Multiple hosts's IP need to be set the same subnet when communicating each other?

[liyingzhi]

System info:

• A host: ubuntu 16.04
• B host: windows 7
• A and B are connected by a switch.

  Test1:

• A host IP : 160.69.69.69
• B host IP: 192.168.151.79
  1. The talker at A host multicasts a message named 'EXAMPLE' to the network. The listeners at A and B host both receive the message and enter the handle function.

2. The talker at B host multicasts a message named 'EXAMPLE' to the network. The listener at B host can receive the message and enter the handle function. But the listener at A host never enter the handle function. Then i use Wireshark to monitor the network data at A host, the message from B host can be obtained by A host.

Test2:

• A host IP : 192.168.151.167
• B host IP: 192.168.151.79
  1. The talker at A host multicasts a message named 'EXAMPLE' to the network. The listeners at A and B host both receive the message and enter the handle function.

2. The talker at B host multicasts a message named 'EXAMPLE' to the network. The listeners at A and B host both receive the message and enter the handle function. The situation at Test1_2 does not happen!

Is there a problem with my A host configuration? Or multiple hosts's IP need to be set the same subnet when communicating each other?

Thank you and looking forward to your reply.

Codes:

• LCM data type defination

  package lcm_std_msgs;
  struct Header
  {
  int32_t seq;
  int64_t stamp;
  string frame_id;
  }

• talker:

  #include<windows.h>
  #include<iostream>
  #include<stdio.h>
  #include <lcm/lcm-cpp.hpp>
  #include "lcm_std_msgs/Header.hpp"
  int main(int argc, char **argv)
  {
  int i;
  lcm::LCM lcm("udpm://239.1.1.255:7667?ttl=1");
  if (!lcm.good())
      return 1;
  lcm_std_msgs::Header my_data;
  my_data.seq = 1;
  my_data.stamp = 2;
  my_data.frame_id = "OK";
  for(i = 0;i <5; ++i)
  {
      lcm.publish("EXAMPLE", &my_data);
      Sleep(1);
  }
  return 0;
  }

• listener:

  
  #include <stdio.h>
  #include <iostream>
  #include "lcm_std_msgs/Header.hpp"
  #include <lcm/lcm-cpp.hpp>

using namespace std;

class Handler { public: ~Handler() {} void handleMessage(const lcm::ReceiveBuffer rbuf, const std::string &chan, const lcm_std_msgs::Header msg) { int i; printf("Received message on channel \"%s\":\n", chan.c_str()); printf(" timestamp = %lld\n", (long long)msg->seq); printf(" position = (%f, %f, %f)\n", msg->stamp); cout << msg->frame_id << endl; } };

int main(int argc, char *argv[]) { string address = "udpm://239.1.1.255:7667?ttl=1"; int i; lcm::LCM lcm(address) ; if (!lcm.good()) return 1; Handler handlerObject; lcm.subscribe("EXAMPLE", &Handler::handleMessage, &handlerObject);

while (0 == lcm.handle()) {
    // Do nothing
}

return 0;

}

****