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Comparing Linux-Based Network Firewall Software

Published by Nathaniel Stickman
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Implementing a firewall is crucial for securing your Linux system. There are an array of popular software firewalls to choose from, and each offers unique features. So understanding how these tools compare can help you choose the best firewall for your needs.

In this guide, learn more about each of the most common software firewall tools on Linux and how they compare. When available, follow links to our in-depth guides on each of these tools and compare examples of how each handles common firewall configurations.

An Overview of Netfilter (The Linux Kernel-Space Firewall Module)

Netfilter is a packet-filtering framework included in the Linux kernel (since 2.4.0). This framework provides kernel-level hooks that are used to implement packet filtering and network address and port translation (NAT and NPT). Ultimately, it is this framework that all firewall tools leverage for managing packets.

Low-level tools, like nftables and iptables, are the default interfaces for Netfilter. These tools provide a lot of control over firewall rules but they can also be difficult to learn and work with. You can also find high-level tools, like UFW and firewalld, built on top of these low-level tools. Such high-level tools can further simplify firewall configuration.

Low-Level User-Space Firewall Utilities

Linux utilizes dedicated packet classification tools for users to manage network/firewall rules. These tools — nftables and iptables — are built on Netfilter and provide low-level firewall configurations. They are especially helpful when you need fine-grained control of your network’s package filtering.

nftables

nftables has become the default low-level packet classification tool, replacing iptables. Leveraging the Netfilter framework, nftables allows users to configure network rulesets that filter and route packets and ultimately define network traffic.

nftables uses a tables -> chains -> rules structure for managing network rules. Tables organize sets of chains, and each chain consists of a list of rules, processed in order.

Because nftables has superseded iptables, you should opt to use it when possible. The main exception is older Linux systems, many of which do not support nftables. Alternatively, you may prefer a high-level tool like those covered below .

You can learn more about nftables and its usage in our Getting Started with nftables guide.

iptables

iptables traditionally filled the space now occupied by nftables. iptables is, like nftables, a low-level tool for packet classification, providing firewall and network traffic management through the configuration of rulesets. iptables uses a similar tables -> chains -> rules hierarchical model as well.

Even though nftables has replaced iptables as the default, some systems, particularly ones using older Linux versions, only support iptables. Unless you are looking for higher-level firewall configuration (see High-Level Firewall Configuration Managers section below), you need to use iptables in those cases.

You can learn more about iptables and how to configure network rules with them in our Controlling Network Traffics with iptables guide.

High-Level Firewall Configuration Managers

To some users, low-level tools may prove overly cumbersome. High-level tools offer simpler solutions for implementing firewalls that may better fit your needs. By abstracting lower-level details, these tools can make it easier to manage network rules.

UFW

UFW (short for UncomplicatedFirewall) offers firewall management in a user-friendly command-line interface. It comes by default on Ubuntu systems and is typically the go-to choice on Debian and Arch Linux systems as well.

What especially sets UFW apart is the simplicity its commands bring to firewall configuration. Setting up your desired firewall rules and enabling the firewall follows an uncomplicated set of commands.

See more on UFW and steps for getting started in our How to Configure a Firewall with UFW guide.

Firewalld

Firewalld provides an interface for configuring firewall rules both dynamically and persistently. The dynamic configuration feature allows firewalld to set up rules that apply immediately, without having to restart the service or interrupt existing connections. Additionally, firewalld’s zones system provides convenience for categorizing and managing levels of trust.

Firewalld supports most Linux distributions, and it is included by default on RHEL-related systems (e.g., CentOS, Fedora, AlmaLinux, Rocky Linux) and openSUSE.

Take a look at our Configure a Firewall with Firewalld guide to find out more about using firewalld.

Managed Cloud Firewall Service

Cloud firewall services, like Akamai’s Cloud Firewall , offer a different approach to cloud security and have some advantages over local software firewalls. For instance, Akamai’s Cloud Firewall can configure and manage firewall rules across multiple cloud instances.

That said, cloud firewalls often do not cover all of the features of software firewalls. Typically, a software firewall can offer more configuration options and advanced control of network traffic.

One solution — cloud or software firewall — is likely to better fit your needs than the other. But often you can get the best results by using both together. As an example, you can use a cloud firewall to apply “absolute” network rules across multiple cloud instances and prevent unwanted traffic from ever reaching your servers. Then, use a software firewall to fine-tune your network filtering on each server.

Learn more about cloud firewalls and how they compare to software firewalls in our Comparing Cloud Firewalls to Linux Firewall Software guide.

Basic Usage Comparison

To further compare the software firewall tools, what follows are a series of example network filtering rules. Each covers a common scenario and shows how each of the four tools above implements the necessary ruleset. These examples offer a sense of how the tools differ, and for even more, you can refer to the guides linked above.

View Existing Configuration

Whether at the outset of configuring a firewall or when revising an existing configuration, it is helpful to get an overview of existing settings.

sudo nft list ruleset
table inet filter {
    chain input {
        type filter hook input priority filter; policy accept;
    }

    chain forward {
        type filter hook forward priority filter; policy accept;
    }

    chain output {
        type filter hook output priority filter; policy accept;
    }
}

To see IPv4 rules:

sudo iptables -S
-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT

To see IPv6 rules:

sudo ip6tables -S

For firewall status and rules:

sudo ufw status
Status: active

To                         Action      From
--                         ------      ----
22/tcp                     ALLOW       Anywhere
22/tcp (v6)                ALLOW       Anywhere (v6)

For more details, including default policies:

sudo ufw status verbose

To see firewall rules for a specific zone (public in this example):

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

To see firewall rules for all zones:

sudo firewall-cmd --list-all-zones

Block All Traffic

For firewall configuration, it is crucial to be able to block traffic. The examples that follow first show how to block all traffic, then show the more typical policy configuration — denying incoming traffic and allowing outgoing.

Important
Configuring default reject or deny rules can lock you out of your Linode unless explicit allow rules are in place. Ensure that you have configured allow rules for SSH and other critical services before trying any of the following.

Set policies to block incoming and outgoing traffic:

sudo nft add chain inet filter input '{type filter hook input priority 0; policy drop; }'
sudo nft add chain inet filter forward '{type filter hook forward priority 0; policy drop; }'
sudo nft add chain inet filter output '{type filter hook output priority 0; policy drop; }'

Set policies to block incoming traffic and allow outgoing:

sudo nft add chain inet filter input '{type filter hook input priority 0; policy drop; }'
sudo nft add chain inet filter forward '{type filter hook forward priority 0; policy drop; }'
sudo nft add chain inet filter output '{type filter hook output priority 0; policy accept; }'

Set policies to block incoming and outgoing traffic:

sudo iptables -P INPUT DROP
sudo iptables -P FORWARD DROP
sudo iptables -P OUTPUT DROP

Set policies to block incoming traffic and allow outgoing:

sudo iptables -P INPUT DROP
sudo iptables -P FORWARD DROP
sudo iptables -P OUTPUT DROP

The same can be done for IPv6 traffic, replacing iptables with ip6tables.

To configure policies for blocking all traffic:

sudo ufw default deny incoming
sudo ufw default deny outgoing

To set policies blocking incoming and allowing outgoing traffic:

sudo ufw default deny incoming
sudo ufw default allow outgoing

Firewalld blocks incoming traffic by default. But to ensure that policy is in place:

sudo firewall-cmd --zone=public --set-target=DROP --permanent

Firewalld does not regulate outbound traffic by default. To block all outbound traffic, create a custom policy:

sudo firewall-cmd --new-policy outgoing-default --permanent
sudo firewall-cmd --policy outgoing-default --add-ingress-zone HOST --permanent
sudo firewall-cmd --policy outgoing-default --add-egress-zone ANY --permanent
sudo firewall-cmd --policy outgoing-default --set-target DROP --permanent
sudo firewall-cmd --policy outgoing-default --set-priority -100 --permanent

Allow All Traffic From a Specific IP Address

Tighter network security stipulates specifically which IP address has access to the system. Denying incoming traffic by default — as shown above — and adding exceptions as needed helps to ensure access only by known systems.

To allow traffic from an IPv4 source address:

sudo nft add rule inet filter input ip saddr 192.0.2.0 accept

The same command works for an IPv6 address:

sudo nft add rule inet filter input ip6 saddr 2001:db8:e001:1b8c::2 accept

Allow traffic from an IPv4 source address:

sudo iptables -A INPUT -p tcp -s 192.0.2.0 -j ACCEPT

Use the same approach with the ip6tables command for IPv6 source addresses:

sudo ip6tables -A INPUT -p tcp -s 2001:db8:e001:1b8c::2 -j ACCEPT

Allow traffic from a given IP address; the command operates the same whether the address is IPv4 or IPv6:

sudo ufw allow from 192.0.2.0
sudo ufw allow from 2001:db8:e001:1b8c::2

Use the trusted zone to allow traffic from a given source address. The operation is the same regardless of IPv4 or IPv6:

sudo firewall-cmd --zone=trusted --add-source=192.0.2.0
sudo firewall-cmd --zone=trusted --add-source=2001:db8:e001:1b8c::2

Block All Traffic From a Specific IP Address

Each firewall management tool covered here offers an option for blocking traffic from a given IP. Recommended setups and some default policies in these tools may already block all incoming traffic that is not explicitly approved. However, being able to explicitly block a given IP address gives you much more control and may be particularly useful in certain setups.

To block traffic from a given IP address:

sudo nft add rule inet filter input ip saddr 192.0.2.0 drop

Use the same process for IPv6 addresses:

sudo nft add rule inet filter input ip6 saddr 2001:db8:e001:1b8c::2 drop

To block connections from an IPv4 address:

sudo iptables -A INPUT -p tcp -s 192.0.2.0 -j DROP

To block connections from an IPv6 address:

sudo ip6tables -A INPUT -p tcp -s 2001:db8:e001:1b8c::2 -j DROP

Use commands like the ones below to block traffic from a given IP, whether IPv4 or IPv6:

sudo ufw deny from 192.0.2.0
sudo ufw deny from 2001:db8:e001:1b8c::2

Use firwalld’s drop zone to block specific IP addresses. The same method holds whether IPv4 or IPv6:

sudo firewall-cmd --zone=drop --add-source=192.0.2.0
sudo firewall-cmd --zone=drop --add-source=2001:db8:e001:1b8c::2

Allow Incoming Traffic From a Specific Port

Allowing traffic on specific ports is common, especially for web servers. Opening ports allow access for SSH connections (port 22) and for web application usage (ports 80 and 443), among other use cases.

In addition, the firewall tools covered here can use port specifications alongside IP address specifications. Doing so can ensure even tighter security, relegating incoming traffic from specific addresses to specific ports.

Allow traffic on port 22:

sudo nft add rule inet filter input tcp dport 22 accept

Allow traffic from a given IP address to port 22:

sudo nft add rule inet filter input ip saddr 192.0.2.0 tcp dport 22 accept

Open port 22 for traffic:

sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT

Allow traffic from a given address to port 22:

sudo iptables -A INPUT -p tcp -s 192.0.2.0 --dport 22 -j ACCEPT

Use ip6tables instead of iptables above to set rules for IPv6 traffic.

To allow traffic on a given port:

sudo ufw allow 22/tcp

To allow a given IP address to connect via a given port:

sudo ufw allow from 192.0.2.0 proto tcp to any port 22

To open port 22 for traffic:

sudo firewall-cmd --zone=public --allow-port=22/tcp

Create a rich rule to allow traffic from a given IP address into port 22:

sudo firewall-cmd --zone=public --add-rich-rule 'rule source address="192.0.2.0" port port=22 protocol=tcp accept'

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