ipv6 checksum计算

kalexcyc

已于 2023-03-16 23:58:46 修改

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CC 4.0 BY-SA版权

文章标签：网络

于 2023-03-12 22:22:06 首次发布

本文链接：https://blog.youkuaiyun.com/kalexcyc/article/details/129482339

该代码实现了一个计算IPv6数据包中TCP校验和的函数，它遍历IPv6源和目标地址以及TCP头，结合协议类型和TCP负载长度进行计算，并返回校验和。在主函数中，创建并填充了IPv6和TCP头示例，调用此函数并打印结果。

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/ip6.h>
#include <netinet/tcp.h>

unsigned short calculate_tcp_checksum(struct ip6_hdr *ip6hdr, struct tcphdr *tcphdr) {       
    unsigned short *buf;
    unsigned int length = sizeof(struct tcphdr);
    unsigned int sum = 0;
    buf = (unsigned short *)tcphdr;
    while (length > 1) {
        sum += *buf++;
        length -= 2;
    }
    if (length == 1) {
        sum += *((unsigned char *)buf);
    }
    buf = (unsigned short *)&ip6hdr->ip6_src;
    length = sizeof(struct in6_addr) * 2;
    while (length > 1) {
        sum += *buf++;
        length -= 2;
    }
    if (length == 1) {
        sum += *((unsigned char *)buf);
    }
    buf = (unsigned short *)&ip6hdr->ip6_dst;
    length = sizeof(struct in6_addr) * 2;
    while (length > 1) {
        sum += *buf++;
        length -= 2;
    }
    if (length == 1) {
        sum += *((unsigned char *)buf);
    }
    sum += htons(IPPROTO_TCP + ntohs(tcphdr->th_len));
    length = (unsigned int)ntohs(tcphdr->th_sum);
    sum = ~((sum & 0xffff) + (sum >> 16));
    sum += length;
    sum = (sum >> 16) + (sum & 0xffff);
    sum += (sum >> 16);
    return (unsigned short)(~sum);
}

int main() {
    struct ip6_hdr ip6hdr;
    struct tcphdr tcphdr;
    memset(&ip6hdr, 0, sizeof(ip6hdr));
    memset(&tcphdr, 0, sizeof(tcphdr));    // 填充 IPv6 头部和 TCP 头部
    unsigned short checksum = calculate_tcp_checksum(&ip6hdr, &tcphdr);
    printf("TCP checksum: 0x%x\n", checksum);
    return 0;
}