Transparent subnets can be used as a way to extend the proxy ARP concept. You can use transparent subnets as a proxy for an entire subnet, or range of hosts. Transparent subnetting allows stub networks to be assigned addresses out of the primary network address space.
Transparent subnets work for a single host so that you can connect to an entire subnet or range of hosts. You can see in the following figure that the stub networks (10.1.1.x through 10.1.3.x) are assigned addresses out of the primary network address space (10.1.x.x).
The twinaxial LANs are defined in address ranges that are within the real LAN address range. This allows two interfaces in different segments to have addresses that look like they are in the same segment. When the system sees this happen, it automatically performs a proxy ARP for any systems that are attached behind the twinaxial controller. This allows all the systems on the 10.1.x.x network to communicate with all the subnet systems with no changes to the systems on the 10.1.x.x network.
The transparent subnet function can be further expanded to handle real LANs that are remotely located. Transparent subnetting over WANs makes remote networks appear to be connected to the home network. In the preceding figure, three networks are attached to the home 10.1.x.x network through the System i™ platform. These networks are all defined using a subnet mask that makes them transparent to the home network. Proxy ARP responds to any ARP request in the home network for systems in the 10.1.1.x, 10.1.2.x, and 10.1.3.x subnets. This causes the traffic for the home network to be routed automatically to the system in the home network. This system, in turn, routes the data to the correct remote system. The remote system either processes the data, or forwards it to the correct system within the remote LAN. The workstations in the remote LAN must have a default route that points to the remote system in their network as the first hop gateway. The workstations in the home LAN do not need any additional routing entries because no new logical networks are created.