ICMPv6校验和的计算

Question

参考http://www.faqs.org/rfcs/rfc1071.html，我试图推导出计算ICMPv6校验和的c代码。但是通过wireshark的校验和分析，我发现我的代码得到的答案是错误的.

wireshark解析的校验和为0x8e73。

下面是我的代码，与RFC中提到的完全相同。注意:数组数据是从ICMPv6获取的原始数据。

unsigned short checksum(unsigned short *addr, unsigned short count)
{
    unsigned long sum;

    sum = 0;
    while (count > 1) {
            sum += *(unsigned short*)addr++;
            count -= 2;
            printf("sum is %x\n", sum);
    }

    /*  Add left-over byte, if any */
    if (count){
            sum += *(unsigned char *)addr;
            printf("in side left-over byte\n");
    }
    /*  Fold 32-bit sum to 16 bits */
    while (sum >> 16) {
            sum  = (sum & 0xffff) + (sum >> 16);
            printf("IN while:sum is %x\n", sum);
    }
    printf("sum is %x\n", sum);
    return (unsigned short)(~sum);
}

int main() {
    unsigned short count = 32;
    //data is the raw data for ICMPv6 got from wireshark, and I put the checksum field as 0x0000
    unsigned short data[] = {0x8800, 0x0000, 0x6000, 0x0000, 0xfe80, 0x0000, 0x0000, 0x0000, 0xb96b, 0x982f, 0x447a, 0x6a80, 0x0201, 0x6057, 0x187d, 0x7fad};


    printf("check sum is %x\n", checksum(data, 32));
    return 0;
}

Answer 1

ICMP和ICMPv6是两种不同的协议。有关ICMPv6校验和调用，请参阅RFC2463第2.3节，文档在此查询。

Answer 2

谢谢詹斯的帮助。在寻找RFC2463之后。我预先为伪头追加了以下数据。

unsigned short src_ip[8] = {0} //fill the source IP
unsigned short dst_ip[8] = {0} //fill the destination IP
//0x0020 is the packet length of ICMPv6
//fill 3bytes of zero and 0x3a is the type of ICMPv6, so we have
//0x00, 0x003a
unsigned short remain[] = {0x0020, 0x0000, 0x003a} 
unsigned short data[] = {} //as before

所以把所有这些数据连在一起，发送给check_sum算法本部分与icmp相同.，我们就可以得到正确的校验和了！