The following options can be used to select IP addresses for your LAN:
Use public IP addresses. The ISP will assign a required number (range) of IP addresses and set routing parameters.
Use private IP addresses and IP translation (NAT). The ISP mostly assigns only one public IP address. Under such circumstances, the local network will be “hidden” behind this IP address entirely.
Private addresses are represented by special IP ranges that are reserved for local networks which do not belong to the Internet (private networks). These addresses must not exist in the Internet (Internet routers are usually set in order to drop all packets that include these addresses).
The following IP ranges are reserved for private networks:
10.x.x.x, network mask
255.0.0.0
172.16.x.x, network mask
255.240.0.0
192.168.x.x, network mask
255.255.0.0
Warning: Do not use other IP addresses in private networks, otherwise some Web pages (those networks that have the same IP addresses) might be unavailable!
In our example, we will focus on private networks connected to the
Internet through a single public IP address. For the headquarters' LAN,
the private addresses 192.168.1.x with subnet mask
255.255.255.0 (IP subnet 192.168.1.0)
will be used whereas IP addresses10.1.1.x with subnet mask
255.255.255.0 (IP subnet 10.1.1.0) will
be used for the filial's LAN.