通过IP或socket获取对方的MAC地址

1。通过已经连接的socket文件获取：

int getpeermac( int sockfd, char *buf )
{
    int ret =0;
    struct arpreq arpreq;
    struct sockaddr_in dstadd_in;
    socklen_t  len = sizeof( struct sockaddr_in );
    memset( &arpreq, 0, sizeof( struct arpreq ));
    memset( &dstadd_in, 0, sizeof( struct sockaddr_in ));
    if( getpeername( sockfd, (struct sockaddr*)&dstadd_in, &len ) < 0 )
        err_err("getpeername()");
    else
    {
        memcpy( &arpreq.arp_pa, &dstadd_in, sizeof( struct sockaddr_in ));
        strcpy(arpreq.arp_dev, "eth1");
        arpreq.arp_pa.sa_family = AF_INET;
        arpreq.arp_ha.sa_family = AF_UNSPEC;
        if( ioctl( sockfd, SIOCGARP, &arpreq ) < 0 )
            err_err("ioctl SIOCGARP");
        else
        {
            unsigned char* ptr = (unsigned char *)arpreq.arp_ha.sa_data;
            ret = sprintf(buf, "%02x%02x%02x%02x%02x%02x", *ptr, *(ptr+1), *(ptr+2), *(ptr+3), *(ptr+4), *(ptr+5));
        }
    }
    return ret;
}

2。 通过IP获取：

int getpeermac_by_ip(char *ipaddr, char* buf)
{
    int     sockfd;
    unsigned char *ptr;
    struct arpreq arpreq;
    struct sockaddr_in *sin;
    struct sockaddr_storage ss;
    char addr[INET_ADDRSTRLEN+1];

    memset(addr, 0, INET_ADDRSTRLEN+1);
    memset(&ss, 0, sizeof(ss));
    if (argc != 2) {
        printf("USAGE arpg  ip_addr/n");
        return -1;
    }
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd == -1) {
        perror("socket error");
        return -1;
    }
    sin = (struct sockaddr_in *) &ss;
    sin->sin_family = AF_INET;
    if (inet_pton(AF_INET, argv[1], &(sin->sin_addr)) <= 0) {
        perror("inet_pton error");
        return -1;
    }
    sin = (struct sockaddr_in *) &arpreq.arp_pa;
    memcpy(sin, &ss, sizeof(struct sockaddr_in));
    strcpy(arpreq.arp_dev, "eth1");
    arpreq.arp_ha.sa_family = AF_UNSPEC;
    if (ioctl(sockfd, SIOCGARP, &arpreq) < 0) {
        perror("ioctl SIOCGARP: ");
        return -1;
    }
    ptr = (unsigned char *)arpreq.arp_ha.sa_data;
    sprintf(buf,"%x:%x:%x:%x:%x:%x", *ptr, *(ptr+1), *(ptr+2), *(ptr+3), *(ptr+4), *(ptr+5));
    return 0;
}