Firewall configuration

This chapter covers Firewall configuration and theory for Opuntia systems. Opuntia is a Linux based operating system. The firewall subsystem uses the standard Linux Netfilter project tools and methods to provide IPv4 and IPv6 packet filtering.

Major features of Netfilter

  • Stateless Packet Filtering
  • Statefull Packet Filtering
  • Network Address Translation
  • Port Address Translation

In this section of the Opuntia manual we will provide examples of using these features. As a reveiw here is general packet flow[1] through the Linux Netfilter chains and tables.

Packet Flow in Linux Netfilter

Zone based Firewall Theory

The standard Linux firewalling features can result in long and repetitive configuraions if you want a rule to apply to multiple interfaces. To help overcome these issues, Opuntia implments Zone based firewalling. Zones allow you to group multiple interfaces into a Zone and then apply a single firewall rule to the Zone. This simplifies the configuraion of the firewall ruleset by reducing the total number of rules.

Opuntia implments two Zones by default Management and Wan.

Depending on your hardware platform; interfaces may be included in the Wan or Management zones by default. See your QuickStart Guide for more information.

By default Opuntia allows access to the Web GUI on ANY IPv4/IPv6 interface address. The


To navigate to the Firewall configuraion page.

Main Menu - Network –> Firewall

General Settings Tab

The main Firewall General Settings page

The Firewall General Settings tab has three main sections.

  • General Settings
  • Routing/Nat Offloading
  • Zones

General Settings

I know it’s odd that the GUI tab is “General Settings” and there is a subsection that is also named “General Settings” but this is how the GUI organizes these settings. There are two settings in this section. Enable Syn-Flood Protection and Drop Invalid Packets. Syn-Flood Protection is enabled by default on all Opuntia platforms. This option is unlikely to cause any issues.

The Drop Invalid Packets option is not enabled by default on any Opuntia platform. This option creates a series of firewall rules that aim to drop invalid packets flowing through the system. This is often a safe option to enable. The most impactful rule that this option creates is a rule to drop packets that are not known in the Netfilter conntrack table.

In most cases where there is a only a single Internet gateway this configuraion is acceptable. But if any Multi-Path Routing is being used; this option will cause packet loss and interrupted connections. So take care if you decide to enable this configuraion and you have Multi-Path Routing.

Additionally there are the three default policy selections in this section. The by default Opuntia has these all set to accept. It’s possible to change these options but it should be done with care if you modify the INPUT or FORWARD chain.

Routing/Nat Offloading

This section has two options. Software flow Offloading and if you enable that option you will also see the Hardware flow Offloading option. These options can allow you to lower cpu usage by bypassing some of the default Netfilter packet processing for known packet flows. This can sometimes cause issues with applications. So these are not enabled by default.

But if your network design is simple with only a single Internet gateway or no Multi-path Routing, the Software flow Offloading can greatly reduce the cpu load at a given throughput.

Hardware flow Offloading is only supported on specific hardware platforms check your QuickStart Guide to see if your platform supports this feature.


This section descibes the mapping of relationships of the firewall zones to default packet policy in these zones. Here is a detailed screenshot of the zones section.

The main Firewall zones in detail

Here you see the two default zones that are configured in Opuntia. The Wan and Management zones.

Looking at the Management zone, You can see the arrow indicating the direction of the traffic. From the Management zone to the Wan zone.

Limiting External access

By default Opuntia is permisive with access to local services like the Web GUI and ssh login. While very useful for allowing administrator access to the equipment; this can be a security risk. This section of the manual will detail how to remove some of the default firewall rules that allow access to these services from remote.

[1]This image is from This is a Common Creatives work that is based on the Joshua Snyders (Author of this manual) work.