If the device can use DHCP, then you can program your DHCP server to assign a static IP address in response to the device's request. This is usually handled via MAC address. However, some DHCP servers on cheap routers don't have this capability.
By manually configuring the device. The device may have a configuration interface (most do) where the IP adress can be configured.
Either way, you need to manage the IP address assignments to make sure you don't issue the same IP address to more than one device. You choose the manual IP address within your existing subnet but outside the range issued by DHCP. If you need more details beyond this, go ahead & ask.
- John
I can confirm that I have received between 0 and 499 National Security Letters.
Problem fixed--- I use NetworkManager and so did not have dhcpcd running. I added that to rc, started the service, now the device in question has an address. Thanks though.