How We Used eBPF to Build Programmable Packet Filtering in Magic Firewall

Cloudflare actively protects services from sophisticated attacks day after day. For users of Magic Transit, DDoS protection detects and drops attacks, while Magic Firewall allows custom packet-level rules, enabling customers to deprecate hardware firewall appliances and block malicious traffic at Cloudflare’s network. The types of attacks and sophistication of attacks continue to evolve, as recent DDoS and reflection attacks against VoIP services targeting protocols such as Session Initiation Protocol (SIP) have shown. Fighting these attacks requires pushing the limits of packet filtering beyond what traditional firewalls are capable of. We did this by taking best of class technologies and combining them in new ways to turn Magic Firewall into a blazing fast, fully programmable firewall that can stand up to even the most sophisticated of attacks.

Magical Walls of Fire

Magic Firewall is a distributed stateless packet firewall built on Linux nftables. It runs on every server, in every Cloudflare data center around the world. To provide isolation and flexibility, each customer’s nftables rules are configured within their own Linux network namespace.

This diagram shows the life of an example packet when using Magic Transit, which has Magic Firewall built in. First, packets go into the server and DDoS Continue reading