Create a socket with an Ethernet interface (eth0, eth1) (Linux, C, Raspberry Pi)

background

In Raspberry Pi + C language, I sometimes want to communicate with two Ethernet interfaces, and it is a memo of what I learned at that time. Describes how to create an Ethernet socket and how to specify an Ethernet socket. We have confirmed the operation in the following environment. [Hardware] Raspberry Pi2 Model B [OS]Raspbian GNU/Linux8.0(jessie)

Ethernet socket creation

When using the Ethernet interface on Linux for socket communication, you can prepare for socket communication by writing the following code.

eth_com.c

     deststr = IP_ADDRESS; //IP address of the connection destination#define IP_ADRESS ("192.168.0.12")
     /*Generate socket*/
     if((*sock = socket (PF_INET, SOCK_STREAM, 0)) < 0)
     {
          printf("fail to create socket\n");
          return -1;
     }

     /*Creating an address structure for the destination server*/
     memset(&server, 0, sizeof(server));
     server.sin_family = PF_INET;
     server.sin_addr.s_addr = inet_addr(deststr);
     server.sin_port = htons(PORT);

     /*Connection process*/
     if(connect (*sock, (struct sockaddr *)&server, sizeof(server)) < 0)
     {
          printf("fail to connect\n");
          return -1;
     }

However, with this code, if there are multiple Ethernet interfaces, one Ethernet interface will be used automatically. ** For example, if there are two Ethernet interfaces, "eth0" and "eth1", it will be automatically used. Will create a socket using the "eth0" interface. **

I want to create a sokect for "eth1"

Here, if you want sockcet communication using the "eth1" interface, specify the interface with the setsockopt function </ span> .setsockopt () creates a socket Call between `` socket () ``` and the connection process connect () `.

eth_com.c

    deststr = IP_ADDRESS; //Set IP address
     /*Generate socket*/
     if((*sock = socket (PF_INET, SOCK_STREAM, 0)) < 0)
     {
          printf("fail to create socket\n");
          return -1;
     }

     /** For usb-ehternet converter **/
     char *opt;
     opt = "eth1";
     setsockopt(*sock, SOL_SOCKET, SO_BINDTODEVICE, opt, 4);

     /*Creating an address structure for the destination server*/
     memset(&server, 0, sizeof(server));
     server.sin_family = PF_INET;
     server.sin_addr.s_addr = inet_addr(deststr);
     server.sin_port = htons(PORT);

     /*Connection process*/
     if(connect (*sock, (struct sockaddr *)&server, sizeof(server)) < 0)
     {
          printf("fail to connect\n");
          return -1;
     }

Reference: http://stackoverflow.com/questions/3998569/how-to-bind-raw-socket-to-specific-interface

You have to run it on the root

However, ** I could not communicate with the "eth1" interface even with the above code. ** If you read the web page mentioned as a reference carefully,

SO_BINDTODEVICE only works if you run as root, right? (on Linux at least) –  sep332 Nov 27 '12 at 21:29

It is commented. In other words, it seems that you have to execute with root privileges. </ span> By running it with sudo, I can now communicate safely with the "eth1" interface.