Multiple Broadcast Reception on Same port but different interfaces - c++

Question

I'm trying to build a little personal DHCP server to serve a specific scope if the broadcast is received on eth0 and another if received on wlan0 but I can't bind more than a single interface on the same address:port combination (255.255.255.255:67)
I heard about SO_REUSABLE but I have no idea about how to implement it and if of course it's the good way to do it
Actually this is my code :
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <netinet/in.h>
#include <errno.h>
#include <fstream>
#include <iostream>
#include <vector>
#define BUFLEN 1024
#define PORT 67
using namespace std;
char *ipAddrFromInterface(char *apInterfaceName) //this function is not from me
{
return "255.255.255.255";
/*char *if_name = (char *) apInterfaceName;
struct ifreq ifr;
size_t if_name_len = strlen(if_name);
if(if_name_len < sizeof(ifr.ifr_name))
{
memcpy(ifr.ifr_name, if_name, if_name_len);
ifr.ifr_name[if_name_len] = 0;
}
else
printf("interface name is too long\n");
int fd = socket(AF_INET, SOCK_DGRAM, 0);
if(fd == -1)
printf("A => %s\n", strerror(errno));
if(ioctl(fd, SIOCGIFADDR, &ifr) == -1)
{
int temp_errno = errno;
close(fd);
printf("B => %s\n", strerror(temp_errno));
}
if(ioctl(fd, SIOCGIFADDR, &ifr) == -1)
{
int temp_errno = errno;
close(fd);
printf("C => %s\n", strerror(temp_errno));
}
close(fd);
struct sockaddr_in* ipaddr = (struct sockaddr_in*) &ifr.ifr_addr;
return inet_ntoa(ipaddr->sin_addr);*/
}
struct socketData
{
int sock;
sockaddr_in socket;
char *interfaceName;
};
void print(int i)
{
printf("%d\n", i);
fflush(stdout);
}
void server_receive_thread(vector<char*> aInterfaceList)
{
int socketIndex = 0;
struct sockaddr_in localSock;
int socketDescriptor; int socketLength;
vector<socketData> aSockets;
for( ; socketIndex < aInterfaceList.size(); socketIndex++)
{
socketData socketD;
char *apInterfaceName = aInterfaceList.at(socketIndex);
if((socketDescriptor = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)
{
printf("can't listen on interface %s... sleeping\n", apInterfaceName);
}
else
{
memset(&localSock, 0, sizeof(localSock));
localSock.sin_family = AF_INET;
localSock.sin_port = htons(PORT);
inet_aton(ipAddrFromInterface(apInterfaceName), &localSock.sin_addr);
setsockopt(socketDescriptor, SOL_SOCKET, SO_BINDTODEVICE, apInterfaceName, sizeof(apInterfaceName));
if(bind(socketDescriptor, (struct sockaddr *) &localSock, sizeof(localSock)) == -1)
{
printf("can't bind interface %s to listen on port %d... sleeping\n", apInterfaceName, PORT);
}
else
{
printf("bound to interface %s on port %d\n", apInterfaceName, PORT);
socketD.sock = socketDescriptor;
socketD.socket = localSock;
socketD.interfaceName = apInterfaceName;
aSockets.push_back(socketD);
}
}
}
fd_set master;
int fdMax = -1;
while(1)
{
FD_ZERO(&master);
for(int iSock = 0; iSock < aSockets.size(); iSock++)
{
socketData d = aSockets.at(iSock);
FD_SET(d.sock, &master);
if(d.sock > fdMax)
fdMax = d.sock;
}
printf("fdmax is : ");
print(fdMax);
if(select(fdMax + 1, &master, NULL, NULL, NULL) == -1)
print(2);
print(200);
for(int iSock = 0; iSock < aSockets.size(); iSock++)
{
socketData d = aSockets.at(iSock);
if(FD_ISSET(d.sock, &master))
print(3);
}
print(1);
}
}
int main()
{
std::vector<char*> interfaceList;
interfaceList.push_back("wlan0");
interfaceList.push_back("eth0");
server_receive_thread(interfaceList);
return 0;
}

Answer 1

You don't need a socket per interface. Just bind a single socket to 0.0.0.0 and the desired port. Then it will receive via all interfaces. You certainly can't, and don't need to, bind to 255.255.255.255.
Or, bind it to the single IP address that is connected to the scope you want to serve.