High-Speed eBPF/XDP Packet Filtering for Linux Server DDoS Mitigation Executive Summary Executive Summary & Key Security Takeaways ← Back to Articles XDP_DROP Early Decision: Drop malicious UDP/SYN floods before allocating sk_buff memory.
Kernel Map Invalidation: Dynamic IP blocklists via eBPF BPF_MAP_TYPE_HASH maps.
Zero-Copy Performance: Process 10M+ packets per second on commodity server hardware.
Clang/LLVM BPF Compilation: Build C programs directly into BPF bytecode targets.
Table of Contents Understanding XDP Architecture vs Traditional Linux SKB Allocation XDP Packet Processing Actions (XDP_DROP vs XDP_PASS) Writing a Production XDP Packet Filter in C Compiling & Loading Bytecode Targets via Clang/LLVM Dynamic Blocklist Management via BPF Maps High-Throughput Packet Benchmark Verification Frequently Asked Questions (FAQ)
1.
Understanding XDP Architecture vs Traditional Linux SKB Allocation Standard Linux network processing allocates a complex kernel socket buffer data structure (sk_buff) for every incoming packet before firewall rules (iptables/nftables) can evaluate the packet.
Under volumetric DDoS attacks (such as 10 Million Packets Per Second UDP floods), the CPU time spent allocating and freeing sk_buff structures exhausts kernel memory and CPU cache lines, causing severe packet drops and server unresponsiveness. eXpress Data Path (XDP) provides a high-performance bare-metal packet processing framework.
XDP programs execute eBPF bytecode directly inside the network driver's RX ring buffer before sk_buff memory allocation occurs.
2.
XDP Packet Processing Actions (XDP_DROP vs XDP_PASS) An XDP program evaluates raw packet data directly from driver memory and returns one of five verdict codes to the network card driver: XDP_DROP: Immediately recycles the packet buffer in the driver RX ring without allocating memory or notifying the CPU TCP/IP stack.
XDP_PASS: Passes the packet up to the normal Linux TCP/IP network stack for standard processing.
XDP_TX: Bounces the packet back out the same network interface it arrived on (useful for high-speed load balancers).
3.
Writing a Production XDP Packet Filter in C XDP C code uses eBPF helpers and header pointers to parse Ethernet, IPv4, and UDP/TCP protocol headers safely.
The eBPF verifier verifies memory bounds checking before loading bytecode into the kernel, ensuring the XDP program can never crash the Linux kernel.
The following C program parses incoming IPv4 headers and drops packets matching blacklisted source IP addresses stored in an eBPF hash map:
4.
Compiling & Loading Bytecode Targets via Clang/LLVM Compile XDP C code into BPF Executable and Linkable Format (ELF) targets using Clang and LLVM compiler toolchains.
Attach the compiled BPF bytecode to a network interface using standard iproute2 ip link commands.
5.
Dynamic Blocklist Management via BPF Maps BPF Maps are high-speed shared memory structures bridging kernel space and user-space daemons.
User-space monitoring daemons (such as Fail2ban or custom Go/Python agents) populate blocked IP addresses into the BPF map dynamically without reloading the XDP program.
6.
High-Throughput Packet Benchmark Verification Verify XDP packet drop counters using ethtool or bpftool stats.
Benchmark packet processing throughput under simulated UDP floods using pktgen.
Frequently Asked Questions (FAQ) What is the difference between XDP_DROP and iptables DROP?
XDP_DROP drops packets in driver memory before Linux creates socket buffers, yielding 10x higher throughput.
Does XDP require special network card hardware?
No.
XDP supports native mode (driver level), offloaded mode (SmartNIC hardware), and generic mode (fallback for any network driver).
Digital Forensics & Incident Response (DFIR) Specialist & Security Researcher specializing in Linux kernel hardening, threat hunting, and system security research.
Originally published at https://zyekh.com/blog/ebpf-xdp-packet-filtering-and-ddos-mitigation.html