CCNA Routing & Switching : IP addresss Configuration

Rules to assign the IP address to the router:

1. All the LAN and WAN should be in different networks (or should not repeat the same networks).
2. Router Ethernet IP and the LAN network assigned should be in the same network.
3. Both the interfaces of router facing each other should be in the same network.
4. All the interfaces of routers should be in the different network.

source
ccna