设置网卡为混杂模式

    有时候为嗅探到网络上的数据，需要将网卡设置到混杂模式。进入该模式将网络上的数据一并抓获，为此在设置nic的混杂模式的时候有诸多方法？通过shell命令来实现：
ifconfig eth1 promisc  设置混杂模式
ifconfig eth1 -promisc 取消混杂模式

执行结果如下

[root@localhost tftpboot]# ifconfig

eth6      Link encap:Ethernet  HWaddr 08:00:27:70:1D:79  

          inet6 addr: fe80::a00:27ff:fe70:1d79/64 Scope:Link

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

          RX packets:100124 errors:0 dropped:0 overruns:0 frame:0

          TX packets:8795 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:1000 

          RX bytes:12986638 (12.3 MiB)  TX bytes:6452270 (6.1 MiB)

lo        Link encap:Local Loopback  

          inet addr:127.0.0.1  Mask:255.0.0.0

          inet6 addr: ::1/128 Scope:Host

          UP LOOPBACK RUNNING  MTU:16436  Metric:1

          RX packets:1303 errors:0 dropped:0 overruns:0 frame:0

          TX packets:1303 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:0 

          RX bytes:303973 (296.8 KiB)  TX bytes:303973 (296.8 KiB)

[root@localhost tftpboot]# ifconfig eth6 promisc

[root@localhost tftpboot]# ifconfig

eth6      Link encap:Ethernet  HWaddr 08:00:27:70:1D:79  

          inet6 addr: fe80::a00:27ff:fe70:1d79/64 Scope:Link

          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1

          RX packets:100154 errors:0 dropped:0 overruns:0 frame:0

          TX packets:8795 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:1000 

          RX bytes:13007885 (12.4 MiB)  TX bytes:6452270 (6.1 MiB)

lo        Link encap:Local Loopback  

          inet addr:127.0.0.1  Mask:255.0.0.0

          inet6 addr: ::1/128 Scope:Host

          UP LOOPBACK RUNNING  MTU:16436  Metric:1

          RX packets:1303 errors:0 dropped:0 overruns:0 frame:0

          TX packets:1303 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:0 

          RX bytes:303973 (296.8 KiB)  TX bytes:303973 (296.8 KiB)

[root@localhost tftpboot]# 

也可以通过C语言方式编程来实现，

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#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <linux/if_ether.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <string.h>

#define ETH_NAME    "eth1"

int do_promisc(void) {
    int f, s;
    struct ifreq ifr;
    if ( (f=socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL)))<0){
        return -1;
    }
    strcpy(ifr.ifr_name, ETH_NAME);

    if ((s = ioctl(f, SIOCGIFFLAGS, &ifr))<0){
      close(f);
      return-1;
    }

    if(ifr.ifr_flags & IFF_RUNNING){
        printf("eth link up\n");
    }else{
        printf("eth link down\n");
    }

    ifr.ifr_flags |= IFF_PROMISC;
    if ((s = ioctl(f, SIOCSIFFLAGS, &ifr)) < 0){
      return -1;
    }
    printf("Setting interface ::: %s ::: to promisc\n\n", ifr.ifr_name);
    return 0;
}

int check_nic(void)
{
    struct ifreq ifr;
    int skfd = socket(AF_INET, SOCK_DGRAM, 0);

    strcpy(ifr.ifr_name, ETH_NAME);
    if (ioctl(skfd, SIOCGIFFLAGS, &ifr) < 0)
    {
        close(skfd);
        return -1;
    }
    if(ifr.ifr_flags & IFF_RUNNING){
        printf("link up\n");
        close(skfd);
        return 0; // 网卡已插上网线
    }else {
        printf("link down\n");
        close(skfd);
        return -1;
    }
}



int main(void) {
    do_promisc();
    return 0;
}