Do note that firewall on CentOS 7 system is enabled by default.

Step 1: To check the status of CentOS 7 FirewallD

# systemctl status firewalld.service

● firewalld.service - firewalld - dynamic firewall daemon
   Loaded: loaded (/usr/lib/systemd/system/firewalld.service; disabled; vendor preset: enabled)
   Active: inactive (dead)
     Docs: man:firewalld(1)

The above shows that the firewalld is disabled.

Step 2: To stop the FirewallD

# systemctl stop firewalld.service

Step 3: To completely disable the firewalld service

# systemctl disable firewalld.service