Wireshark 未检测到发送的任何数据包。 发送返回 0

啊哈!我至少掌握了一部分。

i = sendto(sd, buffer, PCKT_LEN, 0, (struct sockaddr *)&sin, sizeof(sin)) < 0等于i = (sendto(sd, buffer, PCKT_LEN, 0, (struct sockaddr *)&sin, sizeof(sin)) < 0)

你可能想要:(i = sendto(sd, buffer, PCKT_LEN, 0, (struct sockaddr *)&sin, sizeof(sin))) < 0

你可能想:

1. 在编译器中打开警告-至少如果您使用gcc，它应该为您在相同的if语句中进行比较和赋值提供警告。
用固定的代码重试。

我肯定你的代码中也可能有其他问题——我不是网络专家。

很难读懂这段代码，也很难理解你在做什么和为什么这么做。所以我建议你看看我的这段代码:dhcp client implementation

查看函数getSock()了解socket是如何创建的，以及函数talker()了解如何形成和发送完整的数据包。

本地IP头结构错误…我的建议是包括你的发行版提供的IP头(你使用linux吗?不是吗?)。

我所做的只是包含linux/ip.h，将ipheader结构引用重命名为iphdr，并根据后一个文件中描述的结构重命名ip头字段。

我试着用tcpdump嗅探数据包，它现在工作了(我没有尝试用wireshark，但它必须工作了)

试试这个固定的代码:

// Must be run by root lol! Just datagram, no payload/data
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netinet/udp.h>
#include <linux/ip.h>
// The packet length
#define PCKT_LEN 35
// UDP header's structure
struct udpheader {
    unsigned short int udph_srcport;
    unsigned short int udph_destport;
    unsigned short int udph_len;
    unsigned short int udph_chksum;
};
// total udp header length: 8 bytes (=64 bits)
// Function for checksum calculation. From the RFC,
// the checksum algorithm is:
//  "The checksum field is the 16 bit one's complement of the one's
//  complement sum of all 16 bit words in the header.  For purposes of
//  computing the checksum, the value of the checksum field is zero."
unsigned short csum(unsigned short *buf, int nwords)
{       //
    unsigned long sum;
    for(sum=0; nwords>0; nwords--)
        sum += *buf++;
    sum = (sum >> 16) + (sum &0xffff);
    sum += (sum >> 16);
    return (unsigned short)(~sum);
}
// Source IP, source port, target IP, target port from the command line arguments
int main(int argc, char *argv[])
{
    int sd;
    // No data/payload just datagram
    char buffer[PCKT_LEN];
    // Our own headers' structures
    struct iphdr *ip = (struct iphdr *) buffer;
    struct udpheader *udp = (struct udpheader *) (buffer + sizeof(struct iphdr));
    // Source and destination addresses: IP and port
    struct sockaddr_in sin, din;
    int one = 1;
    const int *val = &one;
    memset(buffer, 0, PCKT_LEN);
    if(argc != 5)
    {
        printf("- Invalid parameters!!!n");
        printf("- Usage %s <source hostname/IP> <source port> <target hostname/IP> <target port>n", argv[0]);
        exit(-1);
    }
    // Create a raw socket with UDP protocol
    sd = socket(PF_INET, SOCK_RAW, IPPROTO_UDP);
    if(sd < 0)
    {
        perror("socket() error");
        // If something wrong just exit
        exit(-1);
    }
    else
        printf("socket() - Using SOCK_RAW socket and UDP protocol is OK.n");
    // The source is redundant, may be used later if needed
    // The address family
    sin.sin_family = AF_INET;
    din.sin_family = AF_INET;
    // Port numbers
    sin.sin_port = htons(atoi(argv[2]));
    din.sin_port = htons(atoi(argv[4]));
    // IP addresses
    sin.sin_addr.s_addr = inet_addr(argv[1]);
    din.sin_addr.s_addr = inet_addr(argv[3]);
    // Fabricate the IP header or we can use the
    // standard header structures but assign our own values.
    ip->ihl = 5;
    ip->version = 4;
    ip->tos = 16; // Low delay
    ip->tot_len = sizeof(struct iphdr) + sizeof(struct udpheader);
    ip->id = htons(54321);
    ip->ttl = 64; // hops
    ip->protocol = 17; // UDP
    // Source IP address, can use spoofed address here!!!
    ip->saddr = inet_addr(argv[1]);
    // The destination IP address
    ip->daddr = inet_addr(argv[3]);
    // Fabricate the UDP header. Source port number, redundant
    udp->udph_srcport = htons(atoi(argv[2]));
    // Destination port number
    udp->udph_destport = htons(atoi(argv[4]));
    udp->udph_len = htons(sizeof(struct udpheader));
    // Calculate the checksum for integrity
    ip->check = csum((unsigned short *)buffer, sizeof(struct iphdr) + sizeof(struct udpheader));
    // Inform the kernel do not fill up the packet structure. we will build our own...
    if(setsockopt(sd, IPPROTO_IP, IP_HDRINCL, val, sizeof(one)) < 0)
    {
        perror("setsockopt() error");
        exit(-1);
    }
    else
        printf("setsockopt() is OK.n");
    // Send loop, send for every 2 second for 100 count
    printf("Trying...n");
    printf("Using raw socket and UDP protocoln");
    printf("Using Source IP: %s port: %u, Target IP: %s port: %u.n", argv[1], atoi(argv[2]), argv[3], atoi(argv[4]));
    int count;
    int i;
    for(count = 1; count <=20; count++)
    {
        if((i = sendto(sd, buffer, PCKT_LEN, 0, (struct sockaddr *)&sin, sizeof(sin))) < 0)
        // Verify
        {
            perror("sendto() error");
            exit(-1);
        }
        else
        {
            printf("Count #%u - sendto() is OK. Data Length# %dn", count,i);
            sleep(2);
        }
    }
    close(sd);
    return 0;
}

我猜您是基于这个示例代码，它有多个致命的错误。它浪费了我生命中的许多时间。

但是要回答这个特定的问题(并帮助其他不幸试图使用该代码的人)，阻止您在wireshark中看到数据包的错误在这里:

sin.sin_addr.s_addr = inet_addr(argv[1]);

设置sentdo()中用于发送数据包的地址为源地址。因此，报文通过环回接口发送，不去任何地方。(Wireshark或其他捕获工具将能够看到数据包，如果你捕获lo/环回接口，fww)

所以这个特定程序的更正行是:

sin.sin_addr.s_addr = inet_addr(argv[3]);