On a private home or small-business network you can use any IP addresses you like, bu! the DHCP server inside most routers will be preconfigured to use officially reserved ranges. These can vary but, typically, will be in the format 192.168.0.xxx, 192.168.1.xxx or possibly 10.0.0.xxx, allowing you to have up to 254 devices on your Lan with numbers from 001 to 254 replacing the 'xxx' part of the address. By convention the router itself will have an address ending in 001 (the default gateway). You can change to a different scheme but unless there's a good reason it's really not worth it.