The eXpress Data Path: A High-performance Packet Processing Engine

eXpress Data Path (XDP) is an essential feature of eBPF (extended Berkeley Packet Filter), providing a programmable, low-level interface for packet processing, enabling developers to optimize network traffic handling and implement custom functionality directly into the kernel.

In this article, we will explore the key aspects of XDP, its benefits, and how it works alongside eBPF.

We will also provide examples to help you better understand the practical applications of this technology.

The eXpress Data Path: A High-performance Packet Processing Engine

XDP is a high-performance packet processing engine that allows developers to create custom data plane applications for the Linux kernel.

By leveraging eBPF’s programmability, XDP enables the efficient processing of packets at the earliest possible point in the networking stack.

This results in significant performance improvements for various networking use cases, including filtering, routing, load balancing, and security enforcement.

Key Benefits of XDP

1. High performance: XDP’s ability to operate close to the network driver level reduces latency and increases throughput, making it ideal for high-performance packet processing.
2. Flexibility: XDP enables custom eBPF programs to be easily developed, updated, and deployed, allowing for rapid iteration and customization.
3. Safety: eBPF’s verifier ensures that XDP programs are safe to run in the kernel, preventing bugs and vulnerabilities that could compromise system stability.

How XDP Works with eBPF

XDP works with eBPF by attaching eBPF programs to the network driver.

These programs are executed directly within the kernel, allowing processing packets at the earliest possible stage, even before they reach the network stack.

When a packet arrives at the network interface, the XDP eBPF program is invoked to process it.

Based on the eBPF program’s logic, the packet may be:

1. Passed: The packet is allowed to continue through the network stack.
2. Dropped: The packet is discarded, and no further processing occurs.
3. Redirected: The packet is forwarded to another network interface or a user-space application for further processing.

Example: Simple Packet Filtering with XDP

This example demonstrates how to create a simple XDP program that filters packets based on their IP addresses.

The following eBPF C code snippet defines an XDP program that drops packets with a source IP address of 10.0.0.1:

#include <linux/bpf.h> 
#include <linux/in.h> 
#include <linux/if_ether.h> 
#include <linux/ip.h> 
 
#define SEC(NAME) __attribute__((section(NAME), used)) 
 
SEC("prog") 
int xdp_filter_packets(struct xdp_md *ctx) { 
    void *data_end = (void *)(long)ctx->data_end; 
    void *data = (void *)(long)ctx->data; 
 
    struct ethhdr *eth = data; 
    if (eth + 1 > data_end) 
        return XDP_PASS; 
 
    if (ntohs(eth->h_proto) != ETH_P_IP) 
        return XDP_PASS; 
 
    struct iphdr *ip = (struct iphdr *)(eth + 1); 
    if (ip + 1 > data_end) 
        return XDP_PASS; 
 
    if (ip->saddr == htonl(0x0A000001)) // 10.0.0.1 
        return XDP_DROP; 
 
    return XDP_PASS; 
} 
 
char _license[] SEC("license") = "GPL";

This program first checks if the packet is an IP packet by examining the Ethernet header. If the packet is an IP packet, the program inspects the source IP address. If the source IP address matches 10.0.0.1, the packet is dropped; otherwise, it can pass through.

To compile and load this XDP program, follow these steps:

1. Install the required dependencies: Install the clang, llvm, and libbpf-dev packages to compile eBPF programs.
2. Compile the eBPF program: Save the code snippet above in a file called xdp_filter.c, and compile it using the following command:

clang -O2 -target bpf -c xdp_filter.c -o xdp_filter.o

This command generates an object file named xdp_filter.o containing the compiled eBPF program.

3. Load the XDP program: Attach the compiled eBPF program to a network interface using the ip command. Replace <INTERFACE> with the name of the network interface you want to attach the program to:

sudo ip link set dev <INTERFACE> xdp obj xdp_filter.o sec prog

The XDP program is now loaded and active, filtering packets with a source IP address 10.0.0.1.

4. Unload the XDP program: When you want to unload the XDP program, use the following command:

sudo ip link set dev <INTERFACE> xdp off

Conclusion

XDP is a powerful feature of eBPF that enables high-performance packet processing in the Linux kernel. By providing the ability to process packets at the earliest possible point in the network stack, XDP offers significant performance, flexibility, and safety benefits.

In this article, we’ve discussed the critical aspects of XDP, how it works with eBPF, and provided an example of a simple packet filtering program.

As you delve deeper into eBPF and XDP, you’ll discover a world of possibilities for optimizing and customizing your network applications, ultimately leading to more efficient and secure systems.

Stay tuned, and happy coding!

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Luis Soares

CTO | Head of Engineering | Blockchain Engineer | Web3 | Cyber Security | Golang & eBPF Enthusiast

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