如何将原始套接字绑定到特定接口

Question

我的应用程序在CentOS 5.5上运行.我正在使用原始套接字发送数据:

sd = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);
if (sd < 0) {
  // Error
}
const int opt_on = 1;
rc = setsockopt(m_SocketDescriptor, IPPROTO_IP, IP_HDRINCL, &opt_on, sizeof(opt_on));
if (rc < 0) {
  close(sd);
  // Error
}
struct sockaddr_in sin;
memset(&sin, 0, sizeof(sin));
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = my_ip_address;

if (sendto(m_SocketDescriptor, DataBuffer, (size_t)TotalSize, 0, (struct sockaddr *)&sin, sizeof(struct sockaddr)) < 0)  {
  close(sd);
  // Error
}

如何将此套接字绑定到特定的网络接口(例如eth1)？

Answer 1

const char *opt;
opt = "eth0";
const len = strnlen(opt, IFNAMSIZ);
if (len == IFNAMSIZ) {
    fprintf(stderr, "Too long iface name");
    return 1;
}
setsockopt(sd, SOL_SOCKET, SO_BINDTODEVICE, opt, len);

第一行:设置变量

第二行:告诉程序要绑定哪个接口

第3-5行:获取接口名称的长度,并检查它的大小是否太大.

六行:设置套接字的套接字选项sd,绑定到设备opt.

setsockopt原型:

int setsockopt(int s, int level, int optname, const void *optval, socklen_t optlen);

此外,请确保您包括if.h,socket.h和string.h头文件

Answer 2

如前所述,正确的做法是使用struct ifreq指定接口名称.这是我的代码示例.

#define SERVERPORT 5555
...
struct ifreq ifr;


/* Create the socket */
sd = socket(AF_INET, SOCK_STREAM, 0);
if (sd < 0) 
{
    printf("Error in socket() creation - %s", strerror(errno));
}

/* Bind to eth1 interface only - this is a private VLAN */
memset(&ifr, 0, sizeof(ifr));
snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "eth1");
if ((rc = setsockopt(sd, SOL_SOCKET, SO_BINDTODEVICE, (void *)&ifr, sizeof(ifr))) < 0)
{
    perror("Server-setsockopt() error for SO_BINDTODEVICE");
    printf("%s\n", strerror(errno));
    close(sd);
    exit(-1);
}

/* bind to an address */
memset(&serveraddr, 0x00, sizeof(struct sockaddr_in));
serveraddr.sin_family = AF_INET;
serveraddr.sin_port = htons(SERVERPORT);
serveraddr.sin_addr.s_addr = inet_addr("9.1.2.3");

int rc = bind(sd, (struct sockaddr *)&serveraddr, sizeof(serveraddr));

我还想补充一点,从安全角度来看,虽然这是很好的套接字接口绑定,它没有意义的使用INADDR_ANY作为监听的IP地址.这样做会使端口在netstat中在所有网络接口上显示为打开状态.

Proto Recv-Q Send-Q Local Address    Foreign Address    State     User Inode      PID/Program name
tcp   0      0      0.0.0.0:5555     0.0.0.0:*          LISTEN    0    210898     26996/myserver  

相反,我指定了特定于所使用接口的IP地址(专用VLAN).这也修复了netstat输出:

Proto Recv-Q Send-Q Local Address    Foreign Address    State     User Inode      PID/Program name
tcp   0      0      9.1.2.3:5555     0.0.0.0:*          LISTEN    0    210898     26996/myserver