@NeilR_M Thanks, that is exactly what I had in mind (or MAC address) but I can't find where to do that? If i go to Settings and ACL (under Network Security) I can only select "Network" as my source...

Our client has four ER605's (3 are V2 and 1 is V2.20), each is its own site running on a Software Controller in Windows remotely. Each is on its building, own network, own internet. The client wants...