Rockwell Automation 1756-NEX Nexus Module - Manual (Page 32)

3-6 About the NeXUS Network
Publication 1756-UM524B-EN-P - December 2008
Gateways
A gateway connects 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 can then resolve C’s
IP address to a MAC address and communicate 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). In order 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.
128.1.0.1
128.2.0.1 128.2.0.2
128.2.0.3
128.1.0.2
A
B C
G
Network 1
Network 2