Web Server often cannot Reach Websites Internally, but website can be accessed externally

Hopefully someone would be able to assist with my situation:

I have a Webserver Hosting a .Net based Web App. Often throughout the day Internally, i seemingly looking Internet access I cannot ping or reach any websites from within. But externally the website is still fully functional and able to browse for my users. And this happens off and on though out the day for 5-10 mins at a time, then I can ping and browser other websites

This is EC2 (Amazon) Server within its on VPC with 3 Elastic IP’s attached too it and 2 Private IP’s to serve different areas of the Webserver and the applications Console and such.

Also any other server within this VPC works fine and has no outages .

Source: Windows Questions