Rockwell Automation 1794-AENTR_AENTRXT FLEX I/O Dual Port EtherNet/IP Adapter Modules - Manual (Page 25)

Publication 1794-UM066A-EN-P - February 2012
Configure the Adapter for Your EtherNet/IP Network 17
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). 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.
Subnet Mask
The subnet mask is used for splitting IP networks into a series of subgroups, or
subnets. The mask is a binary pattern that is matched up with the IP address to
turn part of the Host ID address field into a field for subnets.
Take Network 2 (a Class B network) in the previous example and add another
network. Selecting the following subnet mask would add two additional net ID
bits, allowing for four logical networks:
EXAMPLE Take Network 2 (a Class B network) in the previous example
and add another network. Selecting the following subnet mask
would add two additional net ID bits, allowing for four logical
networks:
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
11111111 11111111 11000000 00000001 = 255.255.192.0
These two bits of the host ID used to
extend the net ID