Rockwell Automation 1738-AENTR, Series B POINT I/O and ArmorPOINT I/O Dual Port EtherNet/IP Adapters User Manual - Manual (Page 30)

22 Rockwell Automation Publication 1734-UM017B-EN-E - October 2013
Chapter 3 Configure the Adapter with RSLogix5000 software
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
.
Two bits of the Class B host ID are used to extend the network ID. Each unique
combination of bits in the part of the Host ID where subnet mask bits are 1
specifies a different physical network.
The new configuration is:
A second network with Hosts D and E was added. Gateway G2 connects
Network 2.1 with Network 2.2.
Hosts D and E will use Gateway G2 to communicate with hosts not on
Network 2.2.
Hosts B and C will use Gateway G to communicate with hosts not on
Network 2.1.
When B is communicating with D, G (the configured Gateway for B) will route
the data from B to D through G2.
EXAMPLE Take Network 2 (a Class B network) in the previous
example and add another physical network. Selecting the
following subnet mask would add two additional
network ID bits, allowing for four physical networks:
11111111 11111111 11000000 00000000 = 255.255.192.0
These two bits of the Host ID are used to
extend the netdwork ID.
Network 1
Network 2.1
Network 2.2
A
B C
D E
128.1.0.2
128.1.0.1
128.2.64.3
128.2.128.2
128.2.64.1 128.2.64.2
128.2.128.3
128.2.128.1
G2
G