A network video recorder (NVR) is a specialized computer system that includes a software program that records video in a digital format to a disk drive, USB flash drive, SD memory card or other mass storage device. An NVR contains no dedicated video capture hardware. However, the software is typically run on a dedicated device, usually with an embedded operating system. Alternatively, to help support increased functionality and serviceability, standard operating systems are used with standard processors and video management software. An NVR is typically deployed in an IP video surveillance system.
A good NVR would allow you to issue your IP cameras there own IP address, as on my NVR my LAN/WAN address would be in the 192.168.x.x and my IP cameras could have there own addresses for instance 10.x.x.x or 172.x.x.x.