Just double checked on the lab, I was going to see if individual machines need to pointed to an IP address of a modbus server to get access to channels. However, issue with fb2 not being able to see channels and report/put values with caget and caput seems to have resolved itself. Only change on the network is that fb0 and fb1 have been powered up.
Not sure what has happened here. Problem solved for now.
Channels seem to work ok when called from caput and caget command line tools on computer acromag1 but fail on computer fb2. The sitemap memd screens also do not load values when started on fb2. This is a problem: none of these tools (StripTool, sitemap, memd etc) are installed on acromag1 (it was only intended to be a dedicated server for modbusapp I'm guessing). I have been loading all the GUI tools by ssh forwarding from fb2 to other computers. Bit hard to diagnose what the problem is here.