Error in binding socket to network interface

Question

I am trying to bind a socket to a interface in my application in Linux.I found some code stuff here but when I tried using this I was getting -1 as return value from setsockopt

Here is my sample code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include "newfile.h"


int main (int argc, const char* argv[])
{

scktfd = socket(AF_INET, SOCK_DGRAM, 0); 
char *opt;
opt = "eth0";

struct ifreq Interface; 
memset(&Interface, 0, sizeof(Interface));
strncpy(Interface.ifr_ifrn.ifrn_name, "eth0", IFNAMSIZ); 

int rtrn;
rtrn = setsockopt(scktfd, SOL_SOCKET, SO_BINDTODEVICE,&Interface, sizeof(Interface));

  return 0;
}

I tried by modifying the code by looking at other examples but it didn't work. What might be the problem.

"I was getting -1 as return value from setsockopt" Okay. But what was the error number? — Ignacio Vazquez-Abrams, Oct 16 '15 at 10:43
@IgnacioVazquez-Abrams i am getting operation not permitted error — Paul Sen, Oct 16 '15 at 10:55
My first guess is you'd need to be running as root. If you are, I don't know. — TripeHound, Oct 16 '15 at 11:05
When you get -1 from any system call, call `perror()` immediately. — user207421, Oct 16 '15 at 11:07
@hexasoft I am using strncpy(Interface.ifr_ifrn.ifrn_name, "eth0", IFNAMSIZ); earlier i tried by directly passing "eth0" to setsockopt at the place of &Interface — Paul Sen, Oct 16 '15 at 11:15
Probably not the case but did you check your interface name? Some systems don't name them "ethX". No paint to check. — hexasoft, Oct 16 '15 at 11:22
Well I just copy/paste your code on my laptop (last ubuntu). Just adding `int scktfd;` declaration (lack in your code) and removing the include (newfile.h), and adding call to perror(). Compile fine. As a standard user I get: Operation not permitted (+ returns -1). Running as root I get: Success (+ returns 0). It really looks like a permission problem! — hexasoft, Oct 16 '15 at 11:27
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/92485/discussion-between-hexasoft-and-paul-sen). — hexasoft, Oct 16 '15 at 11:35

score 2 · Accepted Answer · answered Oct 16 '15 at 11:52

After discussion in chat the problem was that the code was not run as root, as stated first by TripeHound.

Binding to network interfaces is not allowed to anyone (you can spy programs/users network data…), so using root or a user with correct access to device is needed.

Error in binding socket to network interface

1 Answers1