Firewalld

https://www.tecmint.com/start-stop-disable-enable-firewalld-iptables-firewall/

Good article: https://www.linode.com/docs/guides/introduction-to-firewalld-on-centos/

firewalld - A wrapper for iptables to allow easier management of iptables rules. Is not an iptables replacement. It's a firewall service daemon that provides a dynamic customizable host-based firewall with a D-Bus interface. It enables creating, changing, and deleting the rules without the necessity to restart the firewall daemon each time the rules are changed.

Check if firewalld is running

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Run:

sudo systemctl status firewalld

If it's active (running), firewalld is enabled.

List active firewall rules

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sudo firewall-cmd --list-all

How to Allow HTTP connectivity in firewall (RHEL8)

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I was configuring apache (httpd) on a RHEL8 server. I had apache running and listening on port 80 and I confirmed that DNS was resolving the domain successfully. However, when I attempted to connect to the server on port 80 (using curl -IvkL) I was getting "No route to host":

curl: (7) Failed to connect to 123.abc.com port 80: No route to host

I checked iptables -L but did not see any iptables rules.

Then I found this article and found that I needed to allow http in the firewall rules.

sudo firewall-cmd --zone=public --add-service=http --permanent
sudo firewall-cmd --zone=public --reload
sudo firewall-cmd --zone=public --list-all

Then confirmed that I was able to connect to the server on port 80 via a web browser.

How to check Firewall configurations for a specific Zone

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$ sudo firewall-cmd --zone=public --list-all
public (active)
  target: default
  icmp-block-inversion: no
  interfaces: eth0
  sources:
  services: cockpit dhcpv6-client http ssh
  ports:
  protocols:
  forward: no
  masquerade: no
  forward-ports:
  source-ports:
  icmp-blocks:
  rich rules: