4-3
4 Determining IP Addresses
NJ/NX-series CPU Unit Built-in EtherNet/IP Port User’s Manual (W506)
4-1 IP Addresses
4
4-1-2 Allocating IP Addresses
You must assign IP addresses nodes so that each IP address is assigned only once in the network or
between several networks.
Operation and management of a network can become very difficult if too many nodes are connected on
a single network. In such a case it can be helpful to configure the system so that a single network is
divided up into several subnetworks. Internally the network can be treated as a number of subnetworks,
but from the outside it acts as a single network and uses only a single network ID. To establish subnet-
works, the host ID in the IP address is divided into a subnet ID and a host ID by using a setting called
the subnet mask. The subnet mask indicates which part of the host ID is to be used as the subnet ID.
All bits in the subnet mask that correspond to the bits in the IP address used either as the network ID or
subnet ID are set to “1,” and the remaining bits, which correspond to the bits in the IP address actually
used for the host ID, are set to “0.”
The following example shows the subnet mask for an 8-bit subnet ID used in class-B IP addresses.
Set the same subnet mask for all of the nodes on that subnetwork. The built-in EtherNet/IP port sup-
ports CIDR (Classless Inter-Domain Routing). The subnet mask can be set to 192.0.0.0 to
255.255.255.252. If subnetworks are not used, set the following subnet mask values for IP address
classes A to C.
A network address is information derived from a subnet mask and used to identify each network. A net-
work address enables users to determine whether multiple nodes belong to the same network. A net-
work address is calculated by performing a logical AND operation on the IP address and subnet mask
of a node.
The following are examples of network address calculation.
In this example, the IP address of node 1 is set to 192.168.250.20, the IP address of node 2 is set to
192.168.245.30, and the subnet mask is set to 255.255.240.0. The network addresses of the two nodes
are calculated as follows.
• Calculating network address of node 1
• Calculating network address of node 2
4-1-2 Allocating IP Addresses
4-1-3 Subnet Masks
Class Subnet mask
Class A 255.0.0.0
Class B 255.255.0.0
Class C 255.255.255.0
Item Decimal notation Binary notation
IP address 192.168.250.20 11000000.10101000.11111010.00010100
Subnet mask 255.255.240.0 11111111.11111111.11110000.00000000
Network address 192.168.240.0 11000000.10101000.11110000.00000000
Item Decimal notation Binary notation
IP address 192.168.245.30 11000000.10101000.11111010.00010100
Subnet mask 255.255.240.0 11111111.11111111.11110000.00000000
Network address 192.168.240.0 11000000.10101000.11110000.00000000
0
1111111111111111 1111111100000000 FF FF FF 00
Host IDSubnet IDNetwork ID
Host number (16 bits)Network number (14 bits)
Subnet mask
Class B
Bit 31 15
1
0
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