I got in the zone :)

Thanks for the feedback! You’re right, my description was a bit messy. Let me clarify the goal and the use case

The goal to make a VPS on the public internet completely invisible to unauthorized scans while allowing access to services (like SSH) only after a valid SPA packet is received

Traditional SPA tools (like fwknop) often use libpcap to sniff packets or iptables to block them. In both cases, unauthorized packets still hit the kernel network stack. If an attacker floods the port with junk, the kernel still spends CPU cycles processing them before they get dropped

By using XDP, I move the “drop-all” logic to the earliest possible stage. This is where the DDoS resilience comes from we drop unauthorized traffic before sk_buff allocation, making it significantly cheaper in terms of CPU resources

It’s designed to run on the host itself, acting as a “stealth” firewall

A major advantage here is that xSpa doesn’t touch the netfilter/iptables stack. Unlike fwknop, which has to dynamically manage firewall rules (often leading to conflicts with Docker, UFW, or complex rulesets), xSpa operates at a lower level. It’s completely independent of whatever you have going on in your iptables configuration

And you can’t use 802.1X to protect an SSH port on a public cloud VPS

caught me! still learning the ‘professional’ way to do things. at least it’s better than ‘fix1’, ‘fix2’, ‘asdfgh’…

I used AI to help with the eBPF parts since it’s a new and complex topic for me. It also helped me translate the README and polish this post because English isn’t my first language