> **Question**: I am running a web/file server on my CentOS box, and to access the server remotely, I need to modify a firewall to allow access to a TCP port on the box. What is a proper way to open a TCP/UDP port in the firewall of CentOS/RHEL?
Out of the box, enterprise Linux distributions such as CentOS or RHEL come with a powerful firewall built-in, and their default firewall rules are pretty restrictive. Thus if you install any custom services (e.g., web server, NFS, Samba), chances are their traffic will be blocked by the firewall rules. You need to open up necessary ports on the firewall to allow their traffic.
On CentOS/RHEL 6 or earlier, the iptables service allows users to interact with netfilter kernel modules to configure firewall rules in the user space. Starting with CentOS/RHEL 7, however, a new userland interface called firewalld has been introduced to replace iptables service.
To check the current firewall rules, use this command:
Now let's see how we can update the firewall to open a port on CentOS/RHEL.
### Open a Port on CentOS/RHEL 7 ###
Starting with CentOS and RHEL 7, firewall rule settings are managed by firewalld service daemon. A command-line client called firewall-cmd can talk to this deamon to update firewall rules permanently.
To open up a new port (e.g., TCP/80) permanently, use these commands.
If you are trying to update the firewall for any well-known service (e.g., web server), you can easily enable the firewall for the service here, and close the tool. If you are trying to open up any arbitrary TCP/UDP port, choose "Forward" button and go to a next window.
