Because the Linux kernel has a built-in firewall and technically all Linux distros have a firewall but it is not configured and activated.

What are inbuilt firewall in Linux?

iptables is a built-in firewall in Linux. It is a user based application for configuring the tables provided by the Linux kernel firewall. iptables is the default firewall installed with Red Hat, CentOS, Fedora Linux, etc.

Do computers have built-in firewalls?

A firewall acts as a barrier or filter between your computer and another network such as the internet. … Your operating system and your security software usually come with a pre-installed firewall. It’s a good idea to make sure those features are turned on.