Operating System (OS) Firewalls (Personal Firewall), has become a more common occurrence. Several Operating Systems are coming with a firewall installed, but so many people are unaware if it is turned on or off.
Microsoft Windows XP, Vista, 7, 8, 8.1, and Windows 10 all have a built in Firewall
Microsoft Servers : Windows 2003, 2003R2, @008, 2008R2, 2012, 2012R2, 2016 all have a built in firewall.
Mac OS X : 10.7-10.14 use ipfw as a Firewall, This hsould be turned on.
Unix: FreeBSD uses ipfw as its firewall
Linux: Firewall is iptables/ipchains and IPFilter