The Sysadmin's Daily Grind: FireHOL
Off the Wall
If you don't have time to tinker with complicated firewall rules, you might want to check out the clever FireHOL approach.
There's no place like home. I can hear a quiet humming sound from the broom cupboard next to the kitchen. At least it's quiet until I open the door. When I do, I'm treated to a noise like a jet with engine trouble. Between lamp fuel, shoe polish, and miscellaneous jars stands the technology that connects me to the outside world. Beside the modems provided by my telco and an asthmatic Cisco – which is to blame for most of the noise – resides a PC old-timer, my firewall.
Originally, my manual iptables rules just handled masquerading for outgoing connections from the LAN, with a couple of custom rules for individual servers. Over time, the rules have become increasingly complex, and as they did, I found myself searching even harder for a management tool.
Finally, I found FireHOL [1]. In contrast to Firewall Builder [2], the FireHOL tool does not have a graphical user interface. Instead, you just add simple directives to a configuration file and FireHOL translates them into iptables commands.
If you just need masquerading and want to restrict it to http traffic, this short configuration is all you need:
interface eth0 home client all accept interface eth1 internet client all accept router to-internet inface eth0 outface eth1 masquerade route http accept
The client all accept lines let the firewall establish arbitrary connections on the LAN and the Internet.
To avoid restricting masquerading to http and open up the door for any protocol, you just need to change the last line like so:
route all accept
Based on this directive, FireHOL generates several dozen iptables commands. The reason for this is that it has special handling for complex protocols such as active FTP. Figure 1 shows part of the rule ruleset that handles FTP.
FireHOL lets you watch it work and offers the practical explain function to facilitate this. You can use the interactive shell to type rules in the syntax shown in the sample, and the tool responds with the corresponding iptables rules, which FireHOL will apply if you ask it to do so.
After quietly simplifying the management of my home firewall, I now have time to think about doing something about the noise coming from the broom cupboard.
Infos
- FireHOL: http://firehol.sourceforge.net
- Firewall Builder: http://www.fwbuilder.org/
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
News
-
Apple M1 Hardware Support to be Merged into Linux Kernel 5.13
Linux users will be able to install their favorite distribution on Apple’s M1-based hardware.
-
KDE Launches the Qt 5 Patch Collection
To support and maintain a stable Qt 5 for KDE Gears and Frameworks, KDE will maintain a patch collection.
-
Linux Creator Warns Next Kernel Could be Delayed
Linus Torvalds has issued concern about the size of kernel 5.12 and possible delays for its release.
-
System76 Updates its Pangolin Laptop
System76 has released a much-anticipated AMD version of their most popular laptop, the Pangolin.
-
New Debian-Based Distribution Arrives on the Market
TelOS is a new Debian-based Linux distribution with a customized, touch-screen-ready KDE Plasma 5 desktop.
-
System76 Releases New Thelio Desktop
One of the most ardent supporters of open source hardware has released a new desktop machine for home or office.
-
Mageia 8 Now Available with Linux 5.10 LTS
The latest release of Mageia includes improved graphics support for both AMD and NVIDIA GPUs.
-
GNOME 40 Beta has been Released
Anyone looking to test the beta for the upcoming GNOME 40 release can now do so.
-
OpenMandriva Lx 4.2 has Arrived
The latest stable version of OpenMandriva has been released and offers the newest KDE desktop and ARM support.
-
Thunderbird 78 Ported to Ubuntu 20.04
The Ubuntu developers have made the decision to port the latest release of Thunderbird to the LTS version of the platform.