Monitor servers with limited connectivity

How can I monitor servers in a network where only certain servers have internet connection?

Working Principle:
The server which has internet connection can act as a proxy for the other intranet servers. The agent installed in the intranet servers will communicate via this proxy server. 

You can also configure proxy for your Windows and Linux (while installing and also after installing) agents.
Use case: 
The image shows the organizational set up of a company. There are two kinds of working environments:
  • Production environment: no access to the internet
  • Office environment: has access to the internet
The user wants to monitor servers in the production environment. So in this case, one of the servers in the office environment will act as proxy for the servers in the production environment. This will collect data from the production environment and post it to the Site24x7 server.