Dima Dima - 1 year ago 201
Linux Question

how to bind raw socket to specific interface

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

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) {
// 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) {
// Error

How can I bind this socket to specific network interface (say eth1)?

Answer Source
char *opt;
opt = "eth0";
setsockopt(sd, SOL_SOCKET, SO_BINDTODEVICE, opt, 4);

First line: set up your variable

Second line: tell the program which interface to bind to

Third line: set the socket options for socket sd, binding to the device opt, and since opt is four characters long set 4 as the length.

setsockopt prototype:

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

Also, make sure you include the socket.h header file

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