L4Drop: XDP DDoS Mitigations

Efficient packet dropping is a key part of Cloudflare’s distributed denial of service (DDoS) attack mitigations. In this post, we introduce a new tool in our packet dropping arsenal: L4Drop.

We've written about our DDoS mitigation pipeline extensively in the past, covering:
- Gatebot: analyzes traffic hitting our edge and deploys DDoS mitigations matching suspect traffic.
- bpftools: generates Berkeley Packet Filter (BPF) bytecode that matches packets based on DNS queries, p0F signatures, or tcpdump filters.
- Iptables: matches traffic against the BPF generated by bpftools using the
xt_bpfmodule, and drops it. - Floodgate: offloads work from iptables during big attacks that could otherwise overwhelm the kernel networking stack. Incoming traffic bypasses the kernel to go directly to a BPF interpreter in userspace, which efficiently drops packets matching the BPF rules produced by bpftools.
Both iptables and Floodgate send samples of received traffic to Gatebot for analysis, and filter incoming packets using rules generated by bpftools. This ends up looking something like this:
This pipeline has served us well, but a lot has changed since we implemented Floodgate. Our new Gen9 and ARM servers use different network Continue reading
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We would like to thank VIAVI Solutions for sponsoring this episode of Network Collective. VIAVI Solutions is an application and network management industry leader focusing on end-user experience by providing products that optimize performance and speed problem resolution. Helping to ensure delivery of critical applications for businesses worldwide, Viavi offers an integrated line of precision-engineered software and hardware systems for effective network monitoring and analysis. Learn more at 



