18 Rockwell Automation Publication 1794-UM066C-EN-E - April 2023
Chapter 3 Configure the Adapter for Your EtherNet/IP Network
IP addresses are written as four decimal integers (0…255) separated by periods where each
integer gives the value of 1 byte of the IP address.
Gateway Address
The Gateway Address is the default address of a network. It provides a single domain name and
point of entry to the site. Gateways connect individual physical networks into a system of networks.
When a node needs to communicate with a node on another network, a gateway transfers the data
between the two networks. The following figure shows gateway G connecting Network 1 with
Network 2.
When host B with IP address 128.2.0.1 communicates with host C, it knows from C’s IP address that
C is on the same network. In an Ethernet environment, B then resolves C’s IP address into a
hardware address (MAC address) and communicates with C directly.
When host B communicates with host A, it knows from A’s IP address that A is on another network
(the net IDs are different). To send data to A, B must have the IP address of the gateway connecting
the two networks. In this example, the gateway’s IP address on Network 2 is 128.2.0.3.
The gateway has two IP addresses (128.1.0.2 and 128.2.0.3). The first must be used by hosts on
Network 1 and the second must be used by hosts on Network 2. To be usable, a host’s gateway
must be addressed using a net ID matching its own.
EXAMPLE For example, the 32-bit IP address:
10000000 00000001 00000000 00000001 is written as 128.1.0.1.
Contact your network administrator or the Network Information Center for a unique
fixed IP address to assign to your module.
Network 1
Network 2
128.2.0.3
128.1.0.2
128.1.0.1
128.2.0.1 128.2.0.2
A
B
C
G
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