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Cara Install, Konfigurasi dan Menggunakan Firewall di CentOS dan Ubuntu

Firewalld (firewall daemon) merupakan alternatif untuk layanan iptables, untuk mengelola firewall dengan dukungan jaringan. sangat mudah untuk di gunakan dan mengkonfigurasinya, dan ini dia managemenr default firewall di RHEL/CentOS, Fedora dan beberapa OS Linux lainnya. Cara Install, Konfigurasi dan Menggunakan Firewall di CentOS dan Ubuntu.

Pada artikel ini, kami akan mendiskusikan bagaimana untuk mengkonfigurasi system firewall dengan firewalld dan mengimplementasikan paket dasar di CentOS/RHEL 7 dan Ubuntu.

 

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Dasar Firewalld

Firewalld terdiri dari tiga lapisan, yaitu:

  • core layer: bertanggung jawab untuk menangani konfigurasi dan bagian belakang berakhir (tercantum di bawah).
  • D-Bus interface: sarana utama untuk mengubah dan membuat konfigurasi firewall.
  • backends: untuk berinteraksi dengan netfilter (modul kernel asli yang digunakan untuk firewall). Termasuk iptables, ip6tables, ebtables, ipset, nft, linnftables, Network Manager dan modul.

Ia mengatur aturan firewall dengan mengimplementasikan zona jaringan / firewall yang menentukan tingkat kepercayaan koneksi jaringan atau antarmuka. Fitur firewall yang didukung lainnya termasuk layanan, konfigurasi langsung (digunakan untuk langsung melewati sintaks iptables mentah), IPSets serta jenis ICMP.

Dua jenis lingkungan konfigurasi didukung oleh firewalld:

  • konfigurasi runtime yang hanya efektif sampai mesin telah di-reboot atau layanan firewall telah di-restart
  • konfigurasi permanen yang disimpan dan bekerja dengan gigih.

Alat baris perintah firewall-cmd digunakan untuk mengelola runtime dan konfigurasi permanen. Atau, Anda dapat menggunakan alat konfigurasi antarmuka grafis konfigurasi firewall-config (GUI) untuk berinteraksi dengan daemon.

Selain itu, firewalld menawarkan antarmuka yang terdefinisi dengan baik untuk layanan atau aplikasi lokal lainnya untuk meminta perubahan pada aturan firewall secara langsung, jika mereka berjalan dengan hak akses root.

File konfigurasi global untuk firewalld terletak di /etc/firewalld/firewalld.conf dan fitur firewall dikonfigurasi dalam format XML.

Understanding Important Firewalld Features

The central feature of firewalld is network/firewall zones. Every other feature is bounded to a zone. A firewall zone describes the trust level for a connection, interface or source address binding.

The default configuration comes with a number of predefined zones sorted according to the default trust level of the zones from untrusted to trusted: drop, block, public, external, dmz, work, home, internal and trusted. They are defined in files stored under the /usr/lib/firewalld/zones directory.

You can configure or add your custom zones using the CLI client or simply create or copy a zone file in /etc/firewalld/zones from existing files and edit it.

Another important concept under firewalld is services. A service is defined using ports and protocols; these definitions represent a given network service such as a web server or remote access service. Services are defined in files stored under the /usr/lib/firewalld/services/ or /etc/firewalld/services/ directory.

If you know basic iptables/ip6tables/ebtables concepts, you can also use the direct interface (or configuration) to gain direct access to the firewall. But, for those without any iptables knowledge, you can employ the rich language for creating more complex firewall rules for IPv4 and IPv6.

How to Install Firewalld Package in Linux

On CentOS 7, the firewalld package comes pre-installed and you can verify using following command.

On Ubuntu 16.04 and 18.04, you can install it using the default package manager as shown.

How to Manage Firewalld Service in Linux

Firewalld is a regular systemd service that can be managed via the systemctl command.

After starting firewalld service, you can also check whether the daemon is running or not, using the firewall-cmd tool (in case it’s not active, this command will output “not running”).

Check Firewalld Status

Check Firewalld Status

If you happen to save any changes permanently, you can reload firewalld. This will reload firewall rules and keep state information. The current permanent configuration will become new runtime configuration.

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How to Work with Firewall Zones in Firewalld

To get a list of all available firewall zones and services, run these commands.

The default zone is the zone that is used for every firewall feature that is not explicitly bounded to another zone. You can get the default zone set for network connections and interfaces by running.

List Default Firewalld Zone

List Default Firewalld Zone

To set the default zone, for example to external, use the following command. Note that adding the option --permanent sets the configuration permanently (or enables querying of information from the permanent configuration environment).

Next, let’s look at how to add an interface to a zone. This example shows how to add your wireless network adapter (wlp1s0) to zone home, which is used in home areas.

Add an Interface to Firewalld Zone

Add an Interface to Firewalld Zone

An interface can only be added to a single zone. To move it to another zone, use the --change-interface switch as shown, or remove it from the previous zone using the –remove-interface switch, then add it to the new zone.

Assuming you want to connect to a public WI-FI network, you should move your wireless interface back to the public zone, like this:

Change Zone Interface in Firewalld

Change Zone Interface in Firewalld

You can use many zones at the same time. To get a list of all active zones with the enabled features such as interfaces, services, ports, protocols, run:

List Active Zones in Firewalld

List Active Zones in Firewalld

In relation to the previous point, If you want to find more information about a particular zone, i.e everything added or enabled in it, use one of these commands:

Find Information of Firewall Zone

Find Information of Firewall Zone

Another useful option is --get-target, which shows you the target of a permanent zone. A target is one of: default, ACCEPT, DROP, REJECT. You can check the target of various zones:

How to Open and Block Ports in Firewalld

To open a port (or port/protocol combination) in the firewall, simply add it in a zone with the --add-port option. If you don’t explicitly specify the zone, it will be enabled in the default zone.

The following example shows how to add port 80 and 443 to allow in-bound web traffic via the HTTP and HTTPS protocols, respectively:

Next, reload firewalld and check the enabled features in the public zone once more, you should be able see the just added ports.

Blocking or closing a port in the firewall is equally easy, simply remove it from a zone with the --remove-port option. For example, to close ports 80 and 443 in the public zone.

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Instead of using port or port/protocol combination, you can use the service name to which a port is assigned as explained in the next section.

How to Open and Block Services in Firewalld

To open a service in the firewall, enable it using the --add-service option. If zone is omitted, default zone will be used.

The following command will permanently enable the http service in the public zone.

The --remove-service option can be used to disable a service.

How to Enable and Disable IP Masquerading Using Firewalld

IP Masquerading (also known as IPMASQ or MASQ) is a NAT (Network Address Translation) mechanism in Linux networking which allows your hosts in a network, with private IP addresses to communicate with the Internet using your Linux server’s (IPMASQ gateway) assigned public IP address.

It is a one-to-many mapping. Traffic from the your invisible hosts will appear to other computers on the internet as if it were coming from your Linux server.

You can enable IP masquerading in a desired zone, for instance the public zone. But before doing that, first check if masquerading is active or not (a “no” means its disabled and a “yes” means otherwise).

A typical use case for masquerading is to perform port forwarding. Assuming you want to SSH from a remote machine to a host in your internal network with the IP 10.20.1.3, on which the sshd daemon is listening on port 5000.

You can forward all connections to port 22 on your Linux server to the intended port on your target host by issuing:

To disable masquerading in a zone, use the --remove-masquerade switch.

How to Enable and Disable IMCP Message in Firewalld

ICMP (Internet Control Message Protocol) messages are either information requests or replies to information requests or in error conditions.

You can enable or disable ICMP messages in the firewall, but before that first list all supported icmp types.

List Supported ICMP Types in Firewalld

List Supported ICMP Types in Firewalld

To add or remove a block type you want.

You can view all icmp types added in a zone using the --list-icmp-blocks switch.

How to Use Direct Interface to Pass Raw iptables Commands

The firewall-cmd also provides direct options (--direct) for you to get more direct access to the firewall. This is useful for those with basic knowledge of iptables.

Important: You should only use the direct options as a last resort when it’s not possible to use the regular firewall-cmd options explained above.

Here is an example of how to pass raw iptables rule, using the --add-rules switch. You can easily remove these rules by replacing --add-rule with --remove-rule:

For more information about iptables, see this guide: How To Setup an Iptables Firewall to Enable Remote Access to Services in Linux.

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If you aren’t familiar with iptables syntax, you can opt for firewalld’s “rich language” for creating more complex firewall rules in an easy to understand manner as explained next.

How to Use Rich Language in Firewalld

The rich language (also known as rich rules) is used to add more complex firewall rules for IPv4 and IPv6 without the knowledge of iptables syntax.

It extends the zone features (service, port, icmp-block, masquerade and forward-port) that we have covered. It supports source and destination addresses, logging, actions and limits for logs and actions.

The --add-rich-rule is used to add rich rules. This example shows how to allow new IPv4 and IPv6 connections for service http and log 1 per minute using audit:

To remove the added rule, replace the --add-rich-rule option with --remove-rich-rule.

This feature also allows for blocking or allowing traffic from a specific IP address. The following example shows how to reject connections from the IP 10.20.1.20.

How to Enable and Disable Panic Mode in Firewalld

Panic mode is a special mode under firewalld where all in-bound and out-bound packets are dropped, and active connections will expire once activated.
You can enable this mode in emergency situations where a threat to your network environment exits.

To query panic mode, use the --query-panic option.

To enable panic mode, use the --panic-on option. You can test if it is working using the ping command as shown. Because the packet is dropped, the name www.google.com can not be resolved, hence the error displayed.

Enable Panic Mode in Firewalld

Enable Panic Mode in Firewalld

To disable panic mode, use the --panic-off option.

How to Lockdown Firewalld

Remember, we mentioned under the basics about firewalld that local applications or services are able to alter the firewall configuration if they are running with root privileges. You can control which applications are able to request firewall changes, by specifying then in a lockdown whitelist.

This feature is turned off by default, you can enable or disable it with the --lockdown-on or --lockdown switch receptively.

Note that it is recommended to enable or disable this feature by editing the main config file, because the firewall-cmd may not exist on lockdown whitelist when you enable lockdown.

Find the parameter Lockdown and change its value from no (means off) to yes (means on).

To make this setting permanent reload firewalld.

Summary

Firewalld is an easy to use replacement for the iptables service, which uses iptables as a backend. In this article, we have shown how to install firewalld package, explained firewalld’s important features and discussed how to configure them in the runtime and permanent configuration environments.

If you have any questions or comments, feel free to reach us via the comment form below. You may refer to the firewalld manual page (man firewalld) or the firewalld documentation in the project website, for more information.

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