|  | 10.5 | Reserved Address Space
| 10.5.2 | Network ID
It is important to understand the significance of the network portion of an IP address - the network ID. Hosts on a network can only communicate directly with devices that have the same network ID. They may share the same physical segment, but if they have different network numbers, they usually cannot communicate with each other - unless there is another device that can make a connection between the networks.