For routing interfaces, you can select the registered address as the address of one of the Screen's interfaces. In this case, the Screen simulates the registered address. The limitation here is that you only have a single address. Also selecting the interface address as the registered address for a static NAT rule can limit your ability to connect to the Screen itself. Because you are not adding additional networks, no routing changes are required.
For example, consider a Screen with routing interfaces. One of the network interfaces has the address 199.190.177.1. You can use this address as your registered address in NAT rules.
For routing interfaces, you can select the unused addresses on one of the networks to which the Screen is directly connected as virtual addresses. In this case, it is necessary so that it can respond to APR requests for these virtual addresses.
For routing interfaces, you can select the virtual addresses from a network not directly connected to the SunScreen. In this case, you must make sure that the correct routing information is propagated so that packets destined for these addresses pass through the SunScreen. If you define new networks (especially ones in which all the addresses on the network are virtual), you may need to add static routing entries on some routers to simulate these networks.