Understanding XDP (Express Data Path) for High-Speed Network Packet Processing

Introduction

XDP (eXpress Data Path) is a framework for fast packet processing in the Linux kernel. It allows the processing of packets at the earliest stage in the kernel networking stack. This leads to a significant reduction in packet processing time and improves the performance of network applications. XDP can be used for packet filtering, forwarding, and load balancing. It is particularly useful for high-speed networking applications, such as those found in data centers and cloud environments.

Architecture of XDP

The XDP architecture consists of a number of components. The first component is the driver or the hardware that is used for packet transmission and reception. The second component is the XDP program, which is a piece of code that is loaded into the kernel and executed on each incoming packet. The XDP program can be written in C, Assembly, or any other language that can be compiled to BPF (Berkeley Packet Filter) bytecode.

The XDP program can be attached to a specific network interface using the XDP hook. The XDP hook is a point in the Linux kernel networking stack where the XDP program can intercept incoming packets. The XDP hook can be attached to the NIC (Network Interface Controller) driver or a network namespace.

Flow of XDP

The flow of XDP starts with the reception of a packet by the network interface. The packet is then passed to the XDP hook, where the XDP program is executed. The XDP program can perform various operations on the packet, such as packet filtering, forwarding, or load balancing. After the XDP program has processed the packet, it can either drop the packet or pass it on to the next stage in the networking stack.

The XDP program can also communicate with user space applications through a map. A map is a shared memory object that can be used to exchange data between the XDP program and user space applications. This allows user space applications to control the behavior of the XDP program and receive statistics about the packet processing.

XDP has five stages

1. XDP_PASS: This stage indicates that the packet should be passed to the next layer of the networking stack. This is typically used for packets that do not require any special processing.
2. XDP_TX: This stage indicates that the packet should be transmitted on the same network interface. This is typically used for packets that require some modification before transmission.
3. XDP_REDIRECT: This stage indicates that the packet should be redirected to a different network interface. This is typically used for packets that require forwarding to a different network.
4. XDP_ABORTED: This stage indicates that the packet processing has been aborted. This is typically used for packets that are malformed or contain errors.
5. XDP_DROP: This stage indicates that the packet should be dropped. This is typically used for packets that are filtered out by the XDP program.

Advantages of XDP

XDP offers several advantages over traditional networking technologies, such as sockets. XDP is faster, more scalable, and more flexible than sockets, making it ideal for high-speed networking applications. XDP is also easier to program than sockets, as it provides a simple and consistent API for packet processing.

Uses of XDP

XDP can be used for a wide range of applications, including:

• Intrusion detection and prevention
• DDoS mitigation
• Load balancing
• Firewalling
• Traffic shaping
• Network monitoring

As for my experience, I have used XDP in my MS thesis topic which was "intrusion detection on high-speed networks." XDP allowed me to process packets at line rate and implement custom packet filtering and forwarding logic.

Example of an XDP Program

Here is an example of an XDP program that drops all TCP packets with a source IP address of 192.168.1.1:

#include <linux/bpf.h>
#include <linux/in.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <linux/tcp.h>

SEC("xdp")
int xdp_drop_tcp(struct xdp_md *ctx) {
    void *data = (void *)(long)ctx->data;
    void *data_end = (void *)(long)ctx->data_end;
    struct ethhdr *eth = data;
    struct iphdr *ip = data + sizeof(*eth);
    struct tcphdr *tcp = data + sizeof(*eth) + sizeof(*ip);

    if (eth + 1 > data_end || ip + 1 > data_end || tcp + 1 > data_end) {
        return XDP_ABORTED;
    }

    if (ip->protocol == IPPROTO_TCP && ip->saddr == htonl(0xc0a80101)) {
        return XDP_DROP;
    }

    return XDP_PASS;
}

This program uses the BPF (Berkeley Packet Filter) syntax to filter TCP packets with a source IP address of 192.168.1.1. If the packet matches the filter, it is dropped. Otherwise, it is passed to the next layer of the networking stack.

If you're interested in learning more about XDP, including installation instructions and code examples, check out the official XDP tutorial on GitHub: https://github.com/xdp-project/xdp-tutorial