GE PACSystems RX7i, User Manual

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Chapter 13. Network Administration
GFK-2224Q January 2017 243
Problem example #1:
Figure 98: CPE330 Overlapping Local IP Subnet Example
The issue demonstrated in Figure 97 is that requests entering one CPE330 interface can be routed out the other
interface since both CPE330 Ethernet ports have been configured to be on the same network (255.255.0.0) but
are physically connected to separate networks. Avoid this by assigning non-overlapping Subnets.
Problem example #2:
A user wishes to communicate through a routed network to an RX3i CPU with multiple network interfaces
(CPE330, in this example). This remote IP device is configured with the following IP parameters:
IP 192.168.0.5
Subnet Mask 255.255.255.0
Gateway 192.168.0.250
LAN1 and LAN2 on the CPE330 are initially configured with following problematic IP parameters:
LAN1 LAN2
IP 10.10.0.1 192.168.0.1
Subnet Mask 255.255.255.0 255.255.255.0
Gateway 10.10.0.249 0.0.0.0
The user intends to communicate between the remote device and CPE330 LAN1 (Figure 98). IP Address routing
allows the CPE330 to receive the remote IP requests through the respective gateways (192.168.0.250 for the
remote node and 10.10.0.249 for CPE330 LAN1). However, since CPE330 LAN2 shares the same IP subnet as the
remote network (192.168.0.x), responses may be routed to the local 192.168.0.x network rather than to the
remote network (Figure 99).
The duplicate IP subnet in the example must be eliminated. One way to do this is simply change the IP Address
assigned to CPE330 LAN2 from 192.168.0.1 to 192.168.1.1 thereby creating a non-overlapping 192.168.1.x
network. In short, consider the totality of the network when assigning IP subnets and IP Addresses.