IP Address: (Host Portion)
Host addresses numerically identify specific network interfaces on an IP network. Usually a host has only one network interface; thus, only one IP address. Because no two devices can share the same number at the same time, administrators typically maintain address tables to assure correct assignment of addresses in the host network.
IP Address Structure and Class
An IP address is comprised of 32 bits of information and divided into 4 sections containing 1 byte each section or 4 bytes total: xxx.xxx.xxx.xxx
For efficiency in routing, networks were broken down into three classes, so routing can begin simply by identifying the leading byte of information in the IP address. The three IP addresses that InterNIC assigns are class A, B, and C. The network class determines what each of the four IP address sections identify as shown in Table A.1:
Table A.1 IP Address Class Format
Class | First | Second | Third | Fourth |
| Address | Address | Address | Address |
| Byte | Byte | Byte | Byte |
| xxx. | xxx. | xxx. | xxx |
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A | Network. | Host. | Host. | Host |
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B | Network. | Network. | Host. | Host |
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C | Network. | Network. | Network. | Host |
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ENWW | TCP/IP Overview 87 |