Linux is highly secure, but you should still have a firewall. You should know if your ISP's hardware (gateway) uses a firewall. One of the easiest Linux firewalls is UFW and its GUI sidekick, GUFW.
FireWall-1 is also the most powerful commercial firewall solution now available for the Linux platform. FireWall-1 isn’t the only well-known solution to move into the Linux camp. AXENT Raptor Firewall ...