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POProblems with SO_BINDTODEVICE Linux socket option
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Id
1207746
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0
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11
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3
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CreationDate
2009-07-30T16:29:51.353
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2018-03-27T13:31:08.857
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2014-05-20T01:07:36.520
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119527
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14
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I have a PC with two network cards. One (<code>eth0</code>) is for LAN/internet and the other for UDP communication with one microcontroller device. The microcontroller has an IP (192.168.7.2) and a MAC address. The second pc network adapter (<code>eth1</code>) has 192.168.7.1. The microcontroller has a very simple IP stack, so the easiest way for the mc to send UDP packets is to broadcast them. On the PC side I'd like to receive the broadcasts - but only from <code>eth1</code>. So I try to bind the UDP socket to the <code>eth1</code> device. The problems (source code below): <ol> <li><code>setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, device, sizeof(device))</code> requires root privileges, why? (setting other options works as user)</li> <li><code>getsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, (void *)buffer, &opt_length)</code> gives "Protocol not available". I would like to read back the device I set via <code>setsockopt</code> command.</li> <li>Where can I find good info? I checked some Linux-programming, network books, but for example the <code>SO_BINDTODEVICE</code> option I've only found on the internet.</li> </ol> My lengthy (dirty) test program shows the problems. Setting and getting back the <code>SO_RCVTIMEO</code> and <code>SO_BROADCAST</code> options works as expected. Running the code as user exits with: <pre class="lang-none prettyprint-override"><code>could not set SO_BINDTODEVICE (Operation not permitted)" </code></pre> Running with sudo gives: <pre class="lang-none prettyprint-override"><code>SO_BINDTODEVICE set ./mc-test: could not get SO_BINDTODEVICE (Protocol not available) </code></pre> So, setting the option seems to work but reading it back is not possible? <pre><code>/* SO_BINDTODEVICE test */ #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <netdb.h> #include <stdio.h> #include <unistd.h> #include <string.h> #include <stdlib.h> #include <sys/time.h> #include <errno.h> #define MC_IP "192.168.7.2" #define MC_PORT (54321) #define MY_PORT (54321) #define MY_DEVICE "eth1" #define BUFFERSIZE (1000) /* global variables */ int sock; struct sockaddr_in MC_addr; struct sockaddr_in my_addr; char buffer[BUFFERSIZE]; int main(int argc, char *argv[]) { unsigned int echolen, clientlen; int rc, n; char opt_buffer[1000]; struct protoent *udp_protoent; struct timeval receive_timeout; int optval; socklen_t opt_length; /* Create the UDP socket */ if ((sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0) { printf ("%s: failed to create UDP socket (%s) \n", argv[0], strerror(errno)); exit (EXIT_FAILURE); } printf ("UDP socket created\n"); /* set the recvfrom timeout value */ receive_timeout.tv_sec = 5; receive_timeout.tv_usec = 0; rc=setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, &receive_timeout, sizeof(receive_timeout)); if (rc != 0) { printf ("%s: could not set SO_RCVTIMEO (%s)\n", argv[0], strerror(errno)); exit (EXIT_FAILURE); } printf ("set timeout to\ntime [s]: %d\ntime [ms]: %d\n", receive_timeout.tv_sec, receive_timeout.tv_usec); /* verify the recvfrom timeout value */ rc=getsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, &receive_timeout, &opt_length); if (rc != 0) { printf ("%s: could not get socket options (%s)\n", argv[0], strerror(errno)); exit (EXIT_FAILURE); } printf ("timeout value\ntime [s]: %d\ntime [ms]: %d\n", receive_timeout.tv_sec, receive_timeout.tv_usec); /* allow broadcast messages for the socket */ int true = 1; rc=setsockopt(sock, SOL_SOCKET, SO_BROADCAST, &true, sizeof(true)); if (rc != 0) { printf ("%s: could not set SO_BROADCAST (%s)\n", argv[0], strerror(errno)); exit (EXIT_FAILURE); } printf ("set SO_BROADCAST\n"); /* verify SO_BROADCAST setting */ rc=getsockopt(sock, SOL_SOCKET, SO_BROADCAST, &optval, &opt_length); if (optval != 0) { printf("SO_BROADCAST is enabled\n"); } /* bind the socket to one network device */ const char device[] = MY_DEVICE; rc=setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, device, sizeof(device)); if (rc != 0) { printf ("%s: could not set SO_BINDTODEVICE (%s)\n", argv[0], strerror(errno)); exit (EXIT_FAILURE); } printf ("SO_BINDTODEVICE set\n"); /* verify SO_BINDTODEVICE setting */ rc = getsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, (void *)buffer, &opt_length); if (rc != 0) { printf ("%s: could not get SO_BINDTODEVICE (%s)\n", argv[0], strerror(errno)); exit (EXIT_FAILURE); } if (rc == 0) { printf("SO_BINDTODEVICE is: %s\n", buffer); } /* Construct the server sockaddr_in structure */ memset(&MC_addr, 0, sizeof(MC_addr)); /* Clear struct */ MC_addr.sin_family = AF_INET; /* Internet/IP */ MC_addr.sin_addr.s_addr = inet_addr(MC_IP); /* IP address */ MC_addr.sin_port = htons(MC_PORT); /* server port */ /* bind my own Port */ my_addr.sin_family = AF_INET; my_addr.sin_addr.s_addr = INADDR_ANY; /* INADDR_ANY all local addresses */ my_addr.sin_port = htons(MY_PORT); rc = bind (sock, (struct sockaddr *) &my_addr, sizeof(my_addr)); if (rc < 0) { printf ("%s: could not bind port (%s)\n", argv[0], strerror(errno)); exit (EXIT_FAILURE); } printf ("port bound\n"); /* identify mc */ buffer[0] = (char)1; buffer[1] = (char)0; send_data (buffer, 2); printf ("sent command: %d\n", (char)buffer[0]); rc=receive_data(buffer); printf ("%d bytes received\n", rc); buffer[rc] = (char)0; /* string end symbol */ printf ("%d - %s\n", (int)(char)buffer[0], &buffer[1]); close(sock); printf ("socket closed\n"); exit(0); } /* send data to the MC *****************************************************/ /* buffer points to the bytes to send */ /* buf_length is the number of bytes to send */ /* returns allways 0 */ int send_data( char *buffer, int buf_length ) { int rc; rc = sendto (sock, buffer, buf_length, 0, (struct sockaddr *) &MC_addr, sizeof(MC_addr)); if (rc < 0) { printf ("could not send data\n"); close (sock); exit (EXIT_FAILURE); } return(0); } /* receive data from the MC *****************************************************/ /* buffer points to the memory for the received data */ /* max BUFFERSIZE bytes can be received */ /* returns number of bytes received */ int receive_data(char *buffer) { int rc, MC_addr_length; MC_addr_length = sizeof(MC_addr); rc = recvfrom (sock, buffer, BUFFERSIZE, 0, (struct sockaddr *) &MC_addr, &MC_addr_length); if (rc < 0) { printf ("could not receive data\n"); close (sock); exit (EXIT_FAILURE); } return(rc); } </code></pre>
Tags
<c><linux><sockets><udp><broadcast>
Title
Problems with SO_BINDTODEVICE Linux socket option
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