a single user
account), NAPT is the right choice.
When a packet on the local network arrives at the router and needs to
be sent to the Internet, it already has a (local) source IP address and a
(local) source port number that was generated when the packet was
