11.4. Private Networks and NATBecause IPv4 addresses are relatively scarce, each address typically costs money to use. You may not pay directly for an IP address, but your ISP has a limited supply of them and will use some mechanism to control their use. To allow multiple machines to run behind a limited supply of IP addresses, many networks use a block of private addresses as well as Network Address Translation (NAT) . Supported by most routers, NAT processes all packets bound for the Internet from a private network, transforming the original IP addresses into an address that is reachable from the Internet, before sending the packets on. In effect, packets from the private network appear to be coming from the router running NAT (Figure 11-6). When packets arrive back at the router that corresponds to a connection already in progress, the NAT translates them into a form usable on the private network and sends them back to the original host. Figure 11-6. The NAT processYou can tell if you are on a private network when your IP address is in one of the following ranges:
Using NAT creates two follow-on effects:
You'll need to consult the information about your router to be sure. |