A couple of Apps on my Android phone run webservers, so that I can access them across my local area network. Recently, although the webservers continued to work, I was unable to access them from my Windows 7 PC. The solution took several day to track down, but was very simple.
I had tried restarting my Galaxy Note II (GT-N7100) running Android 4.4.2. I had tried rebooting my PC running Windows 7. The solution was simply to restart my Sky SR-101 router.
Obvious to try in retrospect, but my router was able to ping my Smartphone, but two PCs on the LAN were not, and nor could the mobile ping the two PCs.
The System Info for Android app showed that my mobile had its assigned static IP address, and deleting and recreating the WiFi connection with DHCP also had the correct IP address, and gateway to the route. But the subnet mask was showing as 0.0.0.0, as was the DNS. I though this was incorrect, but it is not.
The webservers were in use by the apps: