You should have kept your original thread going instead of starting a second thread on the exact same topic.
As @pturmel mentioned, you're on different subnets, so these networks will need routed and the proper ACLs in place. You can't just change subnet masks to make things work. I don't know if you can get IT to allow you to put the modem on the same network as Ignition, but it would take the firewall out of the equation.