B-6 APPENDIX B: IP ADDRESSING
To route IP, the two networks to be linked by the OfficeConnect Remote 840 (local LAN and the ISP's or remote site's network) must be on separate IP subnets. For example, all local LAN devices could be on subnet 192.168.1 and all devices in at the remote site could be on subnet 192.168.2. Put another way, all devices connected to the local LAN must be assigned IP addresses that begin with 192.168.1, for example 192.168.1.1, and all devices on the remote LAN must be assigned addresses that begin with 192.168.2, for example, 192.168.2.1.
Each IP address uniquely identifies a machine on an IP network. Therefore, to avoid duplication, IP addresses are regulated and are ultimately purchased from an organization (see the previous section). You probably won't need to purchase your own IP addresses for your home/office LAN. If you are connecting to the Internet, the ISP will provide you with one or more addresses. If you are connecting to a remote office, the network administrator should be able to provide you with a subset of addresses from the set that were assigned to the remote office.
Single IP Address If you are provided with a single IP address, you'll use the OfficeConnect Remote 840's Port Address Translation (PAT) feature. The IP address will be assigned to the OfficeConnect Remote 840's local WAN interface.
PAT allows you to make up an IP network for your LAN, using IP addresses of your own choosing. This network is hidden from the ISP or remote site because all data traffic going out the OfficeConnect Remote 840's WAN port will carry the assigned IP address. Since it is hidden, it does not matter if the addresses you use are duplicated elsewhere. Using PAT, the OfficeConnect Remote 840 keeps track of mapping the data packets to their rightful owners, the workstations on the LAN.
For more information on PAT, see the “Address Translation Tutorial”.
Range of IP If you are provided with a range of IP addresses, it may be given to you in Addresses the form of an IP address and netmask.
Example: We were given the IP address 2xx.xxx.188.176 with mask 255.255.255.248.
The first task is to understand our IP address range and decide which addresses to assign to the workstations and which address to assign to the OfficeConnect Remote 840. We take our first address,
