If a PAC controller has a default gateway configured on the primary Ethernet port, and the secondary port with an open socket becomes disabled, it will no longer be able to communicate through the secondary port, even if the port is re-enabled.
For example, a controller with:
Primary IP address: 10.0.0.1
Primary Subnet Mask: 255.255.255.0
Primary Default Gateway: 10.0.0.10
Secondary IP address: 192.168.0.1
Secondary IP address: 255.255.255.0
Secondary Default Gateway: 0.0.0.0
If the controller is communicating to an I/O unit with an IP address of 192.168.0.2, it is sending information through the secondary Ethernet port. If the secondary port is disconnected, the information for this I/O unit is routed to the primary port, to the default gateway. The default gateway discards the information because the IP configuration does not provide a route from the primary port to the destination address.
Even after the secondary port is re-connected, information continues to be routed through the primary port until the secondary port’s open socket is closed and reopened.
Do not configure a default gateway on either Ethernet port interface.
Opto 22 has resolved this issue.