One Line Answer : Disable the System Firewall
I was developing a small web application in my Laptop using Spring MVC and was testing the application in Laptop browser. In one case, I wanted to see the web page in mobile and so I opened the URL in Android smartphone. But the page was not reachable due to the antivirus in the laptop which was blocking the requests. So I disabled the Antivirus Firewall and was able to access the webpages through smartphone.