这是我到目前为止所尝试的.

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <net/if.h>
#include <string.h>
#include <unistd.h>
#include <assert.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>

int main(int argc,const char *argv[])
{
    struct sockaddr_in dst,src;
    struct ifreq ifr;
    int sock,tmp;
    char payload[128];

    memset(payload,128);

    memset(&dst,sizeof(dst));
    dst.sin_family = AF_INET;
    dst.sin_addr.s_addr = inet_addr("255.255.255.255");
    dst.sin_port = htons(67);

    memset(&src,sizeof(src));
    src.sin_family = AF_INET;
    src.sin_addr.s_addr = inet_addr("0.0.0.0");
    src.sin_port = htons(68);

    sock = socket(AF_INET,SOCK_DGRAM,0);
    if (sock < 0)
        perror("Failed to create socket");

    tmp = 1;
    if (setsockopt(sock,SOL_SOCKET,SO_BROADCAST,&tmp,sizeof(tmp)) < 0)
        perror("SO_BROADCAST Failed");

    if (setsockopt(sock,SO_REUSEADDR,sizeof(tmp)) < 0)
        perror("SO_REUSEADDR Failed");

    if (setsockopt(sock,IPPROTO_IP,IP_FREEBIND,sizeof(tmp)) < 0)
        perror("IP_FREEBIND Failed");

    memset(&ifr,sizeof(ifr));
    strncpy(ifr.ifr_name,"eth1",sizeof(ifr.ifr_name));

    if (setsockopt(sock,SO_BINDTODEVICE,(void *)&ifr,sizeof(ifr)) < 0)
        perror("SO_BINDTODEVICE Failed");

    if (bind(sock,(const struct sockaddr*)&src,sizeof(struct sockaddr_in)) < 0)
        perror("bind Failed");

    if (connect(sock,(const struct sockaddr*)&dst,sizeof(struct sockaddr_in)) < 0)
        perror("bind Failed");

    if (write(sock,payload,128) < 0 )
        perror("Write Failed");

    close(sock);
    return 0;
}

问题是如果没有接口有IPv4地址,则源地址仅设置为0.0.0.0.如果只有一个接口具有IPv4地址,则该地址用作源地址.

我查看了一些现有DHCP客户端的源代码,发现他们正在使用RAW套接字并手动构建IP和UDP头.这是可能的,但我想避免手动这样做.