View Webserver Form Internal and Extenal

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http://serverfault.com – We have a web server hosted out of our office, and it works fine when people access the site from outside the office. The problem is that when people are inside the office and go to the website (www.example.com) it's very slow, as it goes out over the internet and comes back in. Or LAN is Windows with Active Directory and our web server is CentOS with its own internet connection. How can I set when users in my office want see website opens it from local network instead of going out of one internet connection and back in through the other? (HowTos)