Internet Security Router User
’
s Manual
Chapter 9. Configuring Firewall/NAT Settings
47
Figure 9.1 Static NAT
–
Mapping Four Private IP Addresses to Four Globally Valid IP Addresses
9.2.2
Dynamic NAT
Dynamic NAT maps an internal host dynamically to a globally valid Internet address (m-to-n). The mapping
usually contains a pool of internal IP addresses (m) and a pool of globally valid Internet IP addresses (n) with
m usually greater than n. Each internal IP address is mapped to one external IP address on a first come first
serve basis. Figure 9.2 shows that PC B, C and D are mapped to a globally valid IP address respectively,
while PC A does not map to any globally valid IP address. If PC A wants to go to the Internet, PC A must wait
until a global valid IP address is available. For example, in Figure 9.3, PC B must disconnect from the Internet
first to allow PC A to access Internet.
Figure 9.2 Dynamic NAT
–
Four Private IP
addresses Mapped to Three Valid IP Addresses
Figure 9.3 Dynamic NAT
–
PC-A can get an NAT
association after PC-B is disconnected
