Accessing a PLC with a hardcoded IP on our internal DHCP based network
Wondered what type of PLC it is, is it Allen-Bradley / Siemens or other?
You, should be able to set the subnet mask and gateway on the PLC as well ... unless you do not have access to check or change the subnet.
The last answer is also the best way to approach it ... the PLC network should, where possible, be on a separate subnet with only specific ip's and ports allowed through a router connected to the corporate, or local business network.
You can add secondary IP address (network) to your interface and it will work like a charm.