listing multiple interfaces in C program - c

Question

I have a program where i want to forward packet coming from one interface ( VxBridge) & sending it on another interface (ens3:- listing raw sockets ) and vice versa also.
Although my program listens to 3 interfaces
1. VxBridge --> Listing on port 1702
2. ens3 --> listen raw interface
3. tap interface --> tun tap interface
Packet coming from ens3 <--> VxBridge
Problem :-
So program works fine if i have running Wireshark listing on ens3.
If wireshark is stop then Program doesn't listen to packets on ens3. Below is code snippet of program.
Also i believe it is related to somewhat in select() function where waiting of I/O event to occur.
I know i am doing something really wrong here. Any help in redirection would be appreciated.
Below is program :-
main(int argc, char **argv)
{
struct sockaddr_in addr;
struct sockaddr_ll daddr;
fd_set rfds;
fd_set hfds;
int cc,ccd;
struct sockaddr_in from;
size_t fromlen;
int fdmax;
int i;
char* newframe=NULL;
int fdcounter =0;
char *vb = NULL;
int vxSocketfdSet,hwSocketfdSet,tapSocketfdSet;
vxSocketfdSet= hwSocketfdSet=tapSocketfdSet=0;
// Open sockets for L2 device
if (send_to_hw){
if ( ( destsock_fd = socket( PF_PACKET , SOCK_RAW , IPPROTO_RAW) ) < 0){
perror("destsocket creation failed exit");
exit(1);
}
global_fd[fdcounter]=destsock_fd;
fdcounter++;
}
memset(&daddr, 0, sizeof(struct sockaddr_ll));
daddr.sll_family = AF_PACKET;
daddr.sll_protocol = htons(ETH_P_ALL);
daddr.sll_ifindex = if_nametoindex("ens3");
if (bind(destsock_fd, (struct sockaddr*) &daddr, sizeof(daddr)) < 0) {
printf(" ens3 bind failed\n");
close(destsock_fd);
}
struct ifreq ifr;
memset(&ifr, 0, sizeof(ifr));
snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "ens3");
if (setsockopt(destsock_fd, SOL_SOCKET, SO_BINDTODEVICE, (void *)&ifr, sizeof(ifr)) < 0) {
printf("setsockopt to ens3 failed");
}
/* Open a socket for receiving frames from the Bridge, and forwarding to other l2fwd instances of remote host. */
if ((sock_fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
perror("socket");
exit(1);
}
global_fd[fdcounter]=sock_fd;
if (vb != NULL)
{
/* create a TAP interface and attach to virtual bridge */
if ((tap_fd = tap_alloc_via_tun_helper(argv[tap_ip_arg], vb)) < 0) {
exit(1);
}
global_fd[fdcounter]=tap_fd;
fdcounter++;
}
memset(&addr, '\0', sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = INADDR_ANY;
addr.sin_port = htons(DE);
if (bind(sock_fd, (void *) &addr, sizeof(addr)) < 0) {
perror("bind");
exit(1);
}
write(1, "> ", 2);
if (pcap)
tv_wait = &pcap_flush_delay;
for (;;) {
FD_ZERO(&rfds);
fdmax = 0;
for ( i =0;i<=fdcounter;i++){
FD_SET(global_fd[i], &rfds);
if (global_fd[i] > fdmax)
fdmax = global_fd[i];
}
if (select(fdmax + 1, &rfds, 0, 0, tv_wait) < 0) {
perror("select");
continue;
}
for (i = 0;i <= fdcounter; i++)
{
if (FD_ISSET(global_fd[i], &rfds)) {
printf ("\nfdset value is %d &&& %d\n",i,global_fd[i]);
if (i==0)
{
printf("hw set ");
hwSocketfdSet = 1;
destsock_fd=global_fd[i];
}
else if (i==1){
printf ("vx Set x");
vxSocketfdSet = 1;
sock_fd=global_fd[i];
}
else if (i ==2){
tapSocketfdSet = 1;
tap_fd=global_fd[i];
}
break;
}
}
if (vxSocketfdSet){
fromlen = sizeof(from);
cc = recvfrom(sock_fd, buf, sizeof(buf), 0, (void *) &from, &fromlen);
if (cc < 0) {
perror("recvfrom");
continue;
}
printf("\nvx frame buf\n");
tempFrom = &from;
forward(buf, cc, &from,0);
}
if (tapSocketfdSet){
printf("tap frame received");
/* Ethernet frame received from local XC. */
if ((cc = read(tap_fd, buf, sizeof(buf))) < 0) {
perror("read");
continue;
}
forward(buf, cc, NULL,0);
}
if (hwSocketfdSet){
printf ("Packet received on ens3 header buffer\n");
if ((ccd = read(destsock_fd, hbuf, sizeof(hbuf))) < 0) {
printf ("error reading");
perror("read");
continue;
}
if (headerbuff != NULL && tempFrom != NULL)
{
printf("headerbuff =%u\n",headerbuff);
printf("headerbuff+ACTUAL_PAYLOAD_OFFSET %u\n",headerbuff+ACTUAL_PAYLOAD_OFFSET);
memcpy(headerbuff+ACTUAL_PAYLOAD_OFFSET,hbuf,ccd+ACTUAL_PAYLOAD_OFFSET);
newframe=headerbuff;
// printing packet with raw buffer
// weird logic is used don't try to understand this one.
// forward(headerbuff, ccd+ACTUAL_PAYLOAD_OFFSET,tempFrom,1);
}
}
vxSocketfdSet=hwSocketfdSet=tapSocketfdSet=0;
}
}

Answer 1

Enabling promiscuous mode on the interface allows it to receive packets for any address. Otherwise the interface ignores packets for foreign addresses. To do this, set the IFF_PROMISC bit in the flags argument to the SIOCSIFFLAGS ioctl call.
Don't forget to turn it off when the program ends.