|  | 10.5 | Reserved Address Space
| 10.5.3 | Network ID analogy
ZIP Codes and networks IDs are quite similar in how they work. A ZIP Code enables the postal system to direct your mail to your local post office, and to your neighborhood. From there, the street address directs the carrier to the proper destination. A network ID enables a router to put a packet onto the appropriate network segment, while the host ID helps the router address the Layer 2 frame (encapsulating the packet) to the specific host on that network.