如何发送UDP数据报到IGMP设备？

Question

I have a broadband Radar that I want to turn on. To turn it on I have to send two registers like following:

    int reg0[3] = {0x00, 0xC1, 0x01};      
    int reg1[3] = {0x01, 0xC1, 0x01};

The main issue is that my Radar device is working on UDP protocol and works in IGMP (3rd layer of the ISO model). I have read a lot about UDP sending in these sites from the IBM support: https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.3.0/com.ibm.zos.v2r3.hala001/cskudp.htm https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.3.0/com.ibm.zos.v2r3.bpxbd00/setopt.htm …and others.

I fathom it is neither obliged to create a struct ip_mreq nor add options with setsockopt() for I only want to send a datagram.

I have already tried to do this sort of things:

    #define IPM struct ip_mreq
    IPM mcast;
    int sock_err = bind(skemit, (SA *) &emit, lemit);
    mcast.imr_multiaddr.s_addr = MCAST_JOIN_GROUP;//multicastaddress 
    mcast.imr_interface.s_addr = add1;
    setsockopt(semit, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char*)&mcast, sizeof(IPM)); //sizeof(mcast)

This is my code:

#include <stdlib.h>

#include <unistd.h>
#include <stdio.h>
#include <string.h>

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <time.h>
#include <signal.h>

#define SAI struct sockaddr_in
#define SA struct sockaddr

int main(){

  SAI emit;
  uint32_t add1 = htonl(inet_addr("236.6.7.10")); //host address
  unsigned short port = htons(6680); // port

  memset(&emit, '\0', sizeof(emit));
  emit.sin_family = AF_INET;
  emit.sin_port = port;
  emit.sin_addr.s_addr = add1;
  socklen_t lemit = sizeof(SAI);

  int skemit = socket(AF_INET, SOCK_DGRAM, 0);
  if (skemit == -1){ perror("creating socket"); }
  /*
  * Send a message to the multicast address specified by the
  * emit sockaddr structure.
  */

  int reg0[3] = {0x00, 0xC1, 0x01};        //turn_on
  int reg1[3] = {0x01, 0xC1, 0x01};        //turn_on


  /* Send the message in reg0 and reg1 to the server */

  if (sendto(skemit, reg0, sizeof(reg0), 0, (SA*)&emit, lemit) < 0){perror("sending datagram message reg0");}
  if (sendto(skemit, reg1, sizeof(reg1), 0, (SA*)&emit, lemit) < 0){perror("sending datagram message reg1");}
}

I receive this errors:

sending datagram message reg0: Network is unreachable
sending datagram message reg1: Network is unreachable

Could you help me?

Answer 1

I have advanced in my issue, that is why I want to partially answer: I managed to do the connection in python. It cannot be a computer's settings' problem.

Here is the code that works:

import socket
import struct

MCAST_GRP = '236.6.7.8'
MCAST_PORT = 6678

HOST2 = '236.6.7.10'
PORT2 = 6680

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)

sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)



sock.bind(('', MCAST_PORT))  # use MCAST_GRP instead of '' to listen only
                         # to MCAST_GRP, not all groups on MCAST_PORT


mreq = struct.pack("4sl", socket.inet_aton(MCAST_GRP), socket.INADDR_ANY)

sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)

sock2 = socket.socket(socket.AF_INET,socket.SOCK_DGRAM)

reg0=bytes([0x00, 0xC1, 0x01])               #turn_on
reg1=bytes([0x01, 0xC1, 0x01])               #turn_on


sock2.sendto(reg0, (HOST2, PORT2))
sock2.sendto(reg1, (HOST2, PORT2))
sock2.sendto(reg3, (HOST2, PORT2))
pcapfile = open('ragar.txt', 'w')
while True:
  pcapfile.write(str(sock.recv(65536)))
pcapfile.close()
print('the end')

The sock2 manages to send the registers to the device whereas the sock receives the datas correctly.