Firewall & Firewalld

• A firewall is a network security device that monitors and controls incoming and outgoing traffic from a computer network. work on zones and rules....

                        where,
                                  Zones = predefined sets of rules.
                                  Rules =nothing but the premisssions set in the zones.

•  firewall decides which network traffic is allowed to pass through and which traffic is deemed dangerous.
• Essentially, it works by filtering out the good from the bad, or the trusted from the untrusted.
• for controlling firewall you can use both command line intrface or GUI method.
• A firewall system analyzes network traffic based on pre-defined rules. It then filters the traffic and prevents any such traffic coming from unreliable or suspicious sources.

However, before we go into detail, it helps to understand the structure of web-based networks.

firewall working

Concider the example,

                                 As an watchman or security guard of your apartment or society.consider restrict chaireperson commity final the rules and permissions , and send the instrruction to that watchman. as per the instructions meet as the watchman allow only those people who live in society otherwise restict the other people or allow them in perticular permission.

in above example watchman is firewall and society is the system and watchman work on rules to control the external traffic.

Advantages of firewall

1. Firewalls creates a layer of protection against unauthorized access to your network.
2. Firewalls helps organizations manage their bandwidth usage.
3. Firewalls help you monitor your network traffic so you can identify and respond to threats quickly.
4. Firewalls prevents viruses and malware from infecting systems and spreading throughout the network.

Steps to operate firewall

1.For any help or deatils command

                           firewall-cmd --help

2.For details of zones 

                           firewall-cmd --list-all

3.To get current service

                           firewall-cmd --list-services

       or                 firewall-cmd --get-services

4.To immidiate disable network traffic

                           firewall-cmd --panic-on

to on

                            firewall-cmd --panic-off

details about panic mode 

                            firewall-cmd --query-panic

5.As root if you copy the service

                            cp /usr/lib/firewalld/services/service-name.xml /etc/firewalld/services/service-name.xml

6.Incase of ports

.                           firewall-cmd --list-ports

                            firewall-cmd --add-port=port-number/port-type

.To make new setting persistent 

                            firewall-cmd --runtime-to-permanent

to remove port

                            firewall-cmd --remove-port=port-number/port-type

7.For zones

list all the zones

                            firewall-cmd --get-zones

                            firewall-cmd --zone=zone-name --list-all

to display current zone

                            firewall-cmd --get-default-zone

In below example i am trying to add the service and port number to firewall to control the external traffic.

how to remove service and port number on firewall

how to add the service and port number to firewall

If we run the command

                          firewall-cmd --list-all-zones

we get all the available zones in which

block – All incoming network connections rejected. Only network connections initiated from within the system are possible.

dmz – Classic demilitarized zone (DMZ) zone that provided limited access to your LAN and only allows selected incoming ports.

drop – All incoming network connections dropped, and only outgoing network connections allowed.

external – Useful for router type of connections. You need LAN and WAN interfaces too for masquerading (NAT) to work correctly.

home – Useful for home computers such as laptops and desktops within your LAN where you trust other computers. Allows only selected TCP/IP ports.
internal – For use on internal networks when you mostly trust the other servers or computers on the LAN.

public – You do not trust any other computers and servers on the network. You only allow the required ports and services. For cloud servers or server hosted at your place always use public zone.

trusted – All network connections are accepted. I do not recommend this zone for dedicated servers or VMs connected to WAN.

work – For use at your workplace where you trust your coworkers and other servers.

we get all the zones with there settings and configration