I am new to OpenWRT and seem to be running into some issues with my setup and apologies in advance if this is a generic question. Basically what I want is to have a router with OpenWRT be able to communicate with 2 devices on the LAN but will not have the access to the internet at all. I am basically creating a test environment where one device has DICOM images and the other device is hosting a DICOM storage server application and transfer DICOM data. I am able to ping the 2 devices successfully but unable to send the DICOM data, am I missing something else? It is using the DICOM protocols but I have verified it can work if I plug both devices into one another without the router in the mix so I believe it is a setting I am missing.
I'm not familiar with DICOM, but if it's a normal TCP service, you could try running a port scan with something like nmap to see if you can see the server from the other machine. Example would be nmap -p (dicom port) (server IP), you could try this both on the router and client machine.
If two or more hosts are on the same network, the router itself is not involved in the traffic between them. That is because the router's core features (routing and firewall) operate at L3, which is not involved if there is only a single subnet.
The only thing the router will do in this situation is:
provide a DHCP server, if desired
perform as a switch (L2) to connect the two (or more) hosts together.
A simple unmanaged switch would have exactly the same behavior as an airgapped router in your scenario, excpet that a switch would not provide the DHCP service (you'd need static IPs for your hosts, or a DHCP server on one of them).