​​数据链路层（L2）原始套接字，IPv6，UDP发送数据包代码示例​​

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ether.h>
#include <netinet/ip6.h>
#include <netinet/udp.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <netpacket/packet.h>

// 计算校验和
unsigned short checksum(unsigned short *addr, int len) {
    int nleft = len;
    int sum = 0;
    unsigned short *w = addr;
    unsigned short answer = 0;

    while (nleft > 1) {
        sum += *w++;
        nleft -= 2;
    }

    if (nleft == 1) {
        *(unsigned char *)(&answer) = *(unsigned char *)w;
        sum += answer;
    }

    sum = (sum >> 16) + (sum & 0xffff);
    sum += (sum >> 16);
    answer = ~sum;
    return answer;
}

// 计算UDP校验和
unsigned short udp_checksum(struct ip6_hdr *ip6, struct udphdr *udp, char *data, int data_len) {
    int len = sizeof(struct udphdr) + data_len;
    char *buf = malloc(len + sizeof(struct ip6_hdr));
    memcpy(buf, ip6, sizeof(struct ip6_hdr));
    memcpy(buf + sizeof(struct ip6_hdr), udp, sizeof(struct udphdr));
    memcpy(buf + sizeof(struct ip6_hdr) + sizeof(struct udphdr), data, data_len);

    // 伪首部校验和
    unsigned short csum = checksum((unsigned short *)buf, len + sizeof(struct ip6_hdr));
    free(buf);
    return csum;
}

int main(int argc, char *argv[]) {
    if (argc < 2) {
        fprintf(stderr, "Usage: %s <message>\\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    // 要发送的消息
    char *message = argv[1];
    int msg_len = strlen(message);

    // 创建原始套接字
    int sockfd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
    if (sockfd < 0) {
        perror("socket");
        exit(EXIT_FAILURE);
    }

    // 获取ens33接口索引
    struct ifreq if_idx;
    memset(&if_idx, 0, sizeof(struct ifreq));
    strncpy(if_idx.ifr_name, "ens33", IFNAMSIZ - 1);
    if (ioctl(sockfd, SIOCGIFINDEX, &if_idx) < 0) {
        perror("SIOCGIFINDEX");
        close(sockfd);
        exit(EXIT_FAILURE);
    }

    // 设置目标地址
    struct sockaddr_ll sockaddr;
    memset(&sockaddr, 0, sizeof(struct sockaddr_ll));
    sockaddr.sll_ifindex = if_idx.ifr_ifindex;
    sockaddr.sll_halen = ETH_ALEN;

    // 准备以太网头部
    struct ether_header *eth = (struct ether_header *)malloc(sizeof(struct ether_header));
    memset(eth, 0, sizeof(struct ether_header));
    
    // 获取ens33接口的MAC地址
    struct ifreq if_mac;
    memset(&if_mac, 0, sizeof(struct ifreq));
    strncpy(if_mac.ifr_name, "ens33", IFNAMSIZ - 1);
    if (ioctl(sockfd, SIOCGIFHWADDR, &if_mac) < 0) {
        perror("SIOCGIFHWADDR");
        free(eth);
        close(sockfd);
        exit(EXIT_FAILURE);
    }

    // 设置目标MAC地址（这里使用广播地址，实际应用中应使用正确的目标MAC）
    memset(eth->ether_dhost, 0xff, ETH_ALEN);
    // 设置源MAC地址为ens33接口的MAC地址
    memcpy(eth->ether_shost, if_mac.ifr_hwaddr.sa_data, ETH_ALEN);
    eth->ether_type = htons(ETH_P_IPV6);
    memcpy(sockaddr.sll_addr, eth->ether_dhost, ETH_ALEN);

    // 准备IPv6头部
    struct ip6_hdr *ip6 = (struct ip6_hdr *)malloc(sizeof(struct ip6_hdr));
    memset(ip6, 0, sizeof(struct ip6_hdr));
    ip6->ip6_flow = htonl((6 << 28) | (0 << 20) | 0); // 版本6，流量类别0，流标签0
    ip6->ip6_plen = htons(sizeof(struct udphdr) + msg_len); // 负载长度
    ip6->ip6_nxt = IPPROTO_UDP; // 下一个头部是UDP
    ip6->ip6_hlim = 64; // 跳数限制

    // 设置源IPv6地址为本地链路地址，目标IPv6地址为指定地址
    if (inet_pton(AF_INET6, "fe80::1", &ip6->ip6_src) <= 0) {
        perror("inet_pton src_ip");
        free(eth);
        free(ip6);
        close(sockfd);
        exit(EXIT_FAILURE);
    }
    if (inet_pton(AF_INET6, "fe80::328e:a3dc:3971:56b5", &ip6->ip6_dst) <= 0) {
        perror("inet_pton dst_ip");
        free(eth);
        free(ip6);
        close(sockfd);
        exit(EXIT_FAILURE);
    }

    // 准备UDP头部
    struct udphdr *udp = (struct udphdr *)malloc(sizeof(struct udphdr));
    memset(udp, 0, sizeof(struct udphdr));
    udp->source = htons(54321); // 源端口
    udp->dest = htons(12345);   // 目标端口
    udp->len = htons(sizeof(struct udphdr) + msg_len);
    udp->check = 0; // 先设为0，后面计算校验和

    // 计算UDP校验和
    udp->check = udp_checksum(ip6, udp, message, msg_len);
    if (udp->check == 0) {
        udp->check = 0xffff; // RFC 768规定，校验和为0时用0xffff代替
    }

    // 构建完整的数据包
    int packet_size = sizeof(struct ether_header) + sizeof(struct ip6_hdr) + sizeof(struct udphdr) + msg_len;
    char *packet = malloc(packet_size);
    memset(packet, 0, packet_size);

    // 复制各部分到数据包
    memcpy(packet, eth, sizeof(struct ether_header));
    memcpy(packet + sizeof(struct ether_header), ip6, sizeof(struct ip6_hdr));
    memcpy(packet + sizeof(struct ether_header) + sizeof(struct ip6_hdr), udp, sizeof(struct udphdr));
    memcpy(packet + sizeof(struct ether_header) + sizeof(struct ip6_hdr) + sizeof(struct udphdr), message, msg_len);

    // 发送数据包
    if (sendto(sockfd, packet, packet_size, 0, (struct sockaddr *)&sockaddr, sizeof(struct sockaddr_ll)) < 0) {
        perror("sendto");
        free(eth);
        free(ip6);
        free(udp);
        free(packet);
        close(sockfd);
        exit(EXIT_FAILURE);
    }

    printf("Sent IPv6 UDP packet via ens33 to fe80::328e:a3dc:3971:56b5 %s\n", message);

    // 清理资源
    free(eth);
    free(ip6);
    free(udp);
    free(packet);
    close(sockfd);

    return 0;
}