|  | 10.3 | IP Addresses within the IP Header
| 10.3.5 | IP address component fields
The network number of an IP address identifies the network to which a device is attached, while the host portion of an IP address identifies the specific device on that network. Because IP addresses consist of four octets separated by dots, one, two, or three of these octets may be used to identify the network number. Similarly, up to three of these octets may be used to identify the host portion of an IP address.
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| Introduction to the Internet Protocols