Unable to read UDP broadcasts

I have a DSP connected to a Windows 7 laptop by a dedicated Ethernet connection (no routers or anything else in the way).

The laptop has all firewalls disabled (I’ve even tried stopping the Windows firewall service and DHCP).

The DSP is sending well-formed BOOTP broadcast packets every three seconds to port 67. Wireshark running on the laptop sees
these BOOTP packets coming in and shows they are correct.

I have a C++ program running on the laptop with a socket successfully bound to port 67. I can see this using CurrPorts.
Nothing else is shown as accessing port 67.

The program never sees any packets coming in.

If I run a program in the DSP that sends ordinary (non-broadcast) UDP packets to port 67, Wireshark sees them coming in and
reports that they are corrupt BOOTP packets, but now, the same program on the laptop gets them correctly.

Someone suggested that SO_BROADCAST needs to be set as a socket option in the laptop program (even though the Microsoft
documentation says this is for transmission only). I have tried this and, as expected, it has no effect; I still cannot read any
broadcast packets.

Any idea what’s going on here and why I cannot read any broadcast packets?

What type of protocol is used: IPv4 or IPv6?
Note that in case of IPv6 there are some changes of "broadcasting". See http://msdn.microsoft.com/en-us/libr...(v=vs.85).aspx

IPv4

Could you show your code?

For some reason, this board has removed all the indentation...

#include "stdafx.h"
#include <stdio.h>
#include <winsock2.h>
#pragma comment(lib, "ws2_32.lib")

int inner_bootp(SOCKET boot_sock) {
sockaddr_in boot;
sockaddr_in s;
unsigned char B[400];
memset(&boot, 0, sizeof(boot));
boot.sin_family = AF_INET;
boot.sin_addr.s_addr = INADDR_ANY;
boot.sin_port = htons(67);
if (bind(boot_sock, (sockaddr *)&boot, sizeof(boot))==SOCKET_ERROR) return 1;
DWORD br = TRUE;
if (setsockopt(boot_sock, SOL_SOCKET, SO_BROADCAST, (char *)&br, sizeof(br))==SOCKET_ERROR) return 2; // fatuous
printf("Waiting for BOOTP...\n");
for (;;) {
for (;;) {
fd_set readFDS;
timeval tout;
tout.tv_sec = 10;
tout.tv_usec = 0;
FD_ZERO(&readFDS);
FD_SET(boot_sock, &readFDS);
int t = select(-1, &readFDS, 0, 0, &tout);
if (t==SOCKET_ERROR) return 3;
if (t) break; // not time-out
if (MessageBox(0, L"Still waiting", L"No BOOTP detected", MB_RETRYCANCEL | MB_TOPMOST) != IDRETRY) return 0;
}
int size = sizeof(s);
if (recvfrom(boot_sock, (char *)B, sizeof(B), 0, (SOCKADDR *)&s, &size)==SOCKET_ERROR) return 4;
if (B[0] != 1) { // BOOTP
printf("non-BOOTP received\n");
} else {
int Id = (B[4]<<24) | (B[5]<<16) | (B[6]<<8) | B[7];
if (Id == 0x12345678) break;
printf("unexpected transaction ID %08X\n", Id);
}
}
char info[20];
sprintf(info, "%02x-%02x-%02x-%02x-%02x-%02x", B[28],B[29],B[30],B[31],B[32],B[33]);
printf("Info: Bootp request from:\t%s\n", info);
return 0;
}

void WaitForBOOTP(void) {
SOCKET boot_sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (boot_sock==INVALID_SOCKET) {
printf("failed to create bootp socket (%d)\n", WSAGetLastError());
} else {
int n = inner_bootp(boot_sock);
if (n) printf("wait for bootp fails %d (%d)\n", n, WSAGetLastError());
closesocket(boot_sock);
}
}

void main() {
WSADATA Data;
if (WSAStartup(MAKEWORD(1, 1), &Data)) {
printf("Unable to initialize WinSock for host info\n");
} else {
WaitForBOOTP();
WSACleanup();
printf("Done\n");
}
}

This code now works. Problem resolved:


static void Main(string[] args)
{
try
{
var multicastAddress = IPAddress.Parse("239.255.255.250");

string localName = Dns.GetHostName();
IPHostEntry hostEntry = new IPHostEntry();
hostEntry = Dns.GetHostEntry(localName);
IPAddress localIPAddr = null;
foreach (IPAddress address in hostEntry.AddressList)
{
// UPnP only supports IPv4
if (address.AddressFamily == AddressFamily.InterNetwork)
{
localIPAddr = address;
break;
}
}
if (localIPAddr != null)
{
using (var socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp))
{
Console.WriteLine("calling socket.Bind()");
socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, 1);
// Bind to local IP address
EndPoint localEP = (EndPoint)new IPEndPoint(localIPAddr, 1900);
socket.Bind(localEP);
// This is required to see the multicast messages
socket.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, new MulticastOption(multicastAddress, localIPAddr));
// Receive broadcasts from any remote endpoint
EndPoint remoteEP = (EndPoint)new IPEndPoint(IPAddress.Any, 0);
var response = new byte[0x8000];
while (true)
{
socket.ReceiveFrom(response, SocketFlags.None, ref remoteEP);
var stringResponse = Encoding.UTF8.GetString(response).Trim().TrimEnd('\0');
Console.WriteLine(string.Format("Received: {0}", stringResponse));
}
}
}
else
{
Console.WriteLine("Error: Unable to get an IpV4 address.");
}
}
catch (Exception ex)
{
Console.WriteLine(string.Format("Exception: {0}", ex.Message));
}
}
}

I do not see the relevance of this code which relates to multicast issues. My problem is clearly stated as being unable to receive broadcast packets.

My problem has not been resolved.

Quote:

---

Originally Posted by Peter Robertson

For some reason, this board has removed all the indentation...

Code:

---

#include "stdafx.h"
#include <stdio.h>
#include <winsock2.h>
#pragma comment(lib, "ws2_32.lib")

int inner_bootp(SOCKET boot_sock) {
  sockaddr_in  boot;
  sockaddr_in  s;
  unsigned char B[400];
  memset(&boot, 0, sizeof(boot));
  boot.sin_family      = AF_INET;
  boot.sin_addr.s_addr = INADDR_ANY;
  boot.sin_port        = htons(67);
  if (bind(boot_sock, (sockaddr *)&boot, sizeof(boot))==SOCKET_ERROR) return 1;
  DWORD br = TRUE;
  if (setsockopt(boot_sock, SOL_SOCKET, SO_BROADCAST, (char *)&br, sizeof(br))==SOCKET_ERROR) return 2; // fatuous
  printf("Waiting for BOOTP...\n");
  for (;;) {
      for (;;) {
        fd_set  readFDS;
        timeval tout;
        tout.tv_sec  = 10;
        tout.tv_usec = 0;
        FD_ZERO(&readFDS);
        FD_SET(boot_sock, &readFDS);
        int t = select(-1, &readFDS, 0, 0, &tout);
        if (t==SOCKET_ERROR) return 3;
        if (t) break;  // not time-out
        if (MessageBox(0, L"Still waiting", L"No BOOTP detected", MB_RETRYCANCEL | MB_TOPMOST) != IDRETRY) return 0;
      }
      int size = sizeof(s);
      if (recvfrom(boot_sock, (char *)B, sizeof(B), 0, (SOCKADDR *)&s, &size)==SOCKET_ERROR) return 4;
      if (B[0] != 1) {    // BOOTP
        printf("non-BOOTP received\n");
      } else {
        int Id = (B[4]<<24) | (B[5]<<16) | (B[6]<<8) | B[7];
        if (Id == 0x12345678) break;
        printf("unexpected transaction ID %08X\n",  Id);
      }
  }
  char info[20];
  sprintf(info, "%02x-%02x-%02x-%02x-%02x-%02x", B[28],B[29],B[30],B[31],B[32],B[33]);
  printf("Info: Bootp request from:\t%s\n", info);
  return 0;
}

void WaitForBOOTP(void) {
  SOCKET boot_sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
  if (boot_sock==INVALID_SOCKET) {
      printf("failed to create bootp socket (%d)\n", WSAGetLastError());
  } else {
      int n = inner_bootp(boot_sock);
      if (n) printf("wait for bootp fails %d (%d)\n", n, WSAGetLastError());
      closesocket(boot_sock);
  }
}

void main() {
  WSADATA Data;
  if (WSAStartup(MAKEWORD(1, 1), &Data)) {
      printf("Unable to initialize WinSock for host info\n");
  } else {
      WaitForBOOTP();
      WSACleanup();
      printf("Done\n");
  }
}

---

---

You have to use Code tags!

Thanks for that.

I am reminded of the advice of a very wise teacher many years ago: the number one rule of programming is "never fiddle with a user's data".

Life would be so much easier if everyone followed that advice.