I set up a Node.js server on a Ubuntu machine, and it has an IP address of 172.18.x.x, I can visit the service over computers with 172.18.x.x yet some of the devices on the network has IPs of 172.19.x.x, and they are not able to visit the Ubuntu server. Does Ubuntu automatically filter requests and how do I disable this behavior?
I can confirm there is indeed a bridge between the subnet mask 172.19.0.0/16 and 172.18.0.0/16, when I run the same Node.js server on Mac or Windows, it does work as intended.
This is typically due to some type of third party firewall or security package on your Ubuntu installed by apt-get as a dependency or otherwise. Do a complete clean installation and see if this issue sticks.