There has been lot of discussion about which open source firewall,proxy etc you can use for your organization. Lot of queries have been asked to me for the same.
I personally believe that any firewall cannot prevent you entire from attacks you have to in place a proper unified threat management systems installed at your gateway through which you are providing internet access to your employees in your organization.
There are various commercial choices like sonicwall, cyberoam, sophos, untangle etc but if you know how to use open source components you can configure your own UTM easily. Along with open source UTM’s like ipcop, pfsense,shorewall, clearOS is my personal favorite choice still I won’t say any network is 100% secure because you have malicious softwares like malwares,trojans, viruses getting spreaded daily so in order for providing a robust security I would suggest to through my link posted previously on http://www.alokthaker.com/2016/01/21/hardening-and-securing-your-linux-os-servers/
Please feel free for any comments or queries. Going to write on creating your own jarvis soon using python in my next post stay tuned.