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Updating nftables with DDNS
October 9, 2024 Reading time: 18 minutes
Hobbyist admins and home-labbers sometimes want to make services on a remote host available to machines on a home network. Unfortunately, many residential ISP customers are stuck with dynamic IP addresses, even when they're not behind a CGNAT. This makes securing the remote host difficult. You'd like to configure the remote firewall to allow traffic only from friendly IP addresses, but if one or more of your addresses might change at any time, what can you do? One option is to buy a fixed IP address from your ISP, but that can be costly.
This article describes how you can configure a remote server using nftables to automatically update its firewall rules so that dynamic IP traffic is allowed with minimal downtime when the IP address changes. The solution requires making a small change to your nftables configuration and a short script that runs periodically as a cron job.
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Fail2Ban Demystified: Custom Fail2Ban Actions
October 1, 2024 Reading time: 33 minutes
Fail2Ban is a powerful security tool that bridges your public-facing network services (ssh, mail server, web server, etc.) and your firewall. The Fail2Ban daemon constantly monitors your server logs, looking for troublemakers. When an intruder or suspicious activity is detected, it takes action! By default, Fail2Ban writes a temporary firewall rule that blocks the offender’s IP address on selected ports for a short period of time.
The real power in Fail2Ban, though, lies in its customizability. Using custom action scripts, admins can configure how Fail2Ban responds to threats, extending its abilities far beyond simply interfacing with the firewall. For example, you can define actions that will send an email or notification, write to a log file or database, invoke a web API, react differently in different contexts, and so on. The possibilities are unlimited!
This article explains how actions in Fail2Ban are defined and customized so that you can get the most out of Fail2Ban.
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The door opens, and nineteen demons, each a cross between a carrot and a sledge hammer, march out from behind it, knock you senseless, and return, the last closing the door behind it.