title: Raspberry pi is unable to reach gateway
body: <p>Recently we brought raspberry pi 3b.Beginning we used to access the internet using an ethernet cable and it used to connect properly but now raspberry pi is not able to reach the gateway itself and it's taking its default IP address i.e 169.xxx.xxx.xx.
  what would be the issue?we tried to reinstalling the operating system again the same issue .it worked for one day after that same problem.so please help me to solve the issue.</p>