I have an iPad Air 2. I've been using a comic book reader called Bookman for years. It allows importing books over FTP on a set port (2121). It has worked for years without an issue, but ever since I updated to iOS 10.0.2, I keep getting "ECONNREFUSED - Connection refused by server" trying to connect to the iPad's IP.
A ping to the iPad's IP works, and connecting to another app that uses port 80 works. I verified it's not a client side issue, by trying from several machines. At this point, I think something in iOS is blocking the port.
Is there a firewall, or any other configurable part that I can allow traffic through?