how to bind raw socket to specific interface

Question

My application is running on CentOS 5.5. I'm using raw socket to send data:

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 } 

How can I bind this socket to specific network interface (say 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); 

First line: set up your variable

Second line: tell the program which interface to bind to

Lines 3-5: get length of interface name and check if it's size not too big.

Six line: set the socket options for socket sd, binding to the device opt.

setsockopt prototype:

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

Also, make sure you include the if.h, socket.h and string.h header files