Omron CS1W-ETN21 operation manual IP Address Configuration, Allocating IP Addresses

IP Addresses Section 5-1

5-1 IP Addresses

Ethernet networks use IP addresses for communications. IP addresses iden- tify both the Ethernet network and the node (host computer, Ethernet Unit, etc.). IP addresses must be set and controlled so that they are not duplicated.

5-1-1 IP Address Configuration

IP addresses are made up of 32 bits of binary data divided into four 8-bit fields called octets. These four octets provide the network number (net ID) and host number (host ID). The network number identifies the network, and the host number identifies the node (or host) on the network.

The network numbers in an IP address are divided into three classes, A, B, and C, so that the address system can be selected according to the scale of the network. (Classes D and E are not used.) The configuration of the IP address for each of these classes is shown in the following diagram.

	Bit 31						23				0
Class A		0	Network number (7 bits)						Host number (24 bits)
	Bit 31						15				0
Class B		1	0	Network number (14 bits)					Host number (16 bits)
	Bit 31								7		0
Class C		1	1	0		Network number (21 bits)				Host number (8 bits)
	Bit 31										0
Class D		1	1	1	0			Multicast address				(Cannot be used.)
	Bit 31										0
Class E		1	1	1	1			Identification address				(Cannot be used.)

The number of networks in each class and the number of nodes possible on the network differ according to the class.

Class	Number of networks	Number of hosts
Class A	Small	224−2 max. (16,777,214 max.)
Class B	Medium	216−2 max. (65,534 max.)
Class C	Large	28−2 max. (254 max.)

The 32 bits of an IP address are divided into four sections of eight bits each, and expressed as a punctuated number. IP addresses are represented by the decimal equivalent of each of the four octets in the 32-bit address, each sepa- rated by a period. For example, the binary address 10000010 00111010 00010001 00100000 would be represented as 130.58.17.32.

Note The same network number must be set for every node on the same Ethernet network.

5-1-2 Allocating IP Addresses

IP (Internet Protocol) is a standard communications protocol used throughout the world, and is designed to enable communications between any Ethernet nodes regardless of the networks on which they exist. To achieve this, net- work numbers are allocated by the Network Solutions, InterNIC Registration Services, to ensure that all Ethernet networks have unique numbers regard- less of where they exist. The local system administrator is left the responsibil- ity of allocating unique host numbers locally. You therefore should obtain a network number from the InterNIC Registration Services to ensure unique- ness and allow for future network expansions if required.

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